Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least time-align them to always be the same within a few microseconds,
longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse
maybe once a second. A follower would use her (not "his") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as
followers.
The PLL algorithm might be interesting.
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse
maybe once a second. A follower would use her (not "his") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as
followers.
The PLL algorithm might be interesting.
It's certainly possible. However, within whatever tiny loop bandwidth
you wound up with, the lockers would still have
20 log(40e6) = 152 dB
higher phase noise than the lockee.
GPS has that problem too.
It would be interesting to do the math to see whether it's possible to
generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to
that, with some bit of AC coupling or something so that they don't all
wander together off to the edge of the tuning range.
Maybe have one doing the locking with a phase shifter and the others
with VCOs, or something like that.
Definitely a partly-baked idea, but surely one could do better than 152 dB! >>
Cheers
Phil Hobbs
Each box is basically a multichannel power supply, but channels can be programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.
If a follower is told to start locking, it could timestamp the first
incoming 1 PPS with a giant counter clocked by its local 40 MHz VCO.
If a later 1 PPS edge appears to arrive too soon, we could speed up
our VCXO by, say, 1 PPM, and vice versa. So longterm it walks into
alignment with the 1 PPS and eventually dithers a microsecond per
second. Noise on the coax gets fixed over time too.
That's better than just measuring the 1 Hz period once a second,
tweaking the clock, and then throwing away that measurement. I want a
time lock, not a frequency lock.
John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse
maybe once a second. A follower would use her (not "his") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as
followers.
The PLL algorithm might be interesting.
It's certainly possible. However, within whatever tiny loop bandwidth
you wound up with, the lockers would still have
20 log(40e6) = 152 dB
higher phase noise than the lockee.
It would be interesting to do the math to see whether it's possible to >generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to
that, with some bit of AC coupling or something so that they don't all
wander together off to the edge of the tuning range.
Maybe have one doing the locking with a phase shifter and the others
with VCOs, or something like that.
Definitely a partly-baked idea, but surely one could do better than 152 dB!
Cheers
Phil Hobbs
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse
maybe once a second. A follower would use her (not "his") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as
followers.
The PLL algorithm might be interesting.
It's certainly possible. However, within whatever tiny loop bandwidth
you wound up with, the lockers would still have
20 log(40e6) = 152 dB
higher phase noise than the lockee.
GPS has that problem too.
It would be interesting to do the math to see whether it's possible to
generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to
that, with some bit of AC coupling or something so that they don't all
wander together off to the edge of the tuning range.
Maybe have one doing the locking with a phase shifter and the others
with VCOs, or something like that.
Definitely a partly-baked idea, but surely one could do better than 152 dB! >>
Cheers
Phil Hobbs
Each box is basically a multichannel power supply, but channels can be programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.
On 7/20/2022 8:22 PM, John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on >>>> the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse
maybe once a second. A follower would use her (not "his") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as
followers.
The PLL algorithm might be interesting.
It's certainly possible. However, within whatever tiny loop bandwidth
you wound up with, the lockers would still have
20 log(40e6) = 152 dB
higher phase noise than the lockee.
GPS has that problem too.
It would be interesting to do the math to see whether it's possible to
generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to
that, with some bit of AC coupling or something so that they don't all
wander together off to the edge of the tuning range.
Maybe have one doing the locking with a phase shifter and the others
with VCOs, or something like that.
Definitely a partly-baked idea, but surely one could do better than 152 dB! >>>
Cheers
Phil Hobbs
Each box is basically a multichannel power supply, but channels can be
programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.
It sounds like you're looking for a protocol like DMX if what you want
is to trigger sequences of events across boxes to within a millisecond,
I don't understand what this lock-the-40 MHz across boxes is about.
<https://en.wikipedia.org/wiki/DMX512>
John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on >>>> the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse
maybe once a second. A follower would use her (not "his") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as
followers.
The PLL algorithm might be interesting.
It's certainly possible. However, within whatever tiny loop bandwidth
you wound up with, the lockers would still have
20 log(40e6) = 152 dB
higher phase noise than the lockee.
GPS has that problem too.
It would be interesting to do the math to see whether it's possible to
generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to
that, with some bit of AC coupling or something so that they don't all
wander together off to the edge of the tuning range.
Maybe have one doing the locking with a phase shifter and the others
with VCOs, or something like that.
Definitely a partly-baked idea, but surely one could do better than 152 dB! >>>
Cheers
Phil Hobbs
Each box is basically a multichannel power supply, but channels can be
programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.
If a follower is told to start locking, it could timestamp the first
incoming 1 PPS with a giant counter clocked by its local 40 MHz VCO.
If a later 1 PPS edge appears to arrive too soon, we could speed up
our VCXO by, say, 1 PPM, and vice versa. So longterm it walks into
alignment with the 1 PPS and eventually dithers a microsecond per
second. Noise on the coax gets fixed over time too.
That's better than just measuring the 1 Hz period once a second,
tweaking the clock, and then throwing away that measurement. I want a
time lock, not a frequency lock.
Absolutely. The scary 152 dB number doesn't mean that doing something
like that is automatically a bad idea.
Being an old RF and ultrastable laser guy, though, it does make my ears
perk up. ;)
Cheers
Phil Hobbs
Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least time-align them to always be the same within a few microseconds,
longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse
maybe once a second. A follower would use her (not "his") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?
Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least >time-align them to always be the same within a few microseconds,
longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse
maybe once a second. A follower would use her (not "his") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as
followers.
The PLL algorithm might be interesting.
Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least time-align them to always be the same within a few microseconds,
longterm.
On Wednesday, July 20, 2022 at 4:21:08 PM UTC-7, John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least time-align them to always be the same within a few microseconds,If you can tolerate 'a few microseconds' on a 40 MHz signal, that's not a phase-lock
longterm.
problem, it's a frequency-lock problem. Why not just run an up/down counter to generate a correction voltage for each non-leading VCO?
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse
maybe once a second. A follower would use her (not "his") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as
followers.
The PLL algorithm might be interesting.
It's certainly possible. However, within whatever tiny loop bandwidth
you wound up with, the lockers would still have
20 log(40e6) = 152 dB
higher phase noise than the lockee.
GPS has that problem too.
It would be interesting to do the math to see whether it's possible to
generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to
that, with some bit of AC coupling or something so that they don't all
wander together off to the edge of the tuning range.
Maybe have one doing the locking with a phase shifter and the others
with VCOs, or something like that.
Definitely a partly-baked idea, but surely one could do better than 152 dB! >>
Cheers
Phil Hobbs
Each box is basically a multichannel power supply, but channels can be programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.
If a follower is told to start locking, it could timestamp the first
incoming 1 PPS with a giant counter clocked by its local 40 MHz VCO.
If a later 1 PPS edge appears to arrive too soon, we could speed up
our VCXO by, say, 1 PPM, and vice versa. So longterm it walks into
alignment with the 1 PPS and eventually dithers a microsecond per
second. Noise on the coax gets fixed over time too.
That's better than just measuring the 1 Hz period once a second,
tweaking the clock, and then throwing away that measurement. I want a
time lock, not a frequency lock.
Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least time-align them to always be the same within a few microseconds,
longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse
maybe once a second. A follower would use her (not "his") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as
followers.
The PLL algorithm might be interesting.
On 21/07/2022 01:22, John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on >>>> the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse
maybe once a second. A follower would use her (not "his") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as
followers.
The PLL algorithm might be interesting.
It's certainly possible. However, within whatever tiny loop bandwidth
you wound up with, the lockers would still have
20 log(40e6) = 152 dB
higher phase noise than the lockee.
GPS has that problem too.
It would be interesting to do the math to see whether it's possible to
generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to
that, with some bit of AC coupling or something so that they don't all
wander together off to the edge of the tuning range.
Maybe have one doing the locking with a phase shifter and the others
with VCOs, or something like that.
Definitely a partly-baked idea, but surely one could do better than 152 dB! >>>
Cheers
Phil Hobbs
Each box is basically a multichannel power supply, but channels can be
programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.
You really need to define longterm before the problem becomes well
posed. Do you mean hours, days, weeks or months of runtime?
If a follower is told to start locking, it could timestamp the first
incoming 1 PPS with a giant counter clocked by its local 40 MHz VCO.
If a later 1 PPS edge appears to arrive too soon, we could speed up
our VCXO by, say, 1 PPM, and vice versa. So longterm it walks into
alignment with the 1 PPS and eventually dithers a microsecond per
second. Noise on the coax gets fixed over time too.
Have a free running counter on each of the followers and use the value
of that after 1s, 10s, 100s to determine the correct tweak to apply
locally. Tweaks of 1ppm at a time is rather crude you should be able to >determine the right amount to tweak it by better than that.
(especially over longer timebases)
That's better than just measuring the 1 Hz period once a second,
tweaking the clock, and then throwing away that measurement. I want a
time lock, not a frequency lock.
Then you probably want to measure the cumulative error over many
seconds. Each unit can work out how long it can free run without
exceeding tolerance once it has the rough and ready count from the first >second. After that you have a good idea of how many seconds you can free
run for without having any ambiguities from residual drift.
Am 21.07.22 um 01:20 schrieb John Larkin:
Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.
I have a backburner project of locking 16 MTI-260 oscillators
slooowy to another one, and when they are in sync, combine
them with an array of Wilkinsons. That should have a nice
effect on phase noise by averaging over 16.
The CPLD has enough resources to implement that as a delay
locked loop with 1 pps, but low hanging fruit first.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse
maybe once a second. A follower would use her (not "his") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?
No. There is no 1PPS pulse from the sat nor the need for exactly 10 MHz.
The sats transmit a pseudo noise sequence that is
aligned to the second of their local clock source.
The GPS receiver knows the polynomial and runs a local copy of
the polynomial. It knows by cross correlation if the local
pseudo noise is the same as that of the sat and therefore knows
the start of the second. Usually that won't be the case.
Then the receiver delays its own polynomial by omitting a
clock to the shift register that generates it and tries again.
Sooner or later it will fit.
On Wednesday, July 20, 2022 at 4:21:08 PM UTC-7, John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.
If you can tolerate 'a few microseconds' on a 40 MHz signal, that's not a phase-lock
problem, it's a frequency-lock problem. Why not just run an up/down counter >to generate a correction voltage for each non-leading VCO?
Where does the 10 MHz come from?
On 21/07/2022 01:22, John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on >>>> the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse
maybe once a second. A follower would use her (not "his") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as
followers.
The PLL algorithm might be interesting.
It's certainly possible. However, within whatever tiny loop bandwidth
you wound up with, the lockers would still have
20 log(40e6) = 152 dB
higher phase noise than the lockee.
GPS has that problem too.
It would be interesting to do the math to see whether it's possible to
generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to
that, with some bit of AC coupling or something so that they don't all
wander together off to the edge of the tuning range.
Maybe have one doing the locking with a phase shifter and the others
with VCOs, or something like that.
Definitely a partly-baked idea, but surely one could do better than
152 dB!
Cheers
Phil Hobbs
Each box is basically a multichannel power supply, but channels can be
programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.
You really need to define longterm before the problem becomes well
posed. Do you mean hours, days, weeks or months of runtime?
If a follower is told to start locking, it could timestamp the first
incoming 1 PPS with a giant counter clocked by its local 40 MHz VCO.
If a later 1 PPS edge appears to arrive too soon, we could speed up
our VCXO by, say, 1 PPM, and vice versa. So longterm it walks into
alignment with the 1 PPS and eventually dithers a microsecond per
second. Noise on the coax gets fixed over time too.
Have a free running counter on each of the followers and use the value
of that after 1s, 10s, 100s to determine the correct tweak to apply
locally. Tweaks of 1ppm at a time is rather crude you should be able to determine the right amount to tweak it by better than that.
(especially over longer timebases)
That's better than just measuring the 1 Hz period once a second,
tweaking the clock, and then throwing away that measurement. I want a
time lock, not a frequency lock.
Then you probably want to measure the cumulative error over many
seconds. Each unit can work out how long it can free run without
exceeding tolerance once it has the rough and ready count from the first second. After that you have a good idea of how many seconds you can free
run for without having any ambiguities from residual drift.
This is an ancient trick from physics which avoids the smartest students
from having to laboriously count every pendulum swing when determining g
to maximum possible precision in a given time. It used to be (and
probably still is a favourite exam practical). Components needed are
very cheap and the whole thing is a good test of experimental technique.
On Wed, 20 Jul 2022 20:28:35 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on >>>>> the back. Each of them has an open-drain mosfet, a weak pullup, and a >>>>> lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least >>>>> time-align them to always be the same within a few microseconds,
longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse >>>>> maybe once a second. A follower would use her (not "his") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as
followers.
The PLL algorithm might be interesting.
It's certainly possible. However, within whatever tiny loop bandwidth >>>> you wound up with, the lockers would still have
20 log(40e6) = 152 dB
higher phase noise than the lockee.
GPS has that problem too.
It would be interesting to do the math to see whether it's possible to >>>> generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to
that, with some bit of AC coupling or something so that they don't all >>>> wander together off to the edge of the tuning range.
Maybe have one doing the locking with a phase shifter and the others
with VCOs, or something like that.
Definitely a partly-baked idea, but surely one could do better than 152 dB!
Cheers
Phil Hobbs
Each box is basically a multichannel power supply, but channels can be
programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.
If a follower is told to start locking, it could timestamp the first
incoming 1 PPS with a giant counter clocked by its local 40 MHz VCO.
If a later 1 PPS edge appears to arrive too soon, we could speed up
our VCXO by, say, 1 PPM, and vice versa. So longterm it walks into
alignment with the 1 PPS and eventually dithers a microsecond per
second. Noise on the coax gets fixed over time too.
That's better than just measuring the 1 Hz period once a second,
tweaking the clock, and then throwing away that measurement. I want a
time lock, not a frequency lock.
Absolutely. The scary 152 dB number doesn't mean that doing something
like that is automatically a bad idea.
Being an old RF and ultrastable laser guy, though, it does make my ears
perk up. ;)
Cheers
Phil Hobbs
I like thermostats, single-bit-feedback control loops.
We have a couple of boxes that do fan control based on interior
temperature. Once a second, if it's above the setpoint, ratchet fan
speed up some fixed amount, 1% maybe. If it's cooler than the
setpoint, step fan speed down. There's no acoustic drama and it's
perfectly stable.
It dithers around the setpoint but nobody notices.
This is immune to classic control theory so the concept annoys some
people but it works great.
On Thursday, 21 July 2022 at 07:49:43 UTC+1, whit3rd wrote:
On Wednesday, July 20, 2022 at 4:21:08 PM UTC-7, John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector onIf you can tolerate 'a few microseconds' on a 40 MHz signal, that's not a phase-lock
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.
problem, it's a frequency-lock problem. Why not just run an up/down counter >> to generate a correction voltage for each non-leading VCO?
If you have an ethernet interface to each unit then Precision Time Protocol should do exactly what you want. https://en.wikipedia.org/wiki/Precision_Time_Protocol
John
On 21/07/2022 01:22, John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on >>>> the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse
maybe once a second. A follower would use her (not "his") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as
followers.
The PLL algorithm might be interesting.
It's certainly possible. However, within whatever tiny loop bandwidth
you wound up with, the lockers would still have
20 log(40e6) = 152 dB
higher phase noise than the lockee.
GPS has that problem too.
It would be interesting to do the math to see whether it's possible to
generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to
that, with some bit of AC coupling or something so that they don't all
wander together off to the edge of the tuning range.
Maybe have one doing the locking with a phase shifter and the others
with VCOs, or something like that.
Definitely a partly-baked idea, but surely one could do better than
152 dB!
Cheers
Phil Hobbs
Each box is basically a multichannel power supply, but channels can be
programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.
You really need to define longterm before the problem becomes well
posed. Do you mean hours, days, weeks or months of runtime?
On 7/21/2022 4:33 AM, John Walliker wrote:
On Thursday, 21 July 2022 at 07:49:43 UTC+1, whit3rd wrote:
On Wednesday, July 20, 2022 at 4:21:08 PM UTC-7, John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on >>>> the back. Each of them has an open-drain mosfet, a weak pullup, and aIf you can tolerate 'a few microseconds' on a 40 MHz signal, that's
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.
not a phase-lock
problem, it's a frequency-lock problem. Why not just run an up/down
counter
to generate a correction voltage for each non-leading VCO?
If you have an ethernet interface to each unit then Precision Time
Protocol
should do exactly what you want.
https://en.wikipedia.org/wiki/Precision_Time_Protocol
John
Yeah, that sounds like the ticket to me also. Trying to use each box's
system clock for purposes of keeping "user-space" tasks in sync across
boxes makes me uncomfortable, sounds like a srs hack.
Am 21.07.22 um 13:19 schrieb jlarkin@highlandsniptechnology.com:
Where does the 10 MHz come from?
Choise of implementer. One local clock generator is needed.
This clock determines short term stabiity and phase noise.
My Lucent KS24361 uses 5 MHz MTI-260 double ovens; for
redundancy/holdover it has a 2nd unit with another crystal
oven without a receiver.
The redundancy units were really hard to sell without the
receiver; that's why I have 20 of these MTI-260, got a good
price. :-)
They were new old stock built by HP/Agilent for Lucent as
replacement parts. They have never been on a telecom tower
in China like most of those one gets on ebay.
I have expanded the Lucent to 10 MHZ and with a distribution
amplifier:
<  http://www.hoffmann-hochfrequenz.de/downloads/DoubDist.pdf >
cheers, Gerhard
On 7/21/2022 7:06 AM, Martin Brown wrote:
On 21/07/2022 01:22, John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
<pcdhSpamM...@electrooptical.net> wrote:
John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on >>>> the back. Each of them has an open-drain mosfet, a weak pullup, and a >>>> lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least >>>> time-align them to always be the same within a few microseconds,
longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse >>>> maybe once a second. A follower would use her (not "his") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as
followers.
The PLL algorithm might be interesting.
It's certainly possible. However, within whatever tiny loop bandwidth >>> you wound up with, the lockers would still have
20 log(40e6) = 152 dB
higher phase noise than the lockee.
GPS has that problem too.
It would be interesting to do the math to see whether it's possible to >>> generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to
that, with some bit of AC coupling or something so that they don't all >>> wander together off to the edge of the tuning range.
Maybe have one doing the locking with a phase shifter and the others
with VCOs, or something like that.
Definitely a partly-baked idea, but surely one could do better than
152 dB!
Cheers
Phil Hobbs
Each box is basically a multichannel power supply, but channels can be
programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.
You really need to define longterm before the problem becomes wellYeah I don't quite get it, either. My rack of synthesizers can each play
posed. Do you mean hours, days, weeks or months of runtime?
one voice of the Maple Leaf Rag via MIDI and they all stay synced
together really well, at least over a timespan of several
minutes.
On 7/21/2022 7:06 AM, Martin Brown wrote:
On 21/07/2022 01:22, John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on >>>>> the back. Each of them has an open-drain mosfet, a weak pullup, and a >>>>> lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least >>>>> time-align them to always be the same within a few microseconds,
longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse >>>>> maybe once a second. A follower would use her (not "his") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as
followers.
The PLL algorithm might be interesting.
It's certainly possible. However, within whatever tiny loop bandwidth >>>> you wound up with, the lockers would still have
20 log(40e6) = 152 dB
higher phase noise than the lockee.
GPS has that problem too.
It would be interesting to do the math to see whether it's possible to >>>> generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to
that, with some bit of AC coupling or something so that they don't all >>>> wander together off to the edge of the tuning range.
Maybe have one doing the locking with a phase shifter and the others
with VCOs, or something like that.
Definitely a partly-baked idea, but surely one could do better than
152 dB!
Cheers
Phil Hobbs
Each box is basically a multichannel power supply, but channels can be
programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.
You really need to define longterm before the problem becomes well
posed. Do you mean hours, days, weeks or months of runtime?
Yeah I don't quite get it, either. My rack of synthesizers can each play
one voice of the Maple Leaf Rag via MIDI and they all stay synced
together really well, at least over a timespan of several minutes...superficially at least it sounds like he wants a sequencer.
Using the nuts & bolts system clock for synchronization of "user tasks"
also makes me uncomfortable, if the device behavior only need to align
to the millisecond why not trigger them using some simple network
protocol and let their hardware figure out how long a millisecond is independently. Do the timings of these boxes need to be tighter than the Maple Leaf Rag?
torsdag den 21. juli 2022 kl. 16.04.42 UTC+2 skrev bitrex:
On 7/21/2022 7:06 AM, Martin Brown wrote:
On 21/07/2022 01:22, John Larkin wrote:Yeah I don't quite get it, either. My rack of synthesizers can each play
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
<pcdhSpamM...@electrooptical.net> wrote:
John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on >>>>>> the back. Each of them has an open-drain mosfet, a weak pullup, and a >>>>>> lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least >>>>>> time-align them to always be the same within a few microseconds,
longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse >>>>>> maybe once a second. A follower would use her (not "his") clock to >>>>>> measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse >>>>>> from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as
followers.
The PLL algorithm might be interesting.
It's certainly possible. However, within whatever tiny loop bandwidth >>>>> you wound up with, the lockers would still have
20 log(40e6) = 152 dB
higher phase noise than the lockee.
GPS has that problem too.
It would be interesting to do the math to see whether it's possible to >>>>> generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to >>>>> that, with some bit of AC coupling or something so that they don't all >>>>> wander together off to the edge of the tuning range.
Maybe have one doing the locking with a phase shifter and the others >>>>> with VCOs, or something like that.
Definitely a partly-baked idea, but surely one could do better than
152 dB!
Cheers
Phil Hobbs
Each box is basically a multichannel power supply, but channels can be >>>> programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.
You really need to define longterm before the problem becomes well
posed. Do you mean hours, days, weeks or months of runtime?
one voice of the Maple Leaf Rag via MIDI and they all stay synced
together really well, at least over a timespan of several
minutes.
but they are anot free runnign are they? they are all reacting to midi
jlarkin@highlandsniptechnology.com wrote:
On Wed, 20 Jul 2022 20:28:35 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on >>>>>> the back. Each of them has an open-drain mosfet, a weak pullup, and a >>>>>> lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least >>>>>> time-align them to always be the same within a few microseconds,
longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse >>>>>> maybe once a second. A follower would use her (not "his") clock to >>>>>> measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse >>>>>> from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as
followers.
The PLL algorithm might be interesting.
It's certainly possible. However, within whatever tiny loop bandwidth >>>>> you wound up with, the lockers would still have
20 log(40e6) = 152 dB
higher phase noise than the lockee.
GPS has that problem too.
It would be interesting to do the math to see whether it's possible to >>>>> generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to >>>>> that, with some bit of AC coupling or something so that they don't all >>>>> wander together off to the edge of the tuning range.
Maybe have one doing the locking with a phase shifter and the others >>>>> with VCOs, or something like that.
Definitely a partly-baked idea, but surely one could do better than 152 dB!
Cheers
Phil Hobbs
Each box is basically a multichannel power supply, but channels can be >>>> programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.
If a follower is told to start locking, it could timestamp the first
incoming 1 PPS with a giant counter clocked by its local 40 MHz VCO.
If a later 1 PPS edge appears to arrive too soon, we could speed up
our VCXO by, say, 1 PPM, and vice versa. So longterm it walks into
alignment with the 1 PPS and eventually dithers a microsecond per
second. Noise on the coax gets fixed over time too.
That's better than just measuring the 1 Hz period once a second,
tweaking the clock, and then throwing away that measurement. I want a
time lock, not a frequency lock.
Absolutely. The scary 152 dB number doesn't mean that doing something
like that is automatically a bad idea.
Being an old RF and ultrastable laser guy, though, it does make my ears
perk up. ;)
Cheers
Phil Hobbs
I like thermostats, single-bit-feedback control loops.
We have a couple of boxes that do fan control based on interior
temperature. Once a second, if it's above the setpoint, ratchet fan
speed up some fixed amount, 1% maybe. If it's cooler than the
setpoint, step fan speed down. There's no acoustic drama and it's
perfectly stable.
It dithers around the setpoint but nobody notices.
This is immune to classic control theory so the concept annoys some
people but it works great.
A real old time control guy like Tim Wescott would probably be a fan
too--the great virtue of a bang-bang controller is that (as you say)
it's highly resistant to variations in the _plant_.
Your furnace doesn't go nuts when you have a Christmas party, even
though all those people generate a lot of heat, and there's lots of
opening and closing of doors and ovens.
Cheers
Phil Hobbs
Martin Brown wrote:
On 21/07/2022 01:22, John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on >>>>> the back. Each of them has an open-drain mosfet, a weak pullup, and a >>>>> lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least >>>>> time-align them to always be the same within a few microseconds,
longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse >>>>> maybe once a second. A follower would use her (not "his") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as
followers.
The PLL algorithm might be interesting.
It's certainly possible. However, within whatever tiny loop bandwidth >>>> you wound up with, the lockers would still have
20 log(40e6) = 152 dB
higher phase noise than the lockee.
GPS has that problem too.
It would be interesting to do the math to see whether it's possible to >>>> generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to
that, with some bit of AC coupling or something so that they don't all >>>> wander together off to the edge of the tuning range.
Maybe have one doing the locking with a phase shifter and the others
with VCOs, or something like that.
Definitely a partly-baked idea, but surely one could do better than
152 dB!
Cheers
Phil Hobbs
Each box is basically a multichannel power supply, but channels can be
programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.
You really need to define longterm before the problem becomes well
posed. Do you mean hours, days, weeks or months of runtime?
If a follower is told to start locking, it could timestamp the first
incoming 1 PPS with a giant counter clocked by its local 40 MHz VCO.
If a later 1 PPS edge appears to arrive too soon, we could speed up
our VCXO by, say, 1 PPM, and vice versa. So longterm it walks into
alignment with the 1 PPS and eventually dithers a microsecond per
second. Noise on the coax gets fixed over time too.
Have a free running counter on each of the followers and use the value
of that after 1s, 10s, 100s to determine the correct tweak to apply
locally. Tweaks of 1ppm at a time is rather crude you should be able to
determine the right amount to tweak it by better than that.
(especially over longer timebases)
That's better than just measuring the 1 Hz period once a second,
tweaking the clock, and then throwing away that measurement. I want a
time lock, not a frequency lock.
Then you probably want to measure the cumulative error over many
seconds. Each unit can work out how long it can free run without
exceeding tolerance once it has the rough and ready count from the first
second. After that you have a good idea of how many seconds you can free
run for without having any ambiguities from residual drift.
This is an ancient trick from physics which avoids the smartest students
from having to laboriously count every pendulum swing when determining g
to maximum possible precision in a given time. It used to be (and
probably still is a favourite exam practical). Components needed are
very cheap and the whole thing is a good test of experimental technique.
It's not as efficient as 'dry labbing'. ;)
On 7/21/2022 10:12 AM, bitrex wrote:
On 7/21/2022 4:33 AM, John Walliker wrote:
On Thursday, 21 July 2022 at 07:49:43 UTC+1, whit3rd wrote:
On Wednesday, July 20, 2022 at 4:21:08 PM UTC-7, John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on >>>>> the back. Each of them has an open-drain mosfet, a weak pullup, and a >>>>> lowpass filtered schmitt gate back into our FPGA.If you can tolerate 'a few microseconds' on a 40 MHz signal, that's
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least >>>>> time-align them to always be the same within a few microseconds,
longterm.
not a phase-lock
problem, it's a frequency-lock problem. Why not just run an up/down
counter
to generate a correction voltage for each non-leading VCO?
If you have an ethernet interface to each unit then Precision Time
Protocol
should do exactly what you want.
https://en.wikipedia.org/wiki/Precision_Time_Protocol
John
Yeah, that sounds like the ticket to me also. Trying to use each box's
system clock for purposes of keeping "user-space" tasks in sync across
boxes makes me uncomfortable, sounds like a srs hack.
At minimum it likely won't scale very well. Why implicitly discourage
one's customers from buying only a limited number of units
On Thu, 21 Jul 2022 09:27:39 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
jlarkin@highlandsniptechnology.com wrote:
On Wed, 20 Jul 2022 20:28:35 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on >>>>>>> the back. Each of them has an open-drain mosfet, a weak pullup, and a >>>>>>> lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least >>>>>>> time-align them to always be the same within a few microseconds, >>>>>>> longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse >>>>>>> maybe once a second. A follower would use her (not "his") clock to >>>>>>> measure the incoming period and tweak its local VCXO in the right >>>>>>> direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse >>>>>>> from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as
followers.
The PLL algorithm might be interesting.
It's certainly possible. However, within whatever tiny loop bandwidth >>>>>> you wound up with, the lockers would still have
20 log(40e6) = 152 dB
higher phase noise than the lockee.
GPS has that problem too.
It would be interesting to do the math to see whether it's possible to >>>>>> generate a concensus lock for the group: if you get everybody close >>>>>> enough, just sum their sine wave outputs and lock each one of them to >>>>>> that, with some bit of AC coupling or something so that they don't all >>>>>> wander together off to the edge of the tuning range.
Maybe have one doing the locking with a phase shifter and the others >>>>>> with VCOs, or something like that.
Definitely a partly-baked idea, but surely one could do better than 152 dB!
Cheers
Phil Hobbs
Each box is basically a multichannel power supply, but channels can be >>>>> programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent >>>>> RMS phase noise is OK as long as we stay time aligned longterm.
If a follower is told to start locking, it could timestamp the first >>>>> incoming 1 PPS with a giant counter clocked by its local 40 MHz VCO. >>>>> If a later 1 PPS edge appears to arrive too soon, we could speed up
our VCXO by, say, 1 PPM, and vice versa. So longterm it walks into
alignment with the 1 PPS and eventually dithers a microsecond per
second. Noise on the coax gets fixed over time too.
That's better than just measuring the 1 Hz period once a second,
tweaking the clock, and then throwing away that measurement. I want a >>>>> time lock, not a frequency lock.
Absolutely. The scary 152 dB number doesn't mean that doing something >>>> like that is automatically a bad idea.
Being an old RF and ultrastable laser guy, though, it does make my ears >>>> perk up. ;)
Cheers
Phil Hobbs
I like thermostats, single-bit-feedback control loops.
We have a couple of boxes that do fan control based on interior
temperature. Once a second, if it's above the setpoint, ratchet fan
speed up some fixed amount, 1% maybe. If it's cooler than the
setpoint, step fan speed down. There's no acoustic drama and it's
perfectly stable.
It dithers around the setpoint but nobody notices.
This is immune to classic control theory so the concept annoys some
people but it works great.
A real old time control guy like Tim Wescott would probably be a fan
too--the great virtue of a bang-bang controller is that (as you say)
it's highly resistant to variations in the _plant_.
Your furnace doesn't go nuts when you have a Christmas party, even
though all those people generate a lot of heat, and there's lots of
opening and closing of doors and ovens.
Cheers
Phil Hobbs
My power supply box has 8 plugin modules of various types. Some don't
need much air but some really do. The two big fans are howlers at 48
volts.
Each module can present one bit to the motherboard software: I want
more air, or I don't. If any board wants more, ratchet the fans up a
bit. If none want more, jog the fans down.
On Thu, 21 Jul 2022 10:15:20 -0400, bitrex <user@example.net> wrote:
On 7/21/2022 10:12 AM, bitrex wrote:
On 7/21/2022 4:33 AM, John Walliker wrote:
On Thursday, 21 July 2022 at 07:49:43 UTC+1, whit3rd wrote:
On Wednesday, July 20, 2022 at 4:21:08 PM UTC-7, John Larkin wrote: >>>>>> Suppose I have several rackmount boxes and each has a BNC connector on >>>>>> the back. Each of them has an open-drain mosfet, a weak pullup, and a >>>>>> lowpass filtered schmitt gate back into our FPGA.
If you can tolerate 'a few microseconds' on a 40 MHz signal, that's
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least >>>>>> time-align them to always be the same within a few microseconds,
longterm.
not a phase-lock
problem, it's a frequency-lock problem. Why not just run an up/down
counter
to generate a correction voltage for each non-leading VCO?
If you have an ethernet interface to each unit then Precision Time
Protocol
should do exactly what you want.
https://en.wikipedia.org/wiki/Precision_Time_Protocol
John
Yeah, that sounds like the ticket to me also. Trying to use each box's
system clock for purposes of keeping "user-space" tasks in sync across
boxes makes me uncomfortable, sounds like a srs hack.
At minimum it likely won't scale very well. Why implicitly discourage
one's customers from buying only a limited number of units
Time synchronization of programmable power supplies and loads is
precisely one selling feature that my customers want but nobody else
seems to make. It works fine in one box but I want to extend the
function to multiple boxes in a rack.
The controller in each box is a MicroZed and doesn't support the PTP
thing, and my customers may not be able top provide it anyhow. The 1
PPS thing works with just a BNC cable.
Besides, what I do is design things.
bitrex wrote:
On 7/21/2022 7:06 AM, Martin Brown wrote:Given that it's so simple to do it right, why not do that?
On 21/07/2022 01:22, John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC
connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a >>>>>> lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least >>>>>> time-align them to always be the same within a few microseconds,
longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse >>>>>> maybe once a second. A follower would use her (not "his") clock to >>>>>> measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse >>>>>> from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as
followers.
The PLL algorithm might be interesting.
It's certainly possible. However, within whatever tiny loop bandwidth >>>>> you wound up with, the lockers would still have
20 log(40e6) = 152 dB
higher phase noise than the lockee.
GPS has that problem too.
It would be interesting to do the math to see whether it's possible to >>>>> generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to >>>>> that, with some bit of AC coupling or something so that they don't all >>>>> wander together off to the edge of the tuning range.
Maybe have one doing the locking with a phase shifter and the others >>>>> with VCOs, or something like that.
Definitely a partly-baked idea, but surely one could do better than
152 dB!
Cheers
Phil Hobbs
Each box is basically a multichannel power supply, but channels can be >>>> programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.
You really need to define longterm before the problem becomes well
posed. Do you mean hours, days, weeks or months of runtime?
Yeah I don't quite get it, either. My rack of synthesizers can each
play one voice of the Maple Leaf Rag via MIDI and they all stay synced
together really well, at least over a timespan of several
minutes...superficially at least it sounds like he wants a sequencer.
Using the nuts & bolts system clock for synchronization of "user
tasks" also makes me uncomfortable, if the device behavior only need
to align to the millisecond why not trigger them using some simple
network protocol and let their hardware figure out how long a
millisecond is independently. Do the timings of these boxes need to be
tighter than the Maple Leaf Rag?
Cheers
Phil Hobbs
On 7/21/2022 10:21 AM, Lasse Langwadt Christensen wrote:
torsdag den 21. juli 2022 kl. 16.04.42 UTC+2 skrev bitrex:
On 7/21/2022 7:06 AM, Martin Brown wrote:
On 21/07/2022 01:22, John Larkin wrote:Yeah I don't quite get it, either. My rack of synthesizers can each play >> one voice of the Maple Leaf Rag via MIDI and they all stay synced
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
<pcdhSpamM...@electrooptical.net> wrote:
John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on >>>>>> the back. Each of them has an open-drain mosfet, a weak pullup, and a >>>>>> lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least >>>>>> time-align them to always be the same within a few microseconds, >>>>>> longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse >>>>>> maybe once a second. A follower would use her (not "his") clock to >>>>>> measure the incoming period and tweak its local VCXO in the right >>>>>> direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse >>>>>> from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as
followers.
The PLL algorithm might be interesting.
It's certainly possible. However, within whatever tiny loop bandwidth >>>>> you wound up with, the lockers would still have
20 log(40e6) = 152 dB
higher phase noise than the lockee.
GPS has that problem too.
It would be interesting to do the math to see whether it's possible to >>>>> generate a concensus lock for the group: if you get everybody close >>>>> enough, just sum their sine wave outputs and lock each one of them to >>>>> that, with some bit of AC coupling or something so that they don't all >>>>> wander together off to the edge of the tuning range.
Maybe have one doing the locking with a phase shifter and the others >>>>> with VCOs, or something like that.
Definitely a partly-baked idea, but surely one could do better than >>>>> 152 dB!
Cheers
Phil Hobbs
Each box is basically a multichannel power supply, but channels can be >>>> programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent >>>> RMS phase noise is OK as long as we stay time aligned longterm.
You really need to define longterm before the problem becomes well
posed. Do you mean hours, days, weeks or months of runtime?
together really well, at least over a timespan of several
minutes.
but they are anot free runnign are they? they are all reacting to midi
There's a system clock in each one surely but they don't try to sync
their system clocks, they receive an instruction "do X for Y ms" and
their processor figures out how long Y ms is, and does it for that long.
It is literally good enough for rock & roll, but whether it's good
enough for power supply sequencing IDK, there is gonna be some latency.
HP used to have GPIB on their power supplies, I've never used it but I
expect it wasn't really useful for tight synchronization.
On 7/21/2022 10:26 AM, Phil Hobbs wrote:
bitrex wrote:
On 7/21/2022 7:06 AM, Martin Brown wrote:Given that it's so simple to do it right, why not do that?
On 21/07/2022 01:22, John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC
connector on
the back. Each of them has an open-drain mosfet, a weak pullup,
and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at
least
time-align them to always be the same within a few microseconds, >>>>>>> longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low
pulse
maybe once a second. A follower would use her (not "his") clock to >>>>>>> measure the incoming period and tweak its local VCXO in the right >>>>>>> direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse >>>>>>> from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as
followers.
The PLL algorithm might be interesting.
It's certainly possible. However, within whatever tiny loop
bandwidth
you wound up with, the lockers would still have
20 log(40e6) = 152 dB
higher phase noise than the lockee.
GPS has that problem too.
It would be interesting to do the math to see whether it's
possible to
generate a concensus lock for the group: if you get everybody close >>>>>> enough, just sum their sine wave outputs and lock each one of them to >>>>>> that, with some bit of AC coupling or something so that they don't >>>>>> all
wander together off to the edge of the tuning range.
Maybe have one doing the locking with a phase shifter and the others >>>>>> with VCOs, or something like that.
Definitely a partly-baked idea, but surely one could do better
than 152 dB!
Cheers
Phil Hobbs
Each box is basically a multichannel power supply, but channels can be >>>>> programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent >>>>> RMS phase noise is OK as long as we stay time aligned longterm.
You really need to define longterm before the problem becomes well
posed. Do you mean hours, days, weeks or months of runtime?
Yeah I don't quite get it, either. My rack of synthesizers can each
play one voice of the Maple Leaf Rag via MIDI and they all stay
synced together really well, at least over a timespan of several
minutes...superficially at least it sounds like he wants a sequencer.
Using the nuts & bolts system clock for synchronization of "user
tasks" also makes me uncomfortable, if the device behavior only need
to align to the millisecond why not trigger them using some simple
network protocol and let their hardware figure out how long a
millisecond is independently. Do the timings of these boxes need to
be tighter than the Maple Leaf Rag?
Cheers
Phil Hobbs
If there's a way to get by letting each box synchronize to GPS on its
own and then using some simple network protocol to sequence them that's
what I'd do, yeah.
Trying to get their system clocks to sync up over a cable makes me uncomfortable, why do they need to share info about their inner lives.
jlarkin@highlandsniptechnology.com wrote:
On Thu, 21 Jul 2022 09:27:39 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
jlarkin@highlandsniptechnology.com wrote:
On Wed, 20 Jul 2022 20:28:35 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on >>>>>>>> the back. Each of them has an open-drain mosfet, a weak pullup, and a >>>>>>>> lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least >>>>>>>> time-align them to always be the same within a few microseconds, >>>>>>>> longterm.
I could call one the leader (not "master") and make the others >>>>>>>> followers (not "slaves") and have the leader make an active low pulse >>>>>>>> maybe once a second. A follower would use her (not "his") clock to >>>>>>>> measure the incoming period and tweak its local VCXO in the right >>>>>>>> direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse >>>>>>>> from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as >>>>>>>> followers.
The PLL algorithm might be interesting.
It's certainly possible. However, within whatever tiny loop bandwidth >>>>>>> you wound up with, the lockers would still have
20 log(40e6) = 152 dB
higher phase noise than the lockee.
GPS has that problem too.
It would be interesting to do the math to see whether it's possible to >>>>>>> generate a concensus lock for the group: if you get everybody close >>>>>>> enough, just sum their sine wave outputs and lock each one of them to >>>>>>> that, with some bit of AC coupling or something so that they don't all >>>>>>> wander together off to the edge of the tuning range.
Maybe have one doing the locking with a phase shifter and the others >>>>>>> with VCOs, or something like that.
Definitely a partly-baked idea, but surely one could do better than 152 dB!
Cheers
Phil Hobbs
Each box is basically a multichannel power supply, but channels can be >>>>>> programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent >>>>>> RMS phase noise is OK as long as we stay time aligned longterm.
If a follower is told to start locking, it could timestamp the first >>>>>> incoming 1 PPS with a giant counter clocked by its local 40 MHz VCO. >>>>>> If a later 1 PPS edge appears to arrive too soon, we could speed up >>>>>> our VCXO by, say, 1 PPM, and vice versa. So longterm it walks into >>>>>> alignment with the 1 PPS and eventually dithers a microsecond per
second. Noise on the coax gets fixed over time too.
That's better than just measuring the 1 Hz period once a second,
tweaking the clock, and then throwing away that measurement. I want a >>>>>> time lock, not a frequency lock.
Absolutely. The scary 152 dB number doesn't mean that doing something >>>>> like that is automatically a bad idea.
Being an old RF and ultrastable laser guy, though, it does make my ears >>>>> perk up. ;)
Cheers
Phil Hobbs
I like thermostats, single-bit-feedback control loops.
We have a couple of boxes that do fan control based on interior
temperature. Once a second, if it's above the setpoint, ratchet fan
speed up some fixed amount, 1% maybe. If it's cooler than the
setpoint, step fan speed down. There's no acoustic drama and it's
perfectly stable.
It dithers around the setpoint but nobody notices.
This is immune to classic control theory so the concept annoys some
people but it works great.
A real old time control guy like Tim Wescott would probably be a fan
too--the great virtue of a bang-bang controller is that (as you say)
it's highly resistant to variations in the _plant_.
Your furnace doesn't go nuts when you have a Christmas party, even
though all those people generate a lot of heat, and there's lots of
opening and closing of doors and ovens.
Cheers
Phil Hobbs
My power supply box has 8 plugin modules of various types. Some don't
need much air but some really do. The two big fans are howlers at 48
volts.
Each module can present one bit to the motherboard software: I want
more air, or I don't. If any board wants more, ratchet the fans up a
bit. If none want more, jog the fans down.
Yup. We do the Class H supplies for our TEC driver boards like that--if
the linear amp rails, immediately jack up the supply by 0.5 V or so,
then gradually ramp it down again. We could use two ADC channels, of
course, but one comparator is simpler and works very well.
Cheers
Phil Hobbs
I wonder if there's an advantage to using the closure phase for an array
that large. With 17 oscillators you've got 136 independent phase differences, so maybe there's a way to get 22 dB instead of 12 dB improvement.
CheersGerhard
bitrex wrote:
On 7/21/2022 10:26 AM, Phil Hobbs wrote:
bitrex wrote:
On 7/21/2022 7:06 AM, Martin Brown wrote:Given that it's so simple to do it right, why not do that?
On 21/07/2022 01:22, John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC
connector on
the back. Each of them has an open-drain mosfet, a weak pullup, >>>>>>>> and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at >>>>>>>> least
time-align them to always be the same within a few microseconds, >>>>>>>> longterm.
I could call one the leader (not "master") and make the others >>>>>>>> followers (not "slaves") and have the leader make an active low >>>>>>>> pulse
maybe once a second. A follower would use her (not "his") clock to >>>>>>>> measure the incoming period and tweak its local VCXO in the right >>>>>>>> direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse >>>>>>>> from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as >>>>>>>> followers.
The PLL algorithm might be interesting.
It's certainly possible. However, within whatever tiny loop
bandwidth
you wound up with, the lockers would still have
20 log(40e6) = 152 dB
higher phase noise than the lockee.
GPS has that problem too.
It would be interesting to do the math to see whether it's
possible to
generate a concensus lock for the group: if you get everybody close >>>>>>> enough, just sum their sine wave outputs and lock each one of them to >>>>>>> that, with some bit of AC coupling or something so that they don't >>>>>>> all
wander together off to the edge of the tuning range.
Maybe have one doing the locking with a phase shifter and the others >>>>>>> with VCOs, or something like that.
Definitely a partly-baked idea, but surely one could do better
than 152 dB!
Cheers
Phil Hobbs
Each box is basically a multichannel power supply, but channels can be >>>>>> programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent >>>>>> RMS phase noise is OK as long as we stay time aligned longterm.
You really need to define longterm before the problem becomes well
posed. Do you mean hours, days, weeks or months of runtime?
Yeah I don't quite get it, either. My rack of synthesizers can each
play one voice of the Maple Leaf Rag via MIDI and they all stay
synced together really well, at least over a timespan of several
minutes...superficially at least it sounds like he wants a sequencer.
Using the nuts & bolts system clock for synchronization of "user
tasks" also makes me uncomfortable, if the device behavior only need
to align to the millisecond why not trigger them using some simple
network protocol and let their hardware figure out how long a
millisecond is independently. Do the timings of these boxes need to
be tighter than the Maple Leaf Rag?
Cheers
Phil Hobbs
If there's a way to get by letting each box synchronize to GPS on its
own and then using some simple network protocol to sequence them that's
what I'd do, yeah.
Trying to get their system clocks to sync up over a cable makes me
uncomfortable, why do they need to share info about their inner lives.
And to think you went to art school.
Cheers
Phil Hobbs
On 7/21/2022 10:55 AM, jlarkin@highlandsniptechnology.com wrote:
On Thu, 21 Jul 2022 10:15:20 -0400, bitrex <user@example.net> wrote:
On 7/21/2022 10:12 AM, bitrex wrote:
On 7/21/2022 4:33 AM, John Walliker wrote:
On Thursday, 21 July 2022 at 07:49:43 UTC+1, whit3rd wrote:
On Wednesday, July 20, 2022 at 4:21:08 PM UTC-7, John Larkin wrote: >>>>>>> Suppose I have several rackmount boxes and each has a BNC connector on >>>>>>> the back. Each of them has an open-drain mosfet, a weak pullup, and a >>>>>>> lowpass filtered schmitt gate back into our FPGA.
If you can tolerate 'a few microseconds' on a 40 MHz signal, that's >>>>>> not a phase-lock
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least >>>>>>> time-align them to always be the same within a few microseconds, >>>>>>> longterm.
problem, it's a frequency-lock problem. Why not just run an up/down >>>>>> counter
to generate a correction voltage for each non-leading VCO?
If you have an ethernet interface to each unit then Precision Time
Protocol
should do exactly what you want.
https://en.wikipedia.org/wiki/Precision_Time_Protocol
John
Yeah, that sounds like the ticket to me also. Trying to use each box's >>>> system clock for purposes of keeping "user-space" tasks in sync across >>>> boxes makes me uncomfortable, sounds like a srs hack.
At minimum it likely won't scale very well. Why implicitly discourage
one's customers from buying only a limited number of units
Time synchronization of programmable power supplies and loads is
precisely one selling feature that my customers want but nobody else
seems to make. It works fine in one box but I want to extend the
function to multiple boxes in a rack.
The controller in each box is a MicroZed and doesn't support the PTP
thing, and my customers may not be able top provide it anyhow. The 1
PPS thing works with just a BNC cable.
Besides, what I do is design things.
So if it works fine in one box why can't you just send some simple
packet data that says like OK box 4, run program 2 now for 1,084 ms.
If they're all already locked individually to GPS or whatever other
standard they know how long a ms is. There will be some overhead latency
but syncing a bunch of boxes within a ms doesn't seem unreasonable.
It's at least easier to ballpark how well a digital scheme like that
would scale on paper. The BNC scheme is analog, how do you know.
On Thu, 21 Jul 2022 11:36:01 -0400, bitrex <user@example.net> wrote:I see.
On 7/21/2022 10:55 AM, jlarkin@highlandsniptechnology.com wrote:
On Thu, 21 Jul 2022 10:15:20 -0400, bitrex <user@example.net> wrote:
On 7/21/2022 10:12 AM, bitrex wrote:
On 7/21/2022 4:33 AM, John Walliker wrote:
On Thursday, 21 July 2022 at 07:49:43 UTC+1, whit3rd wrote:
On Wednesday, July 20, 2022 at 4:21:08 PM UTC-7, John Larkin wrote: >>>>>>>> Suppose I have several rackmount boxes and each has a BNC connector on >>>>>>>> the back. Each of them has an open-drain mosfet, a weak pullup, and a >>>>>>>> lowpass filtered schmitt gate back into our FPGA.
If you can tolerate 'a few microseconds' on a 40 MHz signal, that's >>>>>>> not a phase-lock
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least >>>>>>>> time-align them to always be the same within a few microseconds, >>>>>>>> longterm.
problem, it's a frequency-lock problem. Why not just run an up/down >>>>>>> counter
to generate a correction voltage for each non-leading VCO?
If you have an ethernet interface to each unit then Precision Time >>>>>> Protocol
should do exactly what you want.
https://en.wikipedia.org/wiki/Precision_Time_Protocol
John
Yeah, that sounds like the ticket to me also. Trying to use each box's >>>>> system clock for purposes of keeping "user-space" tasks in sync across >>>>> boxes makes me uncomfortable, sounds like a srs hack.
At minimum it likely won't scale very well. Why implicitly discourage
one's customers from buying only a limited number of units
Time synchronization of programmable power supplies and loads is
precisely one selling feature that my customers want but nobody else
seems to make. It works fine in one box but I want to extend the
function to multiple boxes in a rack.
The controller in each box is a MicroZed and doesn't support the PTP
thing, and my customers may not be able top provide it anyhow. The 1
PPS thing works with just a BNC cable.
Besides, what I do is design things.
So if it works fine in one box why can't you just send some simple
packet data that says like OK box 4, run program 2 now for 1,084 ms.
If they're all already locked individually to GPS or whatever other
standard they know how long a ms is. There will be some overhead latency
but syncing a bunch of boxes within a ms doesn't seem unreasonable.
It's at least easier to ballpark how well a digital scheme like that
would scale on paper. The BNC scheme is analog, how do you know.
The BNC would be 1 PPS pulses. They could come from GPS if it's
available, or one of the boxes could output the 1 PPS and the others
would sync to that.
When we designed the box, we added two BNCs, open drain drivers with
weak pullups and schmitt receivers, connected into our FPGA. We didn't
know what they were for, but they turn out to be handy.
One is START RUNNING YOUR SEQUENCES NOW and the other is the 1 PPS
lock. That should work.
Each module has a sequencer table in its local fpga RAM, sort of a
primitive program with 5 opcodes. A table entry can write any other
register in the FPGA, ie do anything, and one command is WAIT UNTIL,
against the 1 MHz start counter.
Customers can write fairly simple SCPI script files to program events
in each module, load them up, and fire off a shot and keep the whole experiment time synchronized forever.
All we want to do is revolutionize the power supply business.
It's actually useful to me to type and discuss this sort of thing.
Ideas evolve at their own rates.
Am 21.07.22 um 16:15 schrieb Phil Hobbs:
I wonder if there's an advantage to using the closure phase for an
array that large. With 17 oscillators you've got 136 independent
phase differences, so maybe there's a way to get 22 dB instead of 12
dB improvement.
-v ?
what do you mean with closure phase? Where do the 22 dB come
from?
The idea was simply to have all 16 regulated to the be
synchronous and then feed them into a 16-to--1 Wilkinson
combiner. The phase noise should average out among the
16 units. Just as proof of concept. The MTI-260 are quite ok,
but with bleeding edge oscillators that could be interesting.
In the region where you just cannot improve an oscillator.
CheersGerhard
On Thursday, 21 July 2022 at 15:42:40 UTC+1, bitrex wrote:
On 7/21/2022 10:21 AM, Lasse Langwadt Christensen wrote:
torsdag den 21. juli 2022 kl. 16.04.42 UTC+2 skrev bitrex:
On 7/21/2022 7:06 AM, Martin Brown wrote:
On 21/07/2022 01:22, John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
<pcdhSpamM...@electrooptical.net> wrote:
John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on >>>>>>>> the back. Each of them has an open-drain mosfet, a weak pullup, and a >>>>>>>> lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least >>>>>>>> time-align them to always be the same within a few microseconds, >>>>>>>> longterm.
I could call one the leader (not "master") and make the others >>>>>>>> followers (not "slaves") and have the leader make an active low pulse >>>>>>>> maybe once a second. A follower would use her (not "his") clock to >>>>>>>> measure the incoming period and tweak its local VCXO in the right >>>>>>>> direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse >>>>>>>> from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as >>>>>>>> followers.
The PLL algorithm might be interesting.
It's certainly possible. However, within whatever tiny loop bandwidth >>>>>>> you wound up with, the lockers would still have
20 log(40e6) = 152 dB
higher phase noise than the lockee.
GPS has that problem too.
It would be interesting to do the math to see whether it's possible to >>>>>>> generate a concensus lock for the group: if you get everybody close >>>>>>> enough, just sum their sine wave outputs and lock each one of them to >>>>>>> that, with some bit of AC coupling or something so that they don't all >>>>>>> wander together off to the edge of the tuning range.
Maybe have one doing the locking with a phase shifter and the others >>>>>>> with VCOs, or something like that.
Definitely a partly-baked idea, but surely one could do better than >>>>>>> 152 dB!
Cheers
Phil Hobbs
Each box is basically a multichannel power supply, but channels can be >>>>>> programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent >>>>>> RMS phase noise is OK as long as we stay time aligned longterm.
You really need to define longterm before the problem becomes well
posed. Do you mean hours, days, weeks or months of runtime?
There's a system clock in each one surely but they don't try to syncYeah I don't quite get it, either. My rack of synthesizers can each play >>>> one voice of the Maple Leaf Rag via MIDI and they all stay synced
together really well, at least over a timespan of several
minutes.
but they are anot free runnign are they? they are all reacting to midi
their system clocks, they receive an instruction "do X for Y ms" and
their processor figures out how long Y ms is, and does it for that long.
It is literally good enough for rock & roll, but whether it's good
enough for power supply sequencing IDK, there is gonna be some latency.
HP used to have GPIB on their power supplies, I've never used it but I
expect it wasn't really useful for tight synchronization.
The Group Execute Trigger command does allow quite tight synchronisation between different GPIB devices.
Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least time-align them to always be the same within a few microseconds,
longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse
maybe once a second.
A follower would use her (not "his") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.
On 21/07/2022 16:31, John Walliker wrote:
On Thursday, 21 July 2022 at 15:42:40 UTC+1, bitrex wrote:
On 7/21/2022 10:21 AM, Lasse Langwadt Christensen wrote:
torsdag den 21. juli 2022 kl. 16.04.42 UTC+2 skrev bitrex:
On 7/21/2022 7:06 AM, Martin Brown wrote:
On 21/07/2022 01:22, John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
<pcdhSpamM...@electrooptical.net> wrote:
John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC
connector on
the back. Each of them has an open-drain mosfet, a weak pullup, >>>>>>>>> and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at >>>>>>>>> least
time-align them to always be the same within a few microseconds, >>>>>>>>> longterm.
I could call one the leader (not "master") and make the others >>>>>>>>> followers (not "slaves") and have the leader make an active low >>>>>>>>> pulse
maybe once a second. A follower would use her (not "his") clock to >>>>>>>>> measure the incoming period and tweak its local VCXO in the right >>>>>>>>> direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse >>>>>>>>> from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as >>>>>>>>> followers.
The PLL algorithm might be interesting.
It's certainly possible. However, within whatever tiny loop
bandwidth
you wound up with, the lockers would still have
20 log(40e6) = 152 dB
higher phase noise than the lockee.
GPS has that problem too.
It would be interesting to do the math to see whether it's
possible to
generate a concensus lock for the group: if you get everybody close >>>>>>>> enough, just sum their sine wave outputs and lock each one of
them to
that, with some bit of AC coupling or something so that they
don't all
wander together off to the edge of the tuning range.
Maybe have one doing the locking with a phase shifter and the
others
with VCOs, or something like that.
Definitely a partly-baked idea, but surely one could do better than >>>>>>>> 152 dB!
Cheers
Phil Hobbs
Each box is basically a multichannel power supply, but channels
can be
programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once >>>>>>> programs are kicked off together. So, many microseconds of
equivalent
RMS phase noise is OK as long as we stay time aligned longterm.
You really need to define longterm before the problem becomes well >>>>>> posed. Do you mean hours, days, weeks or months of runtime?
There's a system clock in each one surely but they don't try to syncYeah I don't quite get it, either. My rack of synthesizers can each
play
one voice of the Maple Leaf Rag via MIDI and they all stay synced
together really well, at least over a timespan of several
minutes.
but they are anot free runnign are they? they are all reacting to midi >>>>
their system clocks, they receive an instruction "do X for Y ms" and
their processor figures out how long Y ms is, and does it for that long. >>>
It is literally good enough for rock & roll, but whether it's good
enough for power supply sequencing IDK, there is gonna be some latency.
HP used to have GPIB on their power supplies, I've never used it but I
expect it wasn't really useful for tight synchronization.
The Group Execute Trigger command does allow quite tight synchronisation
between different GPIB devices.
GPIB flat out on a good day could manage 1Mbyte/s but in real world situations with interconnect cabling you would be lucky to get 500kb/s.
It's best feature was that it ran at the maximum speed the receiving
device could handle (assuming that the controller was fast enough).
Synchronisation to a GET command would be probably be better than 1us
but would depend on the decoding time in each individual box. Some GPIB devices were rather pedestrian at accepting commands.
IEEE488 was good in its day but a bit long in the tooth now. Still on
some test equipment in service today and was provided as standard on NEC
9801 PC's in Japan although hardly ever used by their customers.
The cables and connectors could only be described as a bit clunky!
They really didn't get on with metal swarf being around but were OK in
clean dry electronics/physics labs - much less so in chemistry ones...
On 7/21/2022 1:21 PM, Martin Brown wrote:
On 21/07/2022 16:31, John Walliker wrote:
On Thursday, 21 July 2022 at 15:42:40 UTC+1, bitrex wrote:
On 7/21/2022 10:21 AM, Lasse Langwadt Christensen wrote:
torsdag den 21. juli 2022 kl. 16.04.42 UTC+2 skrev bitrex:
On 7/21/2022 7:06 AM, Martin Brown wrote:
On 21/07/2022 01:22, John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil HobbsYou really need to define longterm before the problem becomes well >>>>>>> posed. Do you mean hours, days, weeks or months of runtime?
<pcdhSpamM...@electrooptical.net> wrote:
John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC
connector on
the back. Each of them has an open-drain mosfet, a weak
pullup, and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or >>>>>>>>>> at least
time-align them to always be the same within a few microseconds, >>>>>>>>>> longterm.
I could call one the leader (not "master") and make the others >>>>>>>>>> followers (not "slaves") and have the leader make an active >>>>>>>>>> low pulse
maybe once a second. A follower would use her (not "his")
clock to
measure the incoming period and tweak its local VCXO in the right >>>>>>>>>> direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS >>>>>>>>>> pulse
from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as >>>>>>>>>> followers.
The PLL algorithm might be interesting.
It's certainly possible. However, within whatever tiny loop
bandwidth
you wound up with, the lockers would still have
20 log(40e6) = 152 dB
higher phase noise than the lockee.
GPS has that problem too.
It would be interesting to do the math to see whether it's
possible to
generate a concensus lock for the group: if you get everybody >>>>>>>>> close
enough, just sum their sine wave outputs and lock each one of >>>>>>>>> them to
that, with some bit of AC coupling or something so that they >>>>>>>>> don't all
wander together off to the edge of the tuning range.
Maybe have one doing the locking with a phase shifter and the >>>>>>>>> others
with VCOs, or something like that.
Definitely a partly-baked idea, but surely one could do better >>>>>>>>> than
152 dB!
Cheers
Phil Hobbs
Each box is basically a multichannel power supply, but channels >>>>>>>> can be
programmed to do stuff in timed sequences. I want different box >>>>>>>> outputs to time align within, say, one millisecond longterm once >>>>>>>> programs are kicked off together. So, many microseconds of
equivalent
RMS phase noise is OK as long as we stay time aligned longterm. >>>>>>>
There's a system clock in each one surely but they don't try to syncYeah I don't quite get it, either. My rack of synthesizers can
each play
one voice of the Maple Leaf Rag via MIDI and they all stay synced
together really well, at least over a timespan of several
minutes.
but they are anot free runnign are they? they are all reacting to midi >>>>>
their system clocks, they receive an instruction "do X for Y ms" and
their processor figures out how long Y ms is, and does it for that
long.
It is literally good enough for rock & roll, but whether it's good
enough for power supply sequencing IDK, there is gonna be some latency. >>>>
HP used to have GPIB on their power supplies, I've never used it but I >>>> expect it wasn't really useful for tight synchronization.
The Group Execute Trigger command does allow quite tight synchronisation >>> between different GPIB devices.
GPIB flat out on a good day could manage 1Mbyte/s but in real world
situations with interconnect cabling you would be lucky to get
500kb/s. It's best feature was that it ran at the maximum speed the
receiving device could handle (assuming that the controller was fast
enough).
Synchronisation to a GET command would be probably be better than 1us
but would depend on the decoding time in each individual box. Some
GPIB devices were rather pedestrian at accepting commands.
IEEE488 was good in its day but a bit long in the tooth now. Still on
some test equipment in service today and was provided as standard on
NEC 9801 PC's in Japan although hardly ever used by their customers.
The cables and connectors could only be described as a bit clunky!
They really didn't get on with metal swarf being around but were OK in
clean dry electronics/physics labs - much less so in chemistry ones...
I feel like there wasn't really a good relatively inexpensive standard
for interfacing PC peripherals until USB.
On 7/21/2022 1:41 PM, bitrex wrote:
On 7/21/2022 1:21 PM, Martin Brown wrote:
On 21/07/2022 16:31, John Walliker wrote:
On Thursday, 21 July 2022 at 15:42:40 UTC+1, bitrex wrote:
On 7/21/2022 10:21 AM, Lasse Langwadt Christensen wrote:
torsdag den 21. juli 2022 kl. 16.04.42 UTC+2 skrev bitrex:
On 7/21/2022 7:06 AM, Martin Brown wrote:
On 21/07/2022 01:22, John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil HobbsYou really need to define longterm before the problem becomes well >>>>>>> posed. Do you mean hours, days, weeks or months of runtime?
<pcdhSpamM...@electrooptical.net> wrote:
John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC >>>>>>>>>> connector on
the back. Each of them has an open-drain mosfet, a weak
pullup, and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees. >>>>>>>>>>
Each box has a 40 MHz VCXO and I want to phase-lock them, or >>>>>>>>>> at least
time-align them to always be the same within a few microseconds, >>>>>>>>>> longterm.
I could call one the leader (not "master") and make the others >>>>>>>>>> followers (not "slaves") and have the leader make an active >>>>>>>>>> low pulse
maybe once a second. A follower would use her (not "his") >>>>>>>>>> clock to
measure the incoming period and tweak its local VCXO in the right >>>>>>>>>> direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS >>>>>>>>>> pulse
from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as >>>>>>>>>> followers.
The PLL algorithm might be interesting.
It's certainly possible. However, within whatever tiny loop >>>>>>>>> bandwidth
you wound up with, the lockers would still have
20 log(40e6) = 152 dB
higher phase noise than the lockee.
GPS has that problem too.
It would be interesting to do the math to see whether it's >>>>>>>>> possible to
generate a concensus lock for the group: if you get everybody >>>>>>>>> close
enough, just sum their sine wave outputs and lock each one of >>>>>>>>> them to
that, with some bit of AC coupling or something so that they >>>>>>>>> don't all
wander together off to the edge of the tuning range.
Maybe have one doing the locking with a phase shifter and the >>>>>>>>> others
with VCOs, or something like that.
Definitely a partly-baked idea, but surely one could do better >>>>>>>>> than
152 dB!
Cheers
Phil Hobbs
Each box is basically a multichannel power supply, but channels >>>>>>>> can be
programmed to do stuff in timed sequences. I want different box >>>>>>>> outputs to time align within, say, one millisecond longterm once >>>>>>>> programs are kicked off together. So, many microseconds of
equivalent
RMS phase noise is OK as long as we stay time aligned longterm. >>>>>>>
There's a system clock in each one surely but they don't try to sync >>>> their system clocks, they receive an instruction "do X for Y ms" and >>>> their processor figures out how long Y ms is, and does it for thatYeah I don't quite get it, either. My rack of synthesizers can
each play
one voice of the Maple Leaf Rag via MIDI and they all stay synced >>>>>> together really well, at least over a timespan of several
minutes.
but they are anot free runnign are they? they are all reacting to midi >>>>>
long.
It is literally good enough for rock & roll, but whether it's good
enough for power supply sequencing IDK, there is gonna be some latency. >>>>
HP used to have GPIB on their power supplies, I've never used it but I >>>> expect it wasn't really useful for tight synchronization.
The Group Execute Trigger command does allow quite tight synchronisation >>> between different GPIB devices.
GPIB flat out on a good day could manage 1Mbyte/s but in real world
situations with interconnect cabling you would be lucky to get
500kb/s. It's best feature was that it ran at the maximum speed the
receiving device could handle (assuming that the controller was fast
enough).
Synchronisation to a GET command would be probably be better than 1us
but would depend on the decoding time in each individual box. Some
GPIB devices were rather pedestrian at accepting commands.
IEEE488 was good in its day but a bit long in the tooth now. Still on
some test equipment in service today and was provided as standard on
NEC 9801 PC's in Japan although hardly ever used by their customers.
The cables and connectors could only be described as a bit clunky!
They really didn't get on with metal swarf being around but were OK in
clean dry electronics/physics labs - much less so in chemistry ones...
I feel like there wasn't really a good relatively inexpensive standardOops I forgot about AppleTalk. I remember helping some students get
for interfacing PC peripherals until USB.
their Mac SEs on the Internet (email and FTP and maybe some basic web browsing I can't recall) via some kind of Ethernet to AppleTalk adapter,
it wasn't uncommon in the mid 90s for college students to be using hand-me-down Macs from the 80s, but I couldn't for the life of me now remember how I did it.
torsdag den 21. juli 2022 kl. 19.45.26 UTC+2 skrev bitrex:
On 7/21/2022 1:41 PM, bitrex wrote:
On 7/21/2022 1:21 PM, Martin Brown wrote:Oops I forgot about AppleTalk. I remember helping some students get
On 21/07/2022 16:31, John Walliker wrote:
On Thursday, 21 July 2022 at 15:42:40 UTC+1, bitrex wrote:
On 7/21/2022 10:21 AM, Lasse Langwadt Christensen wrote:
torsdag den 21. juli 2022 kl. 16.04.42 UTC+2 skrev bitrex:
On 7/21/2022 7:06 AM, Martin Brown wrote:
On 21/07/2022 01:22, John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil HobbsYou really need to define longterm before the problem becomes well >>>>>>>>> posed. Do you mean hours, days, weeks or months of runtime?
<pcdhSpamM...@electrooptical.net> wrote:
John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC >>>>>>>>>>>> connector on
the back. Each of them has an open-drain mosfet, a weak >>>>>>>>>>>> pullup, and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees. >>>>>>>>>>>>
Each box has a 40 MHz VCXO and I want to phase-lock them, or >>>>>>>>>>>> at least
time-align them to always be the same within a few microseconds, >>>>>>>>>>>> longterm.
I could call one the leader (not "master") and make the others >>>>>>>>>>>> followers (not "slaves") and have the leader make an active >>>>>>>>>>>> low pulse
maybe once a second. A follower would use her (not "his") >>>>>>>>>>>> clock to
measure the incoming period and tweak its local VCXO in the right >>>>>>>>>>>> direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS >>>>>>>>>>>> pulse
from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as >>>>>>>>>>>> followers.
The PLL algorithm might be interesting.
It's certainly possible. However, within whatever tiny loop >>>>>>>>>>> bandwidth
you wound up with, the lockers would still have
20 log(40e6) = 152 dB
higher phase noise than the lockee.
GPS has that problem too.
It would be interesting to do the math to see whether it's >>>>>>>>>>> possible to
generate a concensus lock for the group: if you get everybody >>>>>>>>>>> close
enough, just sum their sine wave outputs and lock each one of >>>>>>>>>>> them to
that, with some bit of AC coupling or something so that they >>>>>>>>>>> don't all
wander together off to the edge of the tuning range.
Maybe have one doing the locking with a phase shifter and the >>>>>>>>>>> others
with VCOs, or something like that.
Definitely a partly-baked idea, but surely one could do better >>>>>>>>>>> than
152 dB!
Cheers
Phil Hobbs
Each box is basically a multichannel power supply, but channels >>>>>>>>>> can be
programmed to do stuff in timed sequences. I want different box >>>>>>>>>> outputs to time align within, say, one millisecond longterm once >>>>>>>>>> programs are kicked off together. So, many microseconds of >>>>>>>>>> equivalent
RMS phase noise is OK as long as we stay time aligned longterm. >>>>>>>>>
There's a system clock in each one surely but they don't try to sync >>>>>> their system clocks, they receive an instruction "do X for Y ms" and >>>>>> their processor figures out how long Y ms is, and does it for that >>>>>> long.Yeah I don't quite get it, either. My rack of synthesizers can >>>>>>>> each play
one voice of the Maple Leaf Rag via MIDI and they all stay synced >>>>>>>> together really well, at least over a timespan of several
minutes.
but they are anot free runnign are they? they are all reacting to midi >>>>>>>
It is literally good enough for rock & roll, but whether it's good >>>>>> enough for power supply sequencing IDK, there is gonna be some latency. >>>>>>
HP used to have GPIB on their power supplies, I've never used it but I >>>>>> expect it wasn't really useful for tight synchronization.
The Group Execute Trigger command does allow quite tight synchronisation >>>>> between different GPIB devices.
GPIB flat out on a good day could manage 1Mbyte/s but in real world
situations with interconnect cabling you would be lucky to get
500kb/s. It's best feature was that it ran at the maximum speed the
receiving device could handle (assuming that the controller was fast
enough).
Synchronisation to a GET command would be probably be better than 1us
but would depend on the decoding time in each individual box. Some
GPIB devices were rather pedestrian at accepting commands.
IEEE488 was good in its day but a bit long in the tooth now. Still on
some test equipment in service today and was provided as standard on
NEC 9801 PC's in Japan although hardly ever used by their customers.
The cables and connectors could only be described as a bit clunky!
They really didn't get on with metal swarf being around but were OK in >>>> clean dry electronics/physics labs - much less so in chemistry ones... >>>>
I feel like there wasn't really a good relatively inexpensive standard
for interfacing PC peripherals until USB.
their Mac SEs on the Internet (email and FTP and maybe some basic web
browsing I can't recall) via some kind of Ethernet to AppleTalk adapter,
it wasn't uncommon in the mid 90s for college students to be using
hand-me-down Macs from the 80s, but I couldn't for the life of me now
remember how I did it.
afaik Apple talk was just a serialport with an RS422 transceiver instead of RS232
Am 21.07.22 um 13:19 schrieb jlarkin@highlandsniptechnology.com:
Where does the 10 MHz come from?
Choise of implementer. One local clock generator is needed.
This clock determines short term stabiity and phase noise.
My Lucent KS24361 uses 5 MHz MTI-260 double ovens; for
redundancy/holdover it has a 2nd unit with another crystal
oven without a receiver.
The redundancy units were really hard to sell without the
receiver; that's why I have 20 of these MTI-260, got a good
price. :-)
They were new old stock built by HP/Agilent for Lucent as
replacement parts. They have never been on a telecom tower
in China like most of those one gets on ebay.
I have expanded the Lucent to 10 MHZ and with a distribution
amplifier:
< http://www.hoffmann-hochfrequenz.de/downloads/DoubDist.pdf >
cheers, Gerhard
Sounds good
It's actually useful to me to type and discuss this sort of thing.
Ideas evolve at their own rates.
I'm just sayin there's also a standard (uh oh!) dating back to the 50s
for synchronizing equipment using time-code:
<https://en.wikipedia.org/wiki/IRIG_timecode>
up to 10,000 pulses per second. I understand now that there's no
facility to program or sequence one box from the others they each run
their own "script" from memory.
On a sunny day (Thu, 21 Jul 2022 12:35:52 -0400) it happened bitrex <user@example.net> wrote in <JffCK.582999$X_i.553981@fx18.iad>:
Sounds good
It's actually useful to me to type and discuss this sort of thing.
Ideas evolve at their own rates.
I'm just sayin there's also a standard (uh oh!) dating back to the 50s
for synchronizing equipment using time-code:
<https://en.wikipedia.org/wiki/IRIG_timecode>
up to 10,000 pulses per second. I understand now that there's no
facility to program or sequence one box from the others they each run
their own "script" from memory.
Yea, used it every day back then :-) audio-video sync
On Thu, 21 Jul 2022 07:43:18 +0200, Gerhard Hoffmann <dk4xp@arcor.de>
wrote:
Am 21.07.22 um 01:20 schrieb John Larkin:
Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.
I have a backburner project of locking 16 MTI-260 oscillators
slooowy to another one, and when they are in sync, combine
them with an array of Wilkinsons. That should have a nice
effect on phase noise by averaging over 16.
The CPLD has enough resources to implement that as a delay
locked loop with 1 pps, but low hanging fruit first.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse
maybe once a second. A follower would use her (not "his") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?
No. There is no 1PPS pulse from the sat nor the need for exactly 10 MHz. >>The sats transmit a pseudo noise sequence that is
aligned to the second of their local clock source.
The GPS receiver knows the polynomial and runs a local copy of
the polynomial. It knows by cross correlation if the local
pseudo noise is the same as that of the sat and therefore knows
the start of the second. Usually that won't be the case.
Then the receiver delays its own polynomial by omitting a
clock to the shift register that generates it and tries again.
Sooner or later it will fit.
Where does the 10 MHz come from?
The cables and connectors could only be described as a bit clunky!
They really didn't get on with metal swarf being around but were OK in clean >> dry electronics/physics labs - much less so in chemistry ones...
I feel like there wasn't really a good relatively inexpensive standard for interfacing PC peripherals until USB. Serial and parallel were slow (occasionally some devices supported ECP, I remember having to enable it in the
BIOS sometimes), and external SCSI wasn't really well-suited to anything but external disk drives.
I don't think you could hot-swap IEE-488 either but it seems like it was pretty
fast and more amenable to a wide class of devices than SCSI, but just didn't seem to catch on outside the test equipment realm.
On Thursday, 21 July 2022 at 15:42:40 UTC+1, bitrex wrote:
HP used to have GPIB on their power supplies, I've never used it but I
expect it wasn't really useful for tight synchronization.
The Group Execute Trigger command does allow quite tight synchronisation between different GPIB devices.
Am 21.07.22 um 13:19 schrieb jlarkin@highlandsniptechnology.com:
Where does the 10 MHz come from?
Choise of implementer. One local clock generator is needed.
This clock determines short term stabiity and phase noise.
You really need to define longterm before the problem becomes well posed. Do >> you mean hours, days, weeks or months of runtime?
Yeah I don't quite get it, either. My rack of synthesizers can each play one voice of the Maple Leaf Rag via MIDI and they all stay synced together really
well, at least over a timespan of several minutes...superficially at least it sounds like he wants a sequencer.
Using the nuts & bolts system clock for synchronization of "user tasks" also makes me uncomfortable, if the device behavior only need to align to the millisecond why not trigger them using some simple network protocol and let their hardware figure out how long a millisecond is independently. Do the timings of these boxes need to be tighter than the Maple Leaf Rag?
On 7/21/2022 7:04 AM, bitrex wrote:
You really need to define longterm before the problem becomes well
posed. Do you mean hours, days, weeks or months of runtime?
Yeah I don't quite get it, either. My rack of synthesizers can each
play one voice of the Maple Leaf Rag via MIDI and they all stay synced
together really
How is "really well" defined? In the domain of human auditory perception?
well, at least over a timespan of several minutes...superficially at
least it sounds like he wants a sequencer.
Can you disconnect the controller and have them continue playing (from
stored
sequence) AND retain that synchornization "indefinitely"?
Using the nuts & bolts system clock for synchronization of "user
tasks" also makes me uncomfortable, if the device behavior only need
to align to the millisecond why not trigger them using some simple
network protocol and let their hardware figure out how long a
millisecond is independently. Do the timings of these boxes need to be
tighter than the Maple Leaf Rag?
Providing (and distributing) individual "events" on a shared medium suffers from scaling problems. How do you tag them so that the intended clients know which events are of significance to them?
On 7/21/2022 4:33 AM, John Walliker wrote:
If you have an ethernet interface to each unit then Precision Time Protocol >> should do exactly what you want.
https://en.wikipedia.org/wiki/Precision_Time_Protocol
John
Yeah, that sounds like the ticket to me also. Trying to use each box's system clock for purposes of keeping "user-space" tasks in sync across boxes makes me
uncomfortable, sounds like a srs hack.
If you need to tightly synchronize events between physically separate hardware
why not use a standard designed for the task rather than some roll-your-own shit
On 7/21/2022 9:04 PM, Don Y wrote:
On 7/21/2022 7:04 AM, bitrex wrote:
You really need to define longterm before the problem becomes well posed. >>>> Do you mean hours, days, weeks or months of runtime?
Yeah I don't quite get it, either. My rack of synthesizers can each play one
voice of the Maple Leaf Rag via MIDI and they all stay synced together really
How is "really well" defined? In the domain of human auditory perception? >>
well, at least over a timespan of several minutes...superficially at least >>> it sounds like he wants a sequencer.
Can you disconnect the controller and have them continue playing (from stored
sequence) AND retain that synchornization "indefinitely"?
Using the nuts & bolts system clock for synchronization of "user tasks" also
makes me uncomfortable, if the device behavior only need to align to the >>> millisecond why not trigger them using some simple network protocol and let >>> their hardware figure out how long a millisecond is independently. Do the >>> timings of these boxes need to be tighter than the Maple Leaf Rag?
Providing (and distributing) individual "events" on a shared medium suffers >> from scaling problems. How do you tag them so that the intended clients
know which events are of significance to them?
His machine's sequences are all programmed individual to a given box, there's no provision for controlling one from the others directly other than telling one to start its program and providing some kind of master sync, whatever it is.
The way this would be handled in the music-world analogy is something like MIDI
timecode, it's not unusual for individual machines to have their own sequencers
and want to gang events together in that realm, either.
<https://en.wikipedia.org/wiki/MIDI_timecode>
The resolution of the timecode doesn't automatically imply the timing resolution, given a "start" command and the clock any good-quality device will
be able to interpolate between quarter-frames to know when it should fire an event, if its internal sequencer has finer granularity than that.
I mentioned elsewhere that there's a more general-purpose sync standard that's
been around a long time:
torsdag den 21. juli 2022 kl. 01.21.08 UTC+2 skrev John Larkin:
Suppose I have several rackmount boxes...
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least time-align them to always be the same within a few microseconds,
longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse
maybe once a second.
why so slow?
A follower would use her (not "his") clock to
measure the incoming period and tweak its local VCXO in the right direction. That should work.
it'll only make the run at at the same speed, not time aligned
jlarkin@highlandsniptechnology.com wrote:
On Thu, 21 Jul 2022 07:43:18 +0200, Gerhard Hoffmann <dk4xp@arcor.de>
wrote:
Am 21.07.22 um 01:20 schrieb John Larkin:
Suppose I have several rackmount boxes and each has a BNC connector on >>>> the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.
I have a backburner project of locking 16 MTI-260 oscillators
slooowy to another one, and when they are in sync, combine
them with an array of Wilkinsons. That should have a nice
effect on phase noise by averaging over 16.
The CPLD has enough resources to implement that as a delay
locked loop with 1 pps, but low hanging fruit first.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse
maybe once a second. A follower would use her (not "his") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?
No. There is no 1PPS pulse from the sat nor the need for exactly 10 MHz. >>>The sats transmit a pseudo noise sequence that is
aligned to the second of their local clock source.
The GPS receiver knows the polynomial and runs a local copy of
the polynomial. It knows by cross correlation if the local
pseudo noise is the same as that of the sat and therefore knows
the start of the second. Usually that won't be the case.
Then the receiver delays its own polynomial by omitting a
clock to the shift register that generates it and tries again.
Sooner or later it will fit.
Where does the 10 MHz come from?
https://en.wikipedia.org/wiki/GPS_disciplined_oscillator
Gerhard Hoffmann wrote:
Am 21.07.22 um 16:15 schrieb Phil Hobbs:
I wonder if there's an advantage to using the closure phase for an
array that large. With 17 oscillators you've got 136 independent
phase differences, so maybe there's a way to get 22 dB instead of 12
dB improvement.
-v ?
what do you mean with closure phase? Where do the 22 dB come
from?
The idea was simply to have all 16 regulated to the be
synchronous and then feed them into a 16-to--1 Wilkinson
combiner. The phase noise should average out among the
16 units. Just as proof of concept. The MTI-260 are quite ok,
but with bleeding edge oscillators that could be interesting.
In the region where you just cannot improve an oscillator.
CheersGerhard
Sure. Thing is, that wastes a lot of information that you could maybe
use to get 10*log(136) = 21.3 dB improvement instead of 10*log(17) =
12.3 dB. [136 = N(N-1)/2 when N = 17.]
Closure is a really cute idea, which I first came across in the context
of very long baseline interferometry (VLBI) radio telescopes. See the discussion from BEOS 3e here:
<https://electrooptical.net/www/sed/closure.png>.
On 7/21/2022 12:09 PM, jlarkin@highlandsniptechnology.com wrote:
On Thu, 21 Jul 2022 11:36:01 -0400, bitrex <user@example.net> wrote:I see.
On 7/21/2022 10:55 AM, jlarkin@highlandsniptechnology.com wrote:
On Thu, 21 Jul 2022 10:15:20 -0400, bitrex <user@example.net> wrote:
On 7/21/2022 10:12 AM, bitrex wrote:
On 7/21/2022 4:33 AM, John Walliker wrote:
On Thursday, 21 July 2022 at 07:49:43 UTC+1, whit3rd wrote:
On Wednesday, July 20, 2022 at 4:21:08 PM UTC-7, John Larkin wrote: >>>>>>>>> Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a >>>>>>>>> lowpass filtered schmitt gate back into our FPGA.If you can tolerate 'a few microseconds' on a 40 MHz signal, that's >>>>>>>> not a phase-lock
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least >>>>>>>>> time-align them to always be the same within a few microseconds, >>>>>>>>> longterm.
problem, it's a frequency-lock problem. Why not just run an up/down >>>>>>>> counter
to generate a correction voltage for each non-leading VCO?
If you have an ethernet interface to each unit then Precision Time >>>>>>> Protocol
should do exactly what you want.
https://en.wikipedia.org/wiki/Precision_Time_Protocol
John
Yeah, that sounds like the ticket to me also. Trying to use each box's >>>>>> system clock for purposes of keeping "user-space" tasks in sync across >>>>>> boxes makes me uncomfortable, sounds like a srs hack.
At minimum it likely won't scale very well. Why implicitly discourage >>>>> one's customers from buying only a limited number of units
Time synchronization of programmable power supplies and loads is
precisely one selling feature that my customers want but nobody else
seems to make. It works fine in one box but I want to extend the
function to multiple boxes in a rack.
The controller in each box is a MicroZed and doesn't support the PTP
thing, and my customers may not be able top provide it anyhow. The 1
PPS thing works with just a BNC cable.
Besides, what I do is design things.
So if it works fine in one box why can't you just send some simple
packet data that says like OK box 4, run program 2 now for 1,084 ms.
If they're all already locked individually to GPS or whatever other
standard they know how long a ms is. There will be some overhead latency >>> but syncing a bunch of boxes within a ms doesn't seem unreasonable.
It's at least easier to ballpark how well a digital scheme like that
would scale on paper. The BNC scheme is analog, how do you know.
The BNC would be 1 PPS pulses. They could come from GPS if it's
available, or one of the boxes could output the 1 PPS and the others
would sync to that.
When we designed the box, we added two BNCs, open drain drivers with
weak pullups and schmitt receivers, connected into our FPGA. We didn't
know what they were for, but they turn out to be handy.
One is START RUNNING YOUR SEQUENCES NOW and the other is the 1 PPS
lock. That should work.
Each module has a sequencer table in its local fpga RAM, sort of a
primitive program with 5 opcodes. A table entry can write any other
register in the FPGA, ie do anything, and one command is WAIT UNTIL,
against the 1 MHz start counter.
Customers can write fairly simple SCPI script files to program events
in each module, load them up, and fire off a shot and keep the whole
experiment time synchronized forever.
Gotcha
All we want to do is revolutionize the power supply business.
Sounds good
It's actually useful to me to type and discuss this sort of thing.
Ideas evolve at their own rates.
I'm just sayin there's also a standard (uh oh!) dating back to the 50s
for synchronizing equipment using time-code:
<https://en.wikipedia.org/wiki/IRIG_timecode>
up to 10,000 pulses per second. I understand now that there's no
facility to program or sequence one box from the others they each run
their own "script" from memory.
It would seem simpler to flip a switch to designate one box as the
master and have the others watch a timecode it sends out at a higher >resolution than the desired sync error. If the master then needs to
itself be synced to real-world time via a GPSDO then ah...well I guess
there should've been a 3rd BNC :-(
torsdag den 21. juli 2022 kl. 01.21.08 UTC+2 skrev John Larkin:
Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse
maybe once a second.
why so slow?
A follower would use her (not "his") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.
it'll only make the run at at the same speed, not time aligned
bitrex wrote:
Yeah I don't quite get it, either. My rack of synthesizers can each play one >> voice of the Maple Leaf Rag via MIDI and they all stay synced together really
How is "really well" defined? In the domain of human auditory perception?
Don Y wrote:
bitrex wrote:
<snip>
Yeah I don't quite get it, either. My rack of synthesizers can each play one
voice of the Maple Leaf Rag via MIDI and they all stay synced together really
How is "really well" defined? In the domain of human auditory perception?
In this case, isn't "really well" defined as an absence of sour note(s)?
On Fri, 22 Jul 2022 00:08:56 -0000 (UTC), Cydrome Leader <presence@MUNGEpanix.com> wrote:
jlarkin@highlandsniptechnology.com wrote:
On Thu, 21 Jul 2022 07:43:18 +0200, Gerhard Hoffmann <dk4xp@arcor.de>
wrote:
Am 21.07.22 um 01:20 schrieb John Larkin:
Suppose I have several rackmount boxes and each has a BNC connector on >>>>> the back. Each of them has an open-drain mosfet, a weak pullup, and a >>>>> lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least >>>>> time-align them to always be the same within a few microseconds,
longterm.
I have a backburner project of locking 16 MTI-260 oscillators
slooowy to another one, and when they are in sync, combine
them with an array of Wilkinsons. That should have a nice
effect on phase noise by averaging over 16.
The CPLD has enough resources to implement that as a delay
locked loop with 1 pps, but low hanging fruit first.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse >>>>> maybe once a second. A follower would use her (not "his") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?
No. There is no 1PPS pulse from the sat nor the need for exactly 10 MHz. >>>>The sats transmit a pseudo noise sequence that is
aligned to the second of their local clock source.
The GPS receiver knows the polynomial and runs a local copy of
the polynomial. It knows by cross correlation if the local
pseudo noise is the same as that of the sat and therefore knows
the start of the second. Usually that won't be the case.
Then the receiver delays its own polynomial by omitting a
clock to the shift register that generates it and tries again.
Sooner or later it will fit.
Where does the 10 MHz come from?
https://en.wikipedia.org/wiki/GPS_disciplined_oscillator
"GPSDOs typically phase-align the internal flywheel oscillator to the
GPS signal by using dividers to generate a 1PPS signal from the
reference oscillator, then phase comparing this 1PPS signal to the GPS-generated 1PPS signal and using the phase differences to control
the local oscillator frequency in small adjustments via the tracking
loop."
That's what I meant: the 10M xo is locked to the 1 PPS GPS output.
The GPS 1 PPS is perfect (by definition) long-term but terrible
short-term, so the XO or rubidium has to be very good itself, and the
loop has to be very slow. Big flywheel.
I'll be doing something similar, locking my 40 MHz clock to some 1 PPS
input, the difference being that I don't mind a few us of jitter, so I
can lock quick and crude.
On 22/7/22 03:10, Phil Hobbs wrote:
Gerhard Hoffmann wrote:
Am 21.07.22 um 16:15 schrieb Phil Hobbs:
I wonder if there's an advantage to using the closure phase for an
array that large. With 17 oscillators you've got 136 independent
phase differences, so maybe there's a way to get 22 dB instead of 12
dB improvement.
-v ?
what do you mean with closure phase? Where do the 22 dB come
from?
The idea was simply to have all 16 regulated to the be
synchronous and then feed them into a 16-to--1 Wilkinson
combiner. The phase noise should average out among the
16 units. Just as proof of concept. The MTI-260 are quite ok,
but with bleeding edge oscillators that could be interesting.
In the region where you just cannot improve an oscillator.
CheersGerhard
Sure. Thing is, that wastes a lot of information that you could maybe
use to get 10*log(136) = 21.3 dB improvement instead of 10*log(17) =
12.3 dB. [136 = N(N-1)/2 when N = 17.]
Closure is a really cute idea, which I first came across in the
context of very long baseline interferometry (VLBI) radio telescopes.
See the discussion from BEOS 3e here:
<https://electrooptical.net/www/sed/closure.png>.
Interesting, thanks.
Some frequency synthesiser chips employ proprietary majick to reduce the phase noise associated with integer divide/multiply ratios. Polyphase oscillator and slipping by partial cycles I think. Perhaps they're doing something like closure against the different clock phases?
Where does the 10 MHz come from?
https://en.wikipedia.org/wiki/GPS_disciplined_oscillator
"GPSDOs typically phase-align the internal flywheel oscillator to the
GPS signal by using dividers to generate a 1PPS signal from the
reference oscillator, then phase comparing this 1PPS signal to the GPS-generated 1PPS signal and using the phase differences to control
the local oscillator frequency in small adjustments via the tracking
loop."
That's what I meant: the 10M xo is locked to the 1 PPS GPS output.
On 7/21/2022 1:21 PM, Martin Brown wrote:
IEEE488 was good in its day but a bit long in the tooth now. Still on
some test equipment in service today and was provided as standard on
NEC 9801 PC's in Japan although hardly ever used by their customers.
The cables and connectors could only be described as a bit clunky!
They really didn't get on with metal swarf being around but were OK in
clean dry electronics/physics labs - much less so in chemistry ones...
I feel like there wasn't really a good relatively inexpensive standard
for interfacing PC peripherals until USB. Serial and parallel were slow (occasionally some devices supported ECP, I remember having to enable it
in the BIOS sometimes), and external SCSI wasn't really well-suited to anything but external disk drives.
I don't think you could hot-swap IEE-488 either but it seems like it was pretty fast and more amenable to a wide class of devices than SCSI, but
just didn't seem to catch on outside the test equipment realm.
On Thu, 21 Jul 2022 12:06:26 +0100, Martin Brown
<'''newspam'''@nonad.co.uk> wrote:
On 21/07/2022 01:22, John Larkin wrote:
If a follower is told to start locking, it could timestamp the first
incoming 1 PPS with a giant counter clocked by its local 40 MHz VCO.
If a later 1 PPS edge appears to arrive too soon, we could speed up
our VCXO by, say, 1 PPM, and vice versa. So longterm it walks into
alignment with the 1 PPS and eventually dithers a microsecond per
second. Noise on the coax gets fixed over time too.
Have a free running counter on each of the followers and use the value
of that after 1s, 10s, 100s to determine the correct tweak to apply
locally. Tweaks of 1ppm at a time is rather crude you should be able to
determine the right amount to tweak it by better than that.
(especially over longer timebases)
I wouldn't expect my VCXO to be more than 10 PPM off at the start of
the lock request. So I can walk it to within 1 PPM, namely 1
microsecond error, in at most 10 seconds using 1 PPM jogs. If the osc
were 50 PPM off, it would take 50 seconds to catch up to the external
pulse.
That's better than just measuring the 1 Hz period once a second,
tweaking the clock, and then throwing away that measurement. I want a
time lock, not a frequency lock.
Then you probably want to measure the cumulative error over many
seconds. Each unit can work out how long it can free run without
exceeding tolerance once it has the rough and ready count from the first
second. After that you have a good idea of how many seconds you can free
run for without having any ambiguities from residual drift.
Yes, I don't want to measure period once a second. I want to compare
time alignment forever after receiving the first 1 pps pulse.
It's actually simple: first received pulse, start a mod 40 million
counter. Every time it rolls over, do an early/late compare to the 1
PPS input, and jog the 40 MHz VCXO 1 PPM in the right direction.
The compare is a dflop, d is the msb of the counter, clock is the 1
PPS input. Occasional metastability is fine; it indicates success.
It doesn't even need to be a 40 million counter. Something a fraction
of that will do. 10,000 maybe.
Maybe the counter can just free-run, never get initialized. Gotta do
the math on that after I wake up.
On 21/07/2022 18:41, bitrex wrote:
On 7/21/2022 1:21 PM, Martin Brown wrote:
IEEE488 was good in its day but a bit long in the tooth now. Still on some >>> test equipment in service today and was provided as standard on NEC 9801 >>> PC's in Japan although hardly ever used by their customers.
The cables and connectors could only be described as a bit clunky!
They really didn't get on with metal swarf being around but were OK in clean
dry electronics/physics labs - much less so in chemistry ones...
I feel like there wasn't really a good relatively inexpensive standard for >> interfacing PC peripherals until USB. Serial and parallel were slow
(occasionally some devices supported ECP, I remember having to enable it in >> the BIOS sometimes), and external SCSI wasn't really well-suited to anything >> but external disk drives.
There were bidirectional parallel ports that could run fairly quick.
A parallel port interface for a CD drive was just about doable on a bog standard PC parallel port.
SCSI was quite good for external bulk data devices like scanners too. It's disadvantage was cost.
Token ring WAN over cheap twisted pairs took over for a while in my neck of the
woods before truly fast Ethernet really got going.
(it was an academic predecessor of IBM's token ring offering)
Early fast ethernet distribution was on expensive thick heavy coax cable marked
up with where to tap into them. The cost difference for wiring up was enormous.
Physically manhandling the cable was a PITA.
On 7/22/2022 2:36 AM, Martin Brown wrote:Yes, I discovered the perils of blind plugging when I tried to plug something in deep inside a rack cabinet. My finger discovered an unguarded fan and it initially felt like an electric shock. I pulled my arm back so fast I hit my face
On 21/07/2022 18:41, bitrex wrote:
On 7/21/2022 1:21 PM, Martin Brown wrote:
IEEE488 was good in its day but a bit long in the tooth now. Still on some
test equipment in service today and was provided as standard on NEC 9801 >>> PC's in Japan although hardly ever used by their customers.
The cables and connectors could only be described as a bit clunky!
They really didn't get on with metal swarf being around but were OK in clean
dry electronics/physics labs - much less so in chemistry ones...
I feel like there wasn't really a good relatively inexpensive standard for >> interfacing PC peripherals until USB. Serial and parallel were slow
(occasionally some devices supported ECP, I remember having to enable it in
the BIOS sometimes), and external SCSI wasn't really well-suited to anything
but external disk drives.
There were bidirectional parallel ports that could run fairly quick.But old ports (without queues) were a bitch for the processor to service.
A parallel port interface for a CD drive was just about doable on a bog standard PC parallel port.
SCSI was quite good for external bulk data devices like scanners too. It's disadvantage was cost.And cable length. Aside from differential (even costlier), you were
stuck to "arm's reach". At least serial and USB can be pushed to
longer lengths (despite limitations of their respective standards).
Token ring WAN over cheap twisted pairs took over for a while in my neck of theIBM's suffered from the same sort of costs as SCSI with their big,
woods before truly fast Ethernet really got going.
(it was an academic predecessor of IBM's token ring offering)
klunky connectors.
Early fast ethernet distribution was on expensive thick heavy coax cable markedAh, yes. "Orange hose" and vampire taps. I suspect one could make a pretty little structure (think: Lincoln Logs) out of lengths of that! A likely factor
up with where to tap into them. The cost difference for wiring up was enormous.
Physically manhandling the cable was a PITA.
in its lack of ubiquity.
I rely on network connectivity for an increasing number of appliances, now. Scanners (direct network connections or USB to SBC host), disks (iSCSI), printers (direct network connections or dedicated print server appliance), other computers, etc.
But, all of the T/TX technologies make cabling a PITA. Every cable has to travel all the way to a switch, even if some other networked device is
nearby (e.g., 10Base2 would tolerate device insertion with just a short length of coax -- though the entire network was disrupted in the process!)
I have thick bundles of CAT5e affixed to the undersides of my workbenches
as the cables from each device (on or under the bench) join the bundle
as it travels to the east or west switch. Add a new device? Ugh!
IMO, most interfaces fall down (in practical terms) when it comes to the choice
of connector. Either too cheap (flimsy) or too costly. The RJ45/8P8C wins in terms of cost... but is a nuisance when the locking tab inevitably breaks off (even if "guarded"): "Great! Now I either repair the cable or replace it!"
And, inevitably, connectors require a bit of "fiddling" to ensure oriented correctly and mated well. How many times do you discover a bent pin on a
HD SCSI cable only because the interface refuses to run properly? (and
trying to repair said pin is essentially impossible).
And, of course, the wide choice of "standards" (SCSI cables being among the worst for lack of uniformity: Old Sun, Apple, SCSI, SCSI2, SCSI3, VHDCI, etc.)
The ideal connector wouldn't have a top or bottom (etc.) Something like
a phone plug where all you have to do is line up plug to hole and jam
it home. Considering most connectors reside on the backs of equipment, expecting the user to be able to VIEW the mate while attempting to connect
is wishful thinking!
On 22/07/2022 03:44, Clifford Heath wrote:
On 22/7/22 03:10, Phil Hobbs wrote:
Gerhard Hoffmann wrote:
Am 21.07.22 um 16:15 schrieb Phil Hobbs:
I wonder if there's an advantage to using the closure phase for an
array that large. With 17 oscillators you've got 136 independent
phase differences, so maybe there's a way to get 22 dB instead of
12 dB improvement.
-v ?
what do you mean with closure phase? Where do the 22 dB come
from?
The idea was simply to have all 16 regulated to the be
synchronous and then feed them into a 16-to--1 Wilkinson
combiner. The phase noise should average out among the
16 units. Just as proof of concept. The MTI-260 are quite ok,
but with bleeding edge oscillators that could be interesting.
In the region where you just cannot improve an oscillator.
CheersGerhard
Sure. Thing is, that wastes a lot of information that you could
maybe use to get 10*log(136) = 21.3 dB improvement instead of
10*log(17) = 12.3 dB. [136 = N(N-1)/2 when N = 17.]
Closure is a really cute idea, which I first came across in the
context of very long baseline interferometry (VLBI) radio telescopes.
See the discussion from BEOS 3e here:
<https://electrooptical.net/www/sed/closure.png>.
Interesting, thanks.
Some frequency synthesiser chips employ proprietary majick to reduce
the phase noise associated with integer divide/multiply ratios.
Polyphase oscillator and slipping by partial cycles I think. Perhaps
they're doing something like closure against the different clock phases?
Quite probably - it has been known for a long time in radio astronomy
first derived by Jennison in 1958 at Jodrell Bank for 3 antennae. This
is the original ground breaking paper for anyone interested
https://articles.adsabs.harvard.edu//full/1958MNRAS.118..276J/0000276.000.html
(easier to understand versions exist today). WIki isn't bad:
https://en.wikipedia.org/wiki/Closure_phase
It allows you to get a good phase observable uncontaminated by the phase error at each node for every distinct subset of 3 nodes. There is a corresponding closure amplitude for distinct subsets of 4 nodes.
Obviously the bigger N is the more useful observables you can get which
is why the big dish telescopes sometimes stay on target and in the loop
for perhaps longer than they really ought to in deteriorating weather.
This book reviews most of the classical tricks used in VLBI and interferometry from the period when they had just become routine:
Indirect Imaging: Measurement and Processing for Indirect Imaging
Editor-J. A. Roberts
 0 ratings by Goodreads
ISBN 10: 0521262828 / ISBN 13: 9780521262828
Published by Cambridge University Press, 1984
Yes, I discovered the perils of blind plugging when I tried to plug something in deep inside a rack cabinet. My finger discovered an unguarded fan and it initially felt like an electric shock. I pulled my arm back so fast I hit my face
and got a nosebleed!
Don wrote:
Don Y wrote:
bitrex wrote:
<snip>
In this case, isn't "really well" defined as an absence of sour note(s)?Yeah I don't quite get it, either. My rack of synthesizers can each playone
voice of the Maple Leaf Rag via MIDI and they all stay synced together really
How is "really well" defined? In the domain of human auditory perception? >>
That assumes the synthesis uses the same clock as timing. I think the discussion here has been wrt durations/intervals.
How sensitive are *your* ears to noticing small differences in pitch,
absence a comparative reference? Can you discern a difference of a few
cents ("perfect pitch")?
On 21/07/2022 12:42, jlarkin@highlandsniptechnology.com wrote:
On Thu, 21 Jul 2022 12:06:26 +0100, Martin Brown
<'''newspam'''@nonad.co.uk> wrote:
On 21/07/2022 01:22, John Larkin wrote:
If a follower is told to start locking, it could timestamp the first
incoming 1 PPS with a giant counter clocked by its local 40 MHz VCO.
If a later 1 PPS edge appears to arrive too soon, we could speed up
our VCXO by, say, 1 PPM, and vice versa. So longterm it walks into
alignment with the 1 PPS and eventually dithers a microsecond per
second. Noise on the coax gets fixed over time too.
Have a free running counter on each of the followers and use the value
of that after 1s, 10s, 100s to determine the correct tweak to apply
locally. Tweaks of 1ppm at a time is rather crude you should be able to
determine the right amount to tweak it by better than that.
(especially over longer timebases)
I wouldn't expect my VCXO to be more than 10 PPM off at the start of
the lock request. So I can walk it to within 1 PPM, namely 1
microsecond error, in at most 10 seconds using 1 PPM jogs. If the osc
were 50 PPM off, it would take 50 seconds to catch up to the external
pulse.
You would have lower systematic error after lockin if you made the >adjustments by reading the full width counter as a two's compliment
number when the synch pulse arrives (and using a 2^N counter).
That's better than just measuring the 1 Hz period once a second,
tweaking the clock, and then throwing away that measurement. I want a
time lock, not a frequency lock.
Then you probably want to measure the cumulative error over many
seconds. Each unit can work out how long it can free run without
exceeding tolerance once it has the rough and ready count from the first >>> second. After that you have a good idea of how many seconds you can free >>> run for without having any ambiguities from residual drift.
Yes, I don't want to measure period once a second. I want to compare
time alignment forever after receiving the first 1 pps pulse.
It's actually simple: first received pulse, start a mod 40 million
counter. Every time it rolls over, do an early/late compare to the 1
PPS input, and jog the 40 MHz VCXO 1 PPM in the right direction.
The compare is a dflop, d is the msb of the counter, clock is the 1
PPS input. Occasional metastability is fine; it indicates success.
It doesn't even need to be a 40 million counter. Something a fraction
of that will do. 10,000 maybe.
Unless you are very wedded to base 10 it might well work better to use a >hardware 16 or 24 bit counter and allow it to free run. The master clock
time pulses could be at some suitable power of 2^N x 0.1us.
Under software control you could even do quick corrections in the first >second to get the basic frequency of all clocks approximately right.
The master could produce a set of pulses that were 1/16s, 1/8s, 1/4s,
1/2, 1s long at the outset. That would speed up the lock in time.
Maybe the counter can just free-run, never get initialized. Gotta do
the math on that after I wake up.
If you want to get the clocks on the various boxes as close to in synch
as possible then it makes sense to correct any errors quickly.
Power of 2 steps decreasing to some floor level being most favourable.
Don Y wrote:
Don wrote:
Don Y wrote:
bitrex wrote:
<snip>
In this case, isn't "really well" defined as an absence of sour note(s)?Yeah I don't quite get it, either. My rack of synthesizers can each playone
voice of the Maple Leaf Rag via MIDI and they all stay synced together really
How is "really well" defined? In the domain of human auditory perception? >>>
That assumes the synthesis uses the same clock as timing. I think the
discussion here has been wrt durations/intervals.
How sensitive are *your* ears to noticing small differences in pitch,
absence a comparative reference? Can you discern a difference of a few
cents ("perfect pitch")?
Can't everyone's ears (except perhaps the autistic tone-deaf and such)
hear a sour note relative to the preceding note? Do you need to name a
note (perfect pitch) in order to hear its sourness?
It's all but impossible for me personally to ignore the sourness of cringeworthy, awkward note(s). Sour notes make me want to get out of
earshot.
Don wrote:
Don Y wrote:
Don wrote:
Don Y wrote:That assumes the synthesis uses the same clock as timing. I think the
bitrex wrote:
<snip>
Yeah I don't quite get it, either. My rack of synthesizers can each play one
voice of the Maple Leaf Rag via MIDI and they all stay synced together really
How is "really well" defined? In the domain of human auditory perception?
In this case, isn't "really well" defined as an absence of sour note(s)? >>>
discussion here has been wrt durations/intervals.
How sensitive are *your* ears to noticing small differences in pitch,
absence a comparative reference? Can you discern a difference of a few
cents ("perfect pitch")?
Can't everyone's ears (except perhaps the autistic tone-deaf and such)
hear a sour note relative to the preceding note? Do you need to name a
note (perfect pitch) in order to hear its sourness?
Perfect pitch is more than just "naming a note".
It's all but impossible for me personally to ignore the sourness of
cringeworthy, awkward note(s). Sour notes make me want to get out of
earshot.
How "sour" does the note have to be before it is perceptible, as such.
A cent? Two? Fifty? A semitone?? (about a 25 cents is typical for
the average, non-musician, listener to be able to detect -- without
context; i.e., if the "previous note" was similarly sour, your estimation
of the correctness of the following note can perceive both as correct...
like singing in an entirely different *key*!)
<https://neurosciencenews.com/pitch-detection-music-21087/>
This is a reference note (middle C) followed by the same note "soured"
by 12 cents:
<https://en.wikipedia.org/wiki/File:Sines_12_cent_difference.wav>
Here's *one* cent difference:
<https://en.wikipedia.org/wiki/File:Sines_1_cent_difference.wav>
And 24 cents (about the point of "normal" perception):
<https://en.wikipedia.org/wiki/File:Sines_24_cent_difference.wav>
If your device's *timing* was off by 0.05%, would that be consequential?
jlarkin@highlandsniptechnology.com wrote:
On Fri, 22 Jul 2022 00:08:56 -0000 (UTC), Cydrome Leader
<presence@MUNGEpanix.com> wrote:
jlarkin@highlandsniptechnology.com wrote:
On Thu, 21 Jul 2022 07:43:18 +0200, Gerhard Hoffmann <dk4xp@arcor.de>
wrote:
Am 21.07.22 um 01:20 schrieb John Larkin:
Suppose I have several rackmount boxes and each has a BNC connector on >>>>>> the back. Each of them has an open-drain mosfet, a weak pullup, and a >>>>>> lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least >>>>>> time-align them to always be the same within a few microseconds,
longterm.
I have a backburner project of locking 16 MTI-260 oscillators
slooowy to another one, and when they are in sync, combine
them with an array of Wilkinsons. That should have a nice
effect on phase noise by averaging over 16.
The CPLD has enough resources to implement that as a delay
locked loop with 1 pps, but low hanging fruit first.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse >>>>>> maybe once a second. A follower would use her (not "his") clock to >>>>>> measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse >>>>>> from the satellites?
No. There is no 1PPS pulse from the sat nor the need for exactly 10 MHz. >>>>>The sats transmit a pseudo noise sequence that is
aligned to the second of their local clock source.
The GPS receiver knows the polynomial and runs a local copy of
the polynomial. It knows by cross correlation if the local
pseudo noise is the same as that of the sat and therefore knows
the start of the second. Usually that won't be the case.
Then the receiver delays its own polynomial by omitting a
clock to the shift register that generates it and tries again.
Sooner or later it will fit.
Where does the 10 MHz come from?
https://en.wikipedia.org/wiki/GPS_disciplined_oscillator
"GPSDOs typically phase-align the internal flywheel oscillator to the
GPS signal by using dividers to generate a 1PPS signal from the
reference oscillator, then phase comparing this 1PPS signal to the
GPS-generated 1PPS signal and using the phase differences to control
the local oscillator frequency in small adjustments via the tracking
loop."
That's what I meant: the 10M xo is locked to the 1 PPS GPS output.
The GPS 1 PPS is perfect (by definition) long-term but terrible
short-term, so the XO or rubidium has to be very good itself, and the
loop has to be very slow. Big flywheel.
GPS timing isn't completely perfect in reality. Antennas blow off roofs, >contractors cut cables etc. Even losing sync for a minute is sort of a big >deal. As you mentioned, jitter is the real problem. There are tradeoffs to >making a flywheel thats too heavy so to speak.
For really fussy stuff, one might have multiple GPS receivers and a quorum
of local 10Mhz oscillators. In fact, 10Mhz is a dinosaur relic for modern >stuff too. We've got racks of 10Mhz oscillators and equipment to monitor
any phase shift between local oscillators and GPS sources. It's all going
to the dumpster when somebody finally notices it's been powered down and >forgotten about.
Fairly accurate nS resolution timing is possible in computers these days, >with the right tricks.
I'll be doing something similar, locking my 40 MHz clock to some 1 PPS
input, the difference being that I don't mind a few us of jitter, so I
can lock quick and crude.
Do you have to worry about fun issues like an the timestamp of a signal
being received before it was even transmitted between pieces of equipment?
I like the toggle switches on the USNO hydrogen masers:
https://www.cnmoc.usff.navy.mil/Organization/United-States-Naval-Observatory/Precise-Time-Department/The-USNO-Master-Clock/The-USNO-Master-Clock/
They were originally made by some weird company called Sigma Tau. Somehow, >Microchip owns them now. New models have a new paint job, but still look
like they might be a transit case for a Dalek.
Don Y wrote:
Don wrote:
Don Y wrote:
Don wrote:
Don Y wrote:That assumes the synthesis uses the same clock as timing. I think the >>>> discussion here has been wrt durations/intervals.
bitrex wrote:
<snip>
Yeah I don't quite get it, either. My rack of synthesizers can each play one
voice of the Maple Leaf Rag via MIDI and they all stay synced together really
How is "really well" defined? In the domain of human auditory perception?
In this case, isn't "really well" defined as an absence of sour note(s)? >>>>
How sensitive are *your* ears to noticing small differences in pitch,
absence a comparative reference? Can you discern a difference of a few >>>> cents ("perfect pitch")?
Can't everyone's ears (except perhaps the autistic tone-deaf and such)
hear a sour note relative to the preceding note? Do you need to name a
note (perfect pitch) in order to hear its sourness?
Perfect pitch is more than just "naming a note".
It's all but impossible for me personally to ignore the sourness of >>> cringeworthy, awkward note(s). Sour notes make me want to get out of
earshot.
How "sour" does the note have to be before it is perceptible, as such.
A cent? Two? Fifty? A semitone?? (about a 25 cents is typical for
the average, non-musician, listener to be able to detect -- without
context; i.e., if the "previous note" was similarly sour, your estimation
of the correctness of the following note can perceive both as correct...
like singing in an entirely different *key*!)
<https://neurosciencenews.com/pitch-detection-music-21087/>
This is a reference note (middle C) followed by the same note "soured"
by 12 cents:
<https://en.wikipedia.org/wiki/File:Sines_12_cent_difference.wav>
Here's *one* cent difference:
<https://en.wikipedia.org/wiki/File:Sines_1_cent_difference.wav>
And 24 cents (about the point of "normal" perception):
<https://en.wikipedia.org/wiki/File:Sines_24_cent_difference.wav>
If your device's *timing* was off by 0.05%, would that be consequential?
Very interesting information. Thank you.
It's easy for me to hear the one cent difference, how about you? My audio perception comes in handy when it's time to tune a keyboard. Some- times musicians purposefully vary tones by a few cents in order to
produce vibrato.
In regards to your 0.05% device timing question, the answer is: it
depends. A 0.05% device timing variance in my Power Bank Keepalive:
https://crcomp.net/mp3mod/index.php
for instance, is inconsequential.
Am 22.07.22 um 04:47 schrieb jlarkin@highlandsniptechnology.com:
Where does the 10 MHz come from?
https://en.wikipedia.org/wiki/GPS_disciplined_oscillator
"GPSDOs typically phase-align the internal flywheel oscillator to the
GPS signal by using dividers to generate a 1PPS signal from the
reference oscillator, then phase comparing this 1PPS signal to the
GPS-generated 1PPS signal and using the phase differences to control
the local oscillator frequency in small adjustments via the tracking
loop."
That's what I meant: the 10M xo is locked to the 1 PPS GPS output.
No. The 1pps is asserted when the CPU thinks it's closest to
the "right" clockcycle. It could be off by half a cycle.
There is no need for 10 MHz, one could have chosen a nice
multiple of the desired baud rate.
On 7/21/2022 7:04 AM, bitrex wrote:
You really need to define longterm before the problem becomes well posed. Do
you mean hours, days, weeks or months of runtime?
Yeah I don't quite get it, either. My rack of synthesizers can each play one >> voice of the Maple Leaf Rag via MIDI and they all stay synced together really
How is "really well" defined? In the domain of human auditory perception?
Don wrote:
Don Y wrote:
Don wrote:
Don Y wrote:
Don wrote:
Don Y wrote:That assumes the synthesis uses the same clock as timing. I think the >>>>> discussion here has been wrt durations/intervals.
bitrex wrote:
<snip>
Yeah I don't quite get it, either. My rack of synthesizers can each play one
voice of the Maple Leaf Rag via MIDI and they all stay synced together really
How is "really well" defined? In the domain of human auditory perception?
In this case, isn't "really well" defined as an absence of sour note(s)? >>>>>
How sensitive are *your* ears to noticing small differences in pitch, >>>>> absence a comparative reference? Can you discern a difference of a few >>>>> cents ("perfect pitch")?
Can't everyone's ears (except perhaps the autistic tone-deaf and such) >>>> hear a sour note relative to the preceding note? Do you need to name a >>>> note (perfect pitch) in order to hear its sourness?
Perfect pitch is more than just "naming a note".
It's all but impossible for me personally to ignore the sourness of >>>> cringeworthy, awkward note(s). Sour notes make me want to get out of
earshot.
How "sour" does the note have to be before it is perceptible, as such.
A cent? Two? Fifty? A semitone?? (about a 25 cents is typical for
the average, non-musician, listener to be able to detect -- without
context; i.e., if the "previous note" was similarly sour, your estimation >>> of the correctness of the following note can perceive both as correct... >>> like singing in an entirely different *key*!)
<https://neurosciencenews.com/pitch-detection-music-21087/>
This is a reference note (middle C) followed by the same note "soured"
by 12 cents:
<https://en.wikipedia.org/wiki/File:Sines_12_cent_difference.wav>
Here's *one* cent difference:
<https://en.wikipedia.org/wiki/File:Sines_1_cent_difference.wav>
And 24 cents (about the point of "normal" perception):
<https://en.wikipedia.org/wiki/File:Sines_24_cent_difference.wav>
If your device's *timing* was off by 0.05%, would that be consequential?
Very interesting information. Thank you.
It's easy for me to hear the one cent difference, how about you? My
audio perception comes in handy when it's time to tune a keyboard. Some-
times musicians purposefully vary tones by a few cents in order to
produce vibrato.
Could you hear a middle C "soured" by one cent when it follows a
(correct) C-sharp immediately preceding it? Or, vice versa?
*I* can't. My threshold is closer to 10 cents and rely on electronic
devices when tuning instruments.
And, if every note was "off key" by 10 cents, I'd not recognize the
tony.
In regards to your 0.05% device timing question, the answer is: it
depends. A 0.05% device timing variance in my Power Bank Keepalive:
https://crcomp.net/mp3mod/index.php
for instance, is inconsequential.
In the context of this thread, it likely has an impact. A cent is
about 500PPM (though in the frequency domain)
On Fri, 22 Jul 2022 06:20:58 -0000 (UTC), Cydrome Leader <presence@MUNGEpanix.com> wrote:
jlarkin@highlandsniptechnology.com wrote:
On Fri, 22 Jul 2022 00:08:56 -0000 (UTC), Cydrome Leader
<presence@MUNGEpanix.com> wrote:
jlarkin@highlandsniptechnology.com wrote:
On Thu, 21 Jul 2022 07:43:18 +0200, Gerhard Hoffmann <dk4xp@arcor.de> >>>>> wrote:
Am 21.07.22 um 01:20 schrieb John Larkin:
Suppose I have several rackmount boxes and each has a BNC connector on >>>>>>> the back. Each of them has an open-drain mosfet, a weak pullup, and a >>>>>>> lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least >>>>>>> time-align them to always be the same within a few microseconds, >>>>>>> longterm.
I have a backburner project of locking 16 MTI-260 oscillators >>>>>>slooowy to another one, and when they are in sync, combine
them with an array of Wilkinsons. That should have a nice
effect on phase noise by averaging over 16.
The CPLD has enough resources to implement that as a delay
locked loop with 1 pps, but low hanging fruit first.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse >>>>>>> maybe once a second. A follower would use her (not "his") clock to >>>>>>> measure the incoming period and tweak its local VCXO in the right >>>>>>> direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse >>>>>>> from the satellites?
No. There is no 1PPS pulse from the sat nor the need for exactly 10 MHz. >>>>>>The sats transmit a pseudo noise sequence that is
aligned to the second of their local clock source.
The GPS receiver knows the polynomial and runs a local copy of
the polynomial. It knows by cross correlation if the local
pseudo noise is the same as that of the sat and therefore knows
the start of the second. Usually that won't be the case.
Then the receiver delays its own polynomial by omitting a
clock to the shift register that generates it and tries again. >>>>>>Sooner or later it will fit.
Where does the 10 MHz come from?
https://en.wikipedia.org/wiki/GPS_disciplined_oscillator
"GPSDOs typically phase-align the internal flywheel oscillator to the
GPS signal by using dividers to generate a 1PPS signal from the
reference oscillator, then phase comparing this 1PPS signal to the
GPS-generated 1PPS signal and using the phase differences to control
the local oscillator frequency in small adjustments via the tracking
loop."
That's what I meant: the 10M xo is locked to the 1 PPS GPS output.
The GPS 1 PPS is perfect (by definition) long-term but terrible
short-term, so the XO or rubidium has to be very good itself, and the
loop has to be very slow. Big flywheel.
GPS timing isn't completely perfect in reality. Antennas blow off roofs, >>contractors cut cables etc. Even losing sync for a minute is sort of a big >>deal. As you mentioned, jitter is the real problem. There are tradeoffs to >>making a flywheel thats too heavy so to speak.
For really fussy stuff, one might have multiple GPS receivers and a quorum >>of local 10Mhz oscillators. In fact, 10Mhz is a dinosaur relic for modern >>stuff too. We've got racks of 10Mhz oscillators and equipment to monitor >>any phase shift between local oscillators and GPS sources. It's all going >>to the dumpster when somebody finally notices it's been powered down and >>forgotten about.
Fairly accurate nS resolution timing is possible in computers these days, >>with the right tricks.
I triggered a scope from a very good ovenized XO and looked at the
rising edge of a rubidium. The edge looked solid, as if it was
internal triggered. Checking every 20 minutes or so, it ws slowly
creeping across the screen, at 5 ns/cm.
I'll be doing something similar, locking my 40 MHz clock to some 1 PPS
input, the difference being that I don't mind a few us of jitter, so I
can lock quick and crude.
Do you have to worry about fun issues like an the timestamp of a signal >>being received before it was even transmitted between pieces of equipment?
It a multi-channel power supply!
On Fri, 22 Jul 2022 10:37:53 +0200, Gerhard Hoffmann <dk4xp@arcor.de>
wrote:
Am 22.07.22 um 04:47 schrieb jlarkin@highlandsniptechnology.com:
Where does the 10 MHz come from?
https://en.wikipedia.org/wiki/GPS_disciplined_oscillator
"GPSDOs typically phase-align the internal flywheel oscillator to the
GPS signal by using dividers to generate a 1PPS signal from the
reference oscillator, then phase comparing this 1PPS signal to the
GPS-generated 1PPS signal and using the phase differences to control
the local oscillator frequency in small adjustments via the tracking
loop."
That's what I meant: the 10M xo is locked to the 1 PPS GPS output.
No. The 1pps is asserted when the CPU thinks it's closest to
the "right" clockcycle. It could be off by half a cycle.
There is no need for 10 MHz, one could have chosen a nice
multiple of the desired baud rate.
Our GPS receivers output 1 PPS and 10 MHz. Argue with Wikipedia.
On Thu, 21 Jul 2022 18:04:22 -0700, Don Y
<blockedofcourse@foo.invalid> wrote:
On 7/21/2022 7:04 AM, bitrex wrote:
You really need to define longterm before the problem becomes well posed. Do
you mean hours, days, weeks or months of runtime?
Yeah I don't quite get it, either. My rack of synthesizers can each play one
voice of the Maple Leaf Rag via MIDI and they all stay synced together really
How is "really well" defined? In the domain of human auditory perception?
Sound travels about a foot per millisecond, so we are used to multiple
time delays. A marching band sounds coordinated to us.
I am thinking about vision a lot lately too. Each eye acquires a
differently scaled image that changes constantly. There are
millisecond-level changes in focus and parallax. I can put my glasses
on, or not, and magnification surely changes. Somehow a brain acquires
two images and distorts them in real time so that all the bits align.
One has much better resolution using two eyes than either alone can
provide.
Nice trick. Sound must work like that to, extensive post-processing of >acquired inputs. Probably time shifting parts of the spectrum, or
something more complex, multiple cross-correlations.
On Thu, 21 Jul 2022 18:04:22 -0700, Don Y
<blocked...@foo.invalid> wrote:
On 7/21/2022 7:04 AM, bitrex wrote:
You really need to define longterm before the problem becomes well posed. Do
you mean hours, days, weeks or months of runtime?
Yeah I don't quite get it, either. My rack of synthesizers can each play one
voice of the Maple Leaf Rag via MIDI and they all stay synced together really
How is "really well" defined? In the domain of human auditory perception? Sound travels about a foot per millisecond, so we are used to multipletime delays. A marching band sounds coordinated to us.
I am thinking about vision a lot lately too. Each eye acquires a
differently scaled image that changes constantly. There are
millisecond-level changes in focus and parallax. I can put my glasses
on, or not, and magnification surely changes. Somehow a brain acquires
two images and distorts them in real time so that all the bits align.
One has much better resolution using two eyes than either alone can
provide.
Nice trick. Sound must work like that to, extensive post-processing of acquired inputs. Probably time shifting parts of the spectrum, or
something more complex, multiple cross-correlations.
On 7/22/2022 7:17 AM, Don wrote:
Don Y wrote:
Don wrote:
Don Y wrote:That assumes the synthesis uses the same clock as timing. I think the
bitrex wrote:
<snip>
Yeah I don't quite get it, either. My rack of synthesizers can each playone
voice of the Maple Leaf Rag via MIDI and they all stay synced together really
How is "really well" defined? In the domain of human auditory perception?
In this case, isn't "really well" defined as an absence of sour note(s)? >>
discussion here has been wrt durations/intervals.
How sensitive are *your* ears to noticing small differences in pitch,
absence a comparative reference? Can you discern a difference of a few
cents ("perfect pitch")?
Can't everyone's ears (except perhaps the autistic tone-deaf and such)Perfect pitch is more than just "naming a note".
hear a sour note relative to the preceding note? Do you need to name a
note (perfect pitch) in order to hear its sourness?
It's all but impossible for me personally to ignore the sourness of cringeworthy, awkward note(s). Sour notes make me want to get out of earshot.How "sour" does the note have to be before it is perceptible, as such.
A cent? Two? Fifty? A semitone?? (about a 25 cents is typical for
the average, non-musician, listener to be able to detect -- without
context; i.e., if the "previous note" was similarly sour, your estimation
of the correctness of the following note can perceive both as correct...
like singing in an entirely different *key*!)
<https://neurosciencenews.com/pitch-detection-music-21087/>
This is a reference note (middle C) followed by the same note "soured"
by 12 cents:
<https://en.wikipedia.org/wiki/File:Sines_12_cent_difference.wav>
Chances are, you can't tell the difference hearing them
in sequence. If you heard just *one*, you'd not be able to tell if it
was correct, or not. The third sound sample plays both simultaneously
so you can hear them beating against each other -- the difference then becomes very noticeable!
Here's *one* cent difference:
<https://en.wikipedia.org/wiki/File:Sines_1_cent_difference.wav>
And 24 cents (about the point of "normal" perception):
<https://en.wikipedia.org/wiki/File:Sines_24_cent_difference.wav>
If your device's *timing* was off by 0.05%, would that be consequential?
On 21/07/2022 16:31, John Walliker wrote:
On Thursday, 21 July 2022 at 15:42:40 UTC+1, bitrex wrote:
On 7/21/2022 10:21 AM, Lasse Langwadt Christensen wrote:
torsdag den 21. juli 2022 kl. 16.04.42 UTC+2 skrev bitrex:
On 7/21/2022 7:06 AM, Martin Brown wrote:
On 21/07/2022 01:22, John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
<pcdhSpamM...@electrooptical.net> wrote:
John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a >>>>>>>>> lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least >>>>>>>>> time-align them to always be the same within a few microseconds, >>>>>>>>> longterm.
I could call one the leader (not "master") and make the others >>>>>>>>> followers (not "slaves") and have the leader make an active low pulse >>>>>>>>> maybe once a second. A follower would use her (not "his") clock to >>>>>>>>> measure the incoming period and tweak its local VCXO in the right >>>>>>>>> direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse >>>>>>>>> from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as >>>>>>>>> followers.
The PLL algorithm might be interesting.
It's certainly possible. However, within whatever tiny loop bandwidth >>>>>>>> you wound up with, the lockers would still have
20 log(40e6) = 152 dB
higher phase noise than the lockee.
GPS has that problem too.
It would be interesting to do the math to see whether it's possible to >>>>>>>> generate a concensus lock for the group: if you get everybody close >>>>>>>> enough, just sum their sine wave outputs and lock each one of them to >>>>>>>> that, with some bit of AC coupling or something so that they don't all >>>>>>>> wander together off to the edge of the tuning range.
Maybe have one doing the locking with a phase shifter and the others >>>>>>>> with VCOs, or something like that.
Definitely a partly-baked idea, but surely one could do better than >>>>>>>> 152 dB!
Cheers
Phil Hobbs
Each box is basically a multichannel power supply, but channels can be >>>>>>> programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once >>>>>>> programs are kicked off together. So, many microseconds of equivalent >>>>>>> RMS phase noise is OK as long as we stay time aligned longterm.
You really need to define longterm before the problem becomes well >>>>>> posed. Do you mean hours, days, weeks or months of runtime?
There's a system clock in each one surely but they don't try to syncYeah I don't quite get it, either. My rack of synthesizers can each play >>>>> one voice of the Maple Leaf Rag via MIDI and they all stay synced
together really well, at least over a timespan of several
minutes.
but they are anot free runnign are they? they are all reacting to midi >>>>
their system clocks, they receive an instruction "do X for Y ms" and
their processor figures out how long Y ms is, and does it for that long. >>>
It is literally good enough for rock & roll, but whether it's good
enough for power supply sequencing IDK, there is gonna be some latency.
HP used to have GPIB on their power supplies, I've never used it but I
expect it wasn't really useful for tight synchronization.
The Group Execute Trigger command does allow quite tight synchronisation
between different GPIB devices.
GPIB flat out on a good day could manage 1Mbyte/s but in real world >situations with interconnect cabling you would be lucky to get 500kb/s.
It's best feature was that it ran at the maximum speed the receiving
device could handle (assuming that the controller was fast enough).
Synchronisation to a GET command would be probably be better than 1us
but would depend on the decoding time in each individual box. Some GPIB >devices were rather pedestrian at accepting commands.
IEEE488 was good in its day but a bit long in the tooth now. Still on
some test equipment in service today and was provided as standard on NEC
9801 PC's in Japan although hardly ever used by their customers.
The cables and connectors could only be described as a bit clunky!
They really didn't get on with metal swarf being around but were OK in
clean dry electronics/physics labs - much less so in chemistry ones...
jlarkin@highlandsniptechnology.com wrote:
On Fri, 22 Jul 2022 10:37:53 +0200, Gerhard Hoffmann <dk4xp@arcor.de>
wrote:
Am 22.07.22 um 04:47 schrieb jlarkin@highlandsniptechnology.com:
Where does the 10 MHz come from?
https://en.wikipedia.org/wiki/GPS_disciplined_oscillator
"GPSDOs typically phase-align the internal flywheel oscillator to the
GPS signal by using dividers to generate a 1PPS signal from the
reference oscillator, then phase comparing this 1PPS signal to the
GPS-generated 1PPS signal and using the phase differences to control
the local oscillator frequency in small adjustments via the tracking
loop."
That's what I meant: the 10M xo is locked to the 1 PPS GPS output.
No. The 1pps is asserted when the CPU thinks it's closest to
the "right" clockcycle. It could be off by half a cycle.
There is no need for 10 MHz, one could have chosen a nice
multiple of the desired baud rate.
Our GPS receivers output 1 PPS and 10 MHz. Argue with Wikipedia.
What he's trying to say is it may not be perfect 10 million cycles between >every 1PPS pulse. For most stuff, this is good enough. For the metrology >folks, using strong words like exactly or in this case "locked" will
always cause an argument.
jlarkin@highlandsniptechnology.com wrote:
On Fri, 22 Jul 2022 06:20:58 -0000 (UTC), Cydrome Leader
<presence@MUNGEpanix.com> wrote:
jlarkin@highlandsniptechnology.com wrote:
On Fri, 22 Jul 2022 00:08:56 -0000 (UTC), Cydrome Leader
<presence@MUNGEpanix.com> wrote:
jlarkin@highlandsniptechnology.com wrote:
On Thu, 21 Jul 2022 07:43:18 +0200, Gerhard Hoffmann <dk4xp@arcor.de> >>>>>> wrote:
Am 21.07.22 um 01:20 schrieb John Larkin:
Suppose I have several rackmount boxes and each has a BNC connector on >>>>>>>> the back. Each of them has an open-drain mosfet, a weak pullup, and a >>>>>>>> lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least >>>>>>>> time-align them to always be the same within a few microseconds, >>>>>>>> longterm.
I have a backburner project of locking 16 MTI-260 oscillators >>>>>>>slooowy to another one, and when they are in sync, combine
them with an array of Wilkinsons. That should have a nice
effect on phase noise by averaging over 16.
The CPLD has enough resources to implement that as a delay
locked loop with 1 pps, but low hanging fruit first.
I could call one the leader (not "master") and make the others >>>>>>>> followers (not "slaves") and have the leader make an active low pulse >>>>>>>> maybe once a second. A follower would use her (not "his") clock to >>>>>>>> measure the incoming period and tweak its local VCXO in the right >>>>>>>> direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse >>>>>>>> from the satellites?
No. There is no 1PPS pulse from the sat nor the need for exactly 10 MHz. >>>>>>>The sats transmit a pseudo noise sequence that is
aligned to the second of their local clock source.
The GPS receiver knows the polynomial and runs a local copy of >>>>>>>the polynomial. It knows by cross correlation if the local
pseudo noise is the same as that of the sat and therefore knows >>>>>>>the start of the second. Usually that won't be the case.
Then the receiver delays its own polynomial by omitting a
clock to the shift register that generates it and tries again. >>>>>>>Sooner or later it will fit.
Where does the 10 MHz come from?
https://en.wikipedia.org/wiki/GPS_disciplined_oscillator
"GPSDOs typically phase-align the internal flywheel oscillator to the
GPS signal by using dividers to generate a 1PPS signal from the
reference oscillator, then phase comparing this 1PPS signal to the
GPS-generated 1PPS signal and using the phase differences to control
the local oscillator frequency in small adjustments via the tracking
loop."
That's what I meant: the 10M xo is locked to the 1 PPS GPS output.
The GPS 1 PPS is perfect (by definition) long-term but terrible
short-term, so the XO or rubidium has to be very good itself, and the
loop has to be very slow. Big flywheel.
GPS timing isn't completely perfect in reality. Antennas blow off roofs, >>>contractors cut cables etc. Even losing sync for a minute is sort of a big >>>deal. As you mentioned, jitter is the real problem. There are tradeoffs to >>>making a flywheel thats too heavy so to speak.
For really fussy stuff, one might have multiple GPS receivers and a quorum >>>of local 10Mhz oscillators. In fact, 10Mhz is a dinosaur relic for modern >>>stuff too. We've got racks of 10Mhz oscillators and equipment to monitor >>>any phase shift between local oscillators and GPS sources. It's all going >>>to the dumpster when somebody finally notices it's been powered down and >>>forgotten about.
Fairly accurate nS resolution timing is possible in computers these days, >>>with the right tricks.
I triggered a scope from a very good ovenized XO and looked at the
rising edge of a rubidium. The edge looked solid, as if it was
internal triggered. Checking every 20 minutes or so, it ws slowly
creeping across the screen, at 5 ns/cm.
I believe they somehow pair the rubidium clocks with another quartz
crystal, even in those new tiny physics modules. I've not had a chance to >tear apart a rubidium clock yet, or the ovenized stuff. They come in
little metal boxes, that remind me of TV tuners.
It a multi-channel power supply!I'll be doing something similar, locking my 40 MHz clock to some 1 PPS >>>> input, the difference being that I don't mind a few us of jitter, so I >>>> can lock quick and crude.
Do you have to worry about fun issues like an the timestamp of a signal >>>being received before it was even transmitted between pieces of equipment? >>
You were also asking about timestamping in other posts. Not entirely sure >what you're upto in the end, but it might be interesting.
fredag den 22. juli 2022 kl. 16.46.36 UTC+2 skrev Don Y:
On 7/22/2022 7:17 AM, Don wrote:
Don Y wrote:Perfect pitch is more than just "naming a note".
Don wrote:
Don Y wrote:That assumes the synthesis uses the same clock as timing. I think the
bitrex wrote:
<snip>
Yeah I don't quite get it, either. My rack of synthesizers can each playone
voice of the Maple Leaf Rag via MIDI and they all stay synced together really
How is "really well" defined? In the domain of human auditory perception?
In this case, isn't "really well" defined as an absence of sour note(s)? >> >>
discussion here has been wrt durations/intervals.
How sensitive are *your* ears to noticing small differences in pitch,
absence a comparative reference? Can you discern a difference of a few
cents ("perfect pitch")?
Can't everyone's ears (except perhaps the autistic tone-deaf and such)
hear a sour note relative to the preceding note? Do you need to name a
note (perfect pitch) in order to hear its sourness?
It's all but impossible for me personally to ignore the sourness ofHow "sour" does the note have to be before it is perceptible, as such.
cringeworthy, awkward note(s). Sour notes make me want to get out of
earshot.
A cent? Two? Fifty? A semitone?? (about a 25 cents is typical for
the average, non-musician, listener to be able to detect -- without
context; i.e., if the "previous note" was similarly sour, your estimation
of the correctness of the following note can perceive both as correct...
like singing in an entirely different *key*!)
<https://neurosciencenews.com/pitch-detection-music-21087/>
This is a reference note (middle C) followed by the same note "soured"
by 12 cents:
<https://en.wikipedia.org/wiki/File:Sines_12_cent_difference.wav>
Chances are, you can't tell the difference hearing them
in sequence. If you heard just *one*, you'd not be able to tell if it
was correct, or not. The third sound sample plays both simultaneously
so you can hear them beating against each other -- the difference then
becomes very noticeable!
Here's *one* cent difference:
<https://en.wikipedia.org/wiki/File:Sines_1_cent_difference.wav>
And 24 cents (about the point of "normal" perception):
<https://en.wikipedia.org/wiki/File:Sines_24_cent_difference.wav>
If your device's *timing* was off by 0.05%, would that be consequential?
https://youtu.be/AFaRIW-wZlw?t=54
On Wed, 20 Jul 2022 23:49:40 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:
On Wednesday, July 20, 2022 at 4:21:08 PM UTC-7, John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.
If you can tolerate 'a few microseconds' on a 40 MHz signal, that's not a phase-lock
problem, it's a frequency-lock problem. Why not just run an up/down counter
to generate a correction voltage for each non-leading VCO?
It's actually a time lock problem. If a follower box starts up and
sees its first 1 PPS input, it can thereafter declare 1 PPS internal
events, based on its local VCO, and then do successive early/late
comparisons to the external pulses. And trim its VCXO accordingly.
There is cross-correlation between left and right ears in the brainstem which is involved in determining the direction of sound sources. Detectable time differences are remarkably small. (I would have to look it up to give a number.)
Also, I'd lose the BNC connectors. Threaded connectors like SMA, TNC,
and Type N are far better.
Or use shielded twisted pair to carry the 1PPS pulses. This would
work better over a backplane.
On Fri, 22 Jul 2022 10:54:30 -0700 (PDT), Lasse Langwadt Christensen <langwadt@fonz.dk> wrote:
If your device's *timing* was off by 0.05%, would that be consequential?
https://youtu.be/AFaRIW-wZlw?t=54
My recollection is the for a chorus to be in unison, all the singers
must be within twenty milliseconds of one another.
This is discussed a lot in the computer music literature.
Don Y wrote:
In the context of this thread, it likely has an impact. A cent is
about 500PPM (though in the frequency domain)
Your question about a one cent following note difference perception is interesting. And, it needs to be followed up by me, so to speak. :)
For some unknown reason, the only thing to truly satisfy me is to
tune instruments by ear.
Joe Gwinn wrote:
<snip>
Also, I'd lose the BNC connectors. Threaded connectors like SMA, TNC,
and Type N are far better.
Or use shielded twisted pair to carry the 1PPS pulses. This would
work better over a backplane.
This is good advice. Even though the lazy guy within me never truly
gives up his fight to take the easy way out with BNC.
Twisted pair (TP) sounds even easier than BNC. So, what's the
"catch" with TP? Where's the "gotcha" to make TP harder than BNC?
On 7/22/2022 1:01 PM, Joe Gwinn wrote:
On Fri, 22 Jul 2022 10:54:30 -0700 (PDT), Lasse Langwadt Christensen <lang...@fonz.dk> wrote:
Note context of post...If your device's *timing* was off by 0.05%, would that be consequential? >>https://youtu.be/AFaRIW-wZlw?t=54
My recollection is the for a chorus to be in unison, all the singers
must be within twenty milliseconds of one another.
This is discussed a lot in the computer music literature.Things get "painful" at about 50ms. I suspect your brain tries to
consider them as different events instead of indistinguishable.
fredag den 22. juli 2022 kl. 23.44.07 UTC+2 skrev Don Y:
On 7/22/2022 1:01 PM, Joe Gwinn wrote:
On Fri, 22 Jul 2022 10:54:30 -0700 (PDT), Lasse Langwadt ChristensenNote context of post...
<lang...@fonz.dk> wrote:
If your device's *timing* was off by 0.05%, would that be consequential? >>>>https://youtu.be/AFaRIW-wZlw?t=54
My recollection is the for a chorus to be in unison, all the singersThings get "painful" at about 50ms. I suspect your brain tries to
must be within twenty milliseconds of one another.
This is discussed a lot in the computer music literature.
consider them as different events instead of indistinguishable.
afaiu the limit for a phone system is >25ms round trip before you need echo canceling
On 7/22/2022 4:52 PM, Lasse Langwadt Christensen wrote:
fredag den 22. juli 2022 kl. 23.44.07 UTC+2 skrev Don Y:
On 7/22/2022 1:01 PM, Joe Gwinn wrote:
On Fri, 22 Jul 2022 10:54:30 -0700 (PDT), Lasse Langwadt ChristensenNote context of post...
<lang...@fonz.dk> wrote:
If your device's *timing* was off by 0.05%, would that be consequential?
https://youtu.be/AFaRIW-wZlw?t=54
My recollection is the for a chorus to be in unison, all the singersThings get "painful" at about 50ms. I suspect your brain tries to
must be within twenty milliseconds of one another.
This is discussed a lot in the computer music literature.
consider them as different events instead of indistinguishable.
afaiu the limit for a phone system is >25ms round trip before you need echo cancelingYes, but that addresses quality. A phone is still usable with
noticeable echo, esp if the echo is many dB down.
It seems like the brain has some (temporal) threshold beyond which it
can no longer treat things as being concurrent and starts a new "recognition process" (so to speak) to deal with the "other" event.
On Thu, 21 Jul 2022 04:17:14 -0700, jla...@highlandsniptechnology.com
wrote:
On Wed, 20 Jul 2022 23:49:40 -0700 (PDT), whit3rd <whi...@gmail.com>
wrote:
On Wednesday, July 20, 2022 at 4:21:08 PM UTC-7, John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on >>> the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.
If you can tolerate 'a few microseconds' on a 40 MHz signal, that's not a phase-lock
problem, it's a frequency-lock problem. Why not just run an up/down counter >>to generate a correction voltage for each non-leading VCO?
It's actually a time lock problem. If a follower box starts up and
sees its first 1 PPS input, it can thereafter declare 1 PPS internal >events, based on its local VCO, and then do successive early/late >comparisons to the external pulses. And trim its VCXO accordingly.
Yes, exactly. And the drift between two reasonably good clocks is
slow, so the correction need not and should not be all that fast.
What I've done in real applications is to periodically measure the
offset between when the external 1PPS is predicted to happen and when
it actually does, and adjust the VCO frequency such that in say 50
seconds of roughly linear convergence they will coincide (and keep on
going). The process is repeated every few seconds (exact interval not important as it is measured).
This is roughly the algorithm a helmsman uses while steering a
sailboat, where effect is very much delayed from action.
In many computer systems it is quite difficult to do anything on a
strict time mark, but easy to measure that actual elapsed time, using
the actual clock that is being steered - it all still converges, so
long as one doesn't try too hard.
So, in your example, the local clock would come from a 40 MHz VCO of
good manufacture (probably needs to be a TCXO of some sort). The 40
MHz output would be fed to a divider that puts out a 1PPS pulse train.
During initialization, when the first external 1PPS leading edge is
received, reset the divider, and start counting 40 MHz cycles. Maybe
wait for things to stabilize.
Thereafter, measure signed offset between external and internal 1PPS
leading edges, and compute how much change (plus or minus) in current
VCO frequency is required for zero offset to occur in say 50 seconds
(make this time-to-zero an adjustable parameter), and change the VCO
control voltage accordingly.
A few seconds later (also an adjustable parameter), repeat the above adjustment process, again looking 50 seconds into the future from now.
Repeat forever.
On Fri, 22 Jul 2022 21:38:39 -0000 (UTC), "Don" <g@crcomp.net> wrote:
Joe Gwinn wrote:
<snip>
Also, I'd lose the BNC connectors. Threaded connectors like SMA, TNC,
and Type N are far better.
Or use shielded twisted pair to carry the 1PPS pulses. This would
work better over a backplane.
This is good advice. Even though the lazy guy within me never truly
gives up his fight to take the easy way out with BNC.
Twisted pair (TP) sounds even easier than BNC. So, what's the
"catch" with TP? Where's the "gotcha" to make TP harder than BNC?
Depends on what you are trying to do.
For nanosecond edges, coax is pretty useful, but short range and often mechanically awkward.
For microsecond edges at 1000 meters, RS422 over shielded twisted pair
is pretty good.
For bus length links, LVDS or the like.
And so on. And there is always optical links.
Joe Gwinn
On 7/22/2022 5:24 PM, Lasse Langwadt Christensen wrote:
at big concerts with speaker towers for the people far away from the stage >> those speakers gets delayed so they are 10-15ms behind the sound from the stage
giving the illusion that all the sound is from the main Pa at the stage
I was near the close-in towers off stage left:
<http://3.bp.blogspot.com/-syHkjhoSSr8/VeV32eq-8EI/AAAAAAABw1w/ippl8bx8kKE/s1600/Grateful%2BDead%2Blive%2Bin%2BRaceway%2BPark%252C%2B1977%2B%252816%2529.jpg>
lørdag den 23. juli 2022 kl. 02.10.41 UTC+2 skrev Don Y:
On 7/22/2022 4:52 PM, Lasse Langwadt Christensen wrote:
fredag den 22. juli 2022 kl. 23.44.07 UTC+2 skrev Don Y:Yes, but that addresses quality. A phone is still usable with
On 7/22/2022 1:01 PM, Joe Gwinn wrote:
On Fri, 22 Jul 2022 10:54:30 -0700 (PDT), Lasse Langwadt Christensen >>>>> <lang...@fonz.dk> wrote:Note context of post...
If your device's *timing* was off by 0.05%, would that be consequential?
https://youtu.be/AFaRIW-wZlw?t=54
My recollection is the for a chorus to be in unison, all the singers >>>>> must be within twenty milliseconds of one another.Things get "painful" at about 50ms. I suspect your brain tries to
This is discussed a lot in the computer music literature.
consider them as different events instead of indistinguishable.
afaiu the limit for a phone system is >25ms round trip before you need echo canceling
noticeable echo, esp if the echo is many dB down.
sure, but it seems that below ~25ms it is not noticable
It seems like the brain has some (temporal) threshold beyond which it
can no longer treat things as being concurrent and starts a new "recognition >> process" (so to speak) to deal with the "other" event.
at big concerts with speaker towers for the people far away from the stage those speakers gets delayed so they are 10-15ms behind the sound from the stage
giving the illusion that all the sound is from the main Pa at the stage
jlarkin@highlandsniptechnology.com wrote:<snip>
It dithers around the setpoint but nobody notices.
This is immune to classic control theory so the concept annoys some
people but it works great.
A real old time control guy like Tim Wescott would probably be a fan
too--the great virtue of a bang-bang controller is that (as you say)
it's highly resistant to variations in the _plant_.
Your furnace doesn't go nuts when you have a Christmas party, even
though all those people generate a lot of heat, and there's lots of
opening and closing of doors and ovens.
Cheers
Phil Hobbs
Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least time-align them to always be the same within a few microseconds,
longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse
maybe once a second. A follower would use her (not "his") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as
followers.
The PLL algorithm might be interesting.
bitrex wrote:
On 7/20/2022 8:22 PM, John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
<pcdhSpamM...@electrooptical.net> wrote:
John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on >>>> the back. Each of them has an open-drain mosfet, a weak pullup, and a >>>> lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least >>>> time-align them to always be the same within a few microseconds,
longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse >>>> maybe once a second. A follower would use her (not "his") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as
followers.
The PLL algorithm might be interesting.
It's certainly possible. However, within whatever tiny loop bandwidth >>> you wound up with, the lockers would still have
20 log(40e6) = 152 dB
higher phase noise than the lockee.
GPS has that problem too.
It would be interesting to do the math to see whether it's possible to >>> generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to >>> that, with some bit of AC coupling or something so that they don't all >>> wander together off to the edge of the tuning range.
Maybe have one doing the locking with a phase shifter and the others
with VCOs, or something like that.
Definitely a partly-baked idea, but surely one could do better than
152 dB!
Cheers
Phil Hobbs
Each box is basically a multichannel power supply, but channels can be
programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.
It sounds like you're looking for a protocol like DMX if what you want
is to trigger sequences of events across boxes to within a millisecond,
I don't understand what this lock-the-40 MHz across boxes is about.
<https://en.wikipedia.org/wiki/DMX512>
DMX for this is like hunting deer with an artillery piece. DMX is for
the big-ass risk scenarios in distributed topologies; this is a lot
less profound.
On 7/20/2022 8:22 PM, John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on >>>> the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse
maybe once a second. A follower would use her (not "his") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as
followers.
The PLL algorithm might be interesting.
It's certainly possible. However, within whatever tiny loop bandwidth
you wound up with, the lockers would still have
20 log(40e6) = 152 dB
higher phase noise than the lockee.
GPS has that problem too.
It would be interesting to do the math to see whether it's possible to
generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to
that, with some bit of AC coupling or something so that they don't all
wander together off to the edge of the tuning range.
Maybe have one doing the locking with a phase shifter and the others
with VCOs, or something like that.
Definitely a partly-baked idea, but surely one could do better than
152 dB!
Cheers
Phil Hobbs
Each box is basically a multichannel power supply, but channels can be
programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.
It sounds like you're looking for a protocol like DMX if what you want
is to trigger sequences of events across boxes to within a millisecond,
I don't understand what this lock-the-40 MHz across boxes is about.
<https://en.wikipedia.org/wiki/DMX512>
On Thu, 21 Jul 2022 11:42:28 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:<snip>
Phil Hobbs
Mathematicians often like music. In my experience, music fandom is
negatively correlated to engineering design skill. Different brain
structure or something.
One other thing I see a lot is undue respect for standards. As in "you
can't do that because it violates SCPI standards." Where are the SCPI
Police when you need them?
lørdag den 23. juli 2022 kl. 03.57.33 UTC+2 skrev Les Cargill:
bitrex wrote:
On 7/20/2022 8:22 PM, John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
<pcdhSpamM...@electrooptical.net> wrote:
John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on >>>>>> the back. Each of them has an open-drain mosfet, a weak pullup, and a >>>>>> lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least >>>>>> time-align them to always be the same within a few microseconds,
longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse >>>>>> maybe once a second. A follower would use her (not "his") clock to >>>>>> measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse >>>>>> from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as
followers.
The PLL algorithm might be interesting.
It's certainly possible. However, within whatever tiny loop bandwidth >>>>> you wound up with, the lockers would still have
20 log(40e6) = 152 dB
higher phase noise than the lockee.
GPS has that problem too.
It would be interesting to do the math to see whether it's possible to >>>>> generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to >>>>> that, with some bit of AC coupling or something so that they don't all >>>>> wander together off to the edge of the tuning range.
Maybe have one doing the locking with a phase shifter and the others >>>>> with VCOs, or something like that.
Definitely a partly-baked idea, but surely one could do better than
152 dB!
Cheers
Phil Hobbs
Each box is basically a multichannel power supply, but channels can be >>>> programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.
It sounds like you're looking for a protocol like DMX if what you want
is to trigger sequences of events across boxes to within a millisecond,
I don't understand what this lock-the-40 MHz across boxes is about.
<https://en.wikipedia.org/wiki/DMX512>
DMX for this is like hunting deer with an artillery piece. DMX is for
the big-ass risk scenarios in distributed topologies; this is a lot
less profound.
? it's a 250kbit uart on RS485, hardly rocket surgery
Joe Gwinn wrote:
Don wrote:
Joe Gwinn wrote:
<snip>
Also, I'd lose the BNC connectors. Threaded connectors like SMA, TNC, >>>> and Type N are far better.
Or use shielded twisted pair to carry the 1PPS pulses. This would
work better over a backplane.
This is good advice. Even though the lazy guy within me never truly
gives up his fight to take the easy way out with BNC.
Twisted pair (TP) sounds even easier than BNC. So, what's the
"catch" with TP? Where's the "gotcha" to make TP harder than BNC?
Depends on what you are trying to do.
For nanosecond edges, coax is pretty useful, but short range and often
mechanically awkward.
For microsecond edges at 1000 meters, RS422 over shielded twisted pair
is pretty good.
For bus length links, LVDS or the like.
And so on. And there is always optical links.
Joe Gwinn
BNCs are the bomb, as long as you aren't putting 500 of them in series,
as with the old 10base2 coax Ethernet.
TNCs are a very small niche, and N connectors belong only on spectrum analyzers.
Joe Gwinn wrote:
<snip>
Also, I'd lose the BNC connectors. Threaded connectors like SMA, TNC,
and Type N are far better.
Or use shielded twisted pair to carry the 1PPS pulses.
Twisted pair (TP) sounds even easier than BNC. So, what's the
"catch" with TP? Where's the "gotcha" to make TP harder than BNC?
For some unknown reason, the only thing to truly satisfy me is toMany instruments (including all stringed instruments) exhibit
tune instruments by ear.
There is cross-correlation between left and right ears in the brainstem which is involved in determining the direction of sound sources. Detectable time differences are remarkably small. (I would have to look it up to give a number.)
On 23/7/22 02:02, Don wrote:
    For some unknown reason, the only thing to truly satisfy me is to >> tune instruments by ear.Many instruments (including all stringed instruments) exhibit
inharmonicity. In the case of strings the harmonics are progressively
sharper than the numerical frequency multiples. So to produce an even-tempered tuning requires balancing the matching of fundamentals
with the harmonics. It's not an exact science.
Piano's are "stretch tuned" by as much as two semitones between the
bottom octave and the top one, and professional pianists have personal preferences for more or less stretching.
You could program an electronic tuner to do this of course, but you
can't easily tell it how much stretching you'd like.
On Thu, 21 Jul 2022 18:21:51 +0100, Martin Brown
<'''newspam'''@nonad.co.uk> wrote:
On 21/07/2022 16:31, John Walliker wrote:
The Group Execute Trigger command does allow quite tight synchronisation >>> between different GPIB devices.
GPIB flat out on a good day could manage 1Mbyte/s but in real world
situations with interconnect cabling you would be lucky to get 500kb/s.
It's best feature was that it ran at the maximum speed the receiving
device could handle (assuming that the controller was fast enough).
Synchronisation to a GET command would be probably be better than 1us
but would depend on the decoding time in each individual box. Some GPIB
devices were rather pedestrian at accepting commands.
IEEE488 was good in its day but a bit long in the tooth now. Still on
some test equipment in service today and was provided as standard on NEC
9801 PC's in Japan although hardly ever used by their customers.
Ever read the actual 488 spec? There is a state diagram that could
wreck your sleep for a week.
488 has a hardware "accepted" line, but for some reason SCPI in other contexts is send-and-pray.
488 is rare on new instruments, which are ethernet and USB. A Rigol
scope makes a great USB power supply for fans and charging phones.
jlarkin@highlandsniptechnology.com wrote:
On Thu, 21 Jul 2022 11:42:28 -0400, Phil Hobbs<snip>
<pcdhSpamMeSenseless@electrooptical.net> wrote:
Phil Hobbs
Mathematicians often like music. In my experience, music fandom is
negatively correlated to engineering design skill. Different brain
structure or something.
Engineering is composition. Composition is the thin edge of the musical >wedge. Musicianship is different; it's pattern identification. As is >composition but in a different way. But it is all the same thing.
It all depends on which wall you prefer to have your back against.
One other thing I see a lot is undue respect for standards. As in "you
can't do that because it violates SCPI standards." Where are the SCPI
Police when you need them?
Over where they MATLAB.
On 22/07/2022 19:21, John Larkin wrote:
On Thu, 21 Jul 2022 18:21:51 +0100, Martin Brown
<'''newspam'''@nonad.co.uk> wrote:
On 21/07/2022 16:31, John Walliker wrote:
The Group Execute Trigger command does allow quite tight
synchronisation
between different GPIB devices.
GPIB flat out on a good day could manage 1Mbyte/s but in real world
situations with interconnect cabling you would be lucky to get 500kb/s.
It's best feature was that it ran at the maximum speed the receiving
device could handle (assuming that the controller was fast enough).
Synchronisation to a GET command would be probably be better than 1us
but would depend on the decoding time in each individual box. Some GPIB
devices were rather pedestrian at accepting commands.
IEEE488 was good in its day but a bit long in the tooth now. Still on
some test equipment in service today and was provided as standard on NEC >>> 9801 PC's in Japan although hardly ever used by their customers.
Ever read the actual 488 spec? There is a state diagram that could
wreck your sleep for a week.
I've implemented it on several chipsets including Motorola 68488, Intel
8292 and TI 9914. We even implemented full pass control between peer controllers and our own bus analyser to capture bus transactions (which
after a redesign could not be blinded by HP's IFC tricks).
Later we reworked things for IEEE488.2 in the early 1990's but I dropped
out of that game not long afterwards to go and work in Japan. Ethernet
had made significant inroads into the instrument market by then.
488 has a hardware "accepted" line, but for some reason SCPI in other
contexts is send-and-pray.
And the accepted line makes sure the slowest thing on the bus gets the message which is why it tended to slow down as longer cables and more
kit was added. It tolerated much longer cables than the official
standard permitted with only modest loss of speed.
488 is rare on new instruments, which are ethernet and USB. A Rigol
scope makes a great USB power supply for fans and charging phones.
It surprises me that it is still present on *any* modern instruments.
I expected it to survive on useful legacy kit until about now though.
Plenty of labs will have good working kit that still uses that interface
and it is plenty fast enough for a lot of ordinary lab use.
Phil Hobbs wrote:
Joe Gwinn wrote:
Don wrote:
Joe Gwinn wrote:
<snip>
Also, I'd lose the BNC connectors. Threaded connectors like SMA, TNC, >>>>> and Type N are far better.
Or use shielded twisted pair to carry the 1PPS pulses. This would
work better over a backplane.
This is good advice. Even though the lazy guy within me never truly
gives up his fight to take the easy way out with BNC.
Twisted pair (TP) sounds even easier than BNC. So, what's the
"catch" with TP? Where's the "gotcha" to make TP harder than BNC?
Depends on what you are trying to do.
For nanosecond edges, coax is pretty useful, but short range and often
mechanically awkward.
For microsecond edges at 1000 meters, RS422 over shielded twisted pair
is pretty good.
For bus length links, LVDS or the like.
And so on. And there is always optical links.
Joe Gwinn
BNCs are the bomb, as long as you aren't putting 500 of them in series,
as with the old 10base2 coax Ethernet.
TNCs are a very small niche, and N connectors belong only on spectrum
analyzers.
The lazy guy within me always tries to use an N connector to BNC
adapter on my boat anchor spectrum analyzer. He convinces himself he's
only interested in frequencies less than 2 GHz, so, what's the harm?
High performance WiFi antennas also use N connectors to squeeze out
every last iota of performance. You need a DIY N connector to reverse- polarity SMA to connect such antennas to consumer WiFi devices.
Danke,
fredag den 22. juli 2022 kl. 22.37.08 UTC+2 skrev Joe Gwinn:
On Thu, 21 Jul 2022 04:17:14 -0700, jla...@highlandsniptechnology.com
wrote:
On Wed, 20 Jul 2022 23:49:40 -0700 (PDT), whit3rd <whi...@gmail.com>Yes, exactly. And the drift between two reasonably good clocks is
wrote:
On Wednesday, July 20, 2022 at 4:21:08 PM UTC-7, John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on >> >>> the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.
If you can tolerate 'a few microseconds' on a 40 MHz signal, that's not a phase-lock
problem, it's a frequency-lock problem. Why not just run an up/down counter
to generate a correction voltage for each non-leading VCO?
It's actually a time lock problem. If a follower box starts up and
sees its first 1 PPS input, it can thereafter declare 1 PPS internal
events, based on its local VCO, and then do successive early/late
comparisons to the external pulses. And trim its VCXO accordingly.
slow, so the correction need not and should not be all that fast.
What I've done in real applications is to periodically measure the
offset between when the external 1PPS is predicted to happen and when
it actually does, and adjust the VCO frequency such that in say 50
seconds of roughly linear convergence they will coincide (and keep on
going). The process is repeated every few seconds (exact interval not
important as it is measured).
This is roughly the algorithm a helmsman uses while steering a
sailboat, where effect is very much delayed from action.
In many computer systems it is quite difficult to do anything on a
strict time mark, but easy to measure that actual elapsed time, using
the actual clock that is being steered - it all still converges, so
long as one doesn't try too hard.
So, in your example, the local clock would come from a 40 MHz VCO of
good manufacture (probably needs to be a TCXO of some sort). The 40
MHz output would be fed to a divider that puts out a 1PPS pulse train.
During initialization, when the first external 1PPS leading edge is
received, reset the divider, and start counting 40 MHz cycles. Maybe
wait for things to stabilize.
Thereafter, measure signed offset between external and internal 1PPS
leading edges, and compute how much change (plus or minus) in current
VCO frequency is required for zero offset to occur in say 50 seconds
(make this time-to-zero an adjustable parameter), and change the VCO
control voltage accordingly.
A few seconds later (also an adjustable parameter), repeat the above
adjustment process, again looking 50 seconds into the future from now.
Repeat forever.
isn't that kind how NTP works?, speeding up or slowing down over some period >to sync time with the server without big jumps and always increasing (except possibly at start up)
come to think of it, some closed loop servo systems (and step generators) for things like CNC machine work similarly
at a fixed interval, say a few kHz, current target and actual position is compared, from that (usually with a PI loop)
the speed of the motor (or frequency of steps) is set so the position will hit the next target at the next timer tick.
On Fri, 22 Jul 2022 17:16:00 -0700 (PDT), Lasse Langwadt Christensen <lang...@fonz.dk> wrote:
fredag den 22. juli 2022 kl. 22.37.08 UTC+2 skrev Joe Gwinn:
On Thu, 21 Jul 2022 04:17:14 -0700, jla...@highlandsniptechnology.com
wrote:
On Wed, 20 Jul 2022 23:49:40 -0700 (PDT), whit3rd <whi...@gmail.com>Yes, exactly. And the drift between two reasonably good clocks is
wrote:
On Wednesday, July 20, 2022 at 4:21:08 PM UTC-7, John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a >> >>> lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least >> >>> time-align them to always be the same within a few microseconds,
longterm.
If you can tolerate 'a few microseconds' on a 40 MHz signal, that's not a phase-lock
problem, it's a frequency-lock problem. Why not just run an up/down counter
to generate a correction voltage for each non-leading VCO?
It's actually a time lock problem. If a follower box starts up and
sees its first 1 PPS input, it can thereafter declare 1 PPS internal
events, based on its local VCO, and then do successive early/late
comparisons to the external pulses. And trim its VCXO accordingly.
slow, so the correction need not and should not be all that fast.
What I've done in real applications is to periodically measure the
offset between when the external 1PPS is predicted to happen and when
it actually does, and adjust the VCO frequency such that in say 50
seconds of roughly linear convergence they will coincide (and keep on
going). The process is repeated every few seconds (exact interval not
important as it is measured).
This is roughly the algorithm a helmsman uses while steering a
sailboat, where effect is very much delayed from action.
In many computer systems it is quite difficult to do anything on a
strict time mark, but easy to measure that actual elapsed time, using
the actual clock that is being steered - it all still converges, so
long as one doesn't try too hard.
So, in your example, the local clock would come from a 40 MHz VCO of
good manufacture (probably needs to be a TCXO of some sort). The 40
MHz output would be fed to a divider that puts out a 1PPS pulse train.
During initialization, when the first external 1PPS leading edge is
received, reset the divider, and start counting 40 MHz cycles. Maybe
wait for things to stabilize.
Thereafter, measure signed offset between external and internal 1PPS
leading edges, and compute how much change (plus or minus) in current
VCO frequency is required for zero offset to occur in say 50 seconds
(make this time-to-zero an adjustable parameter), and change the VCO
control voltage accordingly.
A few seconds later (also an adjustable parameter), repeat the above
adjustment process, again looking 50 seconds into the future from now.
Repeat forever.
isn't that kind how NTP works?, speeding up or slowing down over some period
to sync time with the server without big jumps and always increasing (except possibly at start up)
Yes. This is exactly how part of NTP works, in particular the FLL
(Frequency Lock Loop). Battle-tested. That's where I got the idea.
NTP was developed in the early 1980s, shortly after Ethernet made such
a thing useful.
This kind of thing is extensively discussed on Time Nuts.
come to think of it, some closed loop servo systems (and step generators) for things like CNC machine work similarly
at a fixed interval, say a few kHz, current target and actual position is compared, from that (usually with a PI loop)
the speed of the motor (or frequency of steps) is set so the position will hit the next target at the next timer tick.
Yep.
I forgot to mention one thing, a way to speed initialization up:
The external 1PPS pulse-train is taken as gospel. If one counts local
40 MHz oscillator cycles between any adjacent pair of 1PPS events, one
will get a very accurate measurement of the local oscillator signal frequency. Knowing that it is supposed to be 40 MHz, one can compute
how far off correct (as a ratio) that local oscillator is from truth.
This can be used to jump far closer starting frequency to correct
without waiting for convergence to get there.
I forgot to mention one thing, a way to speed initialization up:
The external 1PPS pulse-train is taken as gospel. If one counts local
40 MHz oscillator cycles between any adjacent pair of 1PPS events, one
will get a very accurate measurement of the local oscillator signal frequency. Knowing that it is supposed to be 40 MHz, one can compute
how far off correct (as a ratio) that local oscillator is from truth.
This can be used to jump far closer starting frequency to correct
without waiting for convergence to get there.
On 24/7/22 05:00, Joe Gwinn wrote:
I forgot to mention one thing, a way to speed initialization up:
The external 1PPS pulse-train is taken as gospel. If one counts local
40 MHz oscillator cycles between any adjacent pair of 1PPS events, one
will get a very accurate measurement of the local oscillator signal
frequency. Knowing that it is supposed to be 40 MHz, one can compute
how far off correct (as a ratio) that local oscillator is from truth.
This can be used to jump far closer starting frequency to correct
without waiting for convergence to get there.
This initial measurement stands alone, not refining a previous body of >measurement knowledge, so it's reasonable to set the gain high. Human >perception does this a lot. If you hear two sounds a certain interval
apart, your hearing is pre-primed to expect a third at exactly the same >interval. If the third comes slightly early or slightly late, slightly >quieter or slightly louder, we jump to conclusions very quickly about
what's happening. Very rapid model-forming, and adapting new sensations
to refine the model. Very necessary for a prey animal!
Is there a name for this idea in filter terminology?
On Sun, 24 Jul 2022 08:40:28 +1000, Clifford Heath
<no_spam@please.net> wrote:
On 24/7/22 05:00, Joe Gwinn wrote:
I forgot to mention one thing, a way to speed initialization up:
The external 1PPS pulse-train is taken as gospel. If one counts local
40 MHz oscillator cycles between any adjacent pair of 1PPS events, one
will get a very accurate measurement of the local oscillator signal
frequency. Knowing that it is supposed to be 40 MHz, one can compute
how far off correct (as a ratio) that local oscillator is from truth.
This can be used to jump far closer starting frequency to correct
without waiting for convergence to get there.
This initial measurement stands alone, not refining a previous body of
measurement knowledge, so it's reasonable to set the gain high. Human
perception does this a lot. If you hear two sounds a certain interval
apart, your hearing is pre-primed to expect a third at exactly the same
interval. If the third comes slightly early or slightly late, slightly
quieter or slightly louder, we jump to conclusions very quickly about
what's happening. Very rapid model-forming, and adapting new sensations
to refine the model. Very necessary for a prey animal!
Is there a name for this idea in filter terminology?
There are two answers, depending on which field you mean, biology or electronics.
In biology, it has been long known that the brain creates a model of
the world, and keys on deviations between prediction and actual. But
this isn't just for expected rhythm, it's far more general and
flexible than that.
With the speedup algorithm I mentioned earlier, the mechanism is
designed with considerable domain knowledge in hand. The primary
driver is to achieve robustness despite the imperfections of real
clocks et al. The continuous look-ahead algorithm is not flummoxed by non-stationary and/or non-Gaussian probability-distributions, et al.
But it's more in the nature of a control system than a filter per se.
On 24/7/22 05:00, Joe Gwinn wrote:
I forgot to mention one thing, a way to speed initialization up:
The external 1PPS pulse-train is taken as gospel. If one counts local
40 MHz oscillator cycles between any adjacent pair of 1PPS events, one
will get a very accurate measurement of the local oscillator signal
frequency. Knowing that it is supposed to be 40 MHz, one can compute
how far off correct (as a ratio) that local oscillator is from truth.
This can be used to jump far closer starting frequency to correct
without waiting for convergence to get there.
This initial measurement stands alone, not refining a previous body of >measurement knowledge, so it's reasonable to set the gain high. Human >perception does this a lot. If you hear two sounds a certain interval
apart, your hearing is pre-primed to expect a third at exactly the same >interval. If the third comes slightly early or slightly late, slightly >quieter or slightly louder, we jump to conclusions very quickly about
what's happening. Very rapid model-forming, and adapting new sensations
to refine the model. Very necessary for a prey animal!
Is there a name for this idea in filter terminology?
On a sunny day (Sun, 24 Jul 2022 08:40:28 +1000) it happened Clifford Heath ><no_spam@please.net> wrote in ><1704967e2e98d7c6$38$2251891$26dd2c6e@news.thecubenet.com>:
On 24/7/22 05:00, Joe Gwinn wrote:
I forgot to mention one thing, a way to speed initialization up:
The external 1PPS pulse-train is taken as gospel. If one counts local
40 MHz oscillator cycles between any adjacent pair of 1PPS events, one
will get a very accurate measurement of the local oscillator signal
frequency. Knowing that it is supposed to be 40 MHz, one can compute
how far off correct (as a ratio) that local oscillator is from truth.
This can be used to jump far closer starting frequency to correct
without waiting for convergence to get there.
This initial measurement stands alone, not refining a previous body of >>measurement knowledge, so it's reasonable to set the gain high. Human >>perception does this a lot. If you hear two sounds a certain interval >>apart, your hearing is pre-primed to expect a third at exactly the same >>interval. If the third comes slightly early or slightly late, slightly >>quieter or slightly louder, we jump to conclusions very quickly about >>what's happening. Very rapid model-forming, and adapting new sensations
to refine the model. Very necessary for a prey animal!
Is there a name for this idea in filter terminology?
No sure, but this is related to 'the alien problem' from cryptography.
It goes like:
Alien comes to earh, wants to take all knowledge humans have back home.
So he gets Encyclopedia Britannica, but it is too heavy and does not fit in his flying saucer.
So he writes the text out as an ASCII hex number and does 1 / that number. >then he takes a stick and puts a mark on it in that ratio
and takes the stick back home.
To say 3 ticks is all you need to convey all information in the universe >given time has no granularity.
The stick in that example does of course have, limited by size of atoms etc, >But does time have granularity?
I use this all the time.
On Sun, 24 Jul 2022 08:58:10 GMT, Jan Panteltje
<pNaonStpealmtje@yahoo.com> wrote:
On a sunny day (Sun, 24 Jul 2022 08:40:28 +1000) it happened Clifford Heath >><no_spam@please.net> wrote in >><1704967e2e98d7c6$38$2251891$26dd2c6e@news.thecubenet.com>:
On 24/7/22 05:00, Joe Gwinn wrote:
I forgot to mention one thing, a way to speed initialization up:
The external 1PPS pulse-train is taken as gospel. If one counts local >>>> 40 MHz oscillator cycles between any adjacent pair of 1PPS events, one >>>> will get a very accurate measurement of the local oscillator signal
frequency. Knowing that it is supposed to be 40 MHz, one can compute
how far off correct (as a ratio) that local oscillator is from truth.
This can be used to jump far closer starting frequency to correct
without waiting for convergence to get there.
This initial measurement stands alone, not refining a previous body of >>>measurement knowledge, so it's reasonable to set the gain high. Human >>>perception does this a lot. If you hear two sounds a certain interval >>>apart, your hearing is pre-primed to expect a third at exactly the same >>>interval. If the third comes slightly early or slightly late, slightly >>>quieter or slightly louder, we jump to conclusions very quickly about >>>what's happening. Very rapid model-forming, and adapting new sensations >>>to refine the model. Very necessary for a prey animal!
Is there a name for this idea in filter terminology?
No sure, but this is related to 'the alien problem' from cryptography.
It goes like:
Alien comes to earh, wants to take all knowledge humans have back home.
So he gets Encyclopedia Britannica, but it is too heavy and does not fit in his flying saucer.
So he writes the text out as an ASCII hex number and does 1 / that number. >>then he takes a stick and puts a mark on it in that ratio
and takes the stick back home.
To say 3 ticks is all you need to convey all information in the universe >>given time has no granularity.
The stick in that example does of course have, limited by size of atoms etc, >>But does time have granularity?
I use this all the time.
Time is thought to have a granularity of sorts, about 10^-43 seconds,
which is a Planck Unit.
.<https://en.wikipedia.org/wiki/Planck_units>
On 24/7/22 09:08, Joe Gwinn wrote:
On Sun, 24 Jul 2022 08:40:28 +1000, Clifford Heath
<no_spam@please.net> wrote:
On 24/7/22 05:00, Joe Gwinn wrote:
I forgot to mention one thing, a way to speed initialization up:
The external 1PPS pulse-train is taken as gospel. If one counts local >>>> 40 MHz oscillator cycles between any adjacent pair of 1PPS events, one >>>> will get a very accurate measurement of the local oscillator signal
frequency. Knowing that it is supposed to be 40 MHz, one can compute
how far off correct (as a ratio) that local oscillator is from truth.
This can be used to jump far closer starting frequency to correct
without waiting for convergence to get there.
This initial measurement stands alone, not refining a previous body of
measurement knowledge, so it's reasonable to set the gain high. Human
perception does this a lot. If you hear two sounds a certain interval
apart, your hearing is pre-primed to expect a third at exactly the same
interval. If the third comes slightly early or slightly late, slightly
quieter or slightly louder, we jump to conclusions very quickly about
what's happening. Very rapid model-forming, and adapting new sensations
to refine the model. Very necessary for a prey animal!
Is there a name for this idea in filter terminology?
There are two answers, depending on which field you mean, biology or
electronics.
In biology, it has been long known that the brain creates a model of
the world, and keys on deviations between prediction and actual. But
this isn't just for expected rhythm, it's far more general and
flexible than that.
With the speedup algorithm I mentioned earlier, the mechanism is
designed with considerable domain knowledge in hand. The primary
driver is to achieve robustness despite the imperfections of real
clocks et al. The continuous look-ahead algorithm is not flummoxed by
non-stationary and/or non-Gaussian probability-distributions, et al.
But it's more in the nature of a control system than a filter per se.
A control system also models the plant, measures deviations from the >prediction, before it applies a loop filter to decide the corrective step.
That's the filter I'm referring to. It's just the same principle with
the human system as when synchronising two clocks.
On a sunny day (Sun, 24 Jul 2022 12:09:21 -0400) it happened Joe Gwinn ><joegwinn@comcast.net> wrote in <ugrqdhp9ldssd95u39nik1n6th9bktbs41@4ax.com>:
On Sun, 24 Jul 2022 08:58:10 GMT, Jan Panteltje
<pNaonStpealmtje@yahoo.com> wrote:
On a sunny day (Sun, 24 Jul 2022 08:40:28 +1000) it happened Clifford Heath >>><no_spam@please.net> wrote in >>><1704967e2e98d7c6$38$2251891$26dd2c6e@news.thecubenet.com>:
On 24/7/22 05:00, Joe Gwinn wrote:
I forgot to mention one thing, a way to speed initialization up:
The external 1PPS pulse-train is taken as gospel. If one counts local >>>>> 40 MHz oscillator cycles between any adjacent pair of 1PPS events, one >>>>> will get a very accurate measurement of the local oscillator signal
frequency. Knowing that it is supposed to be 40 MHz, one can compute >>>>> how far off correct (as a ratio) that local oscillator is from truth. >>>>> This can be used to jump far closer starting frequency to correct
without waiting for convergence to get there.
This initial measurement stands alone, not refining a previous body of >>>>measurement knowledge, so it's reasonable to set the gain high. Human >>>>perception does this a lot. If you hear two sounds a certain interval >>>>apart, your hearing is pre-primed to expect a third at exactly the same >>>>interval. If the third comes slightly early or slightly late, slightly >>>>quieter or slightly louder, we jump to conclusions very quickly about >>>>what's happening. Very rapid model-forming, and adapting new sensations >>>>to refine the model. Very necessary for a prey animal!
Is there a name for this idea in filter terminology?
No sure, but this is related to 'the alien problem' from cryptography.
It goes like:
Alien comes to earh, wants to take all knowledge humans have back home. >>>So he gets Encyclopedia Britannica, but it is too heavy and does not fit in his flying saucer.
So he writes the text out as an ASCII hex number and does 1 / that number. >>>then he takes a stick and puts a mark on it in that ratio
and takes the stick back home.
To say 3 ticks is all you need to convey all information in the universe >>>given time has no granularity.
The stick in that example does of course have, limited by size of atoms etc, >>>But does time have granularity?
I use this all the time.
Time is thought to have a granularity of sorts, about 10^-43 seconds,
which is a Planck Unit.
.<https://en.wikipedia.org/wiki/Planck_units>
Sure but there is a problem, if you scroll down on that site you find the sentence
"the Planck time is the time required for light to travel the distance of 1 Planck length in a vacuum".
That leads to a circular reasoning, as traveling half a Planck length would take half the time...
Just before that the text goes into Planck length, and says in some theories with more dimensions
that length is smaller than the fundamental Planck length
So much twenty-first century physics assumptions...
Start of big bang start of time, obvious bull.
Maybe there are a zillion bangs like there are a zillion stars and something that formed those over time.
Measurement limits like saying length in feet or whatever ...
But sure, what we can measure, being made of matter, probably has a limit. >Wait till they figure out gravity.. I still like Le Sage's model as it provides a MECHANISM for gravity.
Now they are stuck looking for dark matter..
Very interesting, physics, BTW.
Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least >time-align them to always be the same within a few microseconds,
longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse
maybe once a second. A follower would use her (not "his") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as
followers.
The PLL algorithm might be interesting.
Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least time-align them to always be the same within a few microseconds,
longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse
maybe once a second. A follower would use her (not "his") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?
Martin Brown wrote:
On 22/07/2022 03:44, Clifford Heath wrote:
On 22/7/22 03:10, Phil Hobbs wrote:
Gerhard Hoffmann wrote:
Am 21.07.22 um 16:15 schrieb Phil Hobbs:
I wonder if there's an advantage to using the closure phase for an >>>>>> array that large. With 17 oscillators you've got 136 independent
phase differences, so maybe there's a way to get 22 dB instead of
12 dB improvement.
-v ?
what do you mean with closure phase? Where do the 22 dB come
from?
The idea was simply to have all 16 regulated to the be
synchronous and then feed them into a 16-to--1 Wilkinson
combiner. The phase noise should average out among the
16 units. Just as proof of concept. The MTI-260 are quite ok,
but with bleeding edge oscillators that could be interesting.
In the region where you just cannot improve an oscillator.
CheersGerhard
Sure. Thing is, that wastes a lot of information that you could
maybe use to get 10*log(136) = 21.3 dB improvement instead of
10*log(17) = 12.3 dB. [136 = N(N-1)/2 when N = 17.]
Closure is a really cute idea, which I first came across in the
context of very long baseline interferometry (VLBI) radio telescopes.
See the discussion from BEOS 3e here:
<https://electrooptical.net/www/sed/closure.png>.
Interesting, thanks.
Some frequency synthesiser chips employ proprietary majick to reduce
the phase noise associated with integer divide/multiply ratios.
Polyphase oscillator and slipping by partial cycles I think. Perhaps
they're doing something like closure against the different clock phases?
Quite probably - it has been known for a long time in radio astronomy
first derived by Jennison in 1958 at Jodrell Bank for 3 antennae. This
is the original ground breaking paper for anyone interested
<https://articles.adsabs.harvard.edu//full/1958MNRAS.118..276J/0000276.000.html >
(easier to understand versions exist today). WIki isn't bad:
<https://en.wikipedia.org/wiki/Closure_phase>
It allows you to get a good phase observable uncontaminated by the phase
error at each node for every distinct subset of 3 nodes. There is a
corresponding closure amplitude for distinct subsets of 4 nodes.
Obviously the bigger N is the more useful observables you can get which
is why the big dish telescopes sometimes stay on target and in the loop
for perhaps longer than they really ought to in deteriorating weather.
This book reviews most of the classical tricks used in VLBI and
interferometry from the period when they had just become routine:
Indirect Imaging: Measurement and Processing for Indirect Imaging
Editor-J. A. Roberts
0 ratings by Goodreads
ISBN 10: 0521262828 / ISBN 13: 9780521262828
Published by Cambridge University Press, 1984
The real power comes from the number of independent observables from N >instruments going like N**2, so that you win SNR like N**2 instead of N.
Quite a startling improvement for moderate-to-large N!
On Fri, 22 Jul 2022 09:03:16 -0400, Phil Hobbs
"A geometric view of closure phases in interferometry", DOI: <https://doi.org/10.1017/pasa.2022.6>
.<https://www.cambridge.org/core/journals/publications-of-the-astronomical-society-of-australia/article/geometric-view-of-closure-phases-in-interferometry/5E8A5A8D58A2FC72ADFA0587347C4DA7>
I'm still digesting it, but basically deducing the underlying geometry allowed for some significant improvements.
Phil Hobbs wrote:
jlarkin@highlandsniptechnology.com wrote:<snip>
It dithers around the setpoint but nobody notices.
That's what lowpass filters are for.
This is immune to classic control theory so the concept annoys some
people but it works great.
A real old time control guy like Tim Wescott would probably be a fan
too--the great virtue of a bang-bang controller is that (as you say)
it's highly resistant to variations in the _plant_.
Well, yeah - it's naturally constrained. When I jack the temp target on
the A/C here, it take 30-45 seconds to turn everything off.
Tim used to be a lot of fun and put up with much. FWIW rbj showed up
on Reddit and lasted a couple days.
Your furnace doesn't go nuts when you have a Christmas party, even
though all those people generate a lot of heat, and there's lots of
opening and closing of doors and ovens.
You're just doing trust falls with slew rate limiting. :) There's
probably a PhD paper somewhere with a madman low-pass filtering the
output of a bangbang with a lowpass.
Am 25.07.22 um 18:31 schrieb Joe Gwinn:
On Fri, 22 Jul 2022 09:03:16 -0400, Phil Hobbs
"A geometric view of closure phases in interferometry", DOI:
<https://doi.org/10.1017/pasa.2022.6>
.<https://www.cambridge.org/core/journals/publications-of-the-astronomical-society-of-australia/article/geometric-view-of-closure-phases-in-interferometry/5E8A5A8D58A2FC72ADFA0587347C4DA7>
I'm still digesting it, but basically deducing the underlying geometry
allowed for some significant improvements.
I have not yet digested it, but can I assume that it won't help
me to create a carrier that is phase noise wise better than
averaged over 16 oscillators created equally bad?
More suitable for post-processing after-the-fact?
U. Rohde has the math for n injection locked oscillators in one
of his books, but the formulas probably fall apart when you have
to insert hard numbers for real oscillators you can buy, or build.
Methinks he is more into multiple coupled resonators.
Am 25.07.22 um 21:49 schrieb Joe Gwinn:
I have not yet digested it, but can I assume that it won't help
me to create a carrier that is phase noise wise better than
averaged over 16 oscillators created equally bad?
As you suspect, no, it won't. Only better oscillators will help.
Or even more oscillators to average. :-)
I have not yet digested it, but can I assume that it won't help
me to create a carrier that is phase noise wise better than
averaged over 16 oscillators created equally bad?
As you suspect, no, it won't. Only better oscillators will help.
Am 25.07.22 um 18:31 schrieb Joe Gwinn:
On Fri, 22 Jul 2022 09:03:16 -0400, Phil Hobbs
"A geometric view of closure phases in interferometry", DOI:
<https://doi.org/10.1017/pasa.2022.6>
.<https://www.cambridge.org/core/journals/publications-of-the-astronomical-society-of-australia/article/geometric-view-of-closure-phases-in-interferometry/5E8A5A8D58A2FC72ADFA0587347C4DA7>
I'm still digesting it, but basically deducing the underlying geometry
allowed for some significant improvements.
I have not yet digested it, but can I assume that it won't help
me to create a carrier that is phase noise wise better than
averaged over 16 oscillators created equally bad?
More suitable for post-processing after-the-fact?
U. Rohde has the math for n injection locked oscillators in one
of his books, but the formulas probably fall apart when you have
to insert hard numbers for real oscillators you can buy, or build.
Methinks he is more into multiple coupled resonators.
cheers,
Gerhard
On Mon, 25 Jul 2022 22:16:42 +0200, Gerhard Hoffmann <dk4xp@arcor.de>
wrote:
Am 25.07.22 um 21:49 schrieb Joe Gwinn:
I have not yet digested it, but can I assume that it won't help
me to create a carrier that is phase noise wise better than
averaged over 16 oscillators created equally bad?
As you suspect, no, it won't. Only better oscillators will help.
Or even more oscillators to average. :-)
Yes, but the improvement is 5 dB per factor of ten oscillator count.
Longer integration times may be easier.
Low-noise oscillator design is a career.
Joe Gwinn
On Mon, 25 Jul 2022 20:51:18 +0200, Gerhard Hoffmann <dk4xp@arcor.de>
wrote:
Am 25.07.22 um 18:31 schrieb Joe Gwinn:
On Fri, 22 Jul 2022 09:03:16 -0400, Phil Hobbs
"A geometric view of closure phases in interferometry", DOI:
<https://doi.org/10.1017/pasa.2022.6>
.<https://www.cambridge.org/core/journals/publications-of-the-astronomical-society-of-australia/article/geometric-view-of-closure-phases-in-interferometry/5E8A5A8D58A2FC72ADFA0587347C4DA7>
I'm still digesting it, but basically deducing the underlying geometry
allowed for some significant improvements.
I have not yet digested it, but can I assume that it won't help
me to create a carrier that is phase noise wise better than
averaged over 16 oscillators created equally bad?
As you suspect, no, it won't. Only better oscillators will help.
Joe Gwinn wrote:
Yes, but the improvement is 5 dB per factor of ten oscillator count.
Longer integration times may be easier.
Low-noise oscillator design is a career.
Joe Gwinn
Nah, even the simple averaging case you win SNR like N, so it's 10 dB
per decade.
Cheers
Gerhard Hoffmann wrote:
Am 25.07.22 um 18:31 schrieb Joe Gwinn:
On Fri, 22 Jul 2022 09:03:16 -0400, Phil Hobbs
"A geometric view of closure phases in interferometry", DOI:
<https://doi.org/10.1017/pasa.2022.6>
.<https://www.cambridge.org/core/journals/publications-of-the-astronomical-society-of-australia/article/geometric-view-of-closure-phases-in-interferometry/5E8A5A8D58A2FC72ADFA0587347C4DA7>
I'm still digesting it, but basically deducing the underlying geometry
allowed for some significant improvements.
I have not yet digested it, but can I assume that it won't help
me to create a carrier that is phase noise wise better than
averaged over 16 oscillators created equally bad?
More suitable for post-processing after-the-fact?
U. Rohde has the math for n injection locked oscillators in one
of his books, but the formulas probably fall apart when you have
to insert hard numbers for real oscillators you can buy, or build.
Methinks he is more into multiple coupled resonators.
cheers,
Gerhard
I'm not sure--as I say, I haven't got a properly-thought-out scheme, but
it seems as though it ought to be possible to combine the measurements
to produce N-1 oscillator signals, each one N times quieter, so that >averaging _those_ would get you to the N(N-1)/2 level.
It probably needs a whole lot of phase shifters or weighted summers
(like a Wilkinson with attenuators), so it may well not be a win from a >total-hardware POV. Seems like it would be worth a bit of thought, though.
Cheers
Phil Hobbs
On Tue, 26 Jul 2022 08:05:49 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
Gerhard Hoffmann wrote:
Am 25.07.22 um 18:31 schrieb Joe Gwinn:
On Fri, 22 Jul 2022 09:03:16 -0400, Phil Hobbs
"A geometric view of closure phases in interferometry", DOI:
<https://doi.org/10.1017/pasa.2022.6>
.<https://www.cambridge.org/core/journals/publications-of-the-astronomical-society-of-australia/article/geometric-view-of-closure-phases-in-interferometry/5E8A5A8D58A2FC72ADFA0587347C4DA7>
I'm still digesting it, but basically deducing the underlying geometry >>>> allowed for some significant improvements.
I have not yet digested it, but can I assume that it won't help
me to create a carrier that is phase noise wise better than
averaged over 16 oscillators created equally bad?
More suitable for post-processing after-the-fact?
U. Rohde has the math for n injection locked oscillators in one
of his books, but the formulas probably fall apart when you have
to insert hard numbers for real oscillators you can buy, or build.
Methinks he is more into multiple coupled resonators.
cheers,
Gerhard
I'm not sure--as I say, I haven't got a properly-thought-out scheme, but
it seems as though it ought to be possible to combine the measurements
to produce N-1 oscillator signals, each one N times quieter, so that
averaging _those_ would get you to the N(N-1)/2 level.
It probably needs a whole lot of phase shifters or weighted summers
(like a Wilkinson with attenuators), so it may well not be a win from a
total-hardware POV. Seems like it would be worth a bit of thought, though. >>
Cheers
Phil Hobbs
Imagine a single circuit/pcb that has N crystal oscillator circuits, injection locked and summed, in an oven.
XOs near one another, namely in the same room, like to injection lock.
Joe Gwinn wrote:
On Mon, 25 Jul 2022 20:51:18 +0200, Gerhard Hoffmann <dk4xp@arcor.de>
wrote:
Am 25.07.22 um 18:31 schrieb Joe Gwinn:
On Fri, 22 Jul 2022 09:03:16 -0400, Phil Hobbs
"A geometric view of closure phases in interferometry", DOI:
<https://doi.org/10.1017/pasa.2022.6>
.<https://www.cambridge.org/core/journals/publications-of-the-astronomical-society-of-australia/article/geometric-view-of-closure-phases-in-interferometry/5E8A5A8D58A2FC72ADFA0587347C4DA7>
I'm still digesting it, but basically deducing the underlying geometry >>>> allowed for some significant improvements.
I have not yet digested it, but can I assume that it won't help
me to create a carrier that is phase noise wise better than
averaged over 16 oscillators created equally bad?
As you suspect, no, it won't. Only better oscillators will help.
As Kipling might say, "Not so, but far otherwise."
lørdag den 23. juli 2022 kl. 03.57.33 UTC+2 skrev Les Cargill:
bitrex wrote:
On 7/20/2022 8:22 PM, John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
<pcdhSpamM...@electrooptical.net> wrote:
John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on >>>>>> the back. Each of them has an open-drain mosfet, a weak pullup, and a >>>>>> lowpass filtered schmitt gate back into our FPGA.
I can daisy-chain several boxes with BNC cables and tees.
Each box has a 40 MHz VCXO and I want to phase-lock them, or at least >>>>>> time-align them to always be the same within a few microseconds,
longterm.
I could call one the leader (not "master") and make the others
followers (not "slaves") and have the leader make an active low pulse >>>>>> maybe once a second. A follower would use her (not "his") clock to >>>>>> measure the incoming period and tweak its local VCXO in the right
direction. That should work.
Don't GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse >>>>>> from the satellites?
My system should work from a 1 PPS GPS pulse too, all boxes as
followers.
The PLL algorithm might be interesting.
It's certainly possible. However, within whatever tiny loop bandwidth >>>>> you wound up with, the lockers would still have
20 log(40e6) = 152 dB
higher phase noise than the lockee.
GPS has that problem too.
It would be interesting to do the math to see whether it's possible to >>>>> generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to >>>>> that, with some bit of AC coupling or something so that they don't all >>>>> wander together off to the edge of the tuning range.
Maybe have one doing the locking with a phase shifter and the others >>>>> with VCOs, or something like that.
Definitely a partly-baked idea, but surely one could do better than
152 dB!
Cheers
Phil Hobbs
Each box is basically a multichannel power supply, but channels can be >>>> programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.
It sounds like you're looking for a protocol like DMX if what you want
is to trigger sequences of events across boxes to within a millisecond,
I don't understand what this lock-the-40 MHz across boxes is about.
<https://en.wikipedia.org/wiki/DMX512>
DMX for this is like hunting deer with an artillery piece. DMX is for
the big-ass risk scenarios in distributed topologies; this is a lot
less profound.
? it's a 250kbit uart on RS485, hardly rocket surgery
On Fri, 22 Jul 2022 21:10:35 -0500, Les Cargill <lcargil99@gmail.com>
wrote:
jlarkin@highlandsniptechnology.com wrote:
On Thu, 21 Jul 2022 11:42:28 -0400, Phil Hobbs<snip>
<pcdhSpamMeSenseless@electrooptical.net> wrote:
Phil Hobbs
Mathematicians often like music. In my experience, music fandom is
negatively correlated to engineering design skill. Different brain
structure or something.
Engineering is composition. Composition is the thin edge of the musical
wedge. Musicianship is different; it's pattern identification. As is
composition but in a different way. But it is all the same thing.
It all depends on which wall you prefer to have your back against.
I've always wondered about musicians. They have to play a piece
hundreds of times to get it right.
Some have surely performed
something thousands of times. Don't they get bored? Apparently not.
I design something, finish, and then want to design something entirely different.
It depends on boredom thresholds.
One other thing I see a lot is undue respect for standards. As in "you
can't do that because it violates SCPI standards." Where are the SCPI
Police when you need them?
Over where they MATLAB.
SCPI is send-and-forget. There is some query you can send to ask if
the last command worked. And you can have an error queue that you can interrogate now and then for historical forensics.
I told the customer that damn the specs, every command is going to
reply with data, an error message, or "OK". They agree.
On Tue, 26 Jul 2022 08:40:45 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
Joe Gwinn wrote:
On Mon, 25 Jul 2022 20:51:18 +0200, Gerhard Hoffmann <dk4xp@arcor.de>
wrote:
Am 25.07.22 um 18:31 schrieb Joe Gwinn:
On Fri, 22 Jul 2022 09:03:16 -0400, Phil Hobbs
"A geometric view of closure phases in interferometry", DOI:
<https://doi.org/10.1017/pasa.2022.6>
.<https://www.cambridge.org/core/journals/publications-of-the-astronomical-society-of-australia/article/geometric-view-of-closure-phases-in-interferometry/5E8A5A8D58A2FC72ADFA0587347C4DA7>
I'm still digesting it, but basically deducing the underlying geometry >>>>> allowed for some significant improvements.
I have not yet digested it, but can I assume that it won't help
me to create a carrier that is phase noise wise better than
averaged over 16 oscillators created equally bad?
As you suspect, no, it won't. Only better oscillators will help.
As Kipling might say, "Not so, but far otherwise."
Well, for phase noise test sets, the rule is that noise reduces as
10Log10[ Sqrt[N] ], or simply 5Log10[N], where N is the number of correlations performed, where what's being correlated is
data-collection runs with a specified data-collection window
durations. These windows can be over time or over devices, which
should be equivalent in the noise floor.
So, getting to very low PN levels this way soon becomes impractical,
and by far the best approach is to use a better oscillator. State of
the art these days is a noise floor at around -170 dBc/Hz at 10 MHz.
As always, 1/f^a noise can be a big problem, and it doesn't average
out all that well.
We may be talking about different things.
Joe Gwinn
Joe Gwinn wrote:
On Tue, 26 Jul 2022 08:40:45 -0400, Phil Hobbs <pcdhSpamM...@electrooptical.net> wrote:
Joe Gwinn wrote:
On Mon, 25 Jul 2022 20:51:18 +0200, Gerhard Hoffmann <dk...@arcor.de> >>> wrote:
Am 25.07.22 um 18:31 schrieb Joe Gwinn:
On Fri, 22 Jul 2022 09:03:16 -0400, Phil Hobbs
"A geometric view of closure phases in interferometry", DOI:
<https://doi.org/10.1017/pasa.2022.6>
.<https://www.cambridge.org/core/journals/publications-of-the-astronomical-society-of-australia/article/geometric-view-of-closure-phases-in-interferometry/5E8A5A8D58A2FC72ADFA0587347C4DA7>
I'm still digesting it, but basically deducing the underlying geometry >>>>> allowed for some significant improvements.
I have not yet digested it, but can I assume that it won't help
me to create a carrier that is phase noise wise better than
averaged over 16 oscillators created equally bad?
As you suspect, no, it won't. Only better oscillators will help.
As Kipling might say, "Not so, but far otherwise."
Gerhard Hoffmann wrote:
Am 25.07.22 um 18:31 schrieb Joe Gwinn:
On Fri, 22 Jul 2022 09:03:16 -0400, Phil Hobbs
"A geometric view of closure phases in interferometry", DOI:
<https://doi.org/10.1017/pasa.2022.6>
.<https://www.cambridge.org/core/journals/publications-of-the-astronomical-society-of-australia/article/geometric-view-of-closure-phases-in-interferometry/5E8A5A8D58A2FC72ADFA0587347C4DA7>
I'm still digesting it, but basically deducing the underlying geometry
allowed for some significant improvements.
I have not yet digested it, but can I assume that it won't help
me to create a carrier that is phase noise wise better than
averaged over 16 oscillators created equally bad?
More suitable for post-processing after-the-fact?
U. Rohde has the math for n injection locked oscillators in one
of his books, but the formulas probably fall apart when you have
to insert hard numbers for real oscillators you can buy, or build.
Methinks he is more into multiple coupled resonators.
I'm not sure--as I say, I haven't got a properly-thought-out scheme, but
it seems as though it ought to be possible to combine the measurements
to produce N-1 oscillator signals, each one N times quieter, so that averaging _those_ would get you to the N(N-1)/2 level.
It probably needs a whole lot of phase shifters or weighted summers
(like a Wilkinson with attenuators), so it may well not be a win from a total-hardware POV. Seems like it would be worth a bit of thought, though.
jlarkin@highlandsniptechnology.com wrote:
On Fri, 22 Jul 2022 21:10:35 -0500, Les Cargill <lcargil99@gmail.com>
wrote:
jlarkin@highlandsniptechnology.com wrote:
On Thu, 21 Jul 2022 11:42:28 -0400, Phil Hobbs<snip>
<pcdhSpamMeSenseless@electrooptical.net> wrote:
Phil Hobbs
Mathematicians often like music. In my experience, music fandom is
negatively correlated to engineering design skill. Different brain
structure or something.
Engineering is composition. Composition is the thin edge of the musical
wedge. Musicianship is different; it's pattern identification. As is
composition but in a different way. But it is all the same thing.
It all depends on which wall you prefer to have your back against.
I've always wondered about musicians. They have to play a piece
hundreds of times to get it right.
Some do; some don't. Session players from back when studio time
was the dominant cost probably played the parts on a song you later
heard on the radio on the first take.
Some have surely performed
something thousands of times. Don't they get bored? Apparently not.
There's too broad a spectrum to generalize. Some forms are better for
people with mild forms of OCD.
I design something, finish, and then want to design something entirely
different.
It depends on boredom thresholds.
Much does.
One other thing I see a lot is undue respect for standards. As in "you >>>> can't do that because it violates SCPI standards." Where are the SCPI
Police when you need them?
Over where they MATLAB.
SCPI is send-and-forget. There is some query you can send to ask if
the last command worked. And you can have an error queue that you can
interrogate now and then for historical forensics.
I told the customer that damn the specs, every command is going to
reply with data, an error message, or "OK". They agree.
And there you go turning a perfectly good full duplex channel into a
half duplex walkie-talkie channel :)
It'll be fast enough.
On Wednesday, July 27, 2022 at 12:34:40 PM UTC+10, Phil Hobbs wrote:
Joe Gwinn wrote:
As you suspect, no, it won't. Only better oscillators will help.
This might be the better oscillator.6 K."
https://spectrum.ieee.org/for-precision-the-sapphire-clock-outshines-even-the-best-atomic-clocks?utm_campaign=post-teaser&utm_content=7190c3vu
It's a big lump of sapphire in a pool of liquid helium. Long term stability isn't wonderful, but short term stability is uniquely good.
" The team is re-engineering the device to work at 50 K by increasing the concentration of magnetic impurities in the crystal without introducing additional losses. That's a temperature that liquid nitrogen can't quite get to, but it's way easier than
Apparently the Australian Air Force has two of the 6K devices for their radar network. Probably beyond John Larkin's budget.
On 26/07/2022 13:05, Phil Hobbs wrote:
Gerhard Hoffmann wrote:
Am 25.07.22 um 18:31 schrieb Joe Gwinn:
On Fri, 22 Jul 2022 09:03:16 -0400, Phil Hobbs
Entrainment of weakly coupled oscillators at frequencies near to each
other can be quite strong (a problem if you don't want that to happen).
I think the catch is that to do that you would have to provide hardware
to compute the cross correlation of every pair of oscillators so that correlator complexity goes up as N(N-1)/2 too. I can't immediately see a
way to exploit this to get a better average oscillator though.
On Friday, July 22, 2022 at 2:38:45 PM UTC-7, Don wrote:
Joe Gwinn wrote:
<snip>
Also, I'd lose the BNC connectors. Threaded connectors like SMA, TNC,
and Type N are far better.
Or use shielded twisted pair to carry the 1PPS pulses.
Twisted pair (TP) sounds even easier than BNC. So, what's the
"catch" with TP? Where's the "gotcha" to make TP harder than BNC?
Biggest 'gotcha' is the lack of good shielded TP connectors. I had only UHF-style twisted pair shielded connectors last time I wanted some, and that's a polarity-insensitive connector. We applied paint markings
to get it straight.
MiniDIN 3 (don't trust the shield connector) was what Apple used for their LocalTalk/Appletalk hardware,
On 26/07/2022 13:05, Phil Hobbs wrote:
Gerhard Hoffmann wrote:
Am 25.07.22 um 18:31 schrieb Joe Gwinn:
On Fri, 22 Jul 2022 09:03:16 -0400, Phil Hobbs
"A geometric view of closure phases in interferometry", DOI:
<https://doi.org/10.1017/pasa.2022.6>
.<https://www.cambridge.org/core/journals/publications-of-the-astronomical-society-of-australia/article/geometric-view-of-closure-phases-in-interferometry/5E8A5A8D58A2FC72ADFA0587347C4DA7>
I'm still digesting it, but basically deducing the underlying geometry >>>> allowed for some significant improvements.
I have not yet digested it, but can I assume that it won't help
me to create a carrier that is phase noise wise better than
averaged over 16 oscillators created equally bad?
More suitable for post-processing after-the-fact?
U. Rohde has the math for n injection locked oscillators in one
of his books, but the formulas probably fall apart when you have
to insert hard numbers for real oscillators you can buy, or build.
Methinks he is more into multiple coupled resonators.
Entrainment of weakly coupled oscillators at frequencies near to each
other can be quite strong (a problem if you don't want that to happen).
I'm not sure--as I say, I haven't got a properly-thought-out scheme,
but it seems as though it ought to be possible to combine the
measurements to produce N-1 oscillator signals, each one N times
quieter, so that averaging _those_ would get you to the N(N-1)/2 level.
I think the catch is that to do that you would have to provide hardware
to compute the cross correlation of every pair of oscillators so that correlator complexity goes up as N(N-1)/2 too. I can't immediately see a
way to exploit this to get a better average oscillator though.
It probably needs a whole lot of phase shifters or weighted summers
(like a Wilkinson with attenuators), so it may well not be a win from
a total-hardware POV. Seems like it would be worth a bit of thought,
though.
VLBI typically disciplines a hydrogen maser using some other long term
stable centralised terrestrial time source. Getting it just a little bit wrong just makes the white light fringe much harder to find later. Local clock short term stability stability is the key to it working well.
I expect they are a lot better at it by now. In my day it involved
moving around furniture van loads of tweaked VHS video tape cassettes
from the big dishes to the correlator centres.
jlarkin@highlandsniptechnology.com wrote:
On Tue, 26 Jul 2022 08:05:49 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
Gerhard Hoffmann wrote:
Am 25.07.22 um 18:31 schrieb Joe Gwinn:
On Fri, 22 Jul 2022 09:03:16 -0400, Phil Hobbs
"A geometric view of closure phases in interferometry", DOI:
<https://doi.org/10.1017/pasa.2022.6>
.<https://www.cambridge.org/core/journals/publications-of-the-astronomical-society-of-australia/article/geometric-view-of-closure-phases-in-interferometry/5E8A5A8D58A2FC72ADFA0587347C4DA7>
I'm still digesting it, but basically deducing the underlying geometry >>>>> allowed for some significant improvements.
I have not yet digested it, but can I assume that it won't help
me to create a carrier that is phase noise wise better than
averaged over 16 oscillators created equally bad?
More suitable for post-processing after-the-fact?
U. Rohde has the math for n injection locked oscillators in one
of his books, but the formulas probably fall apart when you have
to insert hard numbers for real oscillators you can buy, or build.
Methinks he is more into multiple coupled resonators.
cheers,
Gerhard
I'm not sure--as I say, I haven't got a properly-thought-out scheme, but >>> it seems as though it ought to be possible to combine the measurements
to produce N-1 oscillator signals, each one N times quieter, so that
averaging _those_ would get you to the N(N-1)/2 level.
It probably needs a whole lot of phase shifters or weighted summers
(like a Wilkinson with attenuators), so it may well not be a win from a
total-hardware POV. Seems like it would be worth a bit of thought, though. >>>
Cheers
Phil Hobbs
Imagine a single circuit/pcb that has N crystal oscillator circuits,
injection locked and summed, in an oven.
XOs near one another, namely in the same room, like to injection lock.
Sure. That only gets you 10*log(N), though, AFAICT. Looking at it from
a phase noise POV, you win improved <delta phi> like sqrt(N), just as
you gain lower <delta V> by parallelling JFETs.
Cheers
Phil Hobbs
On Tue, 26 Jul 2022 11:03:15 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
jlarkin@highlandsniptechnology.com wrote:
On Tue, 26 Jul 2022 08:05:49 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
Gerhard Hoffmann wrote:
Am 25.07.22 um 18:31 schrieb Joe Gwinn:
On Fri, 22 Jul 2022 09:03:16 -0400, Phil Hobbs
"A geometric view of closure phases in interferometry", DOI:
<https://doi.org/10.1017/pasa.2022.6>
.<https://www.cambridge.org/core/journals/publications-of-the-astronomical-society-of-australia/article/geometric-view-of-closure-phases-in-interferometry/5E8A5A8D58A2FC72ADFA0587347C4DA7>
I'm still digesting it, but basically deducing the underlying geometry >>>>>> allowed for some significant improvements.
I have not yet digested it, but can I assume that it won't help
me to create a carrier that is phase noise wise better than
averaged over 16 oscillators created equally bad?
More suitable for post-processing after-the-fact?
U. Rohde has the math for n injection locked oscillators in one
of his books, but the formulas probably fall apart when you have
to insert hard numbers for real oscillators you can buy, or build.
Methinks he is more into multiple coupled resonators.
cheers,
Gerhard
I'm not sure--as I say, I haven't got a properly-thought-out scheme, but >>>> it seems as though it ought to be possible to combine the measurements >>>> to produce N-1 oscillator signals, each one N times quieter, so that
averaging _those_ would get you to the N(N-1)/2 level.
It probably needs a whole lot of phase shifters or weighted summers
(like a Wilkinson with attenuators), so it may well not be a win from a >>>> total-hardware POV. Seems like it would be worth a bit of thought, though.
Cheers
Phil Hobbs
Imagine a single circuit/pcb that has N crystal oscillator circuits,
injection locked and summed, in an oven.
XOs near one another, namely in the same room, like to injection lock.
Sure. That only gets you 10*log(N), though, AFAICT. Looking at it from
a phase noise POV, you win improved <delta phi> like sqrt(N), just as
you gain lower <delta V> by parallelling JFETs.
Cheers
Phil Hobbs
I'm beyond my pay grade here, but summing jfets can be done with an
ideal isolated n-port summer and the s/n improvement indeed goes as
sqrt(n). But injection locking 10 oscillators is different. Each one
pulls towards the mean of the other nine. They herd one another.
jlarkin@highlandsniptechnology.com wrote:
On Tue, 26 Jul 2022 11:03:15 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
jlarkin@highlandsniptechnology.com wrote:
On Tue, 26 Jul 2022 08:05:49 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
Gerhard Hoffmann wrote:
Am 25.07.22 um 18:31 schrieb Joe Gwinn:
On Fri, 22 Jul 2022 09:03:16 -0400, Phil Hobbs
"A geometric view of closure phases in interferometry", DOI:
<https://doi.org/10.1017/pasa.2022.6>
.<https://www.cambridge.org/core/journals/publications-of-the-astronomical-society-of-australia/article/geometric-view-of-closure-phases-in-interferometry/5E8A5A8D58A2FC72ADFA0587347C4DA7>
I'm still digesting it, but basically deducing the underlying geometry >>>>>>> allowed for some significant improvements.
I have not yet digested it, but can I assume that it won't help
me to create a carrier that is phase noise wise better than
averaged over 16 oscillators created equally bad?
More suitable for post-processing after-the-fact?
U. Rohde has the math for n injection locked oscillators in one
of his books, but the formulas probably fall apart when you have
to insert hard numbers for real oscillators you can buy, or build. >>>>>> Methinks he is more into multiple coupled resonators.
cheers,
Gerhard
I'm not sure--as I say, I haven't got a properly-thought-out scheme, but >>>>> it seems as though it ought to be possible to combine the measurements >>>>> to produce N-1 oscillator signals, each one N times quieter, so that >>>>> averaging _those_ would get you to the N(N-1)/2 level.
It probably needs a whole lot of phase shifters or weighted summers
(like a Wilkinson with attenuators), so it may well not be a win from a >>>>> total-hardware POV. Seems like it would be worth a bit of thought, though.
Cheers
Phil Hobbs
Imagine a single circuit/pcb that has N crystal oscillator circuits,
injection locked and summed, in an oven.
XOs near one another, namely in the same room, like to injection lock.
Sure. That only gets you 10*log(N), though, AFAICT. Looking at it from >>> a phase noise POV, you win improved <delta phi> like sqrt(N), just as
you gain lower <delta V> by parallelling JFETs.
Cheers
Phil Hobbs
I'm beyond my pay grade here, but summing jfets can be done with an
ideal isolated n-port summer and the s/n improvement indeed goes as
sqrt(n). But injection locking 10 oscillators is different. Each one
pulls towards the mean of the other nine. They herd one another.
Yup. Inside the locking bandwidth, it's probably possible to make the
phases chaotic at some level, so the close-in noise might even be worse.
Outside that, though, as long as the peak phase error is smallish, both >amplitude and phase noise look additive, so the usual theorems apply.
For small epsilon,
sin(t + epsilon) = sin t cos epsilon + cos t sin epsilon
~= sin t + epsilon*cos t, (1)
so
(sin(t) + sin(t + epsilon))/2 ~=
sin t + (epsilon / 2) cos t. (2)
Using (1) backwards,
(sin(t) + sin(t + epsilon))/2 ~= sin(t + epsilon / 2).
With N different epsilons, you have a random phasor sum, which winds up
with an average phase error going like 1/sqrt(N).
Cheers
Phil Hobbs
I expect they are a lot better at it by now. In my day it involved
moving around furniture van loads of tweaked VHS video tape cassettes
from the big dishes to the correlator centres.
As the wise man said, "Never underestimate the bandwidth of a truck full
of tapes."
Am 27.07.22 um 10:36 schrieb Martin Brown:
On 26/07/2022 13:05, Phil Hobbs wrote:
Gerhard Hoffmann wrote:
Am 25.07.22 um 18:31 schrieb Joe Gwinn:
On Fri, 22 Jul 2022 09:03:16 -0400, Phil Hobbs
Entrainment of weakly coupled oscillators at frequencies near to each
other can be quite strong (a problem if you don't want that to happen).
But I want to lock them to the same frequency and phase anyway
with dedicated slooow PLLs. Injection locking would just
take away some control over the corner frequencies of the PLLs.
As long as the corners a low enough that is not a desaster.
Say below 0.5 Hz.
He announced the "Free Univerity Compiler Kit", from the
Free Univerity Amsterdam. :-)
Gerhard
Of course the summing follows the usual linear equations AFTER the oscillators are locked. But the things being summed are changed by the
phase locking, not independent sources any more.
If one oscillator is the big outlier, it gets all nine others pounding
on it to get in sync. Injection locking is fundamentally nonlinear.
Am 27.07.22 um 16:13 schrieb Phil Hobbs:
I expect they are a lot better at it by now. In my day it involved
moving around furniture van loads of tweaked VHS video tape cassettes
from the big dishes to the correlator centres.
As the wise man said, "Never underestimate the bandwidth of a truck
full of tapes."
That was Andy Tanenbaum, either in his book "Structured Computer Organisation" or in a guest lecture i saw at TU Berlin.
I was seldom more impressed by a prof.
He announced the "Free Univerity Compiler Kit", from the
Free Univerity Amsterdam. :-)
jlarkin@highlandsniptechnology.com wrote:
Les Cargill wrote:
jlarkin@highlandsniptechnology.com wrote:
Phil Hobbs wrote:<snip>
Phil Hobbs
Mathematicians often like music. In my experience, music fandom is
negatively correlated to engineering design skill. Different brain
structure or something.
Engineering is composition. Composition is the thin edge of the musical
wedge. Musicianship is different; it's pattern identification. As is
composition but in a different way. But it is all the same thing.
It all depends on which wall you prefer to have your back against.
I've always wondered about musicians. They have to play a piece
hundreds of times to get it right.
Some do; some don't. Session players from back when studio time
was the dominant cost probably played the parts on a song you later
heard on the radio on the first take.
Some have surely performed
something thousands of times. Don't they get bored? Apparently not.
There's too broad a spectrum to generalize. Some forms are better for
people with mild forms of OCD.
I design something, finish, and then want to design something entirely
different.
It depends on boredom thresholds.
Much does.
On Wed, 27 Jul 2022 10:29:44 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
jlarkin@highlandsniptechnology.com wrote:
On Tue, 26 Jul 2022 11:03:15 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
jlarkin@highlandsniptechnology.com wrote:
On Tue, 26 Jul 2022 08:05:49 -0400, Phil HobbsSure. That only gets you 10*log(N), though, AFAICT. Looking at it from >>>> a phase noise POV, you win improved <delta phi> like sqrt(N), just as
<pcdhSpamMeSenseless@electrooptical.net> wrote:
Gerhard Hoffmann wrote:
Am 25.07.22 um 18:31 schrieb Joe Gwinn:
On Fri, 22 Jul 2022 09:03:16 -0400, Phil Hobbs
"A geometric view of closure phases in interferometry", DOI:
<https://doi.org/10.1017/pasa.2022.6>
.<https://www.cambridge.org/core/journals/publications-of-the-astronomical-society-of-australia/article/geometric-view-of-closure-phases-in-interferometry/5E8A5A8D58A2FC72ADFA0587347C4DA7>
I'm still digesting it, but basically deducing the underlying geometry >>>>>>>> allowed for some significant improvements.
I have not yet digested it, but can I assume that it won't help
me to create a carrier that is phase noise wise better than
averaged over 16 oscillators created equally bad?
More suitable for post-processing after-the-fact?
U. Rohde has the math for n injection locked oscillators in one
of his books, but the formulas probably fall apart when you have >>>>>>> to insert hard numbers for real oscillators you can buy, or build. >>>>>>> Methinks he is more into multiple coupled resonators.
cheers,
Gerhard
I'm not sure--as I say, I haven't got a properly-thought-out scheme, but >>>>>> it seems as though it ought to be possible to combine the measurements >>>>>> to produce N-1 oscillator signals, each one N times quieter, so that >>>>>> averaging _those_ would get you to the N(N-1)/2 level.
It probably needs a whole lot of phase shifters or weighted summers >>>>>> (like a Wilkinson with attenuators), so it may well not be a win from a >>>>>> total-hardware POV. Seems like it would be worth a bit of thought, though.
Cheers
Phil Hobbs
Imagine a single circuit/pcb that has N crystal oscillator circuits, >>>>> injection locked and summed, in an oven.
XOs near one another, namely in the same room, like to injection lock. >>>>
you gain lower <delta V> by parallelling JFETs.
Cheers
Phil Hobbs
I'm beyond my pay grade here, but summing jfets can be done with an
ideal isolated n-port summer and the s/n improvement indeed goes as
sqrt(n). But injection locking 10 oscillators is different. Each one
pulls towards the mean of the other nine. They herd one another.
Yup. Inside the locking bandwidth, it's probably possible to make the
phases chaotic at some level, so the close-in noise might even be worse.
Outside that, though, as long as the peak phase error is smallish, both
amplitude and phase noise look additive, so the usual theorems apply.
For small epsilon,
sin(t + epsilon) = sin t cos epsilon + cos t sin epsilon
~= sin t + epsilon*cos t, (1)
so
(sin(t) + sin(t + epsilon))/2 ~=
sin t + (epsilon / 2) cos t. (2)
Using (1) backwards,
(sin(t) + sin(t + epsilon))/2 ~= sin(t + epsilon / 2).
With N different epsilons, you have a random phasor sum, which winds up
with an average phase error going like 1/sqrt(N).
Of course the summing follows the usual linear equations AFTER the oscillators are locked. But the things being summed are changed by the
phase locking, not independent sources any more.
If one oscillator is the big outlier, it gets all nine others pounding
on it to get in sync. Injection locking is fundamentally nonlinear.
Martin Brown wrote:
On 26/07/2022 13:05, Phil Hobbs wrote:
Gerhard Hoffmann wrote:
Am 25.07.22 um 18:31 schrieb Joe Gwinn:
On Fri, 22 Jul 2022 09:03:16 -0400, Phil Hobbs
"A geometric view of closure phases in interferometry", DOI:
<https://doi.org/10.1017/pasa.2022.6>
.<https://www.cambridge.org/core/journals/publications-of-the-astronomical-society-of-australia/article/geometric-view-of-closure-phases-in-interferometry/5E8A5A8D58A2FC72ADFA0587347C4DA7>
I'm still digesting it, but basically deducing the underlying geometry >>>>> allowed for some significant improvements.
I have not yet digested it, but can I assume that it won't help
me to create a carrier that is phase noise wise better than
averaged over 16 oscillators created equally bad?
More suitable for post-processing after-the-fact?
U. Rohde has the math for n injection locked oscillators in one
of his books, but the formulas probably fall apart when you have
to insert hard numbers for real oscillators you can buy, or build.
Methinks he is more into multiple coupled resonators.
Entrainment of weakly coupled oscillators at frequencies near to each
other can be quite strong (a problem if you don't want that to happen).
I'm not sure--as I say, I haven't got a properly-thought-out scheme,
but it seems as though it ought to be possible to combine the
measurements to produce N-1 oscillator signals, each one N times
quieter, so that averaging _those_ would get you to the N(N-1)/2 level.
I think the catch is that to do that you would have to provide hardware
to compute the cross correlation of every pair of oscillators so that
correlator complexity goes up as N(N-1)/2 too. I can't immediately see a
way to exploit this to get a better average oscillator though.
It probably needs a whole lot of phase shifters or weighted summers
(like a Wilkinson with attenuators), so it may well not be a win from
a total-hardware POV. Seems like it would be worth a bit of thought,
though.
VLBI typically disciplines a hydrogen maser using some other long term
stable centralised terrestrial time source. Getting it just a little bit
wrong just makes the white light fringe much harder to find later. Local
clock short term stability stability is the key to it working well.
I expect they are a lot better at it by now. In my day it involved
moving around furniture van loads of tweaked VHS video tape cassettes
from the big dishes to the correlator centres.
As the wise man said, "Never underestimate the bandwidth of a truck full
of tapes."
Also, variously, a 747 full of tapes, CDs, DVDs, MicroSDs, etc. A
747-load of 256-GB MicroSDs is about
256e12 B * 113,400 kg / 0.25 g = 1.16E+23 bytes.
Six of them would be over 1 Avogadro.
Of course reading them out in less than the lifetime of the universe
would take quite a few boxes--it would need a bandwidth of
1.16E+23 / 3.156e+7 / 15e+9 = 245 kB/s just to do that.
Cheers
Phil Hobbs
Joe Gwinn wrote:
On Fri, 22 Jul 2022 21:38:39 -0000 (UTC), "Don" <g@crcomp.net> wrote:
Joe Gwinn wrote:
<snip>
Also, I'd lose the BNC connectors. Threaded connectors like SMA, TNC, >>>> and Type N are far better.
Or use shielded twisted pair to carry the 1PPS pulses. This would
work better over a backplane.
This is good advice. Even though the lazy guy within me never truly
gives up his fight to take the easy way out with BNC.
Twisted pair (TP) sounds even easier than BNC. So, what's the
"catch" with TP? Where's the "gotcha" to make TP harder than BNC?
Depends on what you are trying to do.
For nanosecond edges, coax is pretty useful, but short range and often
mechanically awkward.
For microsecond edges at 1000 meters, RS422 over shielded twisted pair
is pretty good.
For bus length links, LVDS or the like.
And so on. And there is always optical links.
Joe Gwinn
BNCs are the bomb, as long as you aren't putting 500 of them in series,
as with the old 10base2 coax Ethernet.
TNCs are a very small niche, and N connectors belong only on spectrum >analyzers.
On Fri, 22 Jul 2022 21:12:31 -0400, Phil Hobbs <pcdhSpamM...@electrooptical.net> wrote:
Joe Gwinn wrote:
On Fri, 22 Jul 2022 21:38:39 -0000 (UTC), "Don" <g...@crcomp.net> wrote: >>
Joe Gwinn wrote:
<snip>
Also, I'd lose the BNC connectors. Threaded connectors like SMA, TNC, >>>> and Type N are far better.
Or use shielded twisted pair to carry the 1PPS pulses. This would
work better over a backplane.
This is good advice. Even though the lazy guy within me never truly
gives up his fight to take the easy way out with BNC.
Twisted pair (TP) sounds even easier than BNC. So, what's the
"catch" with TP? Where's the "gotcha" to make TP harder than BNC?
Depends on what you are trying to do.
For nanosecond edges, coax is pretty useful, but short range and often
mechanically awkward.
For microsecond edges at 1000 meters, RS422 over shielded twisted pair
is pretty good.
For bus length links, LVDS or the like.
And so on. And there is always optical links.
Joe Gwinn
BNCs are the bomb, as long as you aren't putting 500 of them in series,
as with the old 10base2 coax Ethernet.
TNCs are a very small niche, and N connectors belong only on spectrum >analyzers.
The issue with BNCs in phase-critical radar timing systems is that the
delay through a BNC can jump by a few picoseconds from mechanical
rattling. If the signal traversing the BNC is subsequently multiplied
up into the GHz, the angular phase shifts can become intolerable.
Especially in a high-vibration environment.
BNCs are also somewhat leaky, even in the precision grades.
So, BNCs are usually forbidden except for test outputs. Only threaded
coax connectors, or mechanically stable blind-mate, or the like are
allowed.
On Fri, 22 Jul 2022 21:12:31 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
Joe Gwinn wrote:
On Fri, 22 Jul 2022 21:38:39 -0000 (UTC), "Don" <g@crcomp.net> wrote:
Joe Gwinn wrote:
<snip>
Also, I'd lose the BNC connectors. Threaded connectors like SMA, TNC, >>>>> and Type N are far better.
Or use shielded twisted pair to carry the 1PPS pulses. This would
work better over a backplane.
This is good advice. Even though the lazy guy within me never truly
gives up his fight to take the easy way out with BNC.
Twisted pair (TP) sounds even easier than BNC. So, what's the
"catch" with TP? Where's the "gotcha" to make TP harder than BNC?
Depends on what you are trying to do.
For nanosecond edges, coax is pretty useful, but short range and often
mechanically awkward.
For microsecond edges at 1000 meters, RS422 over shielded twisted pair
is pretty good.
For bus length links, LVDS or the like.
And so on. And there is always optical links.
Joe Gwinn
BNCs are the bomb, as long as you aren't putting 500 of them in series,
as with the old 10base2 coax Ethernet.
TNCs are a very small niche, and N connectors belong only on spectrum
analyzers.
The issue with BNCs in phase-critical radar timing systems is that the
delay through a BNC can jump by a few picoseconds from mechanical
rattling. If the signal traversing the BNC is subsequently multiplied
up into the GHz, the angular phase shifts can become intolerable.
Especially in a high-vibration environment.
BNCs are also somewhat leaky, even in the precision grades.
So, BNCs are usually forbidden except for test outputs. Only threaded
coax connectors, or mechanically stable blind-mate, or the like are
allowed.
Joe Gwinn
On Wednesday, 27 July 2022 at 21:37:14 UTC+1, Joe Gwinn wrote:
On Fri, 22 Jul 2022 21:12:31 -0400, Phil HobbsN connectors have their problems too. I discovered that if they are hand-tightened
<pcdhSpamM...@electrooptical.net> wrote:
Joe Gwinn wrote:
On Fri, 22 Jul 2022 21:38:39 -0000 (UTC), "Don" <g...@crcomp.net> wrote: >> >>
Joe Gwinn wrote:
<snip>
Also, I'd lose the BNC connectors. Threaded connectors like SMA, TNC, >> >>>> and Type N are far better.
Or use shielded twisted pair to carry the 1PPS pulses. This would
work better over a backplane.
This is good advice. Even though the lazy guy within me never truly
gives up his fight to take the easy way out with BNC.
Twisted pair (TP) sounds even easier than BNC. So, what's the
"catch" with TP? Where's the "gotcha" to make TP harder than BNC?
Depends on what you are trying to do.
For nanosecond edges, coax is pretty useful, but short range and often
mechanically awkward.
For microsecond edges at 1000 meters, RS422 over shielded twisted pair
is pretty good.
For bus length links, LVDS or the like.
And so on. And there is always optical links.
Joe Gwinn
BNCs are the bomb, as long as you aren't putting 500 of them in series,
as with the old 10base2 coax Ethernet.
TNCs are a very small niche, and N connectors belong only on spectrum
analyzers.
The issue with BNCs in phase-critical radar timing systems is that the
delay through a BNC can jump by a few picoseconds from mechanical
rattling. If the signal traversing the BNC is subsequently multiplied
up into the GHz, the angular phase shifts can become intolerable.
Especially in a high-vibration environment.
BNCs are also somewhat leaky, even in the precision grades.
So, BNCs are usually forbidden except for test outputs. Only threaded
coax connectors, or mechanically stable blind-mate, or the like are
allowed.
fairly gently they can introduce losses of 1 or 2 dB at about 1.2 or 1.3GHz.
Joe Gwinn wrote:
On Fri, 22 Jul 2022 21:12:31 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
Joe Gwinn wrote:
On Fri, 22 Jul 2022 21:38:39 -0000 (UTC), "Don" <g@crcomp.net> wrote:
Joe Gwinn wrote:
<snip>
Also, I'd lose the BNC connectors. Threaded connectors like SMA, TNC, >>>>>> and Type N are far better.
Or use shielded twisted pair to carry the 1PPS pulses. This would >>>>>> work better over a backplane.
This is good advice. Even though the lazy guy within me never truly
gives up his fight to take the easy way out with BNC.
Twisted pair (TP) sounds even easier than BNC. So, what's the
"catch" with TP? Where's the "gotcha" to make TP harder than BNC?
Depends on what you are trying to do.
For nanosecond edges, coax is pretty useful, but short range and often >>>> mechanically awkward.
For microsecond edges at 1000 meters, RS422 over shielded twisted pair >>>> is pretty good.
For bus length links, LVDS or the like.
And so on. And there is always optical links.
Joe Gwinn
BNCs are the bomb, as long as you aren't putting 500 of them in series,
as with the old 10base2 coax Ethernet.
TNCs are a very small niche, and N connectors belong only on spectrum
analyzers.
The issue with BNCs in phase-critical radar timing systems is that the
delay through a BNC can jump by a few picoseconds from mechanical
rattling. If the signal traversing the BNC is subsequently multiplied
up into the GHz, the angular phase shifts can become intolerable.
Especially in a high-vibration environment.
BNCs are also somewhat leaky, even in the precision grades.
So, BNCs are usually forbidden except for test outputs. Only threaded
coax connectors, or mechanically stable blind-mate, or the like are
allowed.
Joe Gwinn
For synthetic-aperture radars, I believe that--small phase transients
are bad news. I had a similar experience long ago.
When I was a grad student, back around 1985-6, I built a heterodyne >interferometric scanning laser microscope.
It had a 13-bit phase digitizer, which used a nulling technique to
measure phase directly. There was an AM2504 successive-approximation >register, driving an AD DAC80 12-bit DAC, driving a homemade linearized >varactor phase shifter, with a MCL RPD-1 phase detector looking for a
null. (All dead-bug construction.)
One extra SAR cycle (with an external d-flop) made sure it was shooting
for the stable null, making 13 bits in all. It ran at the 60-MHz IF,
and pi phase was about 6000 LSBs, so 1 LSB was equivalent to
dt = 1/(6000 * 60 MHz) = 2.8 ps.
It had an associated calibrator, based on two 60-MHz crystal oscillators >locked together with a divide-by-360 counter on each. The counters had >(iirc) 11C90 10/11 prescalers, and one of them had the appropriate logic
for a pulse-swallower. That way the two outputs could be phase shifted
in exact 1-degree increments. A whole lot of attention was paid to
shielding and isolation amps and so forth, because any leakage of one
signal into the other above the -80 dB level would cause measurable
phase whoopdedoos.
Fortunately that was easy to verify by sitting on the pulse-swallowing >button, which moved the frequency enough to see any spurs on the
spectrum analyzer. (I borrowed an 8566A from another group for the
purpose.)
Calibrating the phase shifter with 1-degree steps made it easy to run a
cubic spline through the data to 1-LSB accuracy. Linearizing the phase >shifter meant that the conversion of 1 LSB to delta phase didn't vary
much across the range--it was always around 3 ps.
Jiggling coax cables during a measurement made for some very
entertaining image artifacts there too.
On Tue, 26 Jul 2022 19:56:53 -0500, Les Cargill <lcargil99@gmail.com>
wrote:
jlarkin@highlandsniptechnology.com wrote:
On Fri, 22 Jul 2022 21:10:35 -0500, Les Cargill <lcargil99@gmail.com>
wrote:
jlarkin@highlandsniptechnology.com wrote:
On Thu, 21 Jul 2022 11:42:28 -0400, Phil Hobbs<snip>
<pcdhSpamMeSenseless@electrooptical.net> wrote:
Phil Hobbs
Mathematicians often like music. In my experience, music fandom is
negatively correlated to engineering design skill. Different brain
structure or something.
Engineering is composition. Composition is the thin edge of the musical >>>> wedge. Musicianship is different; it's pattern identification. As is
composition but in a different way. But it is all the same thing.
It all depends on which wall you prefer to have your back against.
I've always wondered about musicians. They have to play a piece
hundreds of times to get it right.
Some do; some don't. Session players from back when studio time
was the dominant cost probably played the parts on a song you later
heard on the radio on the first take.
Some have surely performed
something thousands of times. Don't they get bored? Apparently not.
There's too broad a spectrum to generalize. Some forms are better for
people with mild forms of OCD.
I design something, finish, and then want to design something entirely
different.
It depends on boredom thresholds.
Much does.
One other thing I see a lot is undue respect for standards. As in "you >>>>> can't do that because it violates SCPI standards." Where are the SCPI >>>>> Police when you need them?
Over where they MATLAB.
SCPI is send-and-forget. There is some query you can send to ask if
the last command worked. And you can have an error queue that you can
interrogate now and then for historical forensics.
I told the customer that damn the specs, every command is going to
reply with data, an error message, or "OK". They agree.
And there you go turning a perfectly good full duplex channel into a
half duplex walkie-talkie channel :)
It'll be fast enough.
One might feel a little silly, having sent 14,000 commands to a box
and then discovering that the power strip is off.
Les Cargill wrote:
jlarkin@highlandsniptechnology.com wrote:
Les Cargill wrote:
jlarkin@highlandsniptechnology.com wrote:
Phil Hobbs wrote:<snip>
Phil Hobbs
Mathematicians often like music. In my experience, music fandom is
negatively correlated to engineering design skill. Different brain
structure or something.
Engineering is composition. Composition is the thin edge of the musical >>>> wedge. Musicianship is different; it's pattern identification. As is
composition but in a different way. But it is all the same thing.
It all depends on which wall you prefer to have your back against.
I've always wondered about musicians. They have to play a piece
hundreds of times to get it right.
Some do; some don't. Session players from back when studio time
was the dominant cost probably played the parts on a song you later
heard on the radio on the first take.
Some have surely performed
something thousands of times. Don't they get bored? Apparently not.
There's too broad a spectrum to generalize. Some forms are better for
people with mild forms of OCD.
I design something, finish, and then want to design something entirely
different.
It depends on boredom thresholds.
Much does.
<snip>
My much older, late partner used to play saxophone in High School in the 1950s. He belonged to an Illinois union and said you had to sight read
sheet music to join the union.
It was the big band era. To keep costs down, the band's core, of say
six musicians, would tour and then hire local union musicians for a one
night stand in order to fill out the big band.
There's a Muscle Shoals studio interview somewhere out on the Inet. In
it one of the sessions players talks about how he played by ear - at
first. Until someone told him he needed to wise-up and learn how to
sight read in order to earn the easiest money.
My church's two volume songbook contains 634 songs. And a different mix
is played each weekend. It's best to simply sight read the songs, as
needed.
Humble symphony orchestras work it about the same. Part-time musicians
pick up their sheet music a day or two before a concert. There's simply
not enough available time to "play a piece hundreds of times to get it right."
Danke,
Martin Brown wrote:
I expect they are a lot better at it by now. In my day it involved
moving around furniture van loads of tweaked VHS video tape cassettes
from the big dishes to the correlator centres.
As the wise man said, "Never underestimate the bandwidth of a truck full
of tapes."
Also, variously, a 747 full of tapes, CDs, DVDs, MicroSDs, etc. A
747-load of 256-GB MicroSDs is about
256e12 B * 113,400 kg / 0.25 g = 1.16E+23 bytes.
Six of them would be over 1 Avogadro.
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