• Mains hum

    From Cursitor Doom@21:1/5 to All on Tue Apr 5 19:05:23 2022
    Greetings, gentlemen,

    I've got one of those ECG boards off Ebay and am having a problem with
    mains hum appearing on the output. I can't understand where it's
    coming from (airborne in some form I guess) and therefore how to get
    rid of it. Initially I assumed the hum would disappear when the board
    was mounted in a screened metal box, but it hasn't made much
    improvement and the noise is very evident on the scope trace (see
    pictures). This *is* mains interference as it works out at exactly
    mains frequency. It's even there if I attach the DC input leads to a
    9V battery instead so it's not coming from the PSU. The links below
    show the noisy trace and the set-up as I've currently implemented it.
    I'm dealing here with high impedance, low level signals approximating
    to a dynamic mic in character I would imagine, so it's a PITA. Any
    suggestions?


    https://disk.yandex.com/i/u7pJajKXHlzv8A


    https://disk.yandex.com/i/W_rLu6HinY26VQ

    --- SoupGate-Win32 v1.05
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  • From whit3rd@21:1/5 to Cursitor Doom on Tue Apr 5 11:51:10 2022
    On Tuesday, April 5, 2022 at 11:05:32 AM UTC-7, Cursitor Doom wrote:
    Greetings, gentlemen,

    I've got one of those ECG boards off Ebay and am having a problem with
    mains hum appearing on the output.
    ...This *is* mains interference as it works out at exactly
    mains frequency. It's even there if I attach the DC input leads to a
    9V battery instead so it's not coming from the PSU.


    If it's not twice mains frequency, it's probably not acoustic. The item has a metal
    box, so light sensitivity is likewise ruled out. That leaves magnetic coupling, i.e.
    ground loops. Less likely, could be capacitive.

    Pairing the input wires, twisting the pairs, would be one approach. Keeping the
    area between the wires small, and orienting it differently, will change the coupling.
    Also, find a room with no large current-draw appliances, and no knob-and-tube wide separation of AC hot and neutral wires. In the old physics building, sensitive experiments were done with lights-off in the library, after hours.
    If there are transformers or motors nearby, unplug 'em (a 12V high intensity light transformer is a BIG magnetic AC source).

    Old-school treatment: put a twin-tee filter in the signal path to trap that pesky power frequency.
    New-school treatment: FFT the signal, and zero out the power frequency: maybe look at the
    harmonics, too, for other artifacts.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From ehsjr@21:1/5 to Cursitor Doom on Tue Apr 5 15:03:40 2022
    On 4/5/2022 2:05 PM, Cursitor Doom wrote:
    Greetings, gentlemen,

    I've got one of those ECG boards off Ebay and am having a problem with
    mains hum appearing on the output. I can't understand where it's
    coming from (airborne in some form I guess) and therefore how to get
    rid of it. Initially I assumed the hum would disappear when the board
    was mounted in a screened metal box, but it hasn't made much
    improvement and the noise is very evident on the scope trace (see
    pictures). This *is* mains interference as it works out at exactly
    mains frequency. It's even there if I attach the DC input leads to a
    9V battery instead so it's not coming from the PSU. The links below
    show the noisy trace and the set-up as I've currently implemented it.
    I'm dealing here with high impedance, low level signals approximating
    to a dynamic mic in character I would imagine, so it's a PITA. Any suggestions?


    https://disk.yandex.com/i/u7pJajKXHlzv8A


    https://disk.yandex.com/i/W_rLu6HinY26VQ

    What happens when the leads are properly terminated?
    In use, they are attached to sensor pads that are
    stuck near the collar bone (1) and on the left and right
    side of the belly

    Ed

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From John Larkin@21:1/5 to All on Tue Apr 5 12:07:56 2022
    On Tue, 05 Apr 2022 19:05:23 +0100, Cursitor Doom <cd@notformail.com>
    wrote:

    Greetings, gentlemen,

    I've got one of those ECG boards off Ebay and am having a problem with
    mains hum appearing on the output. I can't understand where it's
    coming from (airborne in some form I guess) and therefore how to get
    rid of it. Initially I assumed the hum would disappear when the board
    was mounted in a screened metal box, but it hasn't made much
    improvement and the noise is very evident on the scope trace (see
    pictures). This *is* mains interference as it works out at exactly
    mains frequency. It's even there if I attach the DC input leads to a
    9V battery instead so it's not coming from the PSU. The links below
    show the noisy trace and the set-up as I've currently implemented it.
    I'm dealing here with high impedance, low level signals approximating
    to a dynamic mic in character I would imagine, so it's a PITA. Any >suggestions?


    https://disk.yandex.com/i/u7pJajKXHlzv8A


    https://disk.yandex.com/i/W_rLu6HinY26VQ

    Yandex. Russian. Makes sense.

    --

    If a man will begin with certainties, he shall end with doubts,
    but if he will be content to begin with doubts he shall end in certainties. Francis Bacon

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Ricky@21:1/5 to Cursitor Doom on Tue Apr 5 12:15:19 2022
    On Tuesday, April 5, 2022 at 2:05:32 PM UTC-4, Cursitor Doom wrote:
    Greetings, gentlemen,

    I've got one of those ECG boards off Ebay and am having a problem with
    mains hum appearing on the output. I can't understand where it's
    coming from (airborne in some form I guess) and therefore how to get
    rid of it. Initially I assumed the hum would disappear when the board
    was mounted in a screened metal box, but it hasn't made much
    improvement and the noise is very evident on the scope trace (see
    pictures). This *is* mains interference as it works out at exactly
    mains frequency. It's even there if I attach the DC input leads to a
    9V battery instead so it's not coming from the PSU. The links below
    show the noisy trace and the set-up as I've currently implemented it.
    I'm dealing here with high impedance, low level signals approximating
    to a dynamic mic in character I would imagine, so it's a PITA. Any suggestions?


    https://disk.yandex.com/i/u7pJajKXHlzv8A


    https://disk.yandex.com/i/W_rLu6HinY26VQ

    I see the signal, it is clearly not sinusoidal. So you will need to do more than just trap the fundamental, but also deal with harmonics. Since the fundamental frequency drifts, it won't be possible to use an extremely high Q filter. what frequency
    range are you interested in? Is it possible to perform post capture processing to remove the background noise?

    It looks like your leads are made to attach to the patches placed on a person. I would have thought to use coax wire, but maybe there's no point since the person it's attached to is not able to be shielded. Are your probes connected to a subject when
    you see this signal? Have you tried attaching them to a subject? It may be that the high impedance input is seeing a high noise signal which would essentially be grounded through the patient if the leads were connected... just a thought. Also look at
    the signal without the input leads at all.

    BTW, why do you obscure the readout data in the scope capture? I count 4.3 divisions per cycle of the waveform. I can't think of a multiplier that would make that a power line frequency anyplace I know of.

    --

    Rick C.

    - Get 1,000 miles of free Supercharging
    - Tesla referral code - https://ts.la/richard11209

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  • From Phil Allison@21:1/5 to All on Tue Apr 5 14:48:34 2022
    Ricky the IDIOT puked:

    =====================

    I see the signal, it is clearly not sinusoidal.

    ** That is the fucking heart beat you moron !!!
    The 50/60 Hz hum is the superimposed fine wiggling.

    Rest of this retarded wanker's absurd drivel snipped.


    .... Phil

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Allison@21:1/5 to Cursitor Doom on Tue Apr 5 14:45:04 2022
    Cursitor Doom wrote:
    =================


    I've got one of those ECG boards off Ebay and am having a problem with
    mains hum appearing on the output. I can't understand where it's
    coming from (airborne in some form I guess)

    ** 50/60 Hz electric fields are everywhere inside wired buildings.
    That is why you shield things.


    This *is* mains interference as it works out at exactly
    mains frequency. It's even there if I attach the DC input leads to a
    9V battery instead so it's not coming from the PSU.

    ** But you have a DSO connected and that is supply grounded.
    That is your problem creating a lot of common mode hum.

    The links below
    show the noisy trace and the set-up as I've currently implemented it.
    I'm dealing here with high impedance, low level signals approximating
    to a dynamic mic in character I would imagine,

    ** Dynamic mics are low impedance and well shielded.
    ECGs are very special devices.

    ..... Phil

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Ralph Mowery@21:1/5 to All on Tue Apr 5 19:34:33 2022
    In article <cbab2f4d-9771-481b-8577-a2badf6dfa02n@googlegroups.com>, pallison49@gmail.com says...

    Ricky the IDIOT puked:

    =====================

    I see the signal, it is clearly not sinusoidal.

    ** That is the fucking heart beat you moron !!!
    The 50/60 Hz hum is the superimposed fine wiggling.

    Rest of this retarded wanker's absurd drivel snipped.





    Yes, that looks like the typical RST waveform of the heart. The heart
    often beats near 60 Hz.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Cursitor Doom@21:1/5 to gnuarm.deletethisbit@gmail.com on Wed Apr 6 00:39:10 2022
    On Tue, 5 Apr 2022 12:15:19 -0700 (PDT), Ricky
    <gnuarm.deletethisbit@gmail.com> wrote:

    On Tuesday, April 5, 2022 at 2:05:32 PM UTC-4, Cursitor Doom wrote:
    Greetings, gentlemen,

    I've got one of those ECG boards off Ebay and am having a problem with
    mains hum appearing on the output. I can't understand where it's
    coming from (airborne in some form I guess) and therefore how to get
    rid of it. Initially I assumed the hum would disappear when the board
    was mounted in a screened metal box, but it hasn't made much
    improvement and the noise is very evident on the scope trace (see
    pictures). This *is* mains interference as it works out at exactly
    mains frequency. It's even there if I attach the DC input leads to a
    9V battery instead so it's not coming from the PSU. The links below
    show the noisy trace and the set-up as I've currently implemented it.
    I'm dealing here with high impedance, low level signals approximating
    to a dynamic mic in character I would imagine, so it's a PITA. Any
    suggestions?


    https://disk.yandex.com/i/u7pJajKXHlzv8A


    https://disk.yandex.com/i/W_rLu6HinY26VQ

    I see the signal, it is clearly not sinusoidal. So you will need to do more than just trap the fundamental, but also deal with harmonics. Since the fundamental frequency drifts, it won't be possible to use an extremely high Q filter. what frequency
    range are you interested in? Is it possible to perform post capture processing to remove the background noise?

    It looks like your leads are made to attach to the patches placed on a person. I would have thought to use coax wire, but maybe there's no point since the person it's attached to is not able to be shielded. Are your probes connected to a subject when
    you see this signal? Have you tried attaching them to a subject? It may be that the high impedance input is seeing a high noise signal which would essentially be grounded through the patient if the leads were connected... just a thought. Also look at
    the signal without the input leads at all.

    BTW, why do you obscure the readout data in the scope capture? I count 4.3 divisions per cycle of the waveform. I can't think of a multiplier that would make that a power line frequency anyplace I know of.

    Er, yeah, that's why I obscured the time/div., to avoid confusion for
    those in the US. Well, that was the plan, anyway. The period is 20mS
    which equals 50Hz. I'm in Yurp and that's the mains frequency here.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Cursitor Doom@21:1/5 to All on Wed Apr 6 00:42:24 2022
    On Tue, 5 Apr 2022 11:51:10 -0700 (PDT), whit3rd <whit3rd@gmail.com>
    wrote:

    On Tuesday, April 5, 2022 at 11:05:32 AM UTC-7, Cursitor Doom wrote:
    Greetings, gentlemen,

    I've got one of those ECG boards off Ebay and am having a problem with
    mains hum appearing on the output.
    ...This *is* mains interference as it works out at exactly
    mains frequency. It's even there if I attach the DC input leads to a
    9V battery instead so it's not coming from the PSU.


    If it's not twice mains frequency, it's probably not acoustic. The item has a metal
    box, so light sensitivity is likewise ruled out. That leaves magnetic coupling, i.e.
    ground loops. Less likely, could be capacitive.

    I had a similar problem before with another such die-cast box housing
    a very small signal amp. On that occasion I was able to kill the hum
    stone dead by clamping the box to an earthed metal sink. But that
    hasn't worked this time for some reason. :-/


    Pairing the input wires, twisting the pairs, would be one approach. Keeping the
    area between the wires small, and orienting it differently, will change the coupling.
    Also, find a room with no large current-draw appliances, and no knob-and-tube >wide separation of AC hot and neutral wires. In the old physics building, >sensitive experiments were done with lights-off in the library, after hours. >If there are transformers or motors nearby, unplug 'em (a 12V high intensity >light transformer is a BIG magnetic AC source).

    Old-school treatment: put a twin-tee filter in the signal path to trap that pesky power frequency.
    New-school treatment: FFT the signal, and zero out the power frequency: maybe look at the
    harmonics, too, for other artifacts.

    Some good suggestions all in all; cheers.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Allison@21:1/5 to Ralph Mowery on Tue Apr 5 17:08:38 2022
    On Wednesday, April 6, 2022 at 9:34:41 AM UTC+10, Ralph Mowery wrote:
    In article <cbab2f4d-9771-481b...@googlegroups.com>,
    palli...@gmail.com says...

    Ricky the IDIOT puked:

    =====================

    I see the signal, it is clearly not sinusoidal.

    ** That is the fucking heart beat you moron !!!
    The 50/60 Hz hum is the superimposed fine wiggling.

    Rest of this retarded wanker's absurd drivel snipped.



    Yes, that looks like the typical RST waveform of the heart. The heart
    often beats near 60 Hz.

    ** ?????

    More like 60 bpm.


    ...... Phil

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Ricky@21:1/5 to Cursitor Doom on Tue Apr 5 19:41:25 2022
    On Tuesday, April 5, 2022 at 7:39:17 PM UTC-4, Cursitor Doom wrote:
    On Tue, 5 Apr 2022 12:15:19 -0700 (PDT), Ricky
    <gnuarm.del...@gmail.com> wrote:

    On Tuesday, April 5, 2022 at 2:05:32 PM UTC-4, Cursitor Doom wrote:
    Greetings, gentlemen,

    I've got one of those ECG boards off Ebay and am having a problem with
    mains hum appearing on the output. I can't understand where it's
    coming from (airborne in some form I guess) and therefore how to get
    rid of it. Initially I assumed the hum would disappear when the board
    was mounted in a screened metal box, but it hasn't made much
    improvement and the noise is very evident on the scope trace (see
    pictures). This *is* mains interference as it works out at exactly
    mains frequency. It's even there if I attach the DC input leads to a
    9V battery instead so it's not coming from the PSU. The links below
    show the noisy trace and the set-up as I've currently implemented it.
    I'm dealing here with high impedance, low level signals approximating
    to a dynamic mic in character I would imagine, so it's a PITA. Any
    suggestions?


    https://disk.yandex.com/i/u7pJajKXHlzv8A


    https://disk.yandex.com/i/W_rLu6HinY26VQ

    I see the signal, it is clearly not sinusoidal. So you will need to do more than just trap the fundamental, but also deal with harmonics. Since the fundamental frequency drifts, it won't be possible to use an extremely high Q filter. what frequency
    range are you interested in? Is it possible to perform post capture processing to remove the background noise?

    It looks like your leads are made to attach to the patches placed on a person. I would have thought to use coax wire, but maybe there's no point since the person it's attached to is not able to be shielded. Are your probes connected to a subject when
    you see this signal? Have you tried attaching them to a subject? It may be that the high impedance input is seeing a high noise signal which would essentially be grounded through the patient if the leads were connected... just a thought. Also look at the
    signal without the input leads at all.

    BTW, why do you obscure the readout data in the scope capture? I count 4.3 divisions per cycle of the waveform. I can't think of a multiplier that would make that a power line frequency anyplace I know of.
    Er, yeah, that's why I obscured the time/div., to avoid confusion for
    those in the US. Well, that was the plan, anyway. The period is 20mS
    which equals 50Hz. I'm in Yurp and that's the mains frequency here.

    How does hiding info "avoid confusion". I think we all here are aware that the world is not on 60 Hz.

    So this is an actual heart beat with the tiny 50 Hz noise? That doesn't look so bad. I think a notch filter will clean that up very well. That can be implemented easily in the digital domain if you are capturing the signal using an ADC.

    --

    Rick C.

    + Get 1,000 miles of free Supercharging
    + Tesla referral code - https://ts.la/richard11209

    --- SoupGate-Win32 v1.05
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  • From Ricky@21:1/5 to Jan Panteltje on Tue Apr 5 21:27:59 2022
    On Wednesday, April 6, 2022 at 12:20:15 AM UTC-4, Jan Panteltje wrote:
    On a sunny day (Tue, 05 Apr 2022 19:05:23 +0100) it happened Cursitor Doom <c...@notformail.com> wrote in <o70p4h94qqbdftsoe...@4ax.com>:
    Greetings, gentlemen,

    I've got one of those ECG boards off Ebay and am having a problem with >mains hum appearing on the output. I can't understand where it's
    coming from (airborne in some form I guess) and therefore how to get
    rid of it. Initially I assumed the hum would disappear when the board
    was mounted in a screened metal box, but it hasn't made much
    improvement and the noise is very evident on the scope trace (see >pictures). This *is* mains interference as it works out at exactly
    mains frequency. It's even there if I attach the DC input leads to a
    9V battery instead so it's not coming from the PSU. The links below
    show the noisy trace and the set-up as I've currently implemented it.
    I'm dealing here with high impedance, low level signals approximating
    to a dynamic mic in character I would imagine, so it's a PITA. Any >suggestions?
    One way is perhaps to pick up mains with some wire
    and then 180 degrees inverse it with some opamp
    and then subtract that from the output?

    This is sometimes done in ham radio to cancel noise from wallwarts in the house etc
    small antenna indoors to subtract from the real big antenna outside,

    If the pickup is by the wires themselves, the details of the arrangement would modify the details of the pickup, so a static counter signal would not be effective.

    Much better to just narrow band block that frequency. I'm not sure what impact that might have on the signal. I believe an EKG is analyzed by eye, so that the sort of distortion caused by most filtering would not be noticeable. It's easy enough to
    digitize the signal and run a few tests.

    --

    Rick C.

    -- Get 1,000 miles of free Supercharging
    -- Tesla referral code - https://ts.la/richard11209

    --- SoupGate-Win32 v1.05
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  • From Jan Panteltje@21:1/5 to cd@notformail.com on Wed Apr 6 04:19:25 2022
    On a sunny day (Tue, 05 Apr 2022 19:05:23 +0100) it happened Cursitor Doom <cd@notformail.com> wrote in <o70p4h94qqbdftsoe1el8suv1gmklc9np2@4ax.com>:

    Greetings, gentlemen,

    I've got one of those ECG boards off Ebay and am having a problem with
    mains hum appearing on the output. I can't understand where it's
    coming from (airborne in some form I guess) and therefore how to get
    rid of it. Initially I assumed the hum would disappear when the board
    was mounted in a screened metal box, but it hasn't made much
    improvement and the noise is very evident on the scope trace (see
    pictures). This *is* mains interference as it works out at exactly
    mains frequency. It's even there if I attach the DC input leads to a
    9V battery instead so it's not coming from the PSU. The links below
    show the noisy trace and the set-up as I've currently implemented it.
    I'm dealing here with high impedance, low level signals approximating
    to a dynamic mic in character I would imagine, so it's a PITA. Any >suggestions?

    One way is perhaps to pick up mains with some wire
    and then 180 degrees inverse it with some opamp
    and then subtract that from the output?

    This is sometimes done in ham radio to cancel noise from wallwarts in the house etc
    small antenna indoors to subtract from the real big antenna outside,

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Tauno Voipio@21:1/5 to Cursitor Doom on Wed Apr 6 11:58:48 2022
    My guess is that the hum is coming from your patient / target.

    The capacitance of an average person is about 20 pF to the
    active phase line and 200 pF to ground. You can assume that
    the patient has about 10% of the line voltage through a pretty
    high impedance voltage divider.

    When we made ECG equipment in the early 1970's, the solution
    was to make the input of the amplifier differential and as
    high impedance as possible, including guard bootstrapping the
    shield braids of the input cables. The impedance of the
    connection electrodes are hardly ever identical, and this creates
    voltage dividers with the amplifier input impedances. The
    imbalance works directly to convert the common-mode hum into
    differential input.

    --

    -TV


    On 5.4.22 21.05, Cursitor Doom wrote:
    Greetings, gentlemen,

    I've got one of those ECG boards off Ebay and am having a problem with
    mains hum appearing on the output. I can't understand where it's
    coming from (airborne in some form I guess) and therefore how to get
    rid of it. Initially I assumed the hum would disappear when the board
    was mounted in a screened metal box, but it hasn't made much
    improvement and the noise is very evident on the scope trace (see
    pictures). This *is* mains interference as it works out at exactly
    mains frequency. It's even there if I attach the DC input leads to a
    9V battery instead so it's not coming from the PSU. The links below
    show the noisy trace and the set-up as I've currently implemented it.
    I'm dealing here with high impedance, low level signals approximating
    to a dynamic mic in character I would imagine, so it's a PITA. Any suggestions?


    https://disk.yandex.com/i/u7pJajKXHlzv8A


    https://disk.yandex.com/i/W_rLu6HinY26VQ

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Martin Brown@21:1/5 to Cursitor Doom on Wed Apr 6 09:45:40 2022
    On 06/04/2022 00:39, Cursitor Doom wrote:
    On Tue, 5 Apr 2022 12:15:19 -0700 (PDT), Ricky <gnuarm.deletethisbit@gmail.com> wrote:

    On Tuesday, April 5, 2022 at 2:05:32 PM UTC-4, Cursitor Doom wrote:
    Greetings, gentlemen,

    I've got one of those ECG boards off Ebay and am having a problem with
    mains hum appearing on the output. I can't understand where it's
    coming from (airborne in some form I guess) and therefore how to get
    rid of it. Initially I assumed the hum would disappear when the board
    was mounted in a screened metal box, but it hasn't made much
    improvement and the noise is very evident on the scope trace (see
    pictures). This *is* mains interference as it works out at exactly
    mains frequency. It's even there if I attach the DC input leads to a
    9V battery instead so it's not coming from the PSU. The links below
    show the noisy trace and the set-up as I've currently implemented it.
    I'm dealing here with high impedance, low level signals approximating
    to a dynamic mic in character I would imagine, so it's a PITA. Any
    suggestions?


    https://disk.yandex.com/i/u7pJajKXHlzv8A


    https://disk.yandex.com/i/W_rLu6HinY26VQ

    I see the signal, it is clearly not sinusoidal. So you will need to do more than just trap the fundamental, but also deal with harmonics. Since the fundamental frequency drifts, it won't be possible to use an extremely high Q filter. what frequency
    range are you interested in? Is it possible to perform post capture processing to remove the background noise?

    It looks like your leads are made to attach to the patches placed on a person. I would have thought to use coax wire, but maybe there's no point since the person it's attached to is not able to be shielded. Are your probes connected to a subject
    when you see this signal? Have you tried attaching them to a subject? It may be that the high impedance input is seeing a high noise signal which would essentially be grounded through the patient if the leads were connected... just a thought. Also
    look at the signal without the input leads at all.

    BTW, why do you obscure the readout data in the scope capture? I count 4.3 divisions per cycle of the waveform. I can't think of a multiplier that would make that a power line frequency anyplace I know of.

    Er, yeah, that's why I obscured the time/div., to avoid confusion for
    those in the US. Well, that was the plan, anyway. The period is 20mS
    which equals 50Hz. I'm in Yurp and that's the mains frequency here.

    Distinctly unhelpful since at least one poster mistook the heartbeat
    waveform rather than the wiggles for the mains hum. I can't imagine why.

    One distinct possibility is that the ECG is actually filtering out
    *60Hz* mains rather than 50Hz. Most such devices have a notch reject
    filter for mains with a moderately high Q so that they will give good
    rejection for the spot mains frequency +/- 0.05 Hz.

    Try it out in a field away from local mains and on battery power and see
    if it is clean then. Some of your problem could be coming from the bench
    psu.

    Most of it I expect comes from the flying leads capturing magnetic flux
    so plat them together leaving just enough free lead to connect it up.

    Any high gain amplifier will amplify unwanted mains hum but in these
    systems most of it should be common mode and rejected by the front end.

    Finger on the input test works well enough for most high gain audio
    amplifiers if a signal generator is not to hand.

    --
    Regards,
    Martin Brown

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Allison@21:1/5 to Tauno Voipio on Wed Apr 6 02:26:38 2022
    Tauno Voipio wrote:
    =================

    My guess is that the hum is coming from your patient / target.


    ** Spot fucking on.


    The capacitance of an average person is about 20 pF to the
    active phase line and 200 pF to ground. You can assume that
    the patient has about 10% of the line voltage through a pretty
    high impedance voltage divider.

    ** Yep, has the OP never handled a live audio line ?

    Bluuuurp, bluuup.....


    When we made ECG equipment in the early 1970's, the solution
    was to make the input of the amplifier differential and as
    high impedance as possible, including guard bootstrapping the
    shield braids of the input cables. The impedance of the
    connection electrodes are hardly ever identical, and this creates
    voltage dividers with the amplifier input impedances.

    The imbalance works directly to convert the common-mode hum into
    differential input.


    ** As does grounding the diff amp metal enclosure.
    If the whole kaboodle is *floating* - the diff disappears.

    FYI:

    The OP is a notorious idiot and is "dreaming" since his posted scope image is good.



    ...... Phil

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Mike Coon@21:1/5 to All on Wed Apr 6 11:44:38 2022
    In article <MPG.3cb69c19eedb9964989c29@news.eternal-september.org>, rmowery42@charter.net says...

    In article <cbab2f4d-9771-481b-8577-a2badf6dfa02n@googlegroups.com>, pallison49@gmail.com says...

    Ricky the IDIOT puked:

    =====================

    I see the signal, it is clearly not sinusoidal.

    ** That is the fucking heart beat you moron !!!
    The 50/60 Hz hum is the superimposed fine wiggling.

    Rest of this retarded wanker's absurd drivel snipped.





    Yes, that looks like the typical RST waveform of the heart. The heart
    often beats near 60 Hz.

    Although I believe my pacemaker is set to let me get a bit slower before
    it starts geeing me up...

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Cursitor Doom@21:1/5 to pNaonStpealmtje@yahoo.com on Wed Apr 6 13:46:49 2022
    On Wed, 06 Apr 2022 04:19:25 GMT, Jan Panteltje
    <pNaonStpealmtje@yahoo.com> wrote:

    On a sunny day (Tue, 05 Apr 2022 19:05:23 +0100) it happened Cursitor Doom ><cd@notformail.com> wrote in <o70p4h94qqbdftsoe1el8suv1gmklc9np2@4ax.com>:

    Greetings, gentlemen,

    I've got one of those ECG boards off Ebay and am having a problem with >>mains hum appearing on the output. I can't understand where it's
    coming from (airborne in some form I guess) and therefore how to get
    rid of it. Initially I assumed the hum would disappear when the board
    was mounted in a screened metal box, but it hasn't made much
    improvement and the noise is very evident on the scope trace (see >>pictures). This *is* mains interference as it works out at exactly
    mains frequency. It's even there if I attach the DC input leads to a
    9V battery instead so it's not coming from the PSU. The links below
    show the noisy trace and the set-up as I've currently implemented it.
    I'm dealing here with high impedance, low level signals approximating
    to a dynamic mic in character I would imagine, so it's a PITA. Any >>suggestions?

    One way is perhaps to pick up mains with some wire
    and then 180 degrees inverse it with some opamp
    and then subtract that from the output?

    Ingenious, Jan; ingenious. I'd have loved to have tried that idea out
    if I'd had a bit more time to spare. In the end, ferrite beads did the
    trick. Very analogue! :-)


    This is sometimes done in ham radio to cancel noise from wallwarts in the house etc
    small antenna indoors to subtract from the real big antenna outside,

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Cursitor Doom@21:1/5 to tauno.voipio@notused.fi.invalid on Wed Apr 6 13:45:23 2022
    On Wed, 6 Apr 2022 11:58:48 +0300, Tauno Voipio <tauno.voipio@notused.fi.invalid> wrote:

    My guess is that the hum is coming from your patient / target.

    The capacitance of an average person is about 20 pF to the
    active phase line and 200 pF to ground. You can assume that
    the patient has about 10% of the line voltage through a pretty
    high impedance voltage divider.

    Yeah, I know what you mean but no cigar for you this time. I was able
    to clean up the hum by using good old fashioned ferrite beads inside
    the box at the point where the power lead comes in. Worked like a
    charm. Sometimes the best solutions are the old ones...

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Ralph Mowery@21:1/5 to All on Wed Apr 6 10:20:25 2022
    In article <MPG.3cb77f6e2b5215d59896ac@usenet.plus.net>, gravity@mjcoon.plus.com says...


    Yes, that looks like the typical RST waveform of the heart. The heart often beats near 60 Hz.

    Although I believe my pacemaker is set to let me get a bit slower before
    it starts geeing me up...



    The 60 beats is just a number near the average. For people that are in
    very good health and do a lot of physical activity the heart may beat
    slower than the 'nornal average' when at rest, others may beat faster if
    not very active and in good physical shape. I think mine is mnore like
    70 some BPM.

    From what I see this is a simple decvice and maybe has only 2 leads.
    The heart monitors I am familiar with has 3 leads where the internal
    circuits filter out the stray electrical noise picked up by the monitor.
    Big difference in a device under $ 100 and the professional devices.
    Then there are the multilead devices.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Jan Panteltje@21:1/5 to rmowery42@charter.net on Wed Apr 6 15:20:26 2022
    On a sunny day (Wed, 6 Apr 2022 10:20:25 -0400) it happened Ralph Mowery <rmowery42@charter.net> wrote in <MPG.3cb76bb730946ade989c2a@news.eternal-september.org>:

    In article <MPG.3cb77f6e2b5215d59896ac@usenet.plus.net>, >gravity@mjcoon.plus.com says...


    Yes, that looks like the typical RST waveform of the heart. The heart
    often beats near 60 Hz.

    Although I believe my pacemaker is set to let me get a bit slower before
    it starts geeing me up...



    The 60 beats is just a number near the average. For people that are in
    very good health and do a lot of physical activity the heart may beat
    slower than the 'nornal average' when at rest, others may beat faster if
    not very active and in good physical shape. I think mine is mnore like
    70 some BPM.

    From what I see this is a simple decvice and maybe has only 2 leads.
    The heart monitors I am familiar with has 3 leads where the internal
    circuits filter out the stray electrical noise picked up by the monitor.
    Big difference in a device under $ 100 and the professional devices.
    Then there are the multilead devices.


    I just measured 42 per minute when sitting on a chair in front of the table looking at the laptop doing nothing.
    But if I really relax its lower.
    So it seems I am slower than you earthlings,
    I know about some doctor who could control his heart beat.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Tauno Voipio@21:1/5 to Cursitor Doom on Wed Apr 6 18:59:15 2022
    On 6.4.22 15.45, Cursitor Doom wrote:
    On Wed, 6 Apr 2022 11:58:48 +0300, Tauno Voipio <tauno.voipio@notused.fi.invalid> wrote:

    My guess is that the hum is coming from your patient / target.

    The capacitance of an average person is about 20 pF to the
    active phase line and 200 pF to ground. You can assume that
    the patient has about 10% of the line voltage through a pretty
    high impedance voltage divider.

    Yeah, I know what you mean but no cigar for you this time. I was able
    to clean up the hum by using good old fashioned ferrite beads inside
    the box at the point where the power lead comes in. Worked like a
    charm. Sometimes the best solutions are the old ones...


    I do not quite subscribe it.

    The ferrite beads do not attenuate the 50 or 60 Hz hum
    from the mains.

    Do you have a reference electrode on the patient?

    --

    -TV

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Arie de Muijnck@21:1/5 to Cursitor Doom on Wed Apr 6 18:28:39 2022
    On 2022-04-06 14:45, Cursitor Doom wrote:
    On Wed, 6 Apr 2022 11:58:48 +0300, Tauno Voipio <tauno.voipio@notused.fi.invalid> wrote:

    My guess is that the hum is coming from your patient / target.

    The capacitance of an average person is about 20 pF to the
    active phase line and 200 pF to ground. You can assume that
    the patient has about 10% of the line voltage through a pretty
    high impedance voltage divider.

    Yeah, I know what you mean but no cigar for you this time. I was able
    to clean up the hum by using good old fashioned ferrite beads inside
    the box at the point where the power lead comes in. Worked like a
    charm. Sometimes the best solutions are the old ones...


    Since these beads do not attenuate 50/60Hz, you probably had a problem
    with mains modulated interference being rectified in the input circuits
    of the amplifier. You need to add some RF filtering at the input, before
    any non-linear elements like transistors or op-amps.

    Arie

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Ricky@21:1/5 to Tauno Voipio on Wed Apr 6 09:51:56 2022
    On Wednesday, April 6, 2022 at 4:59:35 AM UTC-4, Tauno Voipio wrote:
    My guess is that the hum is coming from your patient / target.

    The capacitance of an average person is about 20 pF to the
    active phase line and 200 pF to ground. You can assume that
    the patient has about 10% of the line voltage through a pretty
    high impedance voltage divider.

    When we made ECG equipment in the early 1970's, the solution
    was to make the input of the amplifier differential and as
    high impedance as possible, including guard bootstrapping the
    shield braids of the input cables. The impedance of the
    connection electrodes are hardly ever identical, and this creates
    voltage dividers with the amplifier input impedances. The
    imbalance works directly to convert the common-mode hum into
    differential input.

    That would make sense if each measurement was relative to ground. These measurements only make sense relative to each other. Treating the body as a capacitor to the power line is not of much use. Noise can be introduced when the different parts of
    the body have different levels of noise. The displayed signals are either one electrode relative to a "reference" electrode, or multiple electrodes are averaged together to form a virtual reference which is the reference for each electrode.

    I don't know for sure, but I expect the body is a relatively low impedance voltage source. I'm willing to bet the best way for removing power line noise is a simple notch filter in the amplifier. The noise amplitude is low, so no worry about over
    driving the amps. Just filter it out, best with a digital filter as the design is not complex and the frequency is not subject to drift with component tolerance, temperature, etc., so high Q can be used.

    --

    Rick C.

    -+ Get 1,000 miles of free Supercharging
    -+ Tesla referral code - https://ts.la/richard11209

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Tauno Voipio@21:1/5 to Ricky on Wed Apr 6 21:21:43 2022
    On 6.4.22 19.51, Ricky wrote:
    On Wednesday, April 6, 2022 at 4:59:35 AM UTC-4, Tauno Voipio wrote:
    My guess is that the hum is coming from your patient / target.

    The capacitance of an average person is about 20 pF to the
    active phase line and 200 pF to ground. You can assume that
    the patient has about 10% of the line voltage through a pretty
    high impedance voltage divider.

    When we made ECG equipment in the early 1970's, the solution
    was to make the input of the amplifier differential and as
    high impedance as possible, including guard bootstrapping the
    shield braids of the input cables. The impedance of the
    connection electrodes are hardly ever identical, and this creates
    voltage dividers with the amplifier input impedances. The
    imbalance works directly to convert the common-mode hum into
    differential input.

    That would make sense if each measurement was relative to ground. These measurements only make sense relative to each other. Treating the body as a capacitor to the power line is not of much use. Noise can be introduced when the different parts of
    the body have different levels of noise. The displayed signals are either one electrode relative to a "reference" electrode, or multiple electrodes are averaged together to form a virtual reference which is the reference for each electrode.

    I don't know for sure, but I expect the body is a relatively low impedance voltage source. I'm willing to bet the best way for removing power line noise is a simple notch filter in the amplifier. The noise amplitude is low, so no worry about over
    driving the amps. Just filter it out, best with a digital filter as the design is not complex and the frequency is not subject to drift with component tolerance, temperature, etc., so high Q can be used.


    That is true, but we do not have contacts to the low impedance
    source. The electrodes can have impedances of tens of kohm,
    with mismatch between the electrodes. We do not hit contact
    spikes through the skin.

    A notch filter is not a good idea, as much of the interesting
    frequency components are in the mains frequency range. The
    ECG signal is spiky by its very nature, and narrow band filters
    will spoil the information looked for.

    --

    -TV

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From whit3rd@21:1/5 to Cursitor Doom on Wed Apr 6 13:42:45 2022
    On Wednesday, April 6, 2022 at 5:45:30 AM UTC-7, Cursitor Doom wrote:
    On Wed, 6 Apr 2022 11:58:48 +0300, Tauno Voipio <tauno....@notused.fi.invalid> wrote:

    My guess is that the hum is coming from your patient / target.

    The capacitance of an average person is about ...

    Yeah, I know what you mean but no cigar for you this time. I was able
    to clean up the hum by using good old fashioned ferrite beads inside
    the box at the point where the power lead comes in. Worked like a
    charm. Sometimes the best solutions are the old ones...

    Didn't the original post say that the problem occurred with battery power? Sounds like you've found PART of the solution, not all of it. Ferrite
    beads don't do much at power-line frequency.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Ricky@21:1/5 to Tauno Voipio on Wed Apr 6 16:06:28 2022
    On Wednesday, April 6, 2022 at 2:21:53 PM UTC-4, Tauno Voipio wrote:
    On 6.4.22 19.51, Ricky wrote:
    On Wednesday, April 6, 2022 at 4:59:35 AM UTC-4, Tauno Voipio wrote:
    My guess is that the hum is coming from your patient / target.

    The capacitance of an average person is about 20 pF to the
    active phase line and 200 pF to ground. You can assume that
    the patient has about 10% of the line voltage through a pretty
    high impedance voltage divider.

    When we made ECG equipment in the early 1970's, the solution
    was to make the input of the amplifier differential and as
    high impedance as possible, including guard bootstrapping the
    shield braids of the input cables. The impedance of the
    connection electrodes are hardly ever identical, and this creates
    voltage dividers with the amplifier input impedances. The
    imbalance works directly to convert the common-mode hum into
    differential input.

    That would make sense if each measurement was relative to ground. These measurements only make sense relative to each other. Treating the body as a capacitor to the power line is not of much use. Noise can be introduced when the different parts of
    the body have different levels of noise. The displayed signals are either one electrode relative to a "reference" electrode, or multiple electrodes are averaged together to form a virtual reference which is the reference for each electrode.

    I don't know for sure, but I expect the body is a relatively low impedance voltage source. I'm willing to bet the best way for removing power line noise is a simple notch filter in the amplifier. The noise amplitude is low, so no worry about over
    driving the amps. Just filter it out, best with a digital filter as the design is not complex and the frequency is not subject to drift with component tolerance, temperature, etc., so high Q can be used.
    That is true, but we do not have contacts to the low impedance
    source. The electrodes can have impedances of tens of kohm,
    with mismatch between the electrodes. We do not hit contact
    spikes through the skin.

    The body is still low impedance with respect to the amplifier inputs. They use paste and a large contact area to minimize skin resistance. Given the high input impedance of the amp, the mismatch in impedance is of little consequence.


    A notch filter is not a good idea, as much of the interesting
    frequency components are in the mains frequency range. The
    ECG signal is spiky by its very nature, and narrow band filters
    will spoil the information looked for.


    You seem to be confusing a notch (band reject) with a narrow band-pass filter. An adequately narrow band reject filter would have virtually no impact on the signal of interest. It only need be wide enough to accommodate the normal variations in mains
    frequency.

    --

    Rick C.

    +- Get 1,000 miles of free Supercharging
    +- Tesla referral code - https://ts.la/richard11209

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Ricky@21:1/5 to All on Wed Apr 6 16:09:46 2022
    On Wednesday, April 6, 2022 at 4:42:48 PM UTC-4, whit3rd wrote:
    On Wednesday, April 6, 2022 at 5:45:30 AM UTC-7, Cursitor Doom wrote:
    On Wed, 6 Apr 2022 11:58:48 +0300, Tauno Voipio <tauno....@notused.fi.invalid> wrote:

    My guess is that the hum is coming from your patient / target.

    The capacitance of an average person is about ...
    Yeah, I know what you mean but no cigar for you this time. I was able
    to clean up the hum by using good old fashioned ferrite beads inside
    the box at the point where the power lead comes in. Worked like a
    charm. Sometimes the best solutions are the old ones...
    Didn't the original post say that the problem occurred with battery power? Sounds like you've found PART of the solution, not all of it. Ferrite
    beads don't do much at power-line frequency.

    I'd like to see what the output looks like with various inputs, all contacts shorted, resistors between contacts, etc. If the problem really has disappeared, I expect it will return and not by removing the ferrite beads.

    --

    Rick C.

    ++ Get 1,000 miles of free Supercharging
    ++ Tesla referral code - https://ts.la/richard11209

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Cursitor Doom@21:1/5 to gnuarm.deletethisbit@gmail.com on Thu Apr 7 00:37:32 2022
    On Wed, 6 Apr 2022 16:06:28 -0700 (PDT), Ricky
    <gnuarm.deletethisbit@gmail.com> wrote:

    On Wednesday, April 6, 2022 at 2:21:53 PM UTC-4, Tauno Voipio wrote:
    On 6.4.22 19.51, Ricky wrote:
    On Wednesday, April 6, 2022 at 4:59:35 AM UTC-4, Tauno Voipio wrote:
    My guess is that the hum is coming from your patient / target.

    The capacitance of an average person is about 20 pF to the
    active phase line and 200 pF to ground. You can assume that
    the patient has about 10% of the line voltage through a pretty
    high impedance voltage divider.

    When we made ECG equipment in the early 1970's, the solution
    was to make the input of the amplifier differential and as
    high impedance as possible, including guard bootstrapping the
    shield braids of the input cables. The impedance of the
    connection electrodes are hardly ever identical, and this creates
    voltage dividers with the amplifier input impedances. The
    imbalance works directly to convert the common-mode hum into
    differential input.

    That would make sense if each measurement was relative to ground. These measurements only make sense relative to each other. Treating the body as a capacitor to the power line is not of much use. Noise can be introduced when the different parts of
    the body have different levels of noise. The displayed signals are either one electrode relative to a "reference" electrode, or multiple electrodes are averaged together to form a virtual reference which is the reference for each electrode.

    I don't know for sure, but I expect the body is a relatively low impedance voltage source. I'm willing to bet the best way for removing power line noise is a simple notch filter in the amplifier. The noise amplitude is low, so no worry about over
    driving the amps. Just filter it out, best with a digital filter as the design is not complex and the frequency is not subject to drift with component tolerance, temperature, etc., so high Q can be used.
    That is true, but we do not have contacts to the low impedance
    source. The electrodes can have impedances of tens of kohm,
    with mismatch between the electrodes. We do not hit contact
    spikes through the skin.

    The body is still low impedance with respect to the amplifier inputs. They use paste and a large contact area to minimize skin resistance. Given the high input impedance of the amp, the mismatch in impedance is of little consequence.


    A notch filter is not a good idea, as much of the interesting
    frequency components are in the mains frequency range. The
    ECG signal is spiky by its very nature, and narrow band filters
    will spoil the information looked for.


    You seem to be confusing a notch (band reject) with a narrow band-pass filter. An adequately narrow band reject filter would have virtually no impact on the signal of interest. It only need be wide enough to accommodate the normal variations in mains
    frequency.

    Leaving aside that the problem has now been resolved, I would have
    thought Tauno was right in what he said. The wanted and unwanted
    components of the waveform are just too close together to target one
    without degrading the other to some meaningful extent.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Allison@21:1/5 to Ricky on Wed Apr 6 16:52:48 2022
    Ricky wrote:
    ==========

    An adequately narrow band reject filter would have virtually no impact on the signal of interest.

    ** Shame you have never looked at the phase and amplitude curve of such a filter.


    It only need be wide enough to accommodate the normal variations in mains frequency.

    ** About 0.1Hz is all the AC supply varies by.


    ...... Phil

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From piglet@21:1/5 to All on Thu Apr 7 09:01:01 2022
    On 06/04/2022 9:42 pm, whit3rd wrote:
    On Wednesday, April 6, 2022 at 5:45:30 AM UTC-7, Cursitor Doom wrote:
    On Wed, 6 Apr 2022 11:58:48 +0300, Tauno Voipio
    <tauno....@notused.fi.invalid> wrote:

    My guess is that the hum is coming from your patient / target.

    The capacitance of an average person is about ...

    Yeah, I know what you mean but no cigar for you this time. I was able
    to clean up the hum by using good old fashioned ferrite beads inside
    the box at the point where the power lead comes in. Worked like a
    charm. Sometimes the best solutions are the old ones...

    Didn't the original post say that the problem occurred with battery power? Sounds like you've found PART of the solution, not all of it. Ferrite
    beads don't do much at power-line frequency.

    I think that when OP tried battery power he was still examining the
    output on a mains connected scope? Interesting would be what is seen
    with a battery powered scope and the whole system free of any connection
    to mains ground.

    No sane amount of ferrite beads will have effect at 50Hz, much more
    likely some tens/hundreds of kHz from a mains SMPS in the vicinity is
    getting in. The ECG amp will probably be heavily low pass filtered
    somewhere along the chain so the HF interference won't be seen at the
    output but it's 100Hz modulation rate will be?

    piglet

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From piglet@21:1/5 to Phil Allison on Thu Apr 7 09:32:47 2022
    On 07/04/2022 09:19, Phil Allison wrote:
    erichp...@hotmail.com wrote:
    =======================

    My guess is that the hum is coming from your patient / target.

    The capacitance of an average person is about ...

    I think that when OP tried battery power he was still examining the
    output on a mains connected scope? Interesting would be what is seen
    with a battery powered scope and the whole system free of any connection
    to mains ground.

    ** That is my contention too, posted 2 days ago.

    The ECG amp will probably be heavily low pass filtered
    somewhere along the chain so the HF interference won't be seen at the
    output but it's 100Hz modulation rate will be?

    ** Huh ? 100Hz ?

    Think is is just simple capacitive coupled injection of the AC supply voltage wave.
    The bane of many poorly shielded electric guitars .


    ...... Phil

    Yes, but later on the OP said he solved the problem with ferrite beads.
    He hasn't said how many beads he used but it seems unlikely he used
    enough ferrite to attenuate mains frequencies directly so the theory now
    is that he instead attenuated some higher frequency pickup that was
    itself power line modulated?

    piglet

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Allison@21:1/5 to erichp...@hotmail.com on Thu Apr 7 01:19:02 2022
    erichp...@hotmail.com wrote:
    =======================

    My guess is that the hum is coming from your patient / target.

    The capacitance of an average person is about ...

    I think that when OP tried battery power he was still examining the
    output on a mains connected scope? Interesting would be what is seen
    with a battery powered scope and the whole system free of any connection
    to mains ground.

    ** That is my contention too, posted 2 days ago.

    The ECG amp will probably be heavily low pass filtered
    somewhere along the chain so the HF interference won't be seen at the
    output but it's 100Hz modulation rate will be?

    ** Huh ? 100Hz ?

    Think is is just simple capacitive coupled injection of the AC supply voltage wave.
    The bane of many poorly shielded electric guitars .


    ...... Phil

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Allison@21:1/5 to erichp...@hotmail.com on Thu Apr 7 01:44:23 2022
    erichp...@hotmail.com wrote:
    ========================


    My guess is that the hum is coming from your patient / target.

    The capacitance of an average person is about ...

    I think that when OP tried battery power he was still examining the
    output on a mains connected scope? Interesting would be what is seen
    with a battery powered scope and the whole system free of any connection >> to mains ground.

    ** That is my contention too, posted 2 days ago.

    The ECG amp will probably be heavily low pass filtered
    somewhere along the chain so the HF interference won't be seen at the
    output but it's 100Hz modulation rate will be?

    ** Huh ? 100Hz ?

    Think is is just simple capacitive coupled injection of the AC supply voltage wave.
    The bane of many poorly shielded electric guitars .



    Yes, but later on the OP said he solved the problem with ferrite beads.

    ** Should have tried Hippy beads or Rosary beads.

    He hasn't said how many beads he used ...

    ** Nor how much weed he smoke daily.

    but it seems unlikely he used
    enough ferrite to attenuate mains frequencies directly so the theory now
    is that he instead attenuated some higher frequency pickup that was
    itself power line modulated?

    ** I can see what looks like 50Hz in that slow ECG trace.

    Try counting the wiggles.



    ..... Phil

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From piglet@21:1/5 to Phil Allison on Thu Apr 7 10:23:39 2022
    On 07/04/2022 09:44, Phil Allison wrote:
    erichp...@hotmail.com wrote:
    ========================


    My guess is that the hum is coming from your patient / target.

    The capacitance of an average person is about ...

    I think that when OP tried battery power he was still examining the
    output on a mains connected scope? Interesting would be what is seen
    with a battery powered scope and the whole system free of any connection >>>> to mains ground.

    ** That is my contention too, posted 2 days ago.

    The ECG amp will probably be heavily low pass filtered
    somewhere along the chain so the HF interference won't be seen at the
    output but it's 100Hz modulation rate will be?

    ** Huh ? 100Hz ?

    Think is is just simple capacitive coupled injection of the AC supply voltage wave.
    The bane of many poorly shielded electric guitars .



    Yes, but later on the OP said he solved the problem with ferrite beads.

    ** Should have tried Hippy beads or Rosary beads.

    He hasn't said how many beads he used ...

    ** Nor how much weed he smoke daily.

    but it seems unlikely he used
    enough ferrite to attenuate mains frequencies directly so the theory now
    is that he instead attenuated some higher frequency pickup that was
    itself power line modulated?

    ** I can see what looks like 50Hz in that slow ECG trace.

    Try counting the wiggles.



    ..... Phil




    With the timebase unhelpfully blurred out I didn't before count the
    wiggles to see if 50Hz or 100Hz but tried just now using the heart rate
    as a guide and agree with you - it looks like it is 50Hz direct mains
    pickup. Thanks Phil.

    piglet

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Allison@21:1/5 to erichp...@hotmail.com on Thu Apr 7 03:35:32 2022
    erichp...@hotmail.com wrote:
    ========================

    ** I can see what looks like 50Hz in that slow ECG trace.

    Try counting the wiggles.

    With the timebase unhelpfully blurred out I didn't before count the
    wiggles to see if 50Hz or 100Hz but tried just now using the heart rate
    as a guide and agree with you - it looks like it is 50Hz direct mains
    pickup.

    ** From the OP's first post.

    " This *is* mains interference as it works out at exactly
    mains frequency. "



    ...... Phil

    --- SoupGate-Win32 v1.05
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  • From DecadentLinuxUserNumeroUno@decadenc@21:1/5 to Jan Pan Dipshit on Thu Apr 7 14:56:49 2022
    Jan Pan Dipshit <pNaonStpealmtje@yahoo.com> wrote in news:t2kb5a$kd8$1@dont-email.me:

    I just measured 42 per minute when sitting on a chair in front of
    the table looking at the laptop doing nothing.

    I'll bet that you sport flawed measurement capability then, because
    that rate claim is bullshit.

    But if I really
    relax its lower.

    And you are still unable to obtain a correct reading.

    Got a BP cuff? What does it say?

    *I* say that you are a liar or simply have no clue how to read your
    pulse.


    So it seems I am slower than you earthlings,

    Right... the utter retard Jan Pan Dipshit thinks he's from
    elsewhere.

    I know about some doctor who could control his heart beat.

    So could our man Flint, but you lack the skill to even take a
    proper reading, so you controlling what you cannot even read is
    unlikely.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From DecadentLinuxUserNumeroUno@decadenc@21:1/5 to Phil Allison on Thu Apr 7 15:27:02 2022
    Phil Allison <pallison49@gmail.com> wrote in news:e9c27709-1c68-47d3-b8db-45e594bd59ccn@googlegroups.com:

    Ricky wrote:
    ==========

    An adequately narrow band reject filter would have virtually no
    impact on the signal of interest.

    ** Shame you have never looked at the phase and amplitude curve
    of such a filter.


    It only need be wide enough to accommodate the normal variations
    in mains frequency.

    ** About 0.1Hz is all the AC supply varies by.

    Yep... practically wordlwide the electrical grids sport near zero
    variance with regard to frequency.

    --- SoupGate-Win32 v1.05
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  • From DecadentLinuxUserNumeroUno@decadenc@21:1/5 to Phil Allison on Thu Apr 7 17:07:04 2022
    Phil Allison <pallison49@gmail.com> wrote in news:02662e66-5f7e-4d87-a583-86f0abbcf9a9n@googlegroups.com:

    ** Huh ? 100Hz ?

    Think is is just simple capacitive coupled injection of the AC
    supply voltage wave. The bane of many poorly shielded electric
    guitars .

    Yes, and it typically sounds off at twice the line frequency.

    So, 60Hz gets 120Hz noise and 50Hz gets 100Hz noise.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Tauno Voipio@21:1/5 to Phil Allison on Thu Apr 7 20:28:52 2022
    On 7.4.22 2.52, Phil Allison wrote:
    Ricky wrote:
    ==========

    An adequately narrow band reject filter would have virtually no impact on the signal of interest.

    ** Shame you have never looked at the phase and amplitude curve of such a filter.


    It only need be wide enough to accommodate the normal variations in mains frequency.

    ** About 0.1Hz is all the AC supply varies by.


    ...... Phil


    Right!

    A narrow notch rings as badly as a narrow peak when fed with
    a spiky signal.

    We did try all kinds of filtering already half a century ago,
    and the basic mathematics, physics and electronics about the
    filter has not changed.

    --

    -TV

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  • From Phil Allison@21:1/5 to DecadentLinux...@decadence.org on Thu Apr 7 14:58:42 2022
    DecadentLinux...@decadence.org wrote:
    ================================

    ** Huh ? 100Hz ?

    Think is is just simple capacitive coupled injection of the AC
    supply voltage wave. The bane of many poorly shielded electric
    guitars .

    Yes, and it typically sounds off at twice the line frequency.


    ** No it does not.

    So, 60Hz gets 120Hz noise and 50Hz gets 100Hz noise.

    ** The AC supply has a fair amount of 3rd and 5th harmonics that are often more audible that the fundamental.
    But SFA 2nd.
    Magnetic hum fields radiated from transformers is mostly 3rd to.

    ..... Phil

    --- SoupGate-Win32 v1.05
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  • From whit3rd@21:1/5 to palli...@gmail.com on Thu Apr 7 15:10:02 2022
    On Thursday, April 7, 2022 at 2:58:46 PM UTC-7, palli...@gmail.com wrote:
    DecadentLinux...@decadence.org wrote:
    ================================

    ** Huh ? 100Hz ?

    Think is is just simple capacitive coupled injection of the AC
    supply voltage wave. The bane of many poorly shielded electric
    guitars .

    Yes, and it typically sounds off at twice the line frequency.

    ** No it does not.
    So, 60Hz gets 120Hz noise and 50Hz gets 100Hz noise.
    ** The AC supply has a fair amount of 3rd and 5th harmonics that are often more audible that the fundamental.
    But SFA 2nd.
    Magnetic hum fields radiated from transformers is mostly 3rd to.

    Second harmonic is the acoustic (magnetostriction) output from transformers, and the light from fluorescent fixtures (or used to be; ballasts are more frequency-rich nowadays). Ripple voltage on a fullwave rectifier, also.

    If you apply enough gain, you'll see lots of sneaky signal inputs. Microphonic tubes
    are /were a major concern, and that's why old HiFi preamps were on a different chassis
    than the power stages.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Ricky@21:1/5 to Cursitor Doom on Thu Apr 7 18:27:50 2022
    On Wednesday, April 6, 2022 at 7:37:40 PM UTC-4, Cursitor Doom wrote:
    On Wed, 6 Apr 2022 16:06:28 -0700 (PDT), Ricky
    <gnuarm.del...@gmail.com> wrote:

    On Wednesday, April 6, 2022 at 2:21:53 PM UTC-4, Tauno Voipio wrote:
    On 6.4.22 19.51, Ricky wrote:
    On Wednesday, April 6, 2022 at 4:59:35 AM UTC-4, Tauno Voipio wrote:
    My guess is that the hum is coming from your patient / target.

    The capacitance of an average person is about 20 pF to the
    active phase line and 200 pF to ground. You can assume that
    the patient has about 10% of the line voltage through a pretty
    high impedance voltage divider.

    When we made ECG equipment in the early 1970's, the solution
    was to make the input of the amplifier differential and as
    high impedance as possible, including guard bootstrapping the
    shield braids of the input cables. The impedance of the
    connection electrodes are hardly ever identical, and this creates
    voltage dividers with the amplifier input impedances. The
    imbalance works directly to convert the common-mode hum into
    differential input.

    That would make sense if each measurement was relative to ground. These measurements only make sense relative to each other. Treating the body as a capacitor to the power line is not of much use. Noise can be introduced when the different parts of
    the body have different levels of noise. The displayed signals are either one electrode relative to a "reference" electrode, or multiple electrodes are averaged together to form a virtual reference which is the reference for each electrode.

    I don't know for sure, but I expect the body is a relatively low impedance voltage source. I'm willing to bet the best way for removing power line noise is a simple notch filter in the amplifier. The noise amplitude is low, so no worry about over
    driving the amps. Just filter it out, best with a digital filter as the design is not complex and the frequency is not subject to drift with component tolerance, temperature, etc., so high Q can be used.
    That is true, but we do not have contacts to the low impedance
    source. The electrodes can have impedances of tens of kohm,
    with mismatch between the electrodes. We do not hit contact
    spikes through the skin.

    The body is still low impedance with respect to the amplifier inputs. They use paste and a large contact area to minimize skin resistance. Given the high input impedance of the amp, the mismatch in impedance is of little consequence.


    A notch filter is not a good idea, as much of the interesting
    frequency components are in the mains frequency range. The
    ECG signal is spiky by its very nature, and narrow band filters
    will spoil the information looked for.


    You seem to be confusing a notch (band reject) with a narrow band-pass filter. An adequately narrow band reject filter would have virtually no impact on the signal of interest. It only need be wide enough to accommodate the normal variations in mains
    frequency.
    Leaving aside that the problem has now been resolved, I would have
    thought Tauno was right in what he said. The wanted and unwanted
    components of the waveform are just too close together to target one
    without degrading the other to some meaningful extent.

    That's simply not true. You can design a filter to satisfy the requirements. It's not like the signal of interest has a critical component at 50/60 Hz. Look at the waveform, or better yet, look at the frequency spectrum. There's nothing important at
    that frequency. Tauno also spoke of it incorrectly, referring to "narrow band filters". What is called for is narrow band reject which is not at all the same thing and will not disturb the signal overall, unless there is a critical component at the
    same exact frequency, which is not the case.

    --

    Rick C.

    --- Get 1,000 miles of free Supercharging
    --- Tesla referral code - https://ts.la/richard11209

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Ricky@21:1/5 to Tauno Voipio on Thu Apr 7 18:31:43 2022
    On Thursday, April 7, 2022 at 1:29:01 PM UTC-4, Tauno Voipio wrote:
    On 7.4.22 2.52, Phil Allison wrote:
    Ricky wrote:
    ==========

    An adequately narrow band reject filter would have virtually no impact on the signal of interest.

    ** Shame you have never looked at the phase and amplitude curve of such a filter.


    It only need be wide enough to accommodate the normal variations in mains frequency.

    ** About 0.1Hz is all the AC supply varies by.


    ...... Phil
    Right!

    A narrow notch rings as badly as a narrow peak when fed with
    a spiky signal.

    At what frequency does it ring?

    --

    Rick C.

    -+- Get 1,000 miles of free Supercharging
    -+- Tesla referral code - https://ts.la/richard11209

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Ricky@21:1/5 to palli...@gmail.com on Thu Apr 7 18:29:17 2022
    On Thursday, April 7, 2022 at 4:44:28 AM UTC-4, palli...@gmail.com wrote:
    erichp...@hotmail.com wrote:
    ========================


    My guess is that the hum is coming from your patient / target.

    The capacitance of an average person is about ...

    I think that when OP tried battery power he was still examining the
    output on a mains connected scope? Interesting would be what is seen
    with a battery powered scope and the whole system free of any connection >> to mains ground.

    ** That is my contention too, posted 2 days ago.

    The ECG amp will probably be heavily low pass filtered
    somewhere along the chain so the HF interference won't be seen at the
    output but it's 100Hz modulation rate will be?

    ** Huh ? 100Hz ?

    Think is is just simple capacitive coupled injection of the AC supply voltage wave.
    The bane of many poorly shielded electric guitars .



    Yes, but later on the OP said he solved the problem with ferrite beads.
    ** Should have tried Hippy beads or Rosary beads.

    He hasn't said how many beads he used ...

    ** Nor how much weed he smoke daily.
    but it seems unlikely he used
    enough ferrite to attenuate mains frequencies directly so the theory now
    is that he instead attenuated some higher frequency pickup that was
    itself power line modulated?
    ** I can see what looks like 50Hz in that slow ECG trace.

    Try counting the wiggles.

    You can count as much as you like. Without knowing the time base of the capture, there's no way to turn a count into a frequency.

    --

    Rick C.

    --+ Get 1,000 miles of free Supercharging
    --+ Tesla referral code - https://ts.la/richard11209

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Allison@21:1/5 to Ricky on Thu Apr 7 19:01:36 2022
    Ricky wrote:
    ===============
    Tauno Voipio wrote:
    Phil Allison wrote:


    An adequately narrow band reject filter would have virtually no impact on the signal of interest.

    ** Shame you have never looked at the phase and amplitude curve of such a filter.

    Right!

    A narrow notch rings as badly as a narrow peak when fed with
    a spiky signal.

    At what frequency does it ring?


    ** Ringing (as seen on a scope) is at the same frequency as the notch minimum.
    But you will not find it in a spectrum analysis.


    ..... Phil

    --- SoupGate-Win32 v1.05
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  • From Ricky@21:1/5 to Ricky on Thu Apr 7 19:18:44 2022
    On Thursday, April 7, 2022 at 9:31:47 PM UTC-4, Ricky wrote:
    On Thursday, April 7, 2022 at 1:29:01 PM UTC-4, Tauno Voipio wrote:
    On 7.4.22 2.52, Phil Allison wrote:
    Ricky wrote:
    ==========

    An adequately narrow band reject filter would have virtually no impact on the signal of interest.

    ** Shame you have never looked at the phase and amplitude curve of such a filter.


    It only need be wide enough to accommodate the normal variations in mains frequency.

    ** About 0.1Hz is all the AC supply varies by.


    ...... Phil
    Right!

    A narrow notch rings as badly as a narrow peak when fed with
    a spiky signal.
    At what frequency does it ring?

    The reason I ask, is because if the ringing is high enough frequency, it is out of band and can be filtered out. I'm willing to bet there is an inverse relationship between the half bandwidth of the notch and the ringing frequency. If it is narrow
    enough (which is what is desired) it will produce ringing that is far out of band and easily filtered. I believe I read the ECG bandwidth is 150 Hz. I expect it would not be too hard to push the ringing frequency up to a range that is easily filtered.

    On doing a bit of research on the matter, it seems to be a much discussed topic, but with no definitive solution. However, here is a paper that seems to say the solution is really in the way the electrodes are attached.

    https://www.aami.org/docs/default-source/bi-t/bit/2012-bit-nd-ecg.pdf

    --

    Rick C.

    -++ Get 1,000 miles of free Supercharging
    -++ Tesla referral code - https://ts.la/richard11209

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Ricky@21:1/5 to palli...@gmail.com on Thu Apr 7 19:23:40 2022
    On Thursday, April 7, 2022 at 10:01:41 PM UTC-4, palli...@gmail.com wrote:
    Ricky wrote:
    ===============
    Tauno Voipio wrote:
    Phil Allison wrote:


    An adequately narrow band reject filter would have virtually no impact on the signal of interest.

    ** Shame you have never looked at the phase and amplitude curve of such a filter.

    Right!

    A narrow notch rings as badly as a narrow peak when fed with
    a spiky signal.

    At what frequency does it ring?
    ** Ringing (as seen on a scope) is at the same frequency as the notch minimum.
    But you will not find it in a spectrum analysis.

    Let's construct a mind experiment to analyze that idea. If you stimulate a notch filter with an impulse, a signal containing all frequencies in equal amplitude, what will emerge from the notch filter is a ring at the frequency at which the filter is
    supposed to have a null?

    Is that logically consistent with the frequency response of the filter?

    --

    Rick C.

    +-- Get 1,000 miles of free Supercharging
    +-- Tesla referral code - https://ts.la/richard11209

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From DecadentLinuxUserNumeroUno@decadenc@21:1/5 to Phil Allison on Fri Apr 8 03:41:23 2022
    Phil Allison <pallison49@gmail.com> wrote in news:70523b25-2f3e-45b5-994f-23abc24669e1n@googlegroups.com:

    DecadentLinux...@decadence.org wrote:
    ================================

    ** Huh ? 100Hz ?

    Think is is just simple capacitive coupled injection of the AC
    supply voltage wave. The bane of many poorly shielded electric
    guitars .

    Yes, and it typically sounds off at twice the line frequency.


    ** No it does not.

    So, 60Hz gets 120Hz noise and 50Hz gets 100Hz noise.

    ** The AC supply has a fair amount of 3rd and 5th harmonics that
    are often more audible that the fundamental.
    But SFA 2nd.
    Magnetic hum fields radiated from transformers is mostly 3rd
    to.

    ..... Phil


    But if it gets rectified, the ripple on a badly designed supply
    exhibits noise at f*2.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Allison@21:1/5 to DecadentLinux...@decadence.org on Thu Apr 7 20:53:00 2022
    DecadentLinux...@decadence.org wrote:
    ================================

    ** The AC supply has a fair amount of 3rd and 5th harmonics that
    are often more audible that the fundamental.
    But SFA 2nd.
    Magnetic hum fields radiated from transformers is mostly 3rd
    to.

    But if it gets rectified, the ripple on a badly designed supply
    exhibits noise at f*2.

    ** Well yes,

    the hum you hear from an amp with bad filter electros is 100 or 120Hz.


    ...... Phil

    --- SoupGate-Win32 v1.05
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  • From Phil Allison@21:1/5 to Ricky on Thu Apr 7 21:13:52 2022
    Ricky wrote:
    ============

    A narrow notch rings as badly as a narrow peak when fed with
    a spiky signal.

    At what frequency does it ring?

    ** Ringing (as seen on a scope) is at the same frequency as the notch minimum.
    But you will not find it in a spectrum analysis.

    Let's construct a mind experiment to analyze that idea.
    If you stimulate a notch filter with an impulse,
    a signal containing all frequencies in equal amplitude,
    what will emerge from the notch filter is a ring at the frequency
    at which the filter is supposed to have a null?


    ** But will not show up on a spectrum analysis.
    That will look as expected, ie missing a chunk.

    Is that logically consistent with the frequency response of the filter?

    ** The " ringing" seen on a scope is an *artefact* - created by missing
    and phase shifted components of the input signal.
    Same goes for square wave inputs.
    All components must be there in the right amounts and phase relationships to get a square looking result.

    Brilliant example for " cognitive dissonance" for most people.


    ...... Phil

    --- SoupGate-Win32 v1.05
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  • From Tauno Voipio@21:1/5 to Ricky on Fri Apr 8 14:47:12 2022
    On 8.4.22 5.18, Ricky wrote:
    On Thursday, April 7, 2022 at 9:31:47 PM UTC-4, Ricky wrote:
    On Thursday, April 7, 2022 at 1:29:01 PM UTC-4, Tauno Voipio wrote:
    On 7.4.22 2.52, Phil Allison wrote:
    Ricky wrote:
    ==========

    An adequately narrow band reject filter would have virtually no impact on the signal of interest.

    ** Shame you have never looked at the phase and amplitude curve of such a filter.


    It only need be wide enough to accommodate the normal variations in mains frequency.

    ** About 0.1Hz is all the AC supply varies by.


    ...... Phil
    Right!

    A narrow notch rings as badly as a narrow peak when fed with
    a spiky signal.
    At what frequency does it ring?

    The reason I ask, is because if the ringing is high enough frequency, it is out of band and can be filtered out. I'm willing to bet there is an inverse relationship between the half bandwidth of the notch and the ringing frequency. If it is narrow
    enough (which is what is desired) it will produce ringing that is far out of band and easily filtered. I believe I read the ECG bandwidth is 150 Hz. I expect it would not be too hard to push the ringing frequency up to a range that is easily filtered.

    On doing a bit of research on the matter, it seems to be a much discussed topic, but with no definitive solution. However, here is a paper that seems to say the solution is really in the way the electrodes are attached.

    https://www.aami.org/docs/default-source/bi-t/bit/2012-bit-nd-ecg.pdf


    So, you're approaching the beef now.

    The kilo-ohm impedances of electrodes are there *after* cleaning
    the skin and removing the dear chest hair. There was also electrode
    paste between the siver plate of the electorode and the skin.

    You did not respond to my question about a reference electrode.

    --

    -TV

    --- SoupGate-Win32 v1.05
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  • From bitrex@21:1/5 to Phil Allison on Fri Apr 8 16:14:53 2022
    On 4/7/2022 4:19 AM, Phil Allison wrote:
    erichp...@hotmail.com wrote:
    =======================

    My guess is that the hum is coming from your patient / target.

    The capacitance of an average person is about ...

    I think that when OP tried battery power he was still examining the
    output on a mains connected scope? Interesting would be what is seen
    with a battery powered scope and the whole system free of any connection
    to mains ground.

    ** That is my contention too, posted 2 days ago.

    The ECG amp will probably be heavily low pass filtered
    somewhere along the chain so the HF interference won't be seen at the
    output but it's 100Hz modulation rate will be?

    ** Huh ? 100Hz ?

    Think is is just simple capacitive coupled injection of the AC supply voltage wave.
    The bane of many poorly shielded electric guitars .


    ...... Phil


    You can tell a guitarist it's a good idea to shield the cavity, 7/10
    times he won't listen though and if you start talking about "capacitive
    coupled injection" he's even less likely to.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Joe Gwinn@21:1/5 to bitrex on Fri Apr 8 17:18:22 2022
    On Fri, 8 Apr 2022 16:14:53 -0400, bitrex <user@example.net> wrote:

    On 4/7/2022 4:19 AM, Phil Allison wrote:
    erichp...@hotmail.com wrote:
    =======================

    My guess is that the hum is coming from your patient / target.

    The capacitance of an average person is about ...

    I think that when OP tried battery power he was still examining the
    output on a mains connected scope? Interesting would be what is seen
    with a battery powered scope and the whole system free of any connection >>> to mains ground.

    ** That is my contention too, posted 2 days ago.

    The ECG amp will probably be heavily low pass filtered
    somewhere along the chain so the HF interference won't be seen at the
    output but it's 100Hz modulation rate will be?

    ** Huh ? 100Hz ?

    Think is is just simple capacitive coupled injection of the AC supply voltage wave.
    The bane of many poorly shielded electric guitars .


    ...... Phil


    You can tell a guitarist it's a good idea to shield the cavity, 7/10
    times he won't listen though and if you start talking about "capacitive >coupled injection" he's even less likely to.

    Some years ago, I was the unofficial chief (and only) engineer of a
    local guitar maker (the owner is a friend of mine).

    You don't try to convince the guitarist (who just wants low noise),
    you talk to the guitar maker (who just wants to know exactly how to do
    that). And few guitar makers are electronic engineers.

    The remedy for capacitive injection was to electro statically shield
    the routed cavity, originally by carefully fitted brass foil shielding
    tubs, then (after I arrived) by nickel-dust based shield paint sprayed
    thickly on the walls of the cavity. The DC resistance between any two
    points on the cavity wall was about 20 ohms. The underside of the
    pick guard had an aluminum foil layer glued on. These shields were
    all grounded to the shield of the coax wire from guitar to amp. The
    strings were also grounded.

    The remedy for magnetic interference, chiefly at power frequencies and harmonics, is various kinds of humbucking construction.


    Joe Gwinn


    PS: What I also did was to invent various kinds of jigs and fixtures,
    and introduce them to various kinds of tool not found in luthier tool
    catalogs. This collectively had a large impact on their manufacturing
    costs. JMG

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Allison@21:1/5 to Joe Gwinn on Fri Apr 8 16:14:36 2022
    Joe Gwinn wrote:
    ==============

    Think is is just simple capacitive coupled injection of the AC supply voltage wave.
    The bane of many poorly shielded electric guitars .

    ...... Phil


    The remedy for capacitive injection was to electro statically shield
    the routed cavity, originally by carefully fitted brass foil shielding
    tubs, then (after I arrived) by nickel-dust based shield paint sprayed thickly on the walls of the cavity. The DC resistance between any two
    points on the cavity wall was about 20 ohms. The underside of the
    pick guard had an aluminum foil layer glued on. These shields were
    all grounded to the shield of the coax wire from guitar to amp. The
    strings were also grounded.

    The remedy for magnetic interference, chiefly at power frequencies and harmonics, is various kinds of humbucking construction.


    ** All these things were well known and adopted by makers like Gibson in the 1950s.
    But they were a luxury brand sold to professionals.
    A radio repair man called Leo Fender began making similar things, very cheaply. https://en.wikipedia.org/wiki/Leo_Fender#Early_life

    Working at a time when triac dimmers were unknown and likewise safety earthing - he gave almost no attention to ES shielding.
    His famous Stratocaster guitar has only a token effort at such and is a first class receiver of hum and buzzing from the AC supply.
    Nearby fluoro lighting drives one crazy.

    https://insounder.org/under-hood-9-evolution-stratocasters-electronics-wiring

    Note the use of plastic covered pickups, unshielded wiring and no cavity shielding at all.
    Fender relied on the player earthing themselves via the steel strings to proved any measure of shielding.
    AFAIK even recent examples are little better.
    The instrument is considered to be is '"sacred" by players and must not be changed.


    ....... Phil

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Ricky@21:1/5 to Tauno Voipio on Fri Apr 8 15:54:17 2022
    On Friday, April 8, 2022 at 7:47:21 AM UTC-4, Tauno Voipio wrote:
    On 8.4.22 5.18, Ricky wrote:
    On Thursday, April 7, 2022 at 9:31:47 PM UTC-4, Ricky wrote:
    On Thursday, April 7, 2022 at 1:29:01 PM UTC-4, Tauno Voipio wrote:
    On 7.4.22 2.52, Phil Allison wrote:
    Ricky wrote:
    ==========

    An adequately narrow band reject filter would have virtually no impact on the signal of interest.

    ** Shame you have never looked at the phase and amplitude curve of such a filter.


    It only need be wide enough to accommodate the normal variations in mains frequency.

    ** About 0.1Hz is all the AC supply varies by.


    ...... Phil
    Right!

    A narrow notch rings as badly as a narrow peak when fed with
    a spiky signal.
    At what frequency does it ring?

    The reason I ask, is because if the ringing is high enough frequency, it is out of band and can be filtered out. I'm willing to bet there is an inverse relationship between the half bandwidth of the notch and the ringing frequency. If it is narrow
    enough (which is what is desired) it will produce ringing that is far out of band and easily filtered. I believe I read the ECG bandwidth is 150 Hz. I expect it would not be too hard to push the ringing frequency up to a range that is easily filtered.

    On doing a bit of research on the matter, it seems to be a much discussed topic, but with no definitive solution. However, here is a paper that seems to say the solution is really in the way the electrodes are attached.

    https://www.aami.org/docs/default-source/bi-t/bit/2012-bit-nd-ecg.pdf

    So, you're approaching the beef now.

    The kilo-ohm impedances of electrodes are there *after* cleaning
    the skin and removing the dear chest hair. There was also electrode
    paste between the siver plate of the electorode and the skin.

    You did not respond to my question about a reference electrode.

    That should be addressed to the OP. It's not my setup.

    I've already mentioned that current practice either uses a single reference electrode, or combines the signals from all electrodes to use as a common reference for all electrodes. This gives N signals for N leads rather than N-1 signals.

    What are you looking for with the question?

    When you mention kilo-ohm impedances, that is low relative to the amplifier input. It's also low enough for stray coupling to only produce a relatively low voltage in the signal. That is what the OP is seeing, a low voltage "hum" on his signal. It
    actually would not take much filtering to make that noise virtually invisible.

    You didn't answer my question about the frequency of the notch filter ringing.

    I believe the required characteristics of the notch filter in this application would not produce noticeable ringing.

    --

    Rick C.

    +-+ Get 1,000 miles of free Supercharging
    +-+ Tesla referral code - https://ts.la/richard11209

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Cursitor Doom@21:1/5 to gnuarm.deletethisbit@gmail.com on Sat Apr 9 00:56:45 2022
    On Thu, 7 Apr 2022 19:23:40 -0700 (PDT), Ricky
    <gnuarm.deletethisbit@gmail.com> wrote:

    On Thursday, April 7, 2022 at 10:01:41 PM UTC-4, palli...@gmail.com wrote:
    Ricky wrote:
    ===============
    Tauno Voipio wrote:
    Phil Allison wrote:


    An adequately narrow band reject filter would have virtually no impact on the signal of interest.

    ** Shame you have never looked at the phase and amplitude curve of such a filter.

    Right!

    A narrow notch rings as badly as a narrow peak when fed with
    a spiky signal.

    At what frequency does it ring?
    ** Ringing (as seen on a scope) is at the same frequency as the notch minimum.
    But you will not find it in a spectrum analysis.

    Let's construct a mind experiment to analyze that idea. If you stimulate a notch filter with an impulse, a signal containing all frequencies in equal amplitude, what will emerge from the notch filter is a ring at the frequency at which the filter is
    supposed to have a null?

    Is that logically consistent with the frequency response of the filter?

    Might I suggest a variation of Jan's idea?

    1. Digitize the waveform
    2. Feed a 50Hz signal of equal amplitude into a mixer together with
    the digitized waveform.
    3. Adjust the phase of the 50Hz signal until the interference is
    cancelled out.

    I believe this method will have the least detrimental effect on the
    desired trace.
    In fact it might be possible to use an app like Audacity to do all the
    above with just a few mouse clicks, as I'm pretty sure there's a spot
    frequency filter somewhere in the software.

    --- SoupGate-Win32 v1.05
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  • From Phil Allison@21:1/5 to Cursitor Dope on Fri Apr 8 17:29:50 2022
    Cursitor Dope wrote:

    ====================


    1. Digitize the waveform
    2. Feed a 50Hz signal of equal amplitude into a mixer together with
    the digitized waveform.
    3. Adjust the phase of the 50Hz signal until the interference is
    cancelled out.

    ** Huh ???

    Makes no sense at all.

    In fact it might be possible to use an app like Audacity to do all the
    above with just a few mouse clicks, as I'm pretty sure there's a spot frequency filter somewhere in the software.

    ** FYI Mr Dope

    The AC mains wave drifts in frequency and phase and changes amplitude in the ECG trace with a host of external factors.



    ....... Phil

    --- SoupGate-Win32 v1.05
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  • From Ricky@21:1/5 to Cursitor Doom on Fri Apr 8 18:38:17 2022
    On Friday, April 8, 2022 at 7:56:53 PM UTC-4, Cursitor Doom wrote:
    On Thu, 7 Apr 2022 19:23:40 -0700 (PDT), Ricky
    <gnuarm.del...@gmail.com> wrote:

    On Thursday, April 7, 2022 at 10:01:41 PM UTC-4, palli...@gmail.com wrote: >> Ricky wrote:
    ===============
    Tauno Voipio wrote:
    Phil Allison wrote:


    An adequately narrow band reject filter would have virtually no impact on the signal of interest.

    ** Shame you have never looked at the phase and amplitude curve of such a filter.

    Right!

    A narrow notch rings as badly as a narrow peak when fed with
    a spiky signal.

    At what frequency does it ring?
    ** Ringing (as seen on a scope) is at the same frequency as the notch minimum.
    But you will not find it in a spectrum analysis.

    Let's construct a mind experiment to analyze that idea. If you stimulate a notch filter with an impulse, a signal containing all frequencies in equal amplitude, what will emerge from the notch filter is a ring at the frequency at which the filter is
    supposed to have a null?

    Is that logically consistent with the frequency response of the filter? Might I suggest a variation of Jan's idea?

    1. Digitize the waveform
    2. Feed a 50Hz signal of equal amplitude into a mixer together with
    the digitized waveform.
    3. Adjust the phase of the 50Hz signal until the interference is
    cancelled out.

    I believe this method will have the least detrimental effect on the
    desired trace.
    In fact it might be possible to use an app like Audacity to do all the
    above with just a few mouse clicks, as I'm pretty sure there's a spot frequency filter somewhere in the software.

    Sure, that will work for an amateur setup like what is discussed here... as long as nothing moves during the recording. That will only work for a stationary signal.

    --

    Rick C.

    ++- Get 1,000 miles of free Supercharging
    ++- Tesla referral code - https://ts.la/richard11209

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Joe Gwinn@21:1/5 to pallison49@gmail.com on Sat Apr 9 18:48:15 2022
    On Fri, 8 Apr 2022 16:14:36 -0700 (PDT), Phil Allison
    <pallison49@gmail.com> wrote:

    Joe Gwinn wrote:
    ==============

    Think is is just simple capacitive coupled injection of the AC supply voltage wave.
    The bane of many poorly shielded electric guitars .

    ...... Phil


    The remedy for capacitive injection was to electro statically shield
    the routed cavity, originally by carefully fitted brass foil shielding
    tubs, then (after I arrived) by nickel-dust based shield paint sprayed
    thickly on the walls of the cavity. The DC resistance between any two
    points on the cavity wall was about 20 ohms. The underside of the
    pick guard had an aluminum foil layer glued on. These shields were
    all grounded to the shield of the coax wire from guitar to amp. The
    strings were also grounded.

    The remedy for magnetic interference, chiefly at power frequencies and
    harmonics, is various kinds of humbucking construction.


    ** All these things were well known and adopted by makers like Gibson in the 1950s.
    But they were a luxury brand sold to professionals.
    A radio repair man called Leo Fender began making similar things, very cheaply.
    https://en.wikipedia.org/wiki/Leo_Fender#Early_life

    That's my understanding too.


    Working at a time when triac dimmers were unknown and likewise safety earthing - he gave almost no attention to ES shielding.
    His famous Stratocaster guitar has only a token effort at such and is a first class receiver of hum and buzzing from the AC supply.
    Nearby fluoro lighting drives one crazy.

    <https://insounder.org/under-hood-9-evolution-stratocasters-electronics-wiring>

    Note the use of plastic covered pickups, unshielded wiring and no cavity shielding at all.
    Fender relied on the player earthing themselves via the steel strings to proved any measure of shielding.
    AFAIK even recent examples are little better.

    All true.


    The instrument is considered to be is '"sacred" by players and must not be changed.

    Also true.

    One thing that people do is to put a larger coil in the bottom of the routed-out tub, and use that to humbuck the old-school singlecoil.
    With good ES shielding and grounding of everything, this can help a
    lot. There is a patent on this, but I don't recall the number
    offhand.

    Joe Gwinn

    --- SoupGate-Win32 v1.05
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  • From Phil Allison@21:1/5 to Joe Gwinn on Sat Apr 9 17:46:30 2022
    Joe Gwinn wrote:
    ===============

    Think is is just simple capacitive coupled injection of the AC supply voltage wave.
    The bane of many poorly shielded electric guitars .



    The remedy for capacitive injection was to electro statically shield
    the routed cavity, originally by carefully fitted brass foil shielding
    tubs, then (after I arrived) by nickel-dust based shield paint sprayed
    thickly on the walls of the cavity. The DC resistance between any two
    points on the cavity wall was about 20 ohms. The underside of the
    pick guard had an aluminum foil layer glued on. These shields were
    all grounded to the shield of the coax wire from guitar to amp. The
    strings were also grounded.

    The remedy for magnetic interference, chiefly at power frequencies and
    harmonics, is various kinds of humbucking construction.


    ** All these things were well known and adopted by makers like Gibson in the 1950s.
    But they were a luxury brand sold to professionals.
    A radio repair man called Leo Fender began making similar things, very cheaply.
    https://en.wikipedia.org/wiki/Leo_Fender#Early_life
    That's my understanding too.
    Working at a time when triac dimmers were unknown and likewise safety earthing - he gave almost no attention to ES shielding.
    His famous Stratocaster guitar has only a token effort at such and is a first class receiver of hum and buzzing from the AC supply.
    Nearby fluoro lighting drives one crazy.

    <https://insounder.org/under-hood-9-evolution-stratocasters-electronics-wiring>

    Note the use of plastic covered pickups, unshielded wiring and no cavity shielding at all.
    Fender relied on the player earthing themselves via the steel strings to proved any measure of shielding.
    AFAIK even recent examples are little better.
    All true.
    The instrument is considered to be is '"sacred" by players and must not be changed.
    Also true.

    One thing that people do is to put a larger coil in the bottom of the routed-out tub, and use that to humbuck the old-school singlecoil.
    With good ES shielding and grounding of everything, this can help a
    lot. There is a patent on this, but I don't recall the number
    offhand.


    ** There is no huge problem with players standing a few metres away from any AC transformers in the vicinity.
    The mag field from an AC transformer is purely short range.
    The need for humbucking PUs arose from those who sit next to or even on top of their amps.

    As it happens, nearly all humbucking PUs have full ES shielding too, so are dead quiet.


    ....... Phil

    --- SoupGate-Win32 v1.05
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  • From John Doe@21:1/5 to Phil Allison on Sun Apr 10 05:28:39 2022
    XPost: free.spam

    Foulmouthed Australian troll...

    --
    Phil Allison <pallison49@gmail.com> wrote:

    X-Received: by 2002:a05:622a:285:b0:2e1:dcda:98fd with SMTP id z5-20020a05622a028500b002e1dcda98fdmr5040036qtw.625.1649195315287; Tue, 05 Apr 2022 14:48:35 -0700 (PDT)
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    Newsgroups: sci.electronics.design
    Date: Tue, 5 Apr 2022 14:48:34 -0700 (PDT)
    In-Reply-To: <11aa16e2-b06b-4256-abe5-da0de50e9c5bn@googlegroups.com> Injection-Info: google-groups.googlegroups.com; posting-host=27.33.69.193; posting-account=B_tJMAoAAAAmar-1r2H3x4CMhbFEou3n
    NNTP-Posting-Host: 27.33.69.193
    References: <o70p4h94qqbdftsoe1el8suv1gmklc9np2@4ax.com> <11aa16e2-b06b-4256-abe5-da0de50e9c5bn@googlegroups.com>
    User-Agent: G2/1.0
    MIME-Version: 1.0
    Message-ID: <cbab2f4d-9771-481b-8577-a2badf6dfa02n@googlegroups.com>
    Subject: Re: Mains hum
    From: Phil Allison <pallison49@gmail.com>
    Injection-Date: Tue, 05 Apr 2022 21:48:35 +0000
    Content-Type: text/plain; charset="UTF-8"
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    Xref: reader02.eternal-september.org sci.electronics.design:665184

    Ricky the IDIOT puked:

    =====================

    I see the signal, it is clearly not sinusoidal.

    ** That is the fucking heart beat you moron !!!
    The 50/60 Hz hum is the superimposed fine wiggling.

    Rest of this retarded wanker's absurd drivel snipped.


    .... Phil



    --- SoupGate-Win32 v1.05
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  • From Edward Hernandez@21:1/5 to All on Sun Apr 10 06:15:37 2022
    XPost: free.spam

    The John Doe troll stated the following in message-id <sdhn7c$pkp$4@dont-email.me>:

    The troll doesn't even know how to format a USENET post...

    And the John Doe troll stated the following in message-id <sg3kr7$qt5$1@dont-email.me>:

    The reason Bozo cannot figure out how to get Google to keep from
    breaking its lines in inappropriate places is because Bozo is
    CLUELESS...

    And yet, the clueless John Doe troll has continued to post incorrectly formatted USENET articles that are devoid of content (latest example on
    Sun, 10 Apr 2022 05:28:39 -0000 (UTC) in message-id <t2tpu6$d1p$1@dont-email.me>).

    NOBODY likes the John Doe troll's contentless spam.

    Further, John Doe stated the following in message-id <svsh05$lbh$5@dont-email.me> posted Fri, 4 Mar 2022 08:01:09 -0000
    (UTC):

    Compared to other regulars, Bozo contributes practically nothing
    except insults to this group.

    Yet, since Wed, 5 Jan 2022 04:10:38 -0000 (UTC) John Doe's post ratio to
    USENET has been 56.7% of its posts contributing "nothing except insults"
    to USENET.

    This posting is a public service announcement for any google groups
    readers who happen by to point out that the John Doe troll does not even
    follow the rules it uses to troll other posters.

    rUSc9rxOsuD0

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Cursitor Doom@21:1/5 to dtgamer99@gmail.com on Sun Apr 10 17:50:14 2022
    XPost: free.spam

    On Sun, 10 Apr 2022 06:15:37 GMT, Edward Hernandez
    <dtgamer99@gmail.com> wrote:

    The John Doe troll stated the following in message-id ><sdhn7c$pkp$4@dont-email.me>:

    The troll doesn't even know how to format a USENET post...

    And the John Doe troll stated the following in message-id ><sg3kr7$qt5$1@dont-email.me>:

    The reason Bozo cannot figure out how to get Google to keep from
    breaking its lines in inappropriate places is because Bozo is
    CLUELESS...

    And yet, the clueless John Doe troll has continued to post incorrectly >formatted USENET articles that are devoid of content (latest example on
    Sun, 10 Apr 2022 05:28:39 -0000 (UTC) in message-id ><t2tpu6$d1p$1@dont-email.me>).

    NOBODY likes the John Doe troll's contentless spam.

    You don't speak for everyone here. I personally find JD's posts very
    relevant, thought-provoking and entertaining. Keep it up, JD!

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Ricky@21:1/5 to Cursitor Doom on Sun Apr 10 10:08:14 2022
    On Sunday, April 10, 2022 at 12:50:21 PM UTC-4, Cursitor Doom wrote:
    On Sun, 10 Apr 2022 06:15:37 GMT, Edward Hernandez
    <dtga...@gmail.com> wrote:

    The John Doe troll stated the following in message-id ><sdhn7c$pkp$4...@dont-email.me>:

    The troll doesn't even know how to format a USENET post...

    And the John Doe troll stated the following in message-id ><sg3kr7$qt5$1...@dont-email.me>:

    The reason Bozo cannot figure out how to get Google to keep from
    breaking its lines in inappropriate places is because Bozo is
    CLUELESS...

    And yet, the clueless John Doe troll has continued to post incorrectly >formatted USENET articles that are devoid of content (latest example on >Sun, 10 Apr 2022 05:28:39 -0000 (UTC) in message-id ><t2tpu6$d1p$1...@dont-email.me>).

    NOBODY likes the John Doe troll's contentless spam.
    You don't speak for everyone here. I personally find JD's posts very relevant, thought-provoking and entertaining. Keep it up, JD!

    You are confused. JD seems to have a predilection for posting metric tonnes of BS between the very few relevant posts. Edward is talking about the spam posts. That's why he wrote "contentless spam" in place of "thought-provoking".

    --

    Rick C.

    +++ Get 1,000 miles of free Supercharging
    +++ Tesla referral code - https://ts.la/richard11209

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Edward Hernandez@21:1/5 to All on Sun Apr 10 17:27:50 2022
    XPost: free.spam

    The John Doe troll stated the following in message-id <sdhn7c$pkp$4@dont-email.me>:

    The troll doesn't even know how to format a USENET post...

    And the John Doe troll stated the following in message-id <sg3kr7$qt5$1@dont-email.me>:

    The reason Bozo cannot figure out how to get Google to keep from
    breaking its lines in inappropriate places is because Bozo is
    CLUELESS...

    And yet, the clueless John Doe troll has continued to post incorrectly formatted USENET articles that are devoid of content (latest example on
    Sun, 10 Apr 2022 17:21:07 -0000 (UTC) in message-id <t2v3m3$b45$5@dont-email.me>).

    NOBODY likes the John Doe troll's contentless spam.

    Further, Troll Doe stated the following in message-id <svsh05$lbh$5@dont-email.me> posted Fri, 4 Mar 2022 08:01:09 -0000
    (UTC):

    Compared to other regulars, Bozo contributes practically nothing
    except insults to this group.

    Yet, since Wed, 5 Jan 2022 04:10:38 -0000 (UTC) Troll Doe's post ratio
    to USENET has been 56.7% of its posts contributing "nothing except
    insults" to USENET.

    This posting is a public service announcement for any google groups
    readers who happen by to point out that the John Doe troll does not even
    follow the rules it uses to troll other posters.

    4n1YqFVLKYL6

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From John Doe@21:1/5 to Ricky on Sun Apr 10 17:21:07 2022
    XPost: free.spam

    Ricksy is confused.

    Eddie's "contentless spam" came from one of my posts.

    Eddie has never contributed anything to USENET, except when he got spanked
    in the electronics repair group.

    https://groups.google.com/g/sci.electronics.repair/c/MesPLcGU4BE

    Hurt Eddie is taking that out on USENET.

    Ricksy loves a troublemaker...


    --
    Ricky <gnuarm.deletethisbit@gmail.com> wrote:

    X-Received: by 2002:a37:5e42:0:b0:69a:eac:d843 with SMTP id s63-20020a375e42000000b0069a0eacd843mr10775283qkb.526.1649610495059; Sun, 10 Apr 2022 10:08:15 -0700 (PDT)
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    Newsgroups: sci.electronics.design
    Date: Sun, 10 Apr 2022 10:08:14 -0700 (PDT)
    In-Reply-To: <uj265hlj286n11b727tdell3tm25loipm3@4ax.com>
    Injection-Info: google-groups.googlegroups.com; posting-host=65.207.89.54; posting-account=I-_H_woAAAA9zzro6crtEpUAyIvzd19b
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    References: <o70p4h94qqbdftsoe1el8suv1gmklc9np2@4ax.com> <11aa16e2-b06b-4256-abe5-da0de50e9c5bn@googlegroups.com> <cbab2f4d-9771-481b-8577-a2badf6dfa02n@googlegroups.com> <t2tpu6$d1p$1@dont-email.me> <dCu4K.172050$I_K3.30356@usenetxs.com> <
    uj265hlj286n11b727tdell3tm25loipm3@4ax.com>
    User-Agent: G2/1.0
    MIME-Version: 1.0
    Message-ID: <fec8505d-b73b-4d5c-8b6f-7e9efc50148cn@googlegroups.com>
    Subject: Re: Mains hum
    From: Ricky <gnuarm.deletethisbit@gmail.com>
    Injection-Date: Sun, 10 Apr 2022 17:08:15 +0000
    Content-Type: text/plain; charset="UTF-8"
    Lines: 32
    Xref: reader02.eternal-september.org sci.electronics.design:665733

    On Sunday, April 10, 2022 at 12:50:21 PM UTC-4, Cursitor Doom wrote:
    On Sun, 10 Apr 2022 06:15:37 GMT, Edward Hernandez
    <dtga...@gmail.com> wrote:

    The John Doe troll stated the following in message-id
    <sdhn7c$pkp$4...@dont-email.me>:

    The troll doesn't even know how to format a USENET post...

    And the John Doe troll stated the following in message-id
    <sg3kr7$qt5$1...@dont-email.me>:

    The reason Bozo cannot figure out how to get Google to keep from
    breaking its lines in inappropriate places is because Bozo is
    CLUELESS...

    And yet, the clueless John Doe troll has continued to post incorrectly
    formatted USENET articles that are devoid of content (latest example on
    Sun, 10 Apr 2022 05:28:39 -0000 (UTC) in message-id
    <t2tpu6$d1p$1...@dont-email.me>).

    NOBODY likes the John Doe troll's contentless spam.
    You don't speak for everyone here. I personally find JD's posts very
    relevant, thought-provoking and entertaining. Keep it up, JD!

    You are confused. JD seems to have a predilection for posting metric tonnes of BS between the very few relevant posts. Edward is talking about the spam posts. That's why he wrote "contentless spam" in place of "thought-provoking".

    --

    Rick C.

    +++ Get 1,000 miles of free Supercharging
    +++ Tesla referral code - https://ts.la/richard11209



    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Jeroen Belleman@21:1/5 to Ricky on Sun Apr 10 19:37:39 2022
    On 2022-04-10 19:08, Ricky wrote:
    On Sunday, April 10, 2022 at 12:50:21 PM UTC-4, Cursitor Doom wrote:
    On Sun, 10 Apr 2022 06:15:37 GMT, Edward Hernandez
    <dtga...@gmail.com> wrote:

    The John Doe troll stated the following in message-id
    <sdhn7c$pkp$4...@dont-email.me>:

    The troll doesn't even know how to format a USENET post...

    And the John Doe troll stated the following in message-id
    <sg3kr7$qt5$1...@dont-email.me>:

    The reason Bozo cannot figure out how to get Google to keep from
    breaking its lines in inappropriate places is because Bozo is
    CLUELESS...

    And yet, the clueless John Doe troll has continued to post incorrectly
    formatted USENET articles that are devoid of content (latest example on
    Sun, 10 Apr 2022 05:28:39 -0000 (UTC) in message-id
    <t2tpu6$d1p$1...@dont-email.me>).

    NOBODY likes the John Doe troll's contentless spam.
    You don't speak for everyone here. I personally find JD's posts very
    relevant, thought-provoking and entertaining. Keep it up, JD!

    You are confused. JD seems to have a predilection for posting metric tonnes of BS between the very few relevant posts. Edward is talking about the spam posts. That's why he wrote "contentless spam" in place of "thought-provoking".


    Do me, and everyone else, a pleasure and killfile him.

    Jeroen Belleman

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From John Doe@21:1/5 to Edward Hernandez on Sun Apr 10 17:54:27 2022
    XPost: free.spam

    Poor liddle Eddie got spanked and just can't get over it.

    Unless Eddie is nym-shifting, it has never posted anything NORMAL
    except when it got a severe spanking...

    https://groups.google.com/g/sci.electronics.repair/c/MesPLcGU4BE

    Is the stalker a nym-shifting troll, or a newbie netcop wannabe?

    See also...
    Peter Weiner <dtgamer99@gmail.com>
    Edward H. <dtgamer99@gmail.com>
    Edward Hernandez <dtgamer99@gmail.com>

    Eddie is an example for all newbies. Don't get spanked!

    Spanked Eddie...

    --
    Edward Hernandez <dtgamer99@gmail.com> wrote:

    Path: eternal-september.org!reader02.eternal-september.org!2.eu.feeder.erje.net!feeder.erje.net!feeder1.feed.usenet.farm!feed.usenet.farm!news-out.netnews.com!news.alt.net!fdc2.netnews.com!peer02.ams1!peer.ams1.xlned.com!news.xlned.com!peer01.ams4!peer.
    am4.highwinds-media.com!news.highwinds-media.com!fx01.ams4.POSTED!not-for-mail
    From: Edward Hernandez <dtgamer99@gmail.com>
    Subject: Re: Mains hum
    Newsgroups: sci.electronics.design,free.spam
    References: <o70p4h94qqbdftsoe1el8suv1gmklc9np2@4ax.com> <11aa16e2-b06b-4256-abe5-da0de50e9c5bn@googlegroups.com> <cbab2f4d-9771-481b-8577-a2badf6dfa02n@googlegroups.com> <t2tpu6$d1p$1@dont-email.me> <dCu4K.172050$I_K3.30356@usenetxs.com> <
    uj265hlj286n11b727tdell3tm25loipm3@4ax.com> <fec8505d-b73b-4d5c-8b6f-7e9efc50148cn@googlegroups.com> <t2v3m3$b45$5@dont-email.me>
    Lines: 36
    Message-ID: <qsE4K.1472441$8b1.1220420@usenetxs.com>
    X-Complaints-To: https://www.astraweb.com/aup
    NNTP-Posting-Date: Sun, 10 Apr 2022 17:27:50 UTC
    Date: Sun, 10 Apr 2022 17:27:50 GMT
    X-Received-Bytes: 2122
    Xref: reader02.eternal-september.org sci.electronics.design:665738 free.spam:17909

    The John Doe troll stated the following in message-id <sdhn7c$pkp$4@dont-email.me>:

    The troll doesn't even know how to format a USENET post...

    And the John Doe troll stated the following in message-id <sg3kr7$qt5$1@dont-email.me>:

    The reason Bozo cannot figure out how to get Google to keep from
    breaking its lines in inappropriate places is because Bozo is
    CLUELESS...

    And yet, the clueless John Doe troll has continued to post incorrectly formatted USENET articles that are devoid of content (latest example on
    Sun, 10 Apr 2022 17:21:07 -0000 (UTC) in message-id <t2v3m3$b45$5@dont-email.me>).

    NOBODY likes the John Doe troll's contentless spam.

    Further, Troll Doe stated the following in message-id <svsh05$lbh$5@dont-email.me> posted Fri, 4 Mar 2022 08:01:09 -0000
    (UTC):

    Compared to other regulars, Bozo contributes practically nothing
    except insults to this group.

    Yet, since Wed, 5 Jan 2022 04:10:38 -0000 (UTC) Troll Doe's post ratio
    to USENET has been 56.7% of its posts contributing "nothing except
    insults" to USENET.

    This posting is a public service announcement for any google groups
    readers who happen by to point out that the John Doe troll does not even follow the rules it uses to troll other posters.

    4n1YqFVLKYL6



    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From John Doe@21:1/5 to Jeroen Belleman on Sun Apr 10 17:49:28 2022
    Here we go again...

    Someone who loves to talk about their imaginary kill file friend.
    It is not technically capable enough to ignore a THREAD BRANCH, so it whines when others reply to an (allegedly) kill-filed poster.

    Stop whining, nobody is responsible for you...


    Jeroen Belleman <jeroen@nospam.please> wrote:

    On 2022-04-10 19:08, Ricky wrote:
    On Sunday, April 10, 2022 at 12:50:21 PM UTC-4, Cursitor Doom wrote:
    On Sun, 10 Apr 2022 06:15:37 GMT, Edward Hernandez
    <dtga...@gmail.com> wrote:

    The John Doe troll stated the following in message-id
    <sdhn7c$pkp$4...@dont-email.me>:

    The troll doesn't even know how to format a USENET post...

    And the John Doe troll stated the following in message-id
    <sg3kr7$qt5$1...@dont-email.me>:

    The reason Bozo cannot figure out how to get Google to keep from
    breaking its lines in inappropriate places is because Bozo is
    CLUELESS...

    And yet, the clueless John Doe troll has continued to post incorrectly >>>> formatted USENET articles that are devoid of content (latest example on >>>> Sun, 10 Apr 2022 05:28:39 -0000 (UTC) in message-id
    <t2tpu6$d1p$1...@dont-email.me>).

    NOBODY likes the John Doe troll's contentless spam.
    You don't speak for everyone here. I personally find JD's posts very
    relevant, thought-provoking and entertaining. Keep it up, JD!

    You are confused. JD seems to have a predilection for posting metric
    tonnes of BS between the very few relevant posts. Edward is talking about
    the spam posts. That's why he wrote "contentless spam" in place of "thought- provoking".


    Do me, and everyone else, a pleasure and killfile him.

    Jeroen Belleman


    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Edward Hernandez@21:1/5 to All on Sun Apr 10 18:06:17 2022
    XPost: free.spam

    The John Doe troll stated the following in message-id <sdhn7c$pkp$4@dont-email.me>:

    The troll doesn't even know how to format a USENET post...

    And the John Doe troll stated the following in message-id <sg3kr7$qt5$1@dont-email.me>:

    The reason Bozo cannot figure out how to get Google to keep from
    breaking its lines in inappropriate places is because Bozo is
    CLUELESS...

    And yet, the clueless John Doe troll has continued to post incorrectly formatted USENET articles that are devoid of content (latest example on
    Sun, 10 Apr 2022 17:54:27 -0000 (UTC) in message-id <t2v5kj$3av$2@dont-email.me>).

    NOBODY likes the John Doe troll's contentless spam.

    Further, John Doe stated the following in message-id <svsh05$lbh$5@dont-email.me> posted Fri, 4 Mar 2022 08:01:09 -0000
    (UTC):

    Compared to other regulars, Bozo contributes practically nothing
    except insults to this group.

    Yet, since Wed, 5 Jan 2022 04:10:38 -0000 (UTC) John Doe's post ratio to
    USENET has been 56.8% of its posts contributing "nothing except insults"
    to USENET.

    This posting is a public service announcement for any google groups
    readers who happen by to point out that the John Doe troll does not even
    follow the rules it uses to troll other posters.

    jGjlGZ4zmCCO

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From John Doe@21:1/5 to All on Sun Apr 10 19:40:57 2022
    Single key ignore sub-thread is the most valuable USENET filter, by far.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Joe Gwinn@21:1/5 to pallison49@gmail.com on Sun Apr 10 16:52:47 2022
    On Sat, 9 Apr 2022 17:46:30 -0700 (PDT), Phil Allison
    <pallison49@gmail.com> wrote:

    Joe Gwinn wrote:
    ===============

    Think is is just simple capacitive coupled injection of the AC supply voltage wave.
    The bane of many poorly shielded electric guitars .



    The remedy for capacitive injection was to electro statically shield
    the routed cavity, originally by carefully fitted brass foil shielding
    tubs, then (after I arrived) by nickel-dust based shield paint sprayed
    thickly on the walls of the cavity. The DC resistance between any two
    points on the cavity wall was about 20 ohms. The underside of the
    pick guard had an aluminum foil layer glued on. These shields were
    all grounded to the shield of the coax wire from guitar to amp. The
    strings were also grounded.

    The remedy for magnetic interference, chiefly at power frequencies and
    harmonics, is various kinds of humbucking construction.


    ** All these things were well known and adopted by makers like Gibson in the 1950s.
    But they were a luxury brand sold to professionals.
    A radio repair man called Leo Fender began making similar things, very cheaply.
    https://en.wikipedia.org/wiki/Leo_Fender#Early_life
    That's my understanding too.
    Working at a time when triac dimmers were unknown and likewise safety earthing - he gave almost no attention to ES shielding.
    His famous Stratocaster guitar has only a token effort at such and is a first class receiver of hum and buzzing from the AC supply.
    Nearby fluoro lighting drives one crazy.

    <https://insounder.org/under-hood-9-evolution-stratocasters-electronics-wiring>

    Note the use of plastic covered pickups, unshielded wiring and no cavity shielding at all.
    Fender relied on the player earthing themselves via the steel strings to proved any measure of shielding.
    AFAIK even recent examples are little better.
    All true.
    The instrument is considered to be is '"sacred" by players and must not be changed.
    Also true.

    One thing that people do is to put a larger coil in the bottom of the
    routed-out tub, and use that to humbuck the old-school singlecoil.
    With good ES shielding and grounding of everything, this can help a
    lot. There is a patent on this, but I don't recall the number
    offhand.


    ** There is no huge problem with players standing a few metres away from any AC transformers in the vicinity.
    The mag field from an AC transformer is purely short range.
    The need for humbucking PUs arose from those who sit next to or even on top of their amps.

    Not so fast. A classic source of widespread hum fields is wiring
    errors or failures in the power wiring of the venue.

    In the US, ring busses are not allowed, so out and back currents are
    close to one another, and their magnetic fields largely cancel. Unless
    someone reversed power neutral (white wire in the US) and safety
    ground (green wire). Which I have personally encountered.

    War story: I've also encountered broken neutrals in 240 Vac
    split-phase (+120 - 0 - +120) power cables. I was attending a summer
    stock play (where my kid sister was acting) held outside on the
    grounds of a local school, as the light of day faded, I was looking
    idly at the stage lighting, and noticed that some lights wee too blue
    and other were too yellow. These lights are incandescent. Hmm. After
    the play, I approached the Director and asked him if he was having
    problems with things blowing out. Stunned look ... how did you
    know??? Told him of the too blue and too yellow lights, and that this
    implied a broken neutral. He was very interested. So we went along
    the main feed cable, opening Edison connectors. We quickly found one
    with the neutral completely un-connected. Director was *very* happy -
    he would have had to pay for all those brand dearly-departed new
    electronic dimmers. But it was the rental company's fault.

    As for ring busses, which are allowed in Europe and I assume
    Australia, while if both rings are intact, magnetic fields will
    generally cancel, all it takes is a single ring break to force
    significant currents to take the long way around.


    As it happens, nearly all humbucking PUs have full ES shielding too, so are dead quiet.

    Yes, that's true these days.


    I did find the patent I mentioned above. It's US 7,259,318 to Illich Chiliachki of California. The patent is now expired because later
    maintenance fees were not paid.


    Joe Gwinn

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Allison@21:1/5 to Joe Gwinn on Sun Apr 10 14:23:56 2022
    Joe Gwinn wrote:
    ================

    ** There is no huge problem with players standing a few metres away from any AC transformers in the vicinity.
    The mag field from an AC transformer is purely short range.
    The need for humbucking PUs arose from those who sit next to or even on top of their amps.

    Not so fast. A classic source of widespread hum fields is wiring
    errors or failures in the power wiring of the venue.

    ** So you say.


    In the US, ring busses are not allowed,

    ** Nor here - only in the UK AFAIK.

    Such a buss feed a loop of AC outlets ( active and neutral) from both ends.

    As it happens, nearly all humbucking PUs have full ES shielding too, so are dead quiet.

    Yes, that's true these days.

    ** Been true since the 1950s.

    All the popular humbuckers ( Gibson, Fender and Asian clones) are metal cased.


    ...... Phil

    --- SoupGate-Win32 v1.05
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  • From Joe Gwinn@21:1/5 to pallison49@gmail.com on Sun Apr 10 18:39:31 2022
    On Sun, 10 Apr 2022 14:23:56 -0700 (PDT), Phil Allison
    <pallison49@gmail.com> wrote:

    Joe Gwinn wrote:
    ================

    ** There is no huge problem with players standing a few metres away from any AC transformers in the vicinity.
    The mag field from an AC transformer is purely short range.
    The need for humbucking PUs arose from those who sit next to or even on top of their amps.

    Not so fast. A classic source of widespread hum fields is wiring
    errors or failures in the power wiring of the venue.

    ** So you say.


    In the US, ring busses are not allowed,

    ** Nor here - only in the UK AFAIK.

    Such a buss feed a loop of AC outlets ( active and neutral) from both ends.

    Yes, unless there is a break somewhere. With luck, all the outlets
    will still work just fine, and nobody will be any the wiser. But the
    current will travel in a room-size or building-size loop, generating a pervasive magnetic field.


    As it happens, nearly all humbucking PUs have full ES shielding too, so are dead quiet.

    Yes, that's true these days.

    ** Been true since the 1950s.

    I did run into lots of exceptions.


    All the popular humbuckers ( Gibson, Fender and Asian clones) are metal cased.

    Yes. I don't know when the transition happened, but it had to be
    gradual.

    Joe Gwinn

    --- SoupGate-Win32 v1.05
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  • From DecadentLinuxUserNumeroUno@decadenc@21:1/5 to Joe Gwinn on Sun Apr 10 23:27:33 2022
    Joe Gwinn <joegwinn@comcast.net> wrote in news:qnf65htct3oq80qj2klema4nkemv962puo@4ax.com:

    In the US, ring busses are not allowed, so out and back currents
    are close to one another, and their magnetic fields largely
    cancel. Unless someone reversed power neutral (white wire in the
    US) and safety ground (green wire). Which I have personally
    encountered.


    I worked in a lab once where the PnP machine and the reflow oven
    benches were 90V to Earth ground. No hard current capacity that I
    could see, but still... They were clueless about ESD much less the introduction of stray line voltages. And it made for a very unpleasant
    tickle when one touched the wrong elements of the work area. I left
    that job pretty quickly. I do not like to work for idiots.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From DecadentLinuxUserNumeroUno@decadenc@21:1/5 to Phil Allison on Sun Apr 10 23:30:53 2022
    Phil Allison <pallison49@gmail.com> wrote in news:ba4a605d-3844-4304-9f09-609fce1679e3n@googlegroups.com:

    Joe Gwinn wrote:
    ================

    ** There is no huge problem with players standing a few metres
    away from any AC transformers in the vicinity.
    The mag field from an AC transformer is purely short range.
    The need for humbucking PUs arose from those who sit next to or
    even on top of their amps.

    Not so fast. A classic source of widespread hum fields is wiring
    errors or failures in the power wiring of the venue.

    ** So you say.


    In the US, ring busses are not allowed,

    ** Nor here - only in the UK AFAIK.

    Such a buss feed a loop of AC outlets ( active and neutral) from
    both ends.

    As it happens, nearly all humbucking PUs have full ES shielding
    too, so are dead quiet.

    Yes, that's true these days.

    ** Been true since the 1950s.

    All the popular humbuckers ( Gibson, Fender and Asian clones) are
    metal cased.


    Grounded metal case, as opposed to an isolated metal case. Can't
    leave that out.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Lasse Langwadt Christensen@21:1/5 to All on Sun Apr 10 16:37:24 2022
    mandag den 11. april 2022 kl. 01.27.40 UTC+2 skrev DecadentLinux...@decadence.org:
    Joe Gwinn <joeg...@comcast.net> wrote in
    news:qnf65htct3oq80qj2...@4ax.com:
    In the US, ring busses are not allowed, so out and back currents
    are close to one another, and their magnetic fields largely
    cancel. Unless someone reversed power neutral (white wire in the
    US) and safety ground (green wire). Which I have personally
    encountered.

    I worked in a lab once where the PnP machine and the reflow oven
    benches were 90V to Earth ground. No hard current capacity that I
    could see, but still... They were clueless about ESD much less the introduction of stray line voltages. And it made for a very unpleasant
    tickle when one touched the wrong elements of the work area. I left
    that job pretty quickly. I do not like to work for idiots.

    likely a missing earth so caps the EMC filters form a capacitive divider
    to what should been earth

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Allison@21:1/5 to Joe Gwinn on Sun Apr 10 17:42:35 2022
    Joe Gwinn wrote:
    ================

    ** There is no huge problem with players standing a few metres away from any AC transformers in the vicinity.
    The mag field from an AC transformer is purely short range.
    The need for humbucking PUs arose from those who sit next to or even on top of their amps.

    Not so fast. A classic source of widespread hum fields is wiring
    errors or failures in the power wiring of the venue.

    ** So you say.


    In the US, ring busses are not allowed,

    ** Nor here - only in the UK AFAIK.

    Such a buss feed a loop of AC outlets ( active and neutral) from both ends.

    Yes, unless there is a break somewhere. With luck, all the outlets
    will still work just fine, and nobody will be any the wiser. But the
    current will travel in a room-size or building-size loop, generating a pervasive magnetic field.

    ** A rare event, only in the UK and the field is weak compared to typical transformers.


    ** Been true since the 1950s.

    I did run into lots of exceptions.

    ** Seems you are accident prone.


    All the popular humbuckers ( Gibson, Fender and Asian clones) are metal cased.

    Yes. I don't know when the transition happened...

    ** What "transition" was that ???



    ..... Phil

    --- SoupGate-Win32 v1.05
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