I have a 23cm G3JVL 47-element loop-Yagi at 24ft AGL. I have not so farone got these figures to hand, please?
been able to find any gain and beamwidth figures for it by searching
online. Has any
TIA.
In message <rrsqm7$d9s$1@dont-email.me>, Andrew Marshall
<news@y-ddraenog-goch.org.uk> writes
I have a 23cm G3JVL 47-element loop-Yagi at 24ft AGL. I have not so far
been able to find any gain and beamwidth figures for it by searching
online. Has any
one got these figures to hand, please?
TIA.
I've a model of a 38 ele loop yagi. Extending it to 47 elements and
running the model gives a gain of 21.56dBi and a 3dB beam width of
between 14 and 16 degrees . The F/B is 24dB.
There's a com
mercial 49 ele here claiming 21.3dbi and 15 deg B/W
http://www.vpa-systems.pl/1296mhz-loop-yagi-49el-213dbi-400cm-p-167.html
work with for now. I'll point it at the 'official' calculator and see
what 'safe distance' is returned. I only wish that it were not so conservative as it is reported to be.
All my other antennas seem to be compliant, except for the 'random' ~130m-long horizontal loop at around 4m AGL running around the garden,
which wouldn't appear to radiate much at a downwards angle of 20 to 30 degrees or so to a person on the ground - according to a model of an 80m full-wave loop in the fairly-recent RSGB 'antennas' book, it pretty much
all goes upwards, which is what I wanted, for 40/80m NVIS working, when
I put it up many years ago.
Many thanks for the modelling and the link.
; (looks) That seems to suggest that 21.5dBi would be a good figure to
work with for now. I'll point it at the 'official' calculator and see
what 'safe distance' is returned. I only wish that it were not so
conservative as it is reported to be.
All my other antennas seem to be compliant, except for the 'random'
~130m-long horizontal loop at around 4m AGL running around the garden,
which wouldn't appear to radiate much at a downwards angle of 20 to 30
degrees or so to a person on the ground - according to a model of an
80m full-wave loop in the fairly-recent RSGB 'antennas' book, it
pretty much all goes upwards, which is what I wanted, for 40/80m NVIS
working, when I put it up many years ago.
Many thanks for the modelling and the link.
For the loop any members of the 'public' are almost certainly going to
be in the near field of the antenna at HF, so it will be the near field
E and H fields that you have to consider for ICNIRP compliance; which at close distances may well be very different from the resultant radiation pattern.
The best way to do that would be to simulate it using a program such as
4NEC2 which will give you those figures (graphically if required).
On 24/12/2020 09:31, Jeff wrote:
(looks) That seems to suggest that 21.5dBi would be a good figure to
work with for now. I'll point it at the 'official' calculator and
see what 'safe distance' is returned. I only wish that it were not
so conservative as it is reported to be.
All my other antennas seem to be compliant, except for the 'random' >>>~130m-long horizontal loop at around 4m AGL running around the
garden, which wouldn't appear to radiate much at a downwards angle
of 20 to 30 degrees or so to a person on the ground - according to a >>>model of an 80m full-wave loop in the fairly-recent RSGB 'antennas' >>>book, it pretty much all goes upwards, which is what I wanted, for >>>40/80m NVIS working, when I put it up many years ago.
Many thanks for the modelling and the link.
For the loop any members of the 'public' are almost certainly going
to be in the near field of the antenna at HF, so it will be the near
field E and H fields that you have to consider for ICNIRP compliance; >>which at close distances may well be very different from the resultant >>radiation pattern.
The best way to do that would be to simulate it using a program such
as 4NEC2 which will give you those figures (graphically if required).
Thank you for that info.
I hadn't seen any mention of near or far fields on the Ofcom calculator >spreadsheet, so I thought that to use it as a compliance demonstrator
would suffice. If that isn't the case, I will have to suspend use of
that antenna until I can find a way of demonstrating compliance in the
near field (unless there is a version of 4NEC2 or other program that
runs under Linux Mint, I will be in some difficulty).
I can only imagine that thousands of HF operators will be in the same
boat as me in this respect.
In message <rs4a5p$rhg$1@dont-email.me>, Andrew Marshall <news@y-ddraenog-goch.org.uk> writes
On 24/12/2020 09:31, Jeff wrote:
> (looks) That seems to suggest that 21.5dBi would be a good figure to >>>> work with for now. I'll point it at the 'official' calculator and
see what 'safe distance' is returned. I only wish that it were not
so conservative as it is reported to be.
All my other antennas seem to be compliant, except for the 'random'
~130m-long horizontal loop at around 4m AGL running around the
garden, which wouldn't appear to radiate much at a downwards angle
of 20 to 30 degrees or so to a person on the ground - according to
a model of an 80m full-wave loop in the fairly-recent RSGB
'antennas' book, it pretty much all goes upwards, which is what I
wanted, for 40/80m NVIS working, when I put it up many years ago.
Many thanks for the modelling and the link.
For the loop any members of the 'public' are almost certainly going
to be in the near field of the antenna at HF, so it will be the near
field E and H fields that you have to consider for ICNIRP
compliance; which at close distances may well be very different from
the resultant radiation pattern.
The best way to do that would be to simulate it using a program such
as 4NEC2 which will give you those figures (graphically if required).
Thank you for that info.
I hadn't seen any mention of near or far fields on the Ofcom
calculator spreadsheet, so I thought that to use it as a compliance
demonstrator would suffice. If that isn't the case, I will have to
suspend use of that antenna until I can find a way of demonstrating
compliance in the near field (unless there is a version of 4NEC2 or
other program that runs under Linux Mint, I will be in some difficulty).
I can only imagine that thousands of HF operators will be in the same
boat as me in this respect.
4NEC2 will run under Wine on Linux Mint.
The Offcom ,model is far-field
only. It is therefore over pessimistic for short distances for HF anyway.
It also includes ground-gain , which is only relevant in the far-field.
I tried comparing it with a hand calculation and the VK3UM model and discovered this fact. The VK3UM model has a ground gain option.
On 25/12/2020 14:07, Brian Howie wrote:
4NEC2 will run under Wine on Linux Mint.
I have a spare laptop running Linux, though I haven't used it for a year
or so. If it still works, I may try downloading and installing Wine and
then 4NEC2 (but see below). I don't want to risk rendering one of my
main Linux boxes unusable because of some installation disaster,
especially as their availability is critically important at the moment
for online food shopping and other important tasks.
On 25/12/2020 14:07, Brian Howie wrote:
In message <rs4a5p$rhg$1@dont-email.me>, Andrew Marshall
<news@y-ddraenog-goch.org.uk> writes
On 24/12/2020 09:31, Jeff wrote:
> (looks) That seems to suggest that 21.5dBi would be a good
> figure to
work with for now. I'll point it at the 'official' calculator and
see what 'safe distance' is returned. I only wish that it were not >>>>> so conservative as it is reported to be.
All my other antennas seem to be compliant, except for the 'random'
~130m-long horizontal loop at around 4m AGL running around the
garden, which wouldn't appear to radiate much at a downwards angle >>>>> of 20 to 30 degrees or so to a person on the ground - according to >>>>> a model of an 80m full-wave loop in the fairly-recent RSGB
'antennas' book, it pretty much all goes upwards, which is what I
wanted, for 40/80m NVIS working, when I put it up many years ago.
Many thanks for the modelling and the link.
For the loop any members of the 'public' are almost certainly going
to be in the near field of the antenna at HF, so it will be the near
field E and H fields that you have to consider for ICNIRP
compliance; which at close distances may well be very different from
the resultant radiation pattern.
The best way to do that would be to simulate it using a program
such
as 4NEC2 which will give you those figures (graphically if
required).
Thank you for that info.
I hadn't seen any mention of near or far fields on the Ofcom
calculator spreadsheet, so I thought that to use it as a compliance
demonstrator would suffice. If that isn't the case, I will have to
suspend use of that antenna until I can find a way of demonstrating
compliance in the near field (unless there is a version of 4NEC2 or
other program that runs under Linux Mint, I will be in some
difficulty).
I can only imagine that thousands of HF operators will be in the same
boat as me in this respect.
4NEC2 will run under Wine on Linux Mint.
I have a spare laptop running Linux, though I haven't used it for a year
or so. If it still works, I may try downloading and installing Wine and
then 4NEC2 (but see below). I don't want to risk rendering one of my
main Linux boxes unusable because of some installation disaster,
especially as their availability is critically important at the moment
for online food shopping and other important tasks.
The Offcom ,model is far-field only. It is therefore over pessimistic
for short distances for HF anyway.
Thank you for that info. In that case, it looks as if I may be OK using
the Ofcom calculator for HF, if I can reasonably use the model of the
80m full-wave loop in 'HF Antennas for Everyone' (RSGB; p221, fig. 5),
where radiation at 0 degrees appears to be minimal (according to the
small graph, apparently somewhere between -10 and -30dB below the peak
quoted gain of 8.3dBi). Allowing a 50% duty cycle should help, too.
It also includes ground-gain , which is only relevant in the far-field.
I tried comparing it with a hand calculation and the VK3UM model and
discovered this fact. The VK3UM model has a ground gain option.
It'll certainly be an interesting modelling to carry out when
circumstances permit. If for any reason I do feel it necessary to
suspend operations using the loop, I will have to do so, but as most of
my operation is above 30MHz, where it seems that all my power/antenna
options will be compliant, it will be no great problem.
I can see a fair few second-hand linear amplifiers coming onto the
market at keen prices before long, though!
Thank you for the information.
Andrew Marshall wrote:
On 25/12/2020 14:07, Brian Howie wrote:
4NEC2 will run under Wine on Linux Mint.
I have a spare laptop running Linux, though I haven't used it for a
year or so. If it still works, I may try downloading and installing
Wine and then 4NEC2 (but see below). I don't want to risk rendering
one of my main Linux boxes unusable because of some installation
disaster, especially as their availability is critically important at
the moment for online food shopping and other important tasks.
Take a spare hard drive and clone over the working disk drive.
With a Linux fleet as important as the one you describe, you
must already be familiar with the drill.
That's how I ended up with two dozen hard drives in this room.
Any time I lack confidence in the outcome of a experiment, it
takes an extra ten minutes to prepare for it. For example, I
have a terabyte of downloads, and that is backed up on a much
less frequent basis. The tiny OS partitions can be backed up or
cloned in ten minutes or so.
On Linux, there is CloneZilla. Boot a USB stick, then do the
drive-to-drive transfer. On Windows I use Macrium Reflect Free,
which handles both NTFS and EXT4 partitions, and is "good enough"
for the Linux installs I do. The current drive in the Test Machine
has 23 partitions at the moment (and Macrium can back up the
whole thing, using just as smart a transfer method as Clonezilla).
I can't really add any more partitions, because the screen is
no longer wide enough. GPT allows 128 partitions, but then you'd
not have a big enough screen to work on them.
It's been a while since I searched for Linux NEC2 programs.
I found xnec2 which is a native Linux version of nec2.
https://www.linuxjournal.com/content/antennas-linux
The debian install command runs fine under Linux Mint. I only got as far
as running the examples, but it seems to work.
The Offcom ,model is far-field only. It is therefore over pessimistic
for short distances for HF anyway.
Thank you for that info. In that case, it looks as if I may be OK using
the Ofcom calculator for HF, if I can reasonably use the model of the
80m full-wave loop in 'HF Antennas for Everyone' (RSGB; p221, fig. 5),
where radiation at 0 degrees appears to be minimal (according to the
small graph, apparently somewhere between -10 and -30dB below the peak
quoted gain of 8.3dBi). Allowing a 50% duty cycle should help, too.
For the loop any members of the 'public' are almost certainly going to
be in the near field of the antenna at HF, so it will be the near field
E and H fields that you have to consider for ICNIRP compliance; which at close distances may well be very different from the resultant radiation pattern.
The Offcom ,model is far-field only. It is therefore over pessimistic
for short distances for HF anyway.
Thank you for that info. In that case, it looks as if I may be OK
using the Ofcom calculator for HF, if I can reasonably use the model
of the 80m full-wave loop in 'HF Antennas for Everyone' (RSGB; p221,
fig. 5), where radiation at 0 degrees appears to be minimal (according
to the small graph, apparently somewhere between -10 and -30dB below
the peak quoted gain of 8.3dBi). Allowing a 50% duty cycle should
help, too.
I think that is a false assumption; in the near field the patterns can
be remarkably different from the far field pattern.
When close to a wire the near E & H fields will look nothing like
resultant fields at a distance, at 0 degrees there will be strong fields.
On 27/12/2020 11:56, Jeff wrote:
The Offcom ,model is far-field only. It is therefore over
pessimistic for short distances for HF anyway.
Thank you for that info. In that case, it looks as if I may be OK
using the Ofcom calculator for HF, if I can reasonably use the model
of the 80m full-wave loop in 'HF Antennas for Everyone' (RSGB; p221,
fig. 5), where radiation at 0 degrees appears to be minimal
(according to the small graph, apparently somewhere between -10 and
-30dB below the peak quoted gain of 8.3dBi). Allowing a 50% duty
cycle should help, too.
I think that is a false assumption; in the near field the patterns can
be remarkably different from the far field pattern.
When close to a wire the near E & H fields will look nothing like
resultant fields at a distance, at 0 degrees there will be strong fields.
I'm thinking more and more that I (and many others) will have to wait
for more precise information on what analysis of radiation patterns will
be required to demonstrate compliance when using HF with wire antennas, before using them in future.
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