Items seen in Southgate ARC news on new licensing conditions regarding
field strengths...
<http://www.southgatearc.org/news/2020/october/emf-ofcom-propose-new-amateur-radio-licence-conditions.htm>
<http://www.southgatearc.org/news/2020/october/ofcom-to-introduce-new-spectrum-licence-conditions.htm>
Items seen in Southgate ARC news on new licensing conditions regarding
field strengths...
On 06/10/2020 13:05, Andrew Marshall wrote:
<http://www.southgatearc.org/news/2020/october/emf-ofcom-propose-new-amateur-radio-licence-conditions.htm>
<http://www.southgatearc.org/news/2020/october/ofcom-to-introduce-new-spectrum-licence-conditions.htm>
Items seen in Southgate ARC news on new licensing conditions regarding
field strengths...
Probably to do with all those Baofengs?
<http://www.southgatearc.org/news/2020/october/emf-ofcom-propose-new-amateur-radio-licence-conditions.htm>
<http://www.southgatearc.org/news/2020/october/ofcom-to-introduce-new-spectrum-licence-conditions.htm>
Items seen in Southgate ARC news on new licensing conditions regarding
field strengths...
Probably to do with all those Baofengs?
For some people with very close neighbours, a Baofeng, or other
handheld, will probably come close to the (apparent) default 10W EIRP exemption limit... with an aftermarket antenna fitted, of a half-wave (2.15dBi) on 70cm, that'll come to 9.15 dBW EIRP.
On 06/10/2020 13:05, Andrew Marshall wrote:
Items seen in Southgate ARC news on new licensing conditions regarding
field strengths...
The US has had such restrictions in its amateur licences for some time
now, but the threshold powers are band dependent, and never less than 50 watts PEP (500 W ERP for repeaters), before routine evaluations are
required, although I think the requirement to comply with field strength limits is absolute.
See part 97.13(c) (in <http://www.arrl.org/files/file/Regulatory/March%208,%202018.pdf).
See <https://www.law.cornell.edu/cfr/text/47/1.1310> for the absolute requirements on exposure limits; I don't know how these compare with the
ones Ofcom is referencing.
A significant part of a, not particularly recent, ARRL handbook, I have,
is devoted to compliance with field strength limits.
The tricky bit for us is working out how far away does Joe Public have
to be from the antennas to be within the guidelines.
I await Ofcom's
online tool to see how it compares with others.
From reading the links from the Southgate article, it looks like the guidelines are to become mandatory.
"We will include a specific condition in Wireless Telegraphy Act
licences requiring licensees to comply with the ICNIRP general public
limits on EMF exposure"
The FCC numbers are different, but I currently exceed the FCC
requirement evaluation limit on 50MHz to 432MHz. I certainly exceed the
10W EIRP on 23cm and up. 10W EIRP is a surprisingly low limit.
I have sympathy with those people who will be unable for whatever
reasons to carry out the necessary calculations, and who may therefore
have to operate at very low powers with very small antennas, or even
give up the hobby altogether.
On Sun, 11 Oct 2020 10:31:33 +0100, just as I was about to take a
herb, Andrew Marshall <news@y-ddraenog-goch.org.uk> disturbed my
reverie and wrote:
I have sympathy with those people who will be unable for whatever
reasons to carry out the necessary calculations, and who may therefore
have to operate at very low powers with very small antennas, or even
give up the hobby altogether.
Why bother with this? OFCOM does not have the resources to start
checking every amateur station. It will be operation as usual at this
QTH.
On 10/10/2020 09:19, Brian Howie wrote:
The tricky bit for us is working out how far away does Joe Public have
to be from the antennas to be within the guidelines.
It'll be likely to make mobile operation very difficult, I reckon. Even
the 5W output setting on typical VHF/UHF mobile gear will deliver over
10W EIRP on 70cm with a 2 x 5/8-wave antenna (about 5dBi gain).
To remain under 10W EIRP on 23cm at my station, which has a G3JVL
47-element loop Yagi for that band (something like 23dBi as far as I can guess; I have not so far found any gain figures online for that antenna)
I would have to limit my power to -13dBw (50mW RF) at the antenna
connector. I don't think the IC-9700 can be turned down that far.
To remain under 10W EIRP at other VHF/UHF frequencies would entail using
only the 3-band (2/70/23) short colinear at the top of my North Mast (abandoning the use of all beams) and feeding it with no more than 5W on
2m (half-wave), and considerably less on the higher bands (5dBi on 70cm (double 5/8) and something like 7dBi on 23cm (triple 5/8)).
On 11/10/2020 10:31, Andrew Marshall wrote:
To remain under 10W EIRP on 23cm at my station, which has a G3JVL
47-element loop Yagi for that band (something like 23dBi as far as I
can guess; I have not so far found any gain figures online for that
antenna) I would have to limit my power to -13dBw (50mW RF) at the
antenna connector. I don't think the IC-9700 can be turned down that far.
I think you are worrying unduly, even with 10W into your JVL yagi the
safe distance is only about 7m on boresight, and very close in other directions, and that assumes continuous CW transmission. Factor in tx/rx ratios and perhaps a reduction for ssb an you are down to about 2.5m.
Trying to stay under the 10W eirp limit is probably more effort that calculating a few safe distances and writing them down!
To remain under 10W EIRP at other VHF/UHF frequencies would entail
using only the 3-band (2/70/23) short colinear at the top of my North
Mast (abandoning the use of all beams) and feeding it with no more
than 5W on 2m (half-wave), and considerably less on the higher bands
(5dBi on 70cm (double 5/8) and something like 7dBi on 23cm (triple 5/8)).
Even with 400W continuous a typical collinear at 6m agl on 2 on 70 (will
not come anywhere near the limit at ground level, so unless there
happens to be a member of the public 6m agl within 6m you will be fine
Trying to stay under the 10W eirp limit is probably more effort that
calculating a few safe distances and writing them down!
You may well be right; it's a reliable means of calculation, which I can access or run using the computers and OSs - Linux Mint and possibly
WinXP) at my disposal, which I need to give me certainty that I can be compliant.
To remain under 10W EIRP at other VHF/UHF frequencies would entail
using only the 3-band (2/70/23) short colinear at the top of my North
Mast (abandoning the use of all beams) and feeding it with no more
than 5W on 2m (half-wave), and considerably less on the higher bands
(5dBi on 70cm (double 5/8) and something like 7dBi on 23cm (triple
5/8)).
Even with 400W continuous a typical collinear at 6m agl on 2 on 70
(will not come anywhere near the limit at ground level, so unless
there happens to be a member of the public 6m agl within 6m you will
be fine
I might just be OK there, as I only run 100W maximum RF out on 2m and
75W on 70cm, less the loss of about 10m of H100 coax. I need to be able
to prove it, though.
May I please ask which software or other means you used to derive your calculations?
Trying to stay under the 10W eirp limit is probably more effort that
calculating a few safe distances and writing them down!
You may well be right; it's a reliable means of calculation, which I
can access or run using the computers and OSs - Linux Mint and
possibly WinXP) at my disposal, which I need to give me certainty that
I can be compliant.
To remain under 10W EIRP at other VHF/UHF frequencies would entail
using only the 3-band (2/70/23) short colinear at the top of my
North Mast (abandoning the use of all beams) and feeding it with no
more than 5W on 2m (half-wave), and considerably less on the higher
bands (5dBi on 70cm (double 5/8) and something like 7dBi on 23cm
(triple 5/8)).
Even with 400W continuous a typical collinear at 6m agl on 2 on 70
(will not come anywhere near the limit at ground level, so unless
there happens to be a member of the public 6m agl within 6m you will
be fine
I might just be OK there, as I only run 100W maximum RF out on 2m and
75W on 70cm, less the loss of about 10m of H100 coax. I need to be
able to prove it, though.
May I please ask which software or other means you used to derive your
calculations?
EMRcalc is a very useful tool, I don't know if it will rum under XP or
in a Linux emulator such as wine.
The other tool is NEC, here running under 4NEC2 on windows to model
complete antenna systens, including near field . I think that will run
under XP, but it is a long time since I did, so can't be sure about the current version.
There are Linux versions of NEC front ends out there.
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