Ham radio Interference
 

On Sun, 19 Feb 2017 12:49:24 +0000, Indy Jess John
wrote:

On 19/02/2017 12:03, David Woolley wrote:
On 18/02/17 15:29, Graham. wrote:
He did qualify the statement you took umbrage at with the words "if it
can be proven that it is his equipment causing the interference."

Again ignoring the age of the thread, interference to Sky system by
amateur radio transmissions is almost certainly not the fault of the
amateur radio equipment. The frequency at which the amateur is likely
to be transmitting is so far removed from the frequencies used for the
satellite broadcasts and the directionality of satellite dishes
sufficiently great that any spurious signals, legitimately received, are
going to be of a negligible level. It is much more likely that the
satellite receiving system is responding to frequencies it is not
intended to receive, which is a fault in the satellite system.

The key phrase in the original message is "and then to the TV, in the
next room, by RF output". My guess is that the RF frequency used for
that relay is susceptible to outside interference, rather than there
being a fault in the satellite system itself.

Jim

Also breakthrough on an audio amplifier or an electronic organ are by
definition not the fault of the transmitter, as neither of those
devices are intended to be receivers.


--

Graham.
%Profound_observation%

Ham radio Interference
 

In article , David Woolley
..demon.invalid scribeth thus
On 18/02/17 15:29, Graham. wrote:
He did qualify the statement you took umbrage at with the words "if it
can be proven that it is his equipment causing the interference."

Again ignoring the age of the thread, interference to Sky system by
amateur radio transmissions is almost certainly not the fault of the
amateur radio equipment. The frequency at which the amateur is likely
to be transmitting is so far removed from the frequencies used for the
satellite broadcasts and the directionality of satellite dishes
sufficiently great that any spurious signals, legitimately received, are
going to be of a negligible level. It is much more likely that the
satellite receiving system is responding to frequencies it is not
intended to receive, which is a fault in the satellite system.

TV interference was something that was associated with, particularly,
band I and band III analogue TVs, and was greatly reduced by the move to
UHF. Interference to cable systems is definitely the fault of the cable
system, and the corresponding is almost certainly the case for satellite
systems as well.

These days, the big problem is the other way round, unintentional
transmissions by things like power line internet, VDSL, solar energy
systems on the room, low energy lighting, etc. will almost certainly
raise the noise level, in the amateur bands, to an unacceptable level,
in all but the most rural areas. Ofcom is under-resourced to deal with
the faulty installations causing these problems, even though many
installations are non-compliant, and some products are illegally CE
marked. (Plasma TVs are also a big problem, but finally dying out.)

I'd also point out that there there are three different sets of power
limits for amateurs, each requiring a stricter examination. One of the
main areas of stress, in the examinations, is on interference.

Although there is the occasional bad egg, the best approach to dealing
with such interference is friendly contacts with the amateur, and a
willingness to approach the problem from your end. Unfortunately, in
today's blame culture, amateurs are unlikely to want to get involved in
making repairs improvements to your system, but should be able to give
guidance to the relevant professionals, and should be able to
demonstrate that their own systems are not affected.

However firing off hundreds of watts close to domestic equipment is very
likely to cause trouble. Simple overload is the usual cause.

You cannot in practice filter / suppress everything as it cannot be done
take for instance an average portable radio it was never designed to be
subject to strong local fields.

And thats just one instance..
--
Tony Sayer

Ham radio Interference
 

In article , Graham.
scribeth thus
On Sun, 19 Feb 2017 12:49:24 +0000, Indy Jess John
wrote:

On 19/02/2017 12:03, David Woolley wrote:
On 18/02/17 15:29, Graham. wrote:
He did qualify the statement you took umbrage at with the words "if it
can be proven that it is his equipment causing the interference."

Again ignoring the age of the thread, interference to Sky system by
amateur radio transmissions is almost certainly not the fault of the
amateur radio equipment. The frequency at which the amateur is likely
to be transmitting is so far removed from the frequencies used for the
satellite broadcasts and the directionality of satellite dishes
sufficiently great that any spurious signals, legitimately received, are
going to be of a negligible level. It is much more likely that the
satellite receiving system is responding to frequencies it is not
intended to receive, which is a fault in the satellite system.

The key phrase in the original message is "and then to the TV, in the
next room, by RF output". My guess is that the RF frequency used for
that relay is susceptible to outside interference, rather than there
being a fault in the satellite system itself.

Jim



Also breakthrough on an audio amplifier or an electronic organ are by
definition not the fault of the transmitter, as neither of those
devices are intended to be receivers.


Well it's not that difficult to tame an audio input stage to RF but even
so they even decent audio amps can be susceptible if the field is that
strong...
--
Tony Sayer

Ham radio Interference
 

On 19/02/17 22:33, tony sayer wrote:
However firing off hundreds of watts close to domestic equipment is very
likely to cause trouble. Simple overload is the usual cause.


200 yards isn't particularly close.

Although the licence limit is up to 400W PEP, most people don't go over
100W. Also, the higher powers tend to be used on short wave, where it
is not possible to have an aerial with a lot of gain, so you would be in
the far field, with signal power going off as the square of distance. A
system that is taken out by 400 W at 200m isn't going to stand a chance
against a mobile phone at 2m, given the same sensitivity at all
frequencies. 400W next door might be a problem, but it shouldn't be 15
doors away.

Ham radio Interference
 

In article , David Woolley
wrote:
On 19/02/17 22:33, tony sayer wrote:
However firing off hundreds of watts close to domestic equipment is
very likely to cause trouble. Simple overload is the usual cause.


200 yards isn't particularly close.

Although the licence limit is up to 400W PEP, most people don't go over
100W. Also, the higher powers tend to be used on short wave, where it
is not possible to have an aerial with a lot of gain, so you would be in
the far field, with signal power going off as the square of distance.

Possible contradiction there. The 'near field' extent is affected by the
wavelength as well as the size of the antenna. If the TX is UHF the
wavelength probably won't matter. But it may do for HF.


A system that is taken out by 400 W at 200m isn't going to stand a
chance against a mobile phone at 2m, given the same sensitivity at all
frequencies. 400W next door might be a problem, but it shouldn't be 15
doors away.

Again, what may matter here is the field levels rather than the power flux.
In the near field - or near objects - these may not relate simply via the
expected free space impedance.

The basic problem, though, is that no real RFI measures can totally protect
from arbitrarily high exposure of just the 'wrong' kind. And in practice
there may also be problems like a poor connection somewhere near the TX
causing frequency conversions for some of the power.

Its fair enough to presume that domestic kit shouldn't be affected. But in
the real world it will be in some cases because the exposure goes beyond
what any designer would have decided was 'reasonable', or they were caught
out by a quirk of the circumstances.

Given that, I'd tend to expect a radio enthusiast to be willing to try and
help fix a problem when it is brought to their attention. No idea about the
ancient case that resurfaced this thread, though.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Ham radio Interference
 

On 20/02/17 10:26, Jim Lesurf wrote:
Possible contradiction there. The 'near field' extent is affected by the
wavelength as well as the size of the antenna. If the TX is UHF the
wavelength probably won't matter. But it may do for HF.

The suggestion was that there was a steerable antenna. Such an antenna
is unlikely at wavelengths greater than 20m. A 10 lambda range ought to
put one well into the far field.

Ham radio Interference
 

In article , David Woolley
wrote:
On 20/02/17 10:26, Jim Lesurf wrote:
Possible contradiction there. The 'near field' extent is affected by
the wavelength as well as the size of the antenna. If the TX is UHF
the wavelength probably won't matter. But it may do for HF.

The suggestion was that there was a steerable antenna. Such an antenna
is unlikely at wavelengths greater than 20m. A 10 lambda range ought to
put one well into the far field.

Again, whilst true in general, that wouldn't necessarily be the case if
you're in the main lobe. The more directional the antenna, the longer the
'near field' range along the main lobe.

So one of the problems here is that factors which *in general* would apply
might fail in some *specific* situations. Thus dumping a far higher burden
on the device being subject to the field.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html