Somewhere around here is a very strong carrier that has the effect on most
FM radios of making the radio less sensitive. Its switching on and off every
few seconds and has been doing so for at least a couple of years. Its most
obvious on weaker stations and worse on the low end of the band, but here is
the thing. I cannot find this carrier on my scanner, though there do appear
to be some cross modulated birdies switching on and off at the same rate.
You can tell these are overload noises as an attenuator removes them.
Its very strange and seems to be mainly very local.
Seems to me it must either be a massive signal to have such a broadband
effect, yet I cannot find it. I was wondering if it was some industrial
process, as there are a lot of small businesses about. When the whether is
warmer I'll have to take a portable fm radio around to see where its coming
from.

Brian

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Could it be getting in via the IF rather than at VHF input? The result
would then look quite 'broadband' but not show up on scanning the VHf
spectrum.

Most radios may have little protection against that.

Jim

In article <ur73s9$3pub1$1@dont-email.me>, Brian Gaff
<brian1gaff@gmail.com> wrote:
> Somewhere around here is a very strong carrier that has the effect on
> most FM radios of making the radio less sensitive. Its switching on and
> off every few seconds and has been doing so for at least a couple of
> years. Its most obvious on weaker stations and worse on the low end of
> the band, but here is the thing. I cannot find this carrier on my
> scanner, though there do appear to be some cross modulated birdies
> switching on and off at the same rate. You can tell these are overload
> noises as an attenuator removes them. Its very strange and seems to be
> mainly very local. Seems to me it must either be a massive signal to
> have such a broadband effect, yet I cannot find it. I was wondering if
> it was some industrial process, as there are a lot of small businesses
> about. When the whether is warmer I'll have to take a portable fm radio
> around to see where its coming from.

> Brian

--
Please use the address on the audiomisc page if you wish to email me.
Electronics https://www.st-andrews.ac.uk/~www_pa/Scots_Guide/intro/electron.htm
biog http://jcgl.orpheusweb.co.uk/history/ups_and_downs.html
Audio Misc http://www.audiomisc.co.uk/index.html

No the Icom is pretty well screened from this sort of thing. Its a multi
conversion radio in any case. I'm no thinking of a nearby rf heating
machine that works on a cycle, but the thing is, why is it there on a
Sunday.
.
Brian

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"Jim Lesurf" <noise@audiomisc.co.uk> wrote in message
news:5b37b02e73noise@audiomisc.co.uk...
> Could it be getting in via the IF rather than at VHF input? The result
> would then look quite 'broadband' but not show up on scanning the VHf
> spectrum.
>
> Most radios may have little protection against that.
>
> Jim
>
>
> In article <ur73s9$3pub1$1@dont-email.me>, Brian Gaff
> <brian1gaff@gmail.com> wrote:
>> Somewhere around here is a very strong carrier that has the effect on
>> most FM radios of making the radio less sensitive. Its switching on and
>> off every few seconds and has been doing so for at least a couple of
>> years. Its most obvious on weaker stations and worse on the low end of
>> the band, but here is the thing. I cannot find this carrier on my
>> scanner, though there do appear to be some cross modulated birdies
>> switching on and off at the same rate. You can tell these are overload
>> noises as an attenuator removes them. Its very strange and seems to be
>> mainly very local. Seems to me it must either be a massive signal to
>> have such a broadband effect, yet I cannot find it. I was wondering if
>> it was some industrial process, as there are a lot of small businesses
>> about. When the whether is warmer I'll have to take a portable fm radio
>> around to see where its coming from.
>
>
>> Brian
>
> --
> Please use the address on the audiomisc page if you wish to email me.
> Electronics
> https://www.st-andrews.ac.uk/~www_pa/Scots_Guide/intro/electron.htm
> biog http://jcgl.orpheusweb.co.uk/history/ups_and_downs.html
> Audio Misc http://www.audiomisc.co.uk/index.html
>

The effect is much reduced this week and sounds like the carriers are
either in different locations or maybe the direction of a beam is different
as it pulses. I still cannot find a fundamental, but it has to be there as
you can hear the effect on a portable at the low end of the fm band.
Brian

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"Brian Gaff" <brian1gaff@gmail.com> wrote in message
news:urkrnn$38fgt$1@dont-email.me...
> No the Icom is pretty well screened from this sort of thing. Its a multi
> conversion radio in any case. I'm no thinking of a nearby rf heating
> machine that works on a cycle, but the thing is, why is it there on a
> Sunday.
> .
> Brian
>
> --
>
> --:
> This newsgroup posting comes to you directly from...
> The Sofa of Brian Gaff...
> briang1@blueyonder.co.uk
> Blind user, so no pictures please
> Note this Signature is meaningless.!
> "Jim Lesurf" <noise@audiomisc.co.uk> wrote in message
> news:5b37b02e73noise@audiomisc.co.uk...
>> Could it be getting in via the IF rather than at VHF input? The result
>> would then look quite 'broadband' but not show up on scanning the VHf
>> spectrum.
>>
>> Most radios may have little protection against that.
>>
>> Jim
>>
>>
>> In article <ur73s9$3pub1$1@dont-email.me>, Brian Gaff
>> <brian1gaff@gmail.com> wrote:
>>> Somewhere around here is a very strong carrier that has the effect on
>>> most FM radios of making the radio less sensitive. Its switching on and
>>> off every few seconds and has been doing so for at least a couple of
>>> years. Its most obvious on weaker stations and worse on the low end of
>>> the band, but here is the thing. I cannot find this carrier on my
>>> scanner, though there do appear to be some cross modulated birdies
>>> switching on and off at the same rate. You can tell these are overload
>>> noises as an attenuator removes them. Its very strange and seems to be
>>> mainly very local. Seems to me it must either be a massive signal to
>>> have such a broadband effect, yet I cannot find it. I was wondering if
>>> it was some industrial process, as there are a lot of small businesses
>>> about. When the whether is warmer I'll have to take a portable fm radio
>>> around to see where its coming from.
>>
>>
>>> Brian
>>
>> --
>> Please use the address on the audiomisc page if you wish to email me.
>> Electronics
>> https://www.st-andrews.ac.uk/~www_pa/Scots_Guide/intro/electron.htm
>> biog http://jcgl.orpheusweb.co.uk/history/ups_and_downs.html
>> Audio Misc http://www.audiomisc.co.uk/index.html
>>
>
>

This would perhaps be a case where a specan and/or sdr would be handy for
investigations...

I recall a case perhaps similar to this from some years ago. Taxidrivers in
town kept finding interference when in a given small area of town. Turned
out to be a self-service machine in one of the shops had started radiating
RF! Took ages to track down as it only did it when used in a particular way
by customers!

Jim

In article <usc49g$107nr$1@dont-email.me>, Brian Gaff
<brian1gaff@gmail.com> wrote:
> The effect is much reduced this week and sounds like the carriers are
> either in different locations or maybe the direction of a beam is
> different as it pulses. I still cannot find a fundamental, but it has to
> be there as you can hear the effect on a portable at the low end of the
> fm band. Brian

--
Please use the address on the audiomisc page if you wish to email me.
Electronics https://www.st-andrews.ac.uk/~www_pa/Scots_Guide/intro/electron.htm
biog http://jcgl.orpheusweb.co.uk/history/ups_and_downs.html
Audio Misc http://www.audiomisc.co.uk/index.html

On 07/03/2024 12:15, Jim Lesurf wrote:
> This would perhaps be a case where a specan and/or sdr would be handy for
> investigations...
>
> I recall a case perhaps similar to this from some years ago. Taxidrivers in
> town kept finding interference when in a given small area of town. Turned
> out to be a self-service machine in one of the shops had started radiating
> RF! Took ages to track down as it only did it when used in a particular way
> by customers!
>
> Jim
>
>
> In article <usc49g$107nr$1@dont-email.me>, Brian Gaff
> <brian1gaff@gmail.com> wrote:
>> The effect is much reduced this week and sounds like the carriers are
>> either in different locations or maybe the direction of a beam is
>> different as it pulses. I still cannot find a fundamental, but it has to
>> be there as you can hear the effect on a portable at the low end of the
>> fm band. Brian

Reminds me of a problem that I had with my video recorder which had a
lot of corruption on channels that were on the PSB1 mux, but was fine on
all others.

It took me an embarrassingly long time to work out that it only happened
at night, and even after that, to work out that it wasn't an after-dark
reception problem but something much more obvious - at night you tend to
switch lights on.

My study, which is lit by a row of GU10 LED bulbs pointing in various
directions, is directly below the TV aerial mast. After a long time, I
worked out that reception got much worse as soon as I turned the study
lights on and got better as soon as I turned them off.

From there it was a process of elimination to remove the bulbs one by
one and find the rogue ones - plural, because two of the same make
seemed to splat all over 482 MHz, Belmont's PSB1, but leave other muxes
near by (490 COM5 and 506 PSB2) untouched.

Replacing those rogue bulbs with ones of a different make solved the
problem. The rogue ones are fine elsewhere in the house, so I could
still use them as long as it was in a different room.

On 07/03/2024 14:21, NY wrote:
> It took me an embarrassingly long time to work out that it only happened
> at night, and even after that, to work out that it wasn't an after-dark
> reception problem but something much more obvious - at night you tend to
> switch lights on.

There is a story of a WWII radar station in North Wales (CHL?) that kept
getting problems with interference.

It was eventually found to be the bulb in the light in the WAAF's latrine.

They changed the bull and all was OK.

On Thu, 7 Mar 2024 15:21:06 +0000
JMB99 <mb@nospam.net> wrote:

> On 07/03/2024 14:21, NY wrote:
> > It took me an embarrassingly long time to work out that it only
> > happened at night, and even after that, to work out that it wasn't
> > an after-dark reception problem but something much more obvious -
> > at night you tend to switch lights on.
>
>
> There is a story of a WWII radar station in North Wales (CHL?) that
> kept getting problems with interference.
>
> It was eventually found to be the bulb in the light in the WAAF's
> latrine.
>
> They changed the bull and all was OK.
>
>
>

Back in my student days, we had one cheap 2nd hand TV set for our digs.
I often took it back home for the holidays.
One evening, it let all the smoke out, along with some spectacular
sparks, and it was later reported that at that time, all TV sets in the
street had suffered unexplained interference for several minutes.
I said nothing.

We also had one that stank of curry, until it had burned off, but that
one lasted a while.

--
Davey.

In message <uscm11$13vsq$1@dont-email.me>, JMB99 <mb@nospam.net> writes
>On 07/03/2024 14:21, NY wrote:
>> It took me an embarrassingly long time to work out that it only
>>happened at night, and even after that, to work out that it wasn't an
>>after-dark reception problem but something much more obvious - at
>>night you tend to switch lights on.
>
>
>There is a story of a WWII radar station in North Wales (CHL?) that
>kept getting problems with interference.
>
>It was eventually found to be the bulb in the light in the WAAF's latrine.
>
>They changed the bull and all was OK.
>
In the early 60s our evening TV viewing (BBC 405-line, channel 5, around
65MHz) was regularly ruined by a faulty light bulb in a neighbour's
house, upstairs on the landing next to their young child's bedroom. The
interference took the form of a searing horizontal line that drifted
slowly up or down the picture.

The parents used to leave the light on until the child fell asleep, and
it was purely by luck that I noticed that the interference coincided
with the light being on, and disappeared immediately the light was
switched off.

Almost certainly the interference was being caused by Barkhausen-Kurz
oscillations in the bulb, which I believe can occur if there is a minute
arcing break in the filament.

The up-till-then friendly neighbour (who, at the time, didn't have TV)
got very huffy when approached with a view to getting the light bulb
changed - and absolutely refused to do anything about it. Fortunately,
after a few weeks the interference suddenly disappeared - presumably
because the bulb had failed and been replaced. [Interestingly, a few
weeks later, the family finally got a TV.]

https://www.ofcom.org.uk/news-centre/2020/interference-issue
--
Ian
Aims and ambitions are neither attainments nor achievements

I'm thinking along the lines of a mixing product due to overload of the
front end. That means the field of frequencies to look on is very much
wider. Add some harmonics as well, and all sorts of odd things occur. Most
FM tuner aerial stages are quite broadband, even though they are tuned, that
does not preclude mixing products from getting in.
Brian

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"Ian Jackson" <ianREMOVETHISjackson@g3ohx.co.uk> wrote in message
news:26bA+CPT1k6lFwbD@brattleho.plus.com...
> In message <uscm11$13vsq$1@dont-email.me>, JMB99 <mb@nospam.net> writes
>>On 07/03/2024 14:21, NY wrote:
>>> It took me an embarrassingly long time to work out that it only happened
>>> at night, and even after that, to work out that it wasn't an after-dark
>>> reception problem but something much more obvious - at night you tend to
>>> switch lights on.
>>
>>
>>There is a story of a WWII radar station in North Wales (CHL?) that kept
>>getting problems with interference.
>>
>>It was eventually found to be the bulb in the light in the WAAF's latrine.
>>
>>They changed the bull and all was OK.
>>
> In the early 60s our evening TV viewing (BBC 405-line, channel 5, around
> 65MHz) was regularly ruined by a faulty light bulb in a neighbour's house,
> upstairs on the landing next to their young child's bedroom. The
> interference took the form of a searing horizontal line that drifted
> slowly up or down the picture.
>
> The parents used to leave the light on until the child fell asleep, and it
> was purely by luck that I noticed that the interference coincided with the
> light being on, and disappeared immediately the light was switched off.
>
> Almost certainly the interference was being caused by Barkhausen-Kurz
> oscillations in the bulb, which I believe can occur if there is a minute
> arcing break in the filament.
>
> The up-till-then friendly neighbour (who, at the time, didn't have TV) got
> very huffy when approached with a view to getting the light bulb changed -
> and absolutely refused to do anything about it. Fortunately, after a few
> weeks the interference suddenly disappeared - presumably because the bulb
> had failed and been replaced. [Interestingly, a few weeks later, the
> family finally got a TV.]
>
> https://www.ofcom.org.uk/news-centre/2020/interference-issue
> --
> Ian
> Aims and ambitions are neither attainments nor achievements
>

On 11/03/2024 12:49, Brian Gaff wrote:
> I'm thinking along the lines of a mixing product due to overload of the
> front end. That means the field of frequencies to look on is very much
> wider. Add some harmonics as well, and all sorts of odd things occur. Most
> FM tuner aerial stages are quite broadband, even though they are tuned, that
> does not preclude mixing products from getting in.

Gets very complicated, I was told that on transmitter sites with
typically the six main services and other lower power services they can
mix in the RF stages of other PMR or utility services on the site. So
they something have to put filters in their outputs - to stop other
services mixing in those output stages.

The rule apparently is the last person to install equipment is
responsible for eliminating any interference even if their equipment is
OK with no nasties.

Its obviously cross modulation of some kind as an attenuator stops it at
about 10dB of reduction.
Some portables are too sensitive for their own good I fancy. I am old
enough to remember local and distant switches on FM radios and TVs. I guess
anything that generates non linearity will cause all sorts of strang
intermodulation components to be heard.
Brian

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"JMB99" <mb@nospam.net> wrote in message
news:usn62f$3lrj5$1@dont-email.me...
> On 11/03/2024 12:49, Brian Gaff wrote:
>> I'm thinking along the lines of a mixing product due to overload of the
>> front end. That means the field of frequencies to look on is very much
>> wider. Add some harmonics as well, and all sorts of odd things occur.
>> Most
>> FM tuner aerial stages are quite broadband, even though they are tuned,
>> that
>> does not preclude mixing products from getting in.
>
>
>
> Gets very complicated, I was told that on transmitter sites with typically
> the six main services and other lower power services they can mix in the
> RF stages of other PMR or utility services on the site. So they something
> have to put filters in their outputs - to stop other services mixing in
> those output stages.
>
> The rule apparently is the last person to install equipment is responsible
> for eliminating any interference even if their equipment is OK with no
> nasties.
>
>
>