Jeff Liebermann wrote in message
...
On Thu, 05 Jan 2012 17:59:54 -0500, micky
wrote:

It sounds sort of like a fog horn, but a somewhat higher
pitch. Or the horn on a diesel locamotive. Or a steady note on a
trumpet. Except it often doesn't end as suddenly as they do, but
might have little noises for a second or two at the end. (I can't
remember how to describe the sound at the end.)

The sound can be medium or loud. That is, sometimes I can sort of
hear the radio program, usually talk, in addition to the noise. Other
times the noise overwhelms the program and I have no idea what they
are saying..

(...)
Any suggestions what the source of this might be?

Good description but not enough to identify the culprit. It doesn't
sound like a heterodyne and there's no indication of any additional
voice or music modulation making intermod an unlikely cause. If you
could record an MP3 audio clip and post it somewhere, it would be a
big help.

FM noise is fairly uncommon. FM was originally designed to ignore
amplitude modulated noise, which it does quite well. However, with
the introduction of HDFM, the digital modulation scheme included AM
components. The result is the sensitivity to AM interference has
increased. The noise description does not sound familiar so this is
unlikely. However, I'm curious if the unspecified maker and model
receiver is and HDFM receiver and were you possibly listening to HD1
or HD2.

Also, try a different FM receiver. If both radios receive the same
interference, then its probably being radiated over the air or
conducted on the power lines. However, if only one radio hears the
interference on the same channel, then it's possible that there's
something wrong with the receiver or the noise is being generated in
the radio.

Also, your description sound vaguely like RFI from a plasma TV. The
level, modulation characteristics, and frequency will vary with what
is on the screen. The timing pattern you describe sounds roughly like
a TV being turned on and off at random times. Do the times when it's
on coincide with prime time TV?

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558



I've no idea if it would work but can you make a portable FM receiver
directional by placing in a metal tube? Perhaps with a metal plate under a
shoe with a grounding wire. Would have to be speaker output , so an earpiece
did not fed RF down