Spark gap exciting a length of wire that just happens to be resonant on a
bad frequency. If its outside the frequency can drift with temperature and
humidity, and if the wire isn't real tight also in the wind. In the case of
a bad switch you may have saved them from a fire, you can get arcing in a
switch either from pitted or corroded contacts or from moisture in it... in
a bathroom where the switch made noise when off I would bet it was full of
water from condensation. Be sure to point that out to neighbors when you
find noises like that from bad appliances or switches, you may be their
early warning of a future electrical problem... and if you are hunting for a
noise like that it may help to point out that possibility also, it may make
them a bit more cooperative.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
> -----Original Message-----
> From: rfi-bounces@contesting.com [mailto:rfi-bounces@contesting.com] On
> Behalf Of Pete Smith
> Sent: Saturday, February 02, 2008 12:31
> To: RFI List
> Subject: Re: [RFI] Strange RFI
>
> About 15 years ago, I ran into something very similar, except that it was
> on 80M. Same asymmetrical frequency distribution, in particular, but in
> my
> case there were two peaks, one at about 3515 and one above 3700. Since I
> was trying to finish 5BDXCC from a townhouse, it was an issue!
>
> I used a portable radio to track it to a neighbor's house - fortunately he
> was agreeable, so we went around the house "sniffing" for the source. As
> we went upstairs, he turned on a bathroom light, and the noise suddenly
> disappeared! Turned it off, and the noise was back. Just some ordinary
> incandescent bulbs, no dimmer, an ordinary 72-cent Leviton switch. But I
> changed out the switch, and the noise went away.
>
> A few weeks ago I discovered another similar noise source in another
> neighbor's house - this one was on a 3-way circuit (one kitchen light, two
> switches). Same cure.
>
> I have no idea what mechanism might be involved, but there you have it.
>
> 73, Pete
>
> At 12:59 PM 2/1/2008, Kelly Johnson wrote:
> >After 9 months of phone calls and complaints, PG&E finally came out
> >this week and "fixed" the two power poles that were causing most of my
> >powerline noise problems. I say "fixed" because it is too early to
> >tell if their "fixes" actually worked since the noise is most
> >prominent in the dry, hot summer. The pole hardware is nice and shiny
> >though :-) After they left I started listening for powerline noise
> >and there is still at least one noise source in the direction of one
> >of the poles, but I don't think it is that pole. The RFI I hear now
> >has some very strange characteristics. I'm wondering if anyone can
> >explain them. Here goes....
> >
> >The RFI I hear now can only be heard on 10 meters: nothing on 12
> >meters, 15 meters, 20 meters, etc. A fellow ham who lives about 200
> >yards away from me hears it too. In fact, he's the one that told ME
> >about it. The RFI sounds just like broadband powerline noise and my
> >noise blanker can eliminate it (the NB2 button on my FT-1000MP). I
> >start to hear the RFI at about S1 way down around 26.000 MHz or so.
> >The signal strength climbs slowly as I tune up the band. NOTE - I
> >have a SteppIR so I am retuning the antenna as I move up so it is
> >resonant at the freq. I'm listening to (or close to it). The signal
> >strength peaks anywhere from about 28.100 to 28.230MHz, but this is
> >where it gets weird. Right after the signal peak it just drops off a
> >cliff. It's like there is a steep low-pass filter at 28.230Mhz. The
> >signal will be S9 at 28.230 and S0 at 28.240. It just drops off.
> >There is no RFI up in the phone band. There are a couple of other
> >strange characteristics. First, the "drop off point" moves around.
> >The first time I heard this RFI it dropped off around 28.230MHz. The
> >next day the drop off was around 28.120. Today it is around
> >28.210MHz. Even while listening it slowly moves around by maybe 2 or
> >3 Khz every second. It just wanders around a bit. The other strange
> >characteristic is that all of the RFI just stops completely every so
> >often and then comes back on a second or more later. The off time
> >varies as well. It seems random.
> >
> >I really don't think this is from that pole. I suspect some piece of
> >consumer electronics or other equipment a few doors down from me.
> >I'll be going out this weekend with my FT-817 and 440MHz yagi to
> >verify that the pole is really quiet and to try to identify the other
> >noise source. Maybe someone has some theories that may help me track
> >down the newly identified noise source more quickly?
> >_______________________________________________
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>
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