On Sunday, 24 December, 2000 7:44 PM, Kris Mraz N5KM
[SMTP:kilo.mike@gte.net] wrote:
> Thanks for lending your expertise to this problem. Others have
> mentioned PC monitor or switching power supply noise. In my case
> the noise is present 24 hrs a day. You say that the touch lamp
> is typically 30-70 khz wide. In my case it is no more that 5 khz
> wide. I don't have a scope handy so I can't say what the envelope
> looks like.
>
> One question, though. How were you able to track down the touch
> lamps over a block away?
This was a different situation the the new neighbor directly behind me. I
used a small Sony portable shortwave rcvr to DF the noise. I found the
noise (or noises since there seemed to be more than one) in a BC band
around 15Mhz on the HF rcvr in the shack then tuned to that freq and went
for a nice walk (it was summer at the time and HOT!). I basically covered
a two block area surrounding my home before I narrowed it down to a couple
of houses.
I actually found several touch lamp type of noises along the way, but only
one that was reasonably close in freq and sound characteristics that I was
tracking. So I left a note on my company's letterhead (I work for the
electric utility here) asking for the homeowner to call me at home and gave
my name, number and address briefly describing the interference problem.
The young woman who lived there had her boyfriend call me a day later. I
then explained the situation and suspecting a touch lamp asked if she owned
any. He asked her and she said she had two in the bedroom (guess he didn't
already know that;^). I asked if they could unplug them while I monitor on
my radio. Sure enough, I heard the last spark as they unplugged them each.
Bullseye!
The rest of the story's too long to go into at this late hour on Christmas
Eve, but I managed to get the noisey lamps quieted down enough. She
eventually got rid of the lamps maybe because I stressed that they weren't
UL listed and could be a fire hazard especially since they made such a
terrible buzzing noise on RF! She also got rid of a nice $12 ferrite core
in the base of one lamp, and a Radio Shack line noise filter as well.
Would've been nice to get these back, but she didn't even know I put the
ferrite in there (boy I can be sneaky, huh?).
Back to your situation Kris. Since the BW is only 5 kc, it probably is a
switching supply in a nearby computer, monitor or something. You've ruled
out everything in your shack and house I suppose? DFing a weak noise is
troublesome, but can be done with enough patience and good weather. I'd
start by asking your immediate neighbors if they could unplug their
computers & TVs while you listen to the noise in the shack. Hope you're on
good terms with them and they don't have any other RFI issues with you ;^).
If that fails to find the problem, go DFing with a portable rcvr. When you
get somewhat close to a similar noise, telescope the antenna down, fold it
in, and cover it with your hands & body to attenuate the signal as much as
possible. Then rotate around to determine direction. I use this trick
when doing transmitter hunts on 2 meters too! Good luck & happy DFing.
73,
de ed -K0iL
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