On Thu, 2010-01-21 at 09:37 -0800, Art Trampler wrote:
> Jerry,
>
> I agree and respectfully noted. I do this in the winter (notify CU)
> and they have been good. Last year they replaced several insulators
> that were arcing and that cleaned things up for a while. It's just a
> bit of an effort to coordinate the timing of investigating so I can be
> home from work so they can snapshot the noise signature.
>
> Fortunately they have purchased the equipment from the fellow out
> east--darn it, don't remember his name--who specializes in this and
> trains utilities, etc on it.
>
> I usually try to narrow things down with a borrowed 2m/440 HT and
> hand-held yagi. I am NOT a good builder and have suggested our club
> build the homebrew ultrasonic microphone as something we might all
> use.
>
> I would have to reset the clocks but since my rig is on a dedicated
> line I just might shut everything else off to be doubly sure.
>
> 73,
> Art
>
>
Using the HT or mobile VHF rig in AM mode rather than FM is a great deal
more effective at finding noise sources. That's how the commercial
finding receivers work, they use AM mode. Many modern hand helds and
mobiles have AM detectors since they tune the aircraft band and most can
be switched to receive on AM mode on 2m or 440. Its easier to carry a
directive antenna at 440 and the antennas used for FM satellite
operation are decent for noise finding. The thing about VHF and up is
that the RF doesn't propagate from pole to pole on the wires, it
radiates and you don't get the false peaks from wire SWR like you do at
1 MHz.
Ultrasonic is another technique that works, but is less commonly used
and might be of limited range though mounting the ultrasonic microphone
at the focus of a Direct TV type dish gets lots of directivity though
the direction is not obvious from the offset dish feed. I use that dish
on 10 GHz with good results.
I had access to a commercial ultrasonic device made for finding leakages
in high voltage equipment back about 1964. It was interesting to see how
much ultrasonic noise things like a circular saw or air nozzle made.
Shouldn't be hard to build or adapt a pocket AM radio. Change the LO to
475 KHz, hook the microphone to the mixer input in place of the
loopstick. Listen with head phones. Might be a problem that the AM radio
has too great a working AVC to hide the peak. I had that problem with a
design a few years ago that the custom board maker had troubles with
alignment because the AVC hid the tuning changes when he used too much
signal.
73, Jerry, K0CQ
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