[RFI] DFing power line interference

EDWARDS, EDDIE J EDWARDS, EDDIE J" <eedwards@oppd.com
Fri, 5 Jan 2001 09:34:02 -0600

> -----Original Message-----
> From:	Jimk8mr@aol.com [SMTP:Jimk8mr@aol.com]
> I haven't noticed it in the magazines, but I recently got a flyer from 
> Amateur Electronic Supply showing a new MFJ Model 852 Power Line Noise
> Meter 
> - 135 MHz AM,  A front panel meter, headphone jack,  built in dual whip 
> dipole antenna, etc.  The price is $90.
	That's not a bad price, but I have to wonder how good it is at
finding line noise.  At 135MHz you could still be looking at dozens of poles
as the possible source if you don't have an attenuator.  Also a dipole just
ain't gonna cut it.  You'll need hand-held Yagi with at least 4 elements.
At 135Mhz it'll be kinda bulky to carry around.  It would've been better to
get above 200Mhz to help narrow down the search to the right pole, and the
yagi would be a bit smaller too.

	Commercial units range from $1150 to $5000.  The low end have an
adjustable freq range around 320-340MHz, and the high end cover 1.8MHz to 1
GHz and have an spectrum scope built in.  Personally I think an adjustable
range is required to DF line noise and should cover all the VHF band at
least.  So at $90 I'm a bit skeptical about the MFJ.  Maybe I should buy one
for work just to see if it is any good.

	To help distinguish between a strong peak caused by standing waves
(not the actual source) versus a peak caused by the real noise source, my
company bought an ultrasonic detector that can pinpoint which piece of
hardware on the pole is generating the sparking!  It has been a tremendous
help for making sure we have the correct pole.  It also allows the tech to
write up the specific problem getting it fixed much faster.  We still use an
RF search to find the suspect pole, then ultrasonics to verify the search
results and determine the cause.

	I might note that many years ago I used a simple multi-band AM/FM/SW
radio and found the source of noise or at least the right pole.  It just
takes a lot longer doing it that way is all, and I didn't know for sure till
the power company came out to verify my search.  (That was before I worked
for them!)

	de ed -K0iL

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