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[RFI] Terrible RFI

To: <rfi@contesting.com>
Subject: [RFI] Terrible RFI
From: n0tt1 at juno.com (n0tt1@juno.com)
Date: Thu Mar 27 21:26:37 2003
Hi Bob,

> Have had a terrible time finding interference sources and been 
> battling the
> power company for over seven, yes, seven years. But, that is a whole 
> story
> in itself. Right now I am at wits end trying to locate the source.

I can relate to that....don't give up!  One important point (that you
probably know) is to make *sure* that the noise isn't coming from
your own house.  Use a battery-powered radio and kill the power
to your house at the main circuit breaker to test.
> Here's the problem. S7-9 Noise Level (worse when it is drier) on 10 
> & 12
> meters with other bands being affected depending on how dry the 
> weather is.
> 160 meters is S 7 at night. A sweep of 1710 KHz AM broad cast band 
> indicates
> peaks on the power line at what appears to be irregular intervals 
> over a 1
> mile stretch.. An MFJ Noise meter indicates one small source about 
> 3/4 mile
> away. However, I do not feel this is the source. 

If you can hear it on the MFJ, and its on/near the power line that feeds
your house, then it's a good possibility that it COULD BE the source!
But if you are using the MFJ 's "built-in" antenna, I found the
to be absolutely worthless in locating a source right down to a 
specific pole.  The built-in telescoping dipole is good for any
general noise surveying work.  For more serious locating, do yourself 
a favor and build the simple Moxon antenna in QST...March 2001
issue....and then build a 50 ohm decade attenuator box, a device one
cannot do without when you get close to a strong noise source!
Mine switches in 6, 10 and 20 db.  I found that the 36db total was
adequate when used with the Moxon antenna.

A handy RFI tool for survey work is a meter for your car radio
I connected a homebrew audio level meter to one of 
the speakers to get a relative indication
of noise level.  It amounted to a 50ua meter, a "large" capacitor
across the meter to dampen the movement somewhat, a full wave
diode bridge to rectify the audio, and a small 8-ohm/2000 ohm
transformer to boost the audio voltage level for the meter circuit.
all of that just fastened to a piece of board that sits on the
dashboard for easy viewing.  Using that tool, in most cases, will 
get you close enough to the noise so it can be heard with the MFJ unit.

> The power company is blaming neon signs from a small strip mall 
> located at a
> further distance from peaks on the power line.

Could be, but I doubt that is the noise you are hearing...the RF would
to get past the transformer, a fair attenuator for RF.  It could
however be carried by the neutral conductor.

Keep in mind there can be several cases of noise on a given power line. 
In my
own experience, I located no less than 6 sources that I could hear on
the 160m band at home.  Some locations were less than 1000 ft away,
and others were over 1 mile away.   BTW, always listen on the AM mode
when testing for noise on the shack receiver, no matter what the

In my own case, I offered to meet with the line crew to help trouble
shoot the noise.  Normally they would drive to my home and then
leave from there.  My local power co didn't have a single piece of
specialized equipment to track down noise, so my "help" was welcome.
We would drive to the various sources, I would let them listen on
the MFJ headphones and show them why I think the noise was
coming from a particular pole.  They would either kill the power
or bypass all the hardware on the pole to isolate the noise
source....very cooperative!  Many problems were repaired that way.
One of the worst noise problems turned out to be a lighning
arrestor at a customer pole....it would noise up the line for
many miles!

If you cannot get cooperation from your local power company,
you might first try contacting the RFI specialist at the ARRL,
or even the FCC to get the power co to respond.

Charlie, N0TT

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