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Re: [RFI] Tower Intermod - Control Lines

To: <rfi@contesting.com>
Subject: Re: [RFI] Tower Intermod - Control Lines
From: "Ed Richardson" <Ed_richardson@shaw.ca>
Date: Thu, 22 Jul 2010 07:36:55 -0500
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>
Thanks Jim

Yes the intermod is the classic 3rd order type 2F1+/-F2. About half a
dozen strong local stations mixing with each other and other strong
stations. Two winters ago I was convinced it was a transmitter issue at
one of the broadcast stations and complained to our local Industry
Canada office. Several other amateurs within 5-8 miles also reported
hearing it. They contacted the station engineer and surprisingly the
problem vanished 2 days later. However it re-appered a couple weeks
later and has been here ever since. Industry Canada has been to the
sites and throughout the area and they now claim it is not a broadcaster
at fault. The other local hams also claim to not hear it anymore.

I am now convinced it is something local, either on my tower or
something weak that the antennas up top can hear but I can not detect at
ground level.

If I get a day without rain and work, I will be making a trip up the
tower with probes and meters.

Ed
VE4EAR


-----Original Message-----
Hi Ed,

First, when you say AM intermod, I assume you mean you're hearing 
multiple AM radio stations every 10 kHz up the band. 

I have a rather different take on this. The tower, and the control 
lines, are antennas, and as such, can RECEIVE that interference and re-
radiate it into the SW radio you are using as a probe. By putting a 
choke on those lines, you are reducing the antenna current, and thus 
their efficiency as antennas. 

SO -- if that's what's happening (and it OFTEN does), the intermod 
source may not be on the tower or the control lines, but somewhere else 
out in the environment. Indeed, it could even be in one of the 
transmitters that is involved in the intermod. 

A year or so ago, I had some noise show up on 160M, and I went looking 
for it with my 2M/440 talkie that has HF/MF receive capability. As I 
passed each power pole, I moved the talkie close to the ground downlead 
to look for noise. At one pole, I heard N7DD loud and clear calling CQ 
on 160. That ground lead wasn't radiating any noise, but it made a great

RX antenna for my talkie!

And thanks for Q last week in NAQP RTTY! 

73, Jim Brown K9YC


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