Several years ago, I had a similar problem with AM stations 1510 and 910
that were 600 khz apart. They were both about 5 miles away from our
repeater. Our 146.94 repeater when it keyed up was hearing the audio
combination of both AM transmitters that were on during the day. The
problem went away at sundown when the one AM station went off the air
and returned the next morning at sunrise when it came back on.
We traced the IMD mix point to a guy wire anchor plate on a nearby 120
ft tower that was rusty and it wasn't even galvanized! We solved the
problem by adding wire jumpers with cable clamps from each guy wire to
the anchor rod which shorted out the diode action of the rusty anchor
plate.
John, K7JL
*************
Message: 21
Date: Thu, 06 May 2004 04:52:01 -0000
From: "Laryn Lohman" <[EMAIL PROTECTED]>
Subject: Re: 2m repeater IMD issue
This is something fairly easy to check, and is my experience with
structure generated IMD.
Two FM broadcast stations, one is 1 mile away from our repeater, the
other is much higher power and about 8 miles away. Their frequencies
are 89.3 and 89.9---600kc apart. The intermod generated was very
broadband because of the FM station deviation at 75kc. It caused no
problems until BOTH stations were transmitting little or no audio,
then it would show up.
Anyway, the intermod was generated at the guy anchor points. Tower
riggers often lace a piece of cable through the turnbuckle centers to
keep them from rotating. Where this cable touches/barely touches the
turnbuckle is where the problem was. Simply isolating these elements
from each other with pieces of cable insulation cured the problem.
Ya never know..... All the best finding your problem.
Laryn K8TVZ
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