Q,
I had a IM problem several years ago with our 146.940
repeater. The repeater was a GE MastrII station with a
dual isolator on the transmitter and a bandpass
bandreject duplexer. The antenna was a Sinclair SRL229
mounted to a 40 Ft wood pole. The other transmitters
found in the IM mix were AM broadcast transmitters
nearby. One was on 910 khz and the other on 1510 khz.
Thats right, they were 600 khz apart. When the 146.94
transmitter came on the mix was present and heard in
the 146.34 receiver until the repeater timed out. One
clue was that the IM would go away at sundown and
return at sunrise. We found that the station on 1510
went to very low power at night. Both AM transmitters
were within 5 miles of this repeater and were very
strong.
It turned out that the mix was coming from a nearby
tower that had 3 rusty guy anchors. This was a 120 Ft
tower that was 200 Ft away. I solved the problem by
putting in jumper wires attached with cable clamps
from each of the guy wire to ground which bypassed the
rusty guy wire combing plate.
Look for any rusty guy wires, rusty joints between guy
wires, rusty tower joints, loose metal rubbing up
against a tower leg or section, loose hardware on a
tower,antenna elements that have come loose from their
mount. This should get you started.
The site that has the strongest interferrence is most
likely to have the problem nearby. This sounds like
the 146.70 location from your description.
I would make sure that both repeaters have dual
isolators on their transmitters. A dual isolator keeps
the transmitter PA from creating the 2A-B and 2B-A mix
from happening and being radiated back out through
your antenna.
I recently found and purchased a tuneable Sinclair
Dual Isolator and I tuned it down to 145.270 just
fine. Insertion loss was under 1 db and the isolation
was 75 DB on frequency. I got mine from Bill Hance,
KD7CWA. Bill knows his stuff and is good to work with.
John Lloyd, K7JL
Date: Sun, 3 Oct 2004 01:18:22 -0400
From: "Q" <[EMAIL PROTECTED]>
Subject: Intermod problem?
Trying to troubleshoot an intermod??? problem between
two repeaters.
The 146.10/.70 repeater's receiver gets blasted by the
147.90/.30 transmitter but only when they are both
transmitting. Yes,the transit freqs are 600khz apart
and they are only 5 miles apart. Would a circulator
help this problem?
Also have similar problem between the 146.07/.67 and
the 147.87/.27 repeaters when they are both keyed up.
Ideas?
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