I've wondered if induced signals into the tower may be causing a
problem with the 2M repeater I have been working with lately. I've
not seen a spark from induced signals yet, but suspect something is
resonant and being re-radiated causing a problem.
The 2M repeater was running on a brand new Celwave PD-340-3. I've
tried several other antennass and have the same problem. The
repeater is a pair of GM-300's back to back, running around 35 W out
of XMIT, going into 8 inch 4 cav duplexer by Wacom. Into the dummy
load, no desense, no duplex noise (I use superflex for all jumpers
and Heliax to the antenna). The antenna was top mounted at 150 feet
of Rohn 25G.
Normally, the repeater would work fine. No problems until early
morning or at night. Mainly in early morning hours, the repeater
would desense itself up to 20 dB, make all kinds of garbage noises
like popping and crackling, it almost sounded like someone was on the
tower taking two screwdrivers and rubbing them together next to the
antenna! Yet nothing on the tower is loose, and shaking the guy
wires when the repeater is actually acting normal doesn't cause
noise. I have even heard video buzz coming out of the receiver.
When I kill the transmitter, all noise goes away and the receive
signal is quiet.
There is a Ch 6 TV tower about 15 miles from me. There are two
pagers 152.480 and 158.700 about 1 mile from me. Other than that,
the tower is in a remote area far away from saturated RF generators.
Like I said, the repeater works fine duplexed to the same antenna
most of the time, just under certain conditions (like enhanced tropo)
does it mess up. I can't find out what's doing it.
I finally wound up using dual antennas, dropping the TX antenna down
30 feet from the RX, and it works like a charm. Could the tower have
induced currents and signals coming in and energizing something
causing a mix? The separation is 600 KHz and I don't know of any
strong AM stations on that frequency except for a 640 KHz station
50000 watts and 30 miles away. Guess I'll have to keep running dual
antennas until I figure out what's wrong?
73, KC4FWC
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