I have a converted motorola mitrek repeater installed at a water
tower. It runs up appx 150' of 7/8 andrews heliax to a DB-420. It has
been playing happily for several months. In the last few days we have
been getting a noise of some sort only on recieve, not on the talk
out. It is only audible on very weak portables and occasionally pops
thru after an un-key. It almost sounds like a 60 cycle electrical
buzz. We have noticed it does change in intensity, sometimes not
audible at all, but it is there most of the time.
I stopped by the site today to see if i could isoate it. I brought
out the spectrum analyzer to see if i could find anything. Nothing,
either locally in the tower or through the repeater antenna. I was
able to isolate the noise down to this: If I unhook the antenna, more
specifically the outer shield, the noise goes away. My first thought
was ground loop of some sort. I disconnected the ground to the
cabinet and polyphaser and used a ground lift on the power supply to
cut the other ground paths but i still had the noise.
Any suggestions?
Tom
W9SRV
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