Here is one that drove me nuts for almost a week when I was still at
the city...
- Mountain-top radio site (1800' elev).
- 260-foot freestanding tower
- 8-bay uhf antenna on top platform
- Connected to a MSF2000 transmitter on the city's 453.xxx paging
freq and a Zetron digital paging
Someone on the mountaintop installed a high-power paging transmitter
on 152.xxxx. Whenever the 152 transmitter and NOAA wx on 162.475
were both on the air, a monster spike would occur on output of the
local ambulance service's 460 freq. (Their repeater was 1/2 mile
down the ridge.)
We got blamed as we were the uhf site the 'interfering' signal
originated from, per the FCC agent from Atlanta.
If you disconnected our MSF2000 from its antenna, the interference
went away.
The problem was, the interference was still present if our
transmitter was off-the-air, and the 110-volt power cable was
unplugged!
We installed a circulator onto our uhf paging transmitter's output,
with a 25 watt load. Within seconds the black paint on the load
blistered and burned off. The load failed within one minute. I
replaced the failed 25 watt load with a 50 watter. Ditto! Running
out of lower-powered loads I connected a 250 watt load. Within
seconds it became too hot to touch, but did not fail.
Apparently the 152 transmitter's signal was mixing with the 162 MHz
weather transmitter's signal, INSIDE OF MY TANK CIRCUIT of my UHF
paging transmitter !!!
Keep this in mind when chasing interference.
Truth is truly stranger than fiction.
Mark Cobbeldick, KB4CVN
Monroe, VA
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