Having had a Butternut vertical when we were in S. FL, all the mechanical
parts and clamps and SS screws lend way for rectification to take place.
Likely it's time to clean it up mechanically.
Intermod is two or more signals which mix to produce products which are the
sum and difference of the two plus the two original signals (4 signals
present) and should 3 or more external signals get involved then things get
worse mathematically. There's software on the web that determines the
probability of IM if certain signals are know.
In a factual case when we lived a few miles east of Nashville, TN, the sum
of channel 4 TV {67.25 MHz}plus channel 5 TV {77.25 MHz} mixed together
produces a signal at 144.500 MHz. and the difference comes out spot on 10.0
MHz. These two signals with their respective video modulation created havoc
with the EME receiver and a big 2 meter antenna when pointed west.
Solution: add an electrical 1/2 wave of coax resonant about the frequencies
across the front end of the receiver. Problem solved.
So the LP filter is doing it's job in removing the offending RF from the TV
transmitter. Oh, these UHF transmitters and their gain antennas often make
for several megawatts of ERP. Other words, lot'a RF.
73
Bob, K4TAX
----- Original Message -----
From: "Phil" <flor0045@metnet.edu>
To: <tentec@contesting.com>
Sent: Thursday, December 13, 2007 2:12 PM
Subject: [TenTec] Omni VI, opt.3 UHF Intermod
I have the subject rig. The intermod was intermittant. It took a looong
time to figure out it was being caused by channel 23 or 29 (I can't
remember) about 7 miles from me. My antenna is a Butternut vertical. The
problem is now gone thanks to an old Drake LP filter.
Phil, K0UBC
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