I have been putzing around trying to improve my 160 meter setup, and
have run into a real problem. Most of the USA is covered by two
directions from here in Maine. SW and W. My problem is that I have an
excessively high noise level on both of the beverages that run in these
directions. In the last six months it has gotten worse, and so bad that
I cannot use either beverage. The wires terminate at the side of my
barn where I have ground rods and the RG-6 goes through PVC conduit up
to the shack on the second floor of the barn. During the day I see
noise levels at -133 or -132 on the two wires, but at night the noise
had climbed to levels around -100 or to -110 on a good night. I
suspected that I was getting noise coupled in from my vertical which is
rather close and on the other side of my barn all of 55 ft away.
Yesterday, I modified the west beverage and shortened it so that it
terminated about 150 feet away from the barn and I ran new coax back
across the field. I kept the SW beverage as is to compare noise levels
at night. Lo and behold, but the noise went to -110 on the SW beverage,
but only about -120 dBm on the modified beverage. This is a 10 dB
improvement. Other directions at night run at about -130, so I am now
seeing a 10 dB extra hit in noise to the west.
The vertical is a shunt fed Rohn 25 with a total height just over 90 ft
with top loading from a 5 element long boom 10 Meter yagi. I am not sure
if it is possible to simply un resonate this tower. Does anyone have
experience with simple ways to decouple a shunt fed tower from the rx
antennas?
The extra 10 dB of noise that I get to the west and SW is mostly due to
the location of a town about 7 or 8 miles away in NH. It is ripe with
all sorts of power line noise. I still can't rule out re radiation from
the vertical though! I spent many years fighting with the electric
utility to quell the noise. I involved Riley Hollingsworth and later on,
Laura Smith, his replacement. The effort was futile and I lost heart as
the problem was just too big for one person to fight. I was hoping that
the noise would not affect 160 meters as it had messed up my VHF
exploits, and so far I only have this ten dB swath of noise that bothers
me in two directions.
Any help with un resonating a shunt fed tower would be appreciated.
Dave K1WHS
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