Dave,
First I see by my log that we've had two QSOs---35 years apart--- one on 2-meter
EME and one on TB.
I'm no Beverage expert---antenna Beverage that is--- but it seems to me that
shortening the west antenna just decreased its sensitivity. If you're pointing
at one or more noise sources, there isn't much antenna improvements can do.
I can't recommend a tower detuning mode, however, you might at least consider
terminating the feedpoint on receive rather than leaving it open. My system is
quite modest on TB, a 55' vertical with an ~85' loading wire. The separation
between the vertical and a tower is 90'. The 85' loading wire is attached (via
an insulating rope) to the tower. The tower supports a triband Yagi and a
dual-band inverted-vee for 40-80. In doing some feedpoint measurements on the
vertical v. number of radials with a vector network analyzer I saw a little
anomaly on the Smith Chart. To make a long investigation short, I discovered
that either lowering the inverted-vee or terminating the coax at the shack end,
rather than having it open, corrected the anomaly. I have no clue as to what
this might have been doing to the pattern.
Wes N7WS
On 3/6/2018 10:30 AM, David Olean wrote:
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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