Pete,
As I was planning my antenna farm here at the new QTH 5 years ago, I took
great pains to lay out most of the Beverages on one side of the property
(12 acres) and the towers on another. Until recently I only had one
Beverage (switchable 342/162 degrees) that came close to a tower, and it
was 130 feet away from the series-tuned 1/4 wave 160m radiator (100 ft
tower plus top loading and small linear base loading).
All the other wires were at least 200 feet, most more, from any of the towers.
I did not find any increase in noise floor on the wire that was closest to
the tower.
Recently, after reading some of W8JI's antenna comparisons, I decided to
try improving my RDF (receive directivity factor) toward JA and 8N1. I
decided on two 935-ft phased Beverages aimed at 320 degrees. This meant one
wire would pass about 20-30 feet from the 160-meter tower, and another wire
would pass about 10-15 feet from 100 feet of Rohn 45 that holds a 3-stack
for 20m, 3-el 40m and 5-el 10m yagis.
I first installed the wire closest to the 160 meter tower, and used this
for several days by itself until I put the second wire up. The single wire
was a significant improvement over my old, shorter JA Beverage (450 feet)
that is more than 200 feet away from any tower. I could hear JA signals
last week on the 935-foot wire that were not there at all on the short
wire, nor on an 880-foot wire at 342-degrees or other wires at 205 or 290
degrees. To my surprise, I did not see any significant increase in noise on
the new long Beverage near the tower. I had fully expected I might need to
detune the tower during reception.
When I installed the second half of the phased pair, I initially just
hooked it up to a separate feedline so I could do some A/B comparisons on
the two wires. The second wire -- which runs near the Rohn 45 tower -- also
runs a few feet from the pole carrying the power line feed to my house,
which has a transformer on it and a vertical service feed down the pole and
then buried to the house.
The second wire was slightly, but noticably, more noisey than the first.
This could be from coupling to the Rohn 45 or the power line feed, or both.
Yet despite the slight noise increase, I found I could hear the weakest
signals about the same on either wire; the noise on No. 2 wasn't enough to
mask any signals that I could also hear on No. 1.
So I went ahead and installed the phasing lines on the pair on Saturday
morning. A benchmark test against a BC signal a few hundred miles to the NW
found the pair had several DB more gain than the single wires, as expected.
These wires are spaced 177 feet. As Tom has pointed out, 350-400 feet would
have been more ideal but I don't have the room to do that without going
under the power line feed, and I had tried that previously with some
Beverages and found they picked up a lot of noise from the power line.
Sunday we had zero signals from JA here, so no comparisons possible. Today
we had a good opening from 1155-1240z (sunrise was 1218) and the phased
pair was clearly the best antenna -- in many cases the only antenna I could
hear the JAs on, and in all cases better than any of the other wires.
During this comparison period we have had fairly clear weather conditions
-- only one snow day and the storm center had already passed to the NE of
us by 1100z, and that day seemed as quiet as the rest. I expect I may see
more noise pickup under more extreme weather conditions, as I found with a
much shorter (185 ft) Beverage that ran 50-feet from my shunt-fed tower at
another QTH back in the '80s. Coupling to the tower with that antenna
actually increased signal pickup, but if a storm was nearby I had to detune
the tower (by switching out the feed in the shack) and the noise and
signals dropped.
73/Jon AA1K
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