I have a temporary low inverted vee for 160 meters. The apex is at 50 ft
ant the ends are at 15 feet. It has a choke on the feedline. Yes, I know
it's a lousy DX antenna. I also have an XM240, 2 element 40 meter beam
at 65 feet. The inverted vee is under the beam. On receive on 160 meters
the 40 meter beam has a much better signal to noise ratio on ALL
signals. My question is WHY?
The noise in question is atmospheric noise. I'm not considering TV
birdies and electric fence noise. The 40 meter beam has a little
directivity on 160 meters but it is better than the inv vee no matter
where it is pointed. I looked at the EZNEC response of these antennas to
see if I could answer the question, but the answer wasn't there, or if
it was, I sure missed it. The patterns of both of these antennas are
close to the same. Looking at the patterns, you would expect the
inverted vee to be little lower noise if the beam was pointed the wrong
direction, but this isn't the case. The gain on the 40 meter beam is
about 12 dB below that of the inv vee. That's mainly because of the
large coax loss due to the huge SWR. And no, the signal to noise ratio
does not change if I add attenuation when using the inverted vee.
So, any of you low band noise gurus care to venture a guess why? I
always had the impression that the only way to improve signal to noise
ratio on 160 was to narrow the receive lobe pattern. Am I missing
something? There has to be a logical explaination for this.
Here is another piece of (maybe unrelated) data. Yesterday I went out
and quickly put out a 1000 ft BOG (unterminated) for the 160 meter
test. It had a ground and a common mode choke on the feedline. It
didn't work. It was noisier than either of the other two antennas.
Shortened it to 700 ft, and still no good. Didn't use it. This was
puzzling also, but not as much as the beam/inv vee question.
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