On 1/18/2019 7:44 AM, john@kk9a.com wrote:
The thread took on a new terrain modeling life but I saw no indication
that you lived on a mountain top. There is essentially no radiation
difference between mounting your 40m beam at 63 or 67 ft. I would not try
to make a tower section out of a mast so I would mount the antenna near
the top of the tower and use a short mast. It will work fine for domestic
and DX.
GL,
John KK9A
Here's another data point. I live in the flatlands. I have A/B'ed a
beam at 40 feet vs a beam at 100 feet with many stations heard on
both beams. The 100 ft beam has an advantage of 0 dB to maybe 20 dB at
the most. I have never observed it to be worse than the 40 ft high
beam. If I make the leap of logic to say that dB are linearly
related to height, then 0-20 dB over 60 feet of height difference
works out such that a 1 dB difference could happen in as little as 3
feet, but more likely it would take 10 feet to get 1 dB a significant
amount of the time. So a difference 4 feet is not worth while. Better
to get lower loss coax. I use RG218 on my big tower.
OTOH, mechanically I concur with John: using a long mast doesn't have
a good cost vs benefit value proposition for a single antenna. A long
mast is only worth the hassle if antennas for different bands are
being stacked.
73
Rick N6RK
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