This does not exactly address the original question about mounting a
vertical with sloping radials on tower sections. Making and adjusting
radial sets for several bands, based on previous experience, can be a time
consuming project.
I have often wondered whether elevating a vertical has any advantage over a
vertical on the ground with a good radial system. "Good being defined as 40
or more radials, 0.2 wavelength or longer at the lowest frequency.
Last summer when lightning took me off the air for several days, I decided
that I needed some backup antennas. Several ideas were considered, but
eventually, I put up 4 verticals, mounted on standoff insulators, around a
tiltable structure of 2 X 4s and a 4 X 4 post in the ground. I installed a
radial field of approximatley 50 wires, from to 25 to 35 ft long. The
verticals were adjusted for lowest SWR at 7.025, 10115, 14050 and 18080 and
fed in parallel (see note below), Several on the air checks confirmed the
antennas were working as they should.
Some weeks later, I decided to purchase a multiband vertical, the
Hygain-MFJ AV640, covering 40-6M. After assembly, I installed it on a 12 ft
mast and adjusted for low SWR on all bands, 40-6M. I made a few A-B checks
between the 2 systems, but did not draw any conclusions (I can switch
antennas in 1-3 seconds). Subsequently, I installed the AV640 on a 24 ft
tower stub.
Listening tests comparing the on ground verticals to the elevated vertical
consistently showed louder RECEIVED signals on 40, 30 and 20M for the on
ground vertical compared to the elevated vertical. I did very few
transmitting tests because of inconclusive results due to QSB and
"emotional data" factors mentioned by others.
I changed the 17M on ground vertical to a 15M one and concluded that the on
ground verticals were still better on 40, 30 and 20M, but the elevated
vertical received better on 17 and 15M. There have not been enough signals
on the other bands to do any listening tests at all.
My conclusion is that the on ground vertical, in my application, is a
better antenna than the elevated vertical for the bands 40, 30 and 20M. For
17-10M, the elevated vertical would appear to be better.
Bear in mind that these are receiving tests only, over my radial system
(for the on ground system), using my equipment and observations. Conditions
might be different elsewhere.
The idea for mounting several verticals in parallel over a radial system
came from an article by WA5ABR in Compendim 5: "Homebrew Seven-Band Vertical".
Maybe a combination vertical-horizontal ( inverted L) wire over a radial
system and fed by an auto tuner at the base, would be a better all-band
backup antenna. I am still trying to come up with an ideal length that will
provide a reasonable impedance to the auto tuner. Possibly a trap will be
needed.
INK N4OO
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See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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