Topbanders-
It's possible that I will operate XE3/W0AH low power, just north of Cancun,
in one of the 160M tests. I'm will be experimenting with a short vertical
here at home in Colorado to see if it is worth transporting to Mexico.
Since I'm limited by several travel constraints, one of which is a
package no longer than 62", I'm expermimenting with a 24' top loaded vertical
composed of five tapered 5' aluminum sections. I erected it this afternoon,
put one 100' radial down and one 12' toploading wire and resonnated it with a
B&W coil. As expected, it's a dummy load. It was about 20 dB down from my
home 90' top loaded vertical which works well. Loading it on 75M, it was
about 10 dB down from a 80M 1/4 wave vertical with lots of radials.
Tomorrow I'll replace the 12' top loading wire with three 15' wires
(hanging down from the top at about a 45 degree angle) and add at least three
more 100' radials and test it again. If I get to the point that this portable
antenna is only 10 dB down from my home vertical, I'll be quite satisfied
since in Mexico it will be mounted on the end of a 30' dock in the Carribean
sea, about 1-3 feet above high tide. Over salt water, I would expect it to
work fairly well.
Does anyone have any experience with such a short antenna over a very
good (salt water) ground? Or care to model it? Does it make any difference
whether it is 1' or 4' above high tide? Years ago, W2FMI wrote a series of
acticles on short verticals. His 40M, six foot, top loaded vertical
resonnated with a coil with about 60 radials worked very well. My 24' 160M
toploaded vertical would be the same approximate electrical wavelength.
I'm also experimenting with some wire antennas, but I'll not be able to
get any wires more than 25' above ground at the little hotel where I will be
staying.
Doug W0AH Colorado
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