Gang,
Thanks for the info on radials, I've put out a bunch of short ones around
the base and a few longer ones wherever they would fit.
KV8Q's very respectable ARRL 160 score using the K6MM short helically wound
vertical got me thinking about building one. While Googling information
about short verticals, I stumbled across an article about spiral top hats.
I was intrigued that many of the lowfers use these on their transmit
antennas with great success.
The recommended amount of wire for the spiral is about one quarter
wavelength. I built a 4' by 4' X frame out of PVC pipe and was able to wind a
spiral that used about 115' of wire. I put it on an 8' mast over my ground
field and found it to be resonant at 2.3 MHz! 2:1 bandwidth was about
15KHz. I did not attempt to put it on the air, but the results suggest that a
slightly larger spiral tophat or a somewhat longer mast would produce
something that might be resonant on 160M.
While I realize that an 8' vertical may not produce outstanding results, I
wonder what the downside is to this type of tophat on taller verticals.
It would seem better to resonate the antenna at the top, where currents are
lower, than using base loading. What is the verdict?
Paul, K5AF
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160 meters is a serious band, it should be treated with respect. - TF4M
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