At present, I have a horizontal loop for 6 meters at about 20'. Six has had
a lot of openings lately so I thought I'd play with a small yagi. In
searching the web, I ran across an article for building a 2 element yagi out
of PVC and coax. (http://www.hamuniverse.com/K4mmg2and6meter.html) The
inspiration was N0KHQ's 17 meter coaxial Moxon.
(http://www.hamuniverse.com/17mcoaxmox.html) The purpose for using coax is
to shorten the antenna elements.
I took the concept and built a three element yagi on a 6' boom. Using double
shielded RG-58 cable, my driven element was resonant on 50.125 at about 66"-
about 40% shorter than a conventional wire dipole. I used the same scaling
to cut the reflector and the director.
With the yagi at the same height as the loop and about 25' away, both
antennas give identical S meter readings on a nearby 6 meter beacon. With a
5 watt source located about 250' away from the antennas, I used an Avcom
spectrum analyzer to measure signal strengths on each and found them to be
within a dB of each other when the yagi is pointed at the source. The
feedlines are identical coax and pretty close to being the same length.
The front to side on the yagi is about 10 dB and the front to back is pretty
much nonexistent. (I suspect that my scaling didn't work very well for the
director and reflector...)
At any rate, it appears that the shortened coaxial elements do work. It
would be an interesting exercise to build a 40 meter Moxon.
Has any one else had experience with these antennas, especially as to
efficiency when compared to full sized elements? Cebik had a page on his
website that discussed N0KHQ's Moxon, but the Google link to it is dead.
Doug
K4DDR
_______________________________________________
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.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|