On 6/24/2014 11:10 PM, Sal M. O'Nella wrote:
I try to take a new antenna to Field Day every year. This year I
decided on the Moxon, AKA the Moxon Rectangle. I signed up for 10m
Phone, figuring I could build that antenna and it would be small enough
to be transportable. I began reading about the Moxon design a few years
ago but this was my first time to construct one.

I drive a van. For a long-past antenna takedown party for the widow of
a Silent Key, I made a wooden frame to add length to my roof rack, about
8 feet, total. The Moxon antenna is 12 1/2 feet long, so my frame
should work.

My Moxon structure is PVC pipe and the elements are #14 wire. The
dimensions fall out of a program called MoxGen and they will come out as
an EZNEC .ez file. Nice. (I bought a licensed download of Roy
Lewallen's EZNEC for the occasion.)

I noticed a couple of things I didn't expect. One, setting the EZNEC
height of the horizontally-polarized Moxon anywhere from 0.2 to 1.0
wavelengths above ground seemed to affect only the radiation pattern in
elevation view -- including take-off angle, upward-pointing lobes. The
resonant freq didn't seem to change much , which surprised me. I've
found a common dipole to be quite sensitive to height vs. resonance.
Does the addition of a parasitic element, in this case a reflector, make
the height-above-ground less influential?

Two, MoxGen seemed to produce a model that was too big . . . and EZNEC
seemed to agree. However, when I built the antenna, it came in around
27.600 MHz, not the 28.4 I asked for. My elements were all cut and
installed to tolerances of a millimeter or two, although I don't know
what I should have had for bend radii -- I just shaped the bends around
my finger so the measured bend point was halfway though the bend. After
I checked it with the analyzer (AA-54) I trimmed the elements and I have
a nice low SWR where I want it.

The Moxon is supposed to offer a few dB gain over a dipole. Its selling
point is a high F/B ratio, exceeding 15 dB. I can aim to Hawaii, for
example (from San Diego) and all of North America gets two S-units
quieter. Whether 10m will be open for Field Day remains a question, I
may sit next to the coffee pot for more time than I spend logging contacts.

Aside: I looked in EZNEC for a quick way to change the height of an
antenna model and found no obvious signs so I just "arrowed-down"
through the "Wires" table and changed all the Z-axis numbers. With only
twelve entries, it was not bad -- this time. Is there a hidden trick to
quickly alter the height-above-ground an EZNEC model? Yes, I could
email Roy but he has other things to do.

"Sal"
(KD6VKW)


In the wire table and dialog box, click on the Wire menu and find Change
Height by...