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?

Generally, yes, as the height above ground exceeds the element spacing.

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 Wires window, click the Wire tab then find Change Heigth by... in
the list that appears.

FYI MFJ is now selling 15, 10, and 6 meter Moxons. The 10M version is
$84.95. I bought one, assembled it, but haven't put it in the air yet.

MFJ is claiming 3.3 dBi gain and 30 Db front to back.

It appears to be good quality for the money but we shall see once it is
in the air.




--
Jim Pennino