I think that the PAR SM-50 Moxon is a good rover antenna and probably the best
improvement I have made to my rover; certainly it was the best thing I have
done for my 6M roving. I think most other rovers who have one feel the same. It
is not a bullet proof-put it up and forget it antenna though, and you will
probably end up having to repair it at one point or another. But it is worth
it. Four dBD gain at 75 mph on 6M! The mind boggles.
I have put about 7000 miles on my PAR Moxon since I bought it, with many of
those miles at interstate speeds of 75 mph (or a bit more) and the antenna 12
feet or so above the pavement. The antenna holds up well at those speeds with
no modifications. Mine has never come apart just from driving at speed, even in
high winds or over rutted New Mexico back roads. Having said that, it is less
forgiving of colliding with overhead obstacles such as low lying trees, covered
gas station pumps, drive through awnings, parking lot ceilings, and motel
porticos. In these collisions, the side tubes usually get bent. You can bend
them back into shape easily, once. After that they work harden and a second or
third attempt to straighten them usually results in a broken side piece. I
carry a spare. If you get a PAR, I suggest that you get an extra side piece at
the same time; you will probably use it sooner or later. They are simple to
repair on the road.
We do live in a part of the country with few trees, so I don’t worry about the
Moxon getting snagged in trees too much. We just try to avoid low overhangs.
About every third trip I forget. But I do spend a lot more time reading those
posted clearance limits with the Moxon on the car than I did before. If I lived
in the east, where there are more trees, I would probably attach one of the
side arms to the driven element so it wouldn’t get lost in the trees if I hit
one. I think it was K4GUN who woke up one morning after an evening of roving in
the dark and found the reflector and side pieces on his Moxon missing, probably
residing in a low lying tree along a back road in Delaware. If you lose the
side pieces entirely, the TS-2000 autotuner will still load up the remaining
piece of the driven element OK and you have a shortened dipole. Similarly if
only a small portion of the side piece breaks off you can put what remains back
in, adjust the other side to match and have a Moxon tuned higher in the band
with a slightly asymmetrical pattern. Still better than a loop.
The Moxon is an excellent performer compared to a loop. It particularly shines
during marginal band openings, when the band is just opening and when it is
closing. Compared to a loop, it is much easier to hold a run frequency and to
attract the attention of strong stations who may not have their antennas
pointed towards you. At 4 dB gain over a dipole, it is probably 5 or 6 dB gain
over a loop, and that makes a big difference, particularly when signals are
near the noise level. If you are running a loop and want to make a big
improvement to your rover, go to a Moxon. The cost of the PAR SM-50, which was
$100 when I bought it, and I think now is close to $120 with the rise in Al
prices. That price is about the same, or not much more than a loop, I see HRO
is selling the M2 6M loop for $140, but the results from the Moxon are much
better than a loop.
At 7 ft wide and 31 inches deep, it is a big antenna, but the wire reflector
and 5/16 inch side pieces make it fairly light weight. You need to plan for it
in the installation. I use 1.25 inch EMT for a mast and that is more than
adequate, even with 8 ft antennas for the other bands installed. We drive with
it at 10 to 12 feet high and extend it to 15 feet or so when stopped. When I
first got the antenna and put it together in the driveway prior to roving, my
first thought was “This is a big antenna”. About that time Virginia came out
of the house looked at the Moxon and said “That is a big antenna. You’re not
going to drive with that on the car are you?” I answered, “No, you are.” After
initial test runs at lower speeds, we concluded that cruising at 75 mph with it
on the car was not a problem. With the additional wind loading the gas mileage
suffers though.
If you are into SOTA or portable operation, the Moxon breaks down nicely into a
3 ft long package about 2 inches in diameter and assembles quickly.
Dale provides excellent support for the antenna and has shipped me side pieces
on short notice. No balun is included so you probably should add one, a string
of ferrite beads do nicely, and, in case you are wondering, and everyone does,
there is nothing magic in that black box except wires connecting the driven
element to the SO-239.
James Duffey KK6MC
Cedar Crest NM
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