I've built several 2m Moxons. They are small and lightweight, and are
my wife's favorite antenna for transmitter hunting on foot (at least for
horizontal polarization.)
This is a good example of the tradeoffs to make in choosing an antenna.
A Moxon doesn't have a lot of gain compared to other beam antennas.
For vertical polarization the pattern is very wide: +/- 120 degrees or
so, with a sharp null in the rear. So it gives a little gain in a lot of
directions. Other designs will give more gain in a narrower range of
directions - it all depends on what you need in your specific situation.
If most of the stations of interest are within a 180 degree azimuth then
a Moxon can be fixed and will cover the whole range somewhat better
than a dipole or groundplane. The Moxon is short enough that it can
be side-mounted on a mast, keeping metal supports out of the field
of the antenna. For horizontal polarization the pattern is more narrow,
and again it gives a reasonable gain and good F/B ratio in a small space.
But in many cases, especially for VHF, a 2-element quad or 3-element
yagi is still a practical size, and they will have more gain than a Moxon
(and correspondingly a sharper pattern.) Although somewhat larger,
they can still be built small and light enough to side mount on a mast
if necessary. In my experience the Moxons were more difficult to build
than quads or yagis, but part of that is the choice of materials that I
happened to use.
As is so often the case on antenna topics, W4RNL's web site has designs
for quads, yagis, Moxons, half square beams, etc., along with pattern
plots and gain figures for each. That allows you to compare them to
see what designs give the compromise between gain and pattern for
your specific needs. Be sure to check his Antenna Options series here:
http://www.cebik.com/ao/ao.htmlespecially the first three articles, which will help you understand the
tradeoffs in beam design and different construction methods.
Remember that there are at least four SEPARATE things to consider
about an antenna: (1) the design, which determines the gain and
pattern; (2) the mechanical construction - the materials used and how
they are connected together; (3) the feed method used to match it
to the feedline; and (4) the frequency it is built for. Although there are
some interactions (for example, using a larger diameter material
requires a change in the element lengths to implement the same
design, and construction techniques that work for 2m may not be
practical for a 40m yagi) these tend to be independent. For example, I
can choose a Moxon, 3-element yagi or quad with various options for
the element dimensions and spacings - that is the design. For each of
those I can build it using aluminum tubing, copper wire, or tape
measure blades for the elements, and a metal or insulated boom.
Then I might feed it with a gamma or delta match if I wanted a continuous
driven element, or split the element and connect the coax directly
across it, possibly with further matching from a shunt coil ('beta match")
or a quarter wave transformer. That same design can be scaled to
2m or 440 MHz or 20m, with appropriate mechanical considerations.
So if you find a particular construction method that seems within your
building capabilities, don't feel constrained that you can only use it to
build the specific antenna you saw that used it. Similarly you don't have
to build an antenna for the same band that you found in an article
(though you do have to be careful about the relative diameters of the
elements and mounting methods, especially for high-performance
designs.) And, just because you find a design posted on the Internet
doesn't mean it really works as claimed!
Here are some other interesting yagi designs that are not hard to build:
http://www.mydarc.de/dk7zb/start1.htm
