Dan,
I have a 4/4 stack of the M2 20M4DX yagis in the air at my home station (105/50
feet). They seem to work quite well so far. Construction wise they have kept
the cost down by building to an 80MPH specification. Result of this is a light
antenna (for a 35 foot boom). The positives are good performance and ease of
construction. I've as yet nothing bad to say about these antennas, but they
have only been up for 1/2 year or so which is hardly a suitable test. The boom
is ~2.5" diameter which is about as small as I would consider for this length
on a 20M beam. A 3" boom would be better but costs and weight go up. They
employ a dacron rope truss to control sag. I would replace with phillystrand
truss if I ever have a problem with the rope. Robust 1:1 balun supplied and I
like the M2 hardware and construction using SS bolts (machine screws) an SS
nylock nuts. On my homebrew beams I use the same construction methods.
F12 antennas are often higher priced than the competition for various reasons.
They perform well according to the folks that have 'em, and the Mag520 does
have an extra element compared to the 20M4DX which adds to cost. Check out the
mechanical specs and see what they are to get a fair comparison to the other
antennas. Also see if the balun is included and if not factor that cost in.
Can't speak to the Mosely antenna, but $1,250 for a 20M monobander of the size
indicated is nuts IMO.
The Cushcraft yagi I assume is the XM series 5L unit? I have the 15M version of
this antenna and it performs well. I would not buy another one, however, as I
personally prefer the M2 or F12 antennas from a construction point of view.
Cush is also apparently getting out of the monobander game which could effect
parts availability. The supplied balun is also crap and several of the parts
were not machined properly.
Hope that helps. If it were my station I would get the mechanical specs for the
F12 and compare it to the 20M4DX. Decide if one is more robust than the other
and what survivability you need. An ~36' boom should give relatively same
gain, but pattern and bandwidth of 4 vs 5L will be different. The 20M4DX
covers the whole band no problem in my hands.
You might also poke around for a Hy-Gain 205CA and see what turns up. I
recently found three 105CAs NIB at good prices by calling around a bit. Only
bought two and should hav grabbed the third but was being frugal with limited
ham bucks at the time :)
Best luck,
Mark
KI7WX
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