And the winner is...
I just had the rare opportunity to compare two very different 40m antennas
"side-by-side" and thought the results would be of interest. I've had a 40m
4-square with 60 buried radials per element for about five years. Yesterday,
I put a used 40-2CD at the top of a 50-foot AB-577/GRC portable guyed
military surplus mast (HD-73 rotor) and compared the two antennas. There was
no contest at all: even at 50ft, the 40-2CD is 1-2 S-units louder than the
4-square. Assuming my 1000MP meter is calibrated for 6dB per S-unit, that
translates to 6-12dB. I'm sure getting the 40-2CD up higher would improve
these results.
I say the opportunity for such a comparison is rare because most people
replace one antenna with another rather than keeping the old one and adding
a new one. We often see claims like "this antenna is so much better than my
old antenna", when the comparison is actually made from memory of what the
old antenna was like. That's subjective at best. There's no substitute for
being able to switch back and forth under a wide variety of conditions. It's
also nice when the difference is definitive, as it was in my test.
I've been wondering about the relative merits of the 4-square and beam for
some time. A couple of years ago, someone at a YCCC meeting complained that
his 40m 4-square just couldn't keep up with the 2-el beams (can't remember
who it was.) I disputed the claim, feeling that my full-size 4-square with
60 radials per element was reasonable close in performance to a 2-el yagi.
This assertion was partly based on having done reasonably well on 40m in
contests, partly based on denial (building a 4-square is a lot of work!),
but mostly based on having misunderstood the theoretical gain numbers for a
4-square. I thought that a 4-square had about 5.5dB gain over a dipole,
roughly equivalent to a 40-2CD. In fact, the gain of a 4-square is only
5.5dB over a single vertical (monopole.) Near as I can figure it, a dipole
over real ground is about 5.5dB louder than a monopole over average ground.
That would make a 4-square about equivalent to a dipole. The 40-2CD would
therefore be at least 5.5dB louder than the 4-square, and probably more if
the 4-square efficiency isn't optimum. That explains the test results pretty
well.
Before you call me a doofus for making that mistake, go try to find the
numbers in the ARRL Antenna Handbook or in ON4UN's Low Band DXing -- the
numbers are there but you have to do a lot of flipping around and converting
of dBi to dBd, adjusting for ground, etc. A simple table comparing various
antenna designs under "typical" conditions would be nice, wouldn't it?
I got really interested in the comparison when I noticed that as my contest
scores got better by improving other antennas, my 40m QSOs always lagged the
competition. Eventually, it became clear that I was giving away too much on
40m and that I must have been wrong about the 4-square. Luckily, the used
40-2CD became available for a one-year loan just as I was pondering what to
do (the same fellow loaned me an extension kit for the AB-577/GRC that can
raise the height to 75 feet.)
Of course, a 4-square has other advantages. If the radial system is good,
the radiation angle should be lower. I'll have to check that out on some
long-haul paths. More important, the F/B of the 4-square is much better than
the 40-2CD. The 4-square has an F/B of at least 20dB, while the 40-2CD seems
to be about 5dB-15dB (hard to measure, but it's clearly not very good.) This
could be important when stateside QRM is bad. Also, the 4-square is
significantly less noisy than the 40-2CD. Finally, the 4-square can switch
directions instantly. Still, all in all, I'll take the extra forward gain! I
should get a chance to check out the 40-2CD in action this weekend in IARU.
I've always loved the "idea" of a 4-square (an antenna you can build with no
concrete and no help), and it really is an excellent compromise antenna, but
it just doesn't cut it for bands higher than 80m.
73, Dick WC1M
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