I was asked if the open-sleeve coupled opposite direction combination for
12 and 17 could be adapted to 40 and 30 meters. The answer is yes, if you
have plenty of side-to-side room.
I scaled the antenna to 7.05 and it covers 7-7.1 with ease. The frequency
relationship between 40 and 30 is closer than between 12 and 17. So when
I scaled and reset that part of the array (which did not affect the
40-meter portion), it handled 30 with better than expected results--about
7.4 dBi (compared to about 6.6 dBi originally)--mostly due to the 40-meter
director acting something like a 30-meter reflector--with no reduction in
F-B. Feed Z still about 20 ohms on both bands for a beta match or
balun/transformer match.
Here is the rub: 70' driver on 40. So far, I have no feasible way to
significantly shorten the elements of the close-spaced DE/Dir arrangement
and preserve the pattern. The DE/Ref is much more forgiving in this
regard.
So the scaling is electronically feasible, but the mechanics may be beyond
the scope of almost all folks. But if someone decides to build one, he
will have a beam that will outperform any of the short element 40 meter
2-el Yagis within the frequency scope, plus have good 30 meter
performance, all on a short (<25') boom, if you can live with the
Janus-faced orientation.
Just thought y'all might be interested in what happens when you think big.
-73-
LB, W4RNL
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