A 29 ft boom on 40M is only 0.2 WL which
maximizes at about 7.0 dBi for a 3L design.
F/B can be tuned to over 20 dB but is not
really a benefit for domestic contests.
A 2L design on a 20 ft boom can come close
to 7.0 dBi if you sacrifice F/B, is MUCH less
cumbersome with a more managable windload.
6.0 to 6.5 dBi is easily achieved with moderate
F/B and feed impedance.
You could even interlace a 2L WARC beam
on the boom if desired. Playing with the
40M feedline length / termination can be
done to minimize interaction.
I have a Cushcraft 2L40 at 95 ft and am very
happy with it, in spite of noticably reduced
performance on SSB (it is tuned for CW).
I has been up for over 5 years and survived
estimated 90 MPH winds that took out many
big trees in my woods. (The inner portions
of each element were double walled).
There are LOTS of tribander and 2L40 combinations
being rotated by HAM series rotors. A 3L40 will
probably eat up such rotors even cause cracking
in the galvanizing of undersized towers (R25).
73 / GL, Tom N4KG
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