Art, Bill, and Towertalkians;
That is interesting data to look at. Thanks for sharign it with us.
I think that Bill is right, it will be difficult to find a 3 or more
element quad design that outperforms a Yagi with the same boomlength.
Wayne Overbeck, N6NB showed this experimentally in his study published in
the May 1979 Ham Radio. He was unable to find a three or more element quad
that outperformed a Yagi with the same boom length.
Moxon has addressed this point in his "HF Antennas for All Locations" book.
His claim, which I am not sure is rigorously correct but is intuitively
enlightening, is that loops do not make good directors as the coupling to
the driven element is largely inductive with loops rather than capacitive
as is needed in a parasitic array.
I would suggest that the 15M/10M coupling problem could be reduced by using
a single driven element rather than nested elements. The 15 M element
should also be resonant on 10 M, being 1.5 wavelengths around, and a
matching network for hte two bands should be rather easy to build. Two
separate reflectors should be used, each spaced optimally for the band. I
think a director loop could be added for 10 M, but if one is added for 15M
then it will probably screen the 10 M director.
Multiple band antennas are of neccesity compromises. I imagine that there
is all sorts of interaction with 5 nested loops in three elements. I think
that quads are at their best as two element antennas.
The computer will help you understand and optimize the solution, but it
cannot change the basic problem of what compromises one is willing to
accept to get multiband operation from a single antenna.
Let us know how it all works out. - Duffey KK6MC/5
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