James. I dont know of a multiband yagi with an 18 foot boom that is better. The
computer and nec wires jaust lets us understand the comprimises. I am now
looking at how to implement 12 m with minimum impact. 73 Art
James R. Duffey wrote:
> 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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