On Mon, 6 Apr 1998, T A RUSSELL wrote:
> Interlacing elements for two bands on a common boom
> is a BAD idea. The low frequency directors act as inefficient
> REFLECTORS on the higher band.
>
> That is why Force 12 forward staggers duo band antennas
> on the same boom.
>
> You CAN line up reflectors in 2 element antennas (e.g. the Force 12 C3)
>
> de Tom N4KG
Another alternative: since 12 and 17 are narrow bands, 2-element Yagis of
DE-Dir design are feasible. With their shorter boom requirements, gthey
can be placed back-to-back on one boom. If you feed the 17 meter DE with
a beta match (best gain and F-B occur at about 20-25 ohms feed Z with
about 0.08 wl spacing), you can open-sleeve couple the two driven
elements.
Another alternative: Use a DE-REF design for 17 and a DE-Dir for 12, with
the 12-meter DE open sleeve coupled to the 17 m DE. This design models
very well, and the low reflector "helps" the 12m elements, while the high
director "helps" the 17 m elements--not a whole lot, but some relative to
monoband 2-element antennas.
Lots of options--and life is too short to build all of them.
-73-
LB, W4RNL
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