Hi Van: L.B.Cebik has done extensive modeling on quads. You can find a
lot of info on his web page www.cebik.com He has also written 2 books on
quads which I have.
He found that multiband quads with separately driven loops on each
band have much better characteristics. He found that good performance
can be obtained by feeding each loop separately using a balun at the
loop then 1/4 wave of 75 ohm coax to the 50 ohm feed line. You can
either use separate feed lines from there or run the 1/4 wave lines to a
relay switching box on the tower. The lines to the unused loops may be
either shorted or open circuited but they cannot use a common ground. In
other words, you need to switch both the center conductor and the shield
at the relay box. Either open or shorted unused loops worked as well as
separate feed lines.
73, Dan, N5AR
K7VS Van wrote:
>
> Have had a three element tri-band Gem Quad up for twenty years and fed with
> single feedline. Has anyone done the work on feeding each driven element
> separately? Would appreciate any information on coax matching sections for
> each band if available. Have no way to get up and measure each driven
> element resistance on the tower and would very much like to feed each driven
> element separately. Thanks for any help available out there.
>
> Van, K7VS
>
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