> 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
Hi Van,
That's exactly what I have done with my Gem Quad and it works great.
I use an RCS-8V remote coax switch and quarter-wavelength feeds of RG-62/U
(92 ohm cable) to each element. From my station notebook (everyone DOES
keep a station notebook, don't they?) the feedline lengths are:
20 meters (14.075 MHz) - 11' 6"
17 meters (18.100 MHz) - 8' 11-1/4"
15 meters (21.110 MHz) - 7' 8"
12 meters (24.900 MHz) - 6' 6"
10 meters (28.250 MHz) - 5' 8-3/4"
You should cut your own stubs to length using an SWR analyzer - cables vary
sufficiently that these lengths could be off by a few percent. Note that I
eventually changed the 10-meter stub back to RG-8X because the 10-meter loop
impedance was lower than 100 ohms and the 50-ohm cable gave a better match
(about 1.3:1 in the shack). RG-62/U is not a high-power cable (I don't have
an amp) so you would want a higher power 90 or 92-ohm cable.
At the element, I used a small piece of perfboard and brass hardware to
attach the feedline to the #20 wire used in the quad and provide strain
relief using small, black Ty-wraps. I also bundled the feed cables
together. To provide additional stabilization, I ran a 1/8" nylon cord from
the spider to the 20-meter feedpoint and all the feedpoints are tied to it.
That's a big wad of cable up there and it can get to swinging around pretty
wildly in the wind. I had continual element wire breakage until I put the
small support boards on the antenna and tied them all together.
73, Ward N0AX
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