[TowerTalk] Shunt Feeding, Can this be?
chilesp at adelphia.net
Tue Nov 15 15:28:51 EST 2005
I now have 30 radials installed on my tower and am shunt-feeding it through new coax, an antenna switch, and a vacuum variable. The coax run is 30ft. The tower is a 55ft crank-up with 20 ft of mast out the top and a TH7 at 56ft and a XM240 at 69ft. The shunt wire is 30 inches away from the tower and is #6 stranded. I am able to get 1:1 on both 80M and 160M with my motor driven variable in a Gamma match configuration.
The 1:1 reading is absolutely flat for about 60-70Khz. It is the same on both bands in as far as being flat and wide. I thought I might have a poor ground, but I have double checked all connections and resoldered everything that looks even remotely bad. I also have 15 ground rods connected to the tower on three legs besides the radials. This is my first attempt at shunt feeding a tower and my question is if it is possible to have such a flat SWR on a shunt fed tower? My numbers are with the MFJ are:
1830Khz R=24 X=167 SWR>25 397pf on the vacuum variable for a 1:1 reading
3500Khz R=24 X=295 SWR>25 157pf on the vacuum variable for a 1:1 reading
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