[TowerTalk] Shunt Feeding, Can this be?

Pat Chiles 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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