Jim Hoge wrote:
>
>
>I have a 70' crankup tower that I am considering shunt-feeding for 160m.
The question is >this: The tower supports a Tennadyne T-12 12 element log
periodic antenna that is not >electrically connected to the mast and tower.
Should I install a relay .....
Jim,
I have done a few of these from scratch to create high performance multiple
band antenna systems in one structure. For W7MCO I calculated 90' of Rohn
25 over the base insulator with a Force 12 C4XL for top loading to make it
resonate on 160 Meters. I had not used one of the Force 12 antennas
previously and did not know how much capacitive coupling to the insulated
elements would take place in actual operation.
As it turned out, I could never get the resonant frequency above ~1700 kHz.
So, I wound up taking one full 10' section out of the tower below the Force
12. Now a short stinger ABOVE the Force 12 is needed to resonate the tower
at 1840 kHz.
Summation, the Force 12 C4XL on top of an elevated, insulated base, series
fed Rohn 25 tower provides capacitive top loading equivalent to
approximately 35 feet (10 Meters). You can see the structure among the
photos at http://www.eaars.com/~n7gp/
Good luck de Milt, N5IA, one of the ops at N7GP and NA5NM
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