Warren,
I thought I had better really simulate the flagpole rather than just dismiss it
out of hand. Here are some possibilities:
1) wire from the top of 35' flag pole to the tower, at the 35' level. Rr = 7
ohms
2) wire from the top of the 35' pole towards the top of the tower. Rr = 16 ohms
3A) wire from the top of the 70' tower (not attached to the tower) towards the
top of the 35' pole. Rr = 16 ohms. Fed at the base.
3B) wire from the top of the 70' tower (not attached to the tower) towards the
top of the 35' pole. Rr = 16 ohms. Feed at the 70' level. About 40 ohms.
4) wire connected to the top of the 70' tower towards the top of the 35' pole.
Rr = 17 ohms. Shunt feed.
5) tower feed. Rr = 16 ohms. Shunt feed with a wire to the top as you proposed.
6) top load the 70' tower with a coil and a top hat or spike. Rr = 25 ohms.
Feed with coax at the base of the spike/top hat. It can be thought of as a
vertical with elevated feed or an Isotron.
Number 1 looks bad. Scratch that one. Numbers 2-6 all look good from a
performance standpoint. Numbers 2, 3A, 3B, 5, and 6 are interesting. Number 6
can be matched with a 90 degree, 75 ohm coax, as the input R is around 140
ohms. Number 6 has the highest performance and might be the way to go if your
ground system is not very good. You get 9 ohms more Rr at the expense of a
couple ohms of top loading coil loss. For ease of getting it to work I would
chose 2, 3A, or 3B.
These sims are subject to having better inputs (dimensions, ground, radials,
etc.) but I believe them to be good for comparison of the different designs.
All of the rest are adjusted to resonance by the length of the horizontal wire.
BTW, I use a 38' top loaded vertical. It is all I can fit in my antenna
unfriendly neighborhood and small back yard.
Dave WX7G
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