Warren,
I thought I had better really 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
3) wire from the top of the 70' tower (not attached to the tower) towards the
top of the 35' pole. Rr = 16 ohms
4) wire connected to the top of the 70' tower towards the top of the 35' pole.
Rr = 17 ohms
5) tower feed. 16 ohms.
6) top load the 70' tower with a coil and a top hat or spike. Rr = 25 ohms.
Number looks bad. Scratch that one. Number 2-5 all look good from a performance
standpoint. Number 2 looks to be the simplest to implement. This can be fed
directly with 50 ohm coax and tweaked with a good tuner at the shack. This is
the one I would seriously consider. Number 6 has the highest performance IF
your ground system is not very good. You get 9 ohms more Rr at the expense of a
few ohms of top loading coil loss. This one needs shunt feeding of the tower
and is a lot more complicated to get going than number 2.
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.
None of these, except for number 6, requires loading coils. All of the rest
are adjusted to resonance by the length of the horizontal wire.
Dave WX7G
----- Original Message -----
From: WarrenWolff@aol.com<mailto:WarrenWolff@aol.com>
To: towertalk@contesting.com<mailto:towertalk@contesting.com> ;
topband@contesting.com<mailto:topband@contesting.com>
Sent: Sunday, December 26, 2004 12:29 PM
Subject: Topband: New Antenna
Greetings,
I have a question about choices on 160 meters.
I expect to have a new home at Lake Havasu City next summer.
I will have a 60/70 foot fixed tower topped by a couple of OptiBeams
(16-4 and a 4-40).
About 100 feet away, I expect to have a 30/35 foot flag pole.
What is my best way to get on 160 with this arrangement? A couple
of ideas come to mind.
1) Shunt feed the tower
2) Use a wire between the top of the tower and the top of the
flagpole to use as top loading for vertical wire in the center
of it.
3) Extend an arm out from the top of the tower, say around 6-8
feet and drop some kind of vertical element to be base-fed.
Advice is needed; please donât say I am nuts.
Warren; W5KKW
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