----- Original Message -----
From: DAVID CUTHBERT<mailto:DAVIDNNAN@MSN.COM>
To: towertalk@contesting.com<mailto:towertalk@contesting.com> ;
topband@contesting.com<mailto:topband@contesting.com> ;
WarrenWolff@aol.com<mailto:WarrenWolff@aol.com>
Sent: Sunday, December 26, 2004 7:38 PM
Subject: More: Topband: New Antenna
ï
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
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.
The only design that does not need the 35' pole.
Number 1 looks bad. Scratch that one. Numbers 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 antenna 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.
If your ground system is good I would not bother with the added complexity of
this one.
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.
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
----- 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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