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[TowerTalk] 160m Vertical

Subject: [TowerTalk] 160m Vertical
From: AB5MM <>
Date: Mon, 17 Sep 2007 11:40:06 -0500
List-post: <>
Thank all of you for the answers and suggestions so far in this hair 
pulling project called "Matching at 160m Vertical".

Larry N8KU, John KK9A, Carl KM1H, Bob W5AH, Rodger KI4NFQ, Frank W3LPL, 
Arlan N4OO, Jeff N8CC

I need to answer a few questions:
(1) The SWR analyzer(s) MFJ-249 and MFJ-259B.
(2) We are also using a Eico 170 GDO.
(3) The ground radials are located on top of the soil. I made a aluminum 
grounding buss bar as a central location for all ground radials to 
terminate at a common location. The buss bar is bolted directly to the 
tower base at around 6" above ground level.
(4) Sweeping the tower directly at the feed point (short RG-8 pig tail) 
I do not have a dip anywhere in the 1.8 to 2.0 MHz range.

It does show a slight dips at;
1.739 MHz with a swr of 3.7/1 with X=29 & R=10.
4.254 MHz, 4.6/1 swr  X=100 R=30
4.734 MHz, 4.0/1 swr  X=28 R=86
5.670 MHz, 3.3/1 swr  X=29 R=80
8.665 MHz, 2.2/1 swr  X=49 R=36

The formula for a 1/4 wave length radiator is 234/fo. I really think 
that is for a reasonably sized wire antenna. The Rohn 25g is ~12" in 
diameter, which would make the Q a little lower (wider band width) as 
well as shift the resonance down a few kc. I think we are very close to 
the correct height, if not a little short at 120 ft. - 6 inches. Do any 
of you think the guy wires are adding a capacitive loading component? Is 
that what's throwing a wrench in the works?

I'll sweep the tower this afternoon with the GDO to see if I can get any 
indication of resonance in or around the 160m band. The path from the 
shack to the tower is well worn now :-))

Steve AB5MM


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