When using the GDO run 1 or 2 elevated radials to complete the 1/2 wave
circuit. Attach them to the vertical with 1-2 loops around the GDO coil.
Guys insulated at or close to the tower will have little or no effect.
If you have a xcvr with full TX capability run a sweep from the shack at low
And as mentioned a noise bridge will also give a reasonable evaluation.
----- Original Message -----
From: "AB5MM" <firstname.lastname@example.org>
Sent: Monday, September 17, 2007 12:40 PM
Subject: [TowerTalk] 160m Vertical
> 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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