[TowerTalk] C3-SS Problems sort-of resolved

[Guy Olinger, K2AV]

If you haven't already, attach an MFJ 259B, or equivalent right at the
antenna. DROP THE FEEDLINE OFF THE ROOF. Nothing up there but the C3SS,
the balun, a short jumper and the analyzer.  See if it's the antenna. Be
sure to leave the balun in the setup. Watch the readings while a helper
rotates the antenna.

If things are  good in two opposite quarters of the compass, and bad in
the others, you're probably coupling conductors in the upper part of the
house. You would be WELL within a half wavelength of any conductors in
the attic of the house or dormer, or ...  I don't know the specifics of
your house. Did finishing off the attic or something like that coincide
with the performance degradation? Some people have clamped split
ferrites around electrical conductors to minimize resonance, but this is
a real tough one to fix. This will also mess up the beam pattern and
performance.

If it's OK without the feedline, then your feedline is it. It must for
some distance run mostly horizontally, and that directly under the
antenna. This definitely qualifies as a conductor. Rotating your antenna
will couple it maximally in one direction and  minimally offset 90
degrees. The length of the feedline may increase or decrease the
coupling due to very unpredictable resonances on/near the feedline,
including the nature of the station ground. (You wouldn't have RF in the
shack problems, would you?)

These two problems are well known disadvantages to your arrangement,
which probably solves other issues for you quite nicely.

There is nothing simple you can do about power wires in the attic being
coupled. If it's the feedline, assuming you have a balun on the C3SS,
try the following, since you have extra feedline coiled up.

Go 10 feet from the balun, and make a coil (8-10 inch diam) with 6 turns
in it. Tape it up and let it lay on the roof. Go 10 feet from that coil
(not counting the length in the coils) and make another one. This should
fairly well break up the feedline into non-resonant sections close to
the beam.

Let us all know what you find. Knowing what it REALLY was and what fixed
it is all the fun.

--... ...--  . ...  --.  .-..

Regards, Guy
k2av@contesting.com
Apex, NC


----- Original Message -----
From: Eric Rosenberg <wd3q@erols.com>
To: <towertalk@contesting.com>
Sent: Friday, October 20, 2000 10:37 PM
Subject: [TowerTalk] C3-SS Problems sort-of resolved


> A couple of months ago, it seemed my very early model C-3SS suffered a
> performance degradation.
>
> Many suggested that I replace the ~100 ft 9913 feedline, so last
> weekend, I did. As it happens, the feedline was 9913 with a 6 ft
RG-213
> jumper at the end.  The new feedline is a single piece of RG-213 --
> this time 125 feet long -- the the excess (25-or so ft) neatly coiled
> up outside the shack
>
> The results were less spectacular than I might have otherwise thought!
>
> The antennas is ~6-2/2 feet above the peak of the roof on a 4-legged
> roof tower.
>
> In checking the SWR, it appears to change depending on the position
> (dorection) of the antenna relative to the roof.  Parallel to the peak
> is different than perpendicular to it!
>
> Is this normal?  My climber, N3OC apparently has a similar experience
> this with his TA-33jr. What a srprise this is!
>
> A question...will subtracting feedline -- making it closer to what it
> was -- make a difference?
>
> Thanks in advance,
>
> Eric W3DQ
> Washington, DC
>
>
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>


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