Hi Bob and all,
Good comments from others about this.
Information exists in the ON4UN and ARRL books. The coverage in ON4UN's
is more complete.
I recently did this on a silly little AB577 surplus guyed pole, with a
TH7 on top. The pole is ~45' tall.
It was a fair amount of work to ensure good connections along the pole
joints, and to the beam and base to ground. Then isolating the pole from
the guys,and making guys nonresonant for the rest of the stuff around
here. I modeled most everything to find out who was talking to what.
I had already tried an inverted L near this thing and it's near
resonance made it impossible to get good results. It was tunable, but
was never close to equal to my inverted vee with apex at 45'.
For the vertical, I elected to place the gamma wire connection near the
top. Just ran a #14 Flexweave wire off the tower, and down thru egg
insulators attached to the guys. Spacing ~ 2'. I tied the wire off with
a small egg and insulated plastic coated line to a rebar stake in the
ground, and pulled it up fairly tight. I've watched it during the recent
85 mph storms and it doesn't move very much, and I never see any
dramatic fluctuations in swr during wind events. The first big snow
storm may be different, and I may need to go out and clear the snow away
from some of the base connections. I may make a plastic bucket snow
guard for it.
The tower base sits on top of the ground and base assy connections to
pole are not real good, so I ran a 2" wide copper strap from the pole
base to the ground rod where the radials connect.
I elected to try the Omega match. I had acquired a few air variable caps
this summer at the annual local swapfest. These got installed in one of
the large sealed fiberglass enclosures I'd found surplus 10 years ago.
After all the setup, it only took one afternoon to get the thing working
with the Omega match.
For CQ Phone, I adjusted the match, with an Autek RF-1, for 3.79, worked
fine. For SS & CQ CW, I adjusted it for 3.55. No problem.
2:1 bandwidth is about 170 Khz.
It has 60 radials, and it started acting like an antenna and was
matching when I got past 20.
Result:
This antenna hears just like a vertical.
It just kicks the inv vee's tail on transmit to Dx every time. The vee
is king for working west coast stuff.
It's a great way to turn an already existing asset into a useful
antenna.
This thing works everything it hears.
As always, the challenge is to be able to hear stuff, that's a different
project!
Now, if we can only get rid of the rest of those rotten cable modems...
Good luck getting yours running!
73, Kurt, K7NV
Bob See wrote:
>
> I would like to feed my windmill type tower on 80 meters with a gamma
> match. The tower has a triband beam at about 57 ft. It has four legs,
> about 5.5 ft apart, (free standing). A .JPG picture available if
> interested. It is grounded by many radials.
> I would like to shunt feed the tower on the low end of 80 meters using a
> gamma match feed. I am 75 yrs old and do not look forward to
> multi-climbings up the tower to find the best point to tie the gamma
> rod. Also, can I use copper wire for the gamma match or would aluminum
> tubing be better?
>
> Can anyone tell me a past QST article or discussions on Towertalk that
> would educate me on the parameters of the gamma match that I might
> expect?
> Thanks, Bob See, N5PC@Poncacity.net
>
> --
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