In a message dated 07.12.99 14:04:49 Pacific Standard Time,
philk5pc@tyler.net writes:
Hi Bob,
ON4UN's new book from ARRL, "Low Band DXing" covers this
topic very thoroughly, plus many other low band antennas. I highly
recommend it.
You do not want the gamma rod (wire) to move around. Aluminum
tubing is great, but large copper wire is OK if it is made immobile.
with insulators.
Use an Omega match; it will allow you to QSY all over the band,
plus it will not matter where you put the gamma wire on the tower.
I suggest about 30 feet up. The stator of the shunt capacitor in the
Omega match and the shield of your coax feedline must be bonded
to your radial system.
If you get it resonated to your desired frequency and you are not at
50 ohms, let me know, and I'll give you further info.
That system will be a real killer antenna on 80m.
GL!
Phil, K5PC
> 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
Phil
Again your suggestion is right on. There is more to do. The shield of
the coax should be grounded to the base of the tower and radials and perhaps
at the entry to the shack. The rotator wires should to by passed to ground
at the tower base also. Hot shacks can result if you don't.
Sometimes 2 Gammas or Omegas for different bands or phone and CW on 75&80M
can be added and just switch between them.
I've been able to GD the tower at the base and added extensions on top of
the beam for resonance. I them added a trap there resonant 3.75 MHz and then
ran a horizontal stub that GD'ed at 1850 MHz. I used a balloon to hold up
the stub vertical on a contest week end.
k7gco
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