[TowerTalk] Gamma Match on 6 meters

[K0FF]

Lee, I look at the Gamma match in simplistic terms. On any dipole, all
grounded, or insulated, no matter, the center point is at zero ohms and the
end is at a high impedance...maybe 3500 Ohms. The impedance is something in
between at each interval along the length.  The rod  part of the Gamma feels
along this length for a spot that is 50 Ohms, and conveys that back to the
feedpoint. Because you have inadvertently inserted "L" into the system, you
have to add series"C" to compensate.
Addition of other elements, and their degree of coupling will alter the
exact spot for 50 Ohms, but on 6 meters it will range from 11 inches all the
way to 18 inches will a "C" of 25 to 50 pF.
My homebrew 6M beams are set for 14 inches of rod and 40 pF of "C".  The
capacitance can be lumped or distributed, no difference. Set the DE length
for center frequency resonance,and then adjust the match for the lowest SWR.
There is a rule of thumb for that, but I don't recall it. Maybe someone else
will mention it, and I'll write it down this time.

Unreal how those things just fade away, if not rehearsed.

Let me know more details of the beam, and maybe I can help with details.
Glad to see 6M on field day.

Geo>K0FF


-----Original Message-----
From: Lee Buller <k0wa@southwind.net>
To: towertalk@contesting.com <towertalk@contesting.com>
Date: Friday, June 16, 2000 8:43 AM
Subject: [TowerTalk] Gamma Match on 6 meters


>
>
>
>I am building a 6-meter beam for FD and have never used a gamma match as a
>feed on a beam.  Although I have looked at numerous designs over the past
>couple of weeks, the gamma match calculations elude me.  I cannot find how
>they come up with the "L" and the "C"
>
>Going to the Cushcraft web site, you can see how one is built, but it
>doesn't show dimensions very well.  I understand the contruction and the
>theory behind it, but I do not understand how they come up with the
>dimensions.  Is there a fomula?  Or, is it just try it until it works?
>
>Lee
>k0wa@southwind.net
>
>
>
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