ok...
I cut a 1/2 wave monopole for 28.4Mhz and used the dimensions according to
what you stated. The capacitor is homebrew from 3/16 acrylic sheet with
aluminum plates, configured as a compression variable, true pf is unknown
(with spacing and dielectric of acrylic and size of plates, should max at
~150 pf) --but plenty of adjustment, both sides of "null" on swr meter.

However, the shorting bar on the gamma rod had to be raised to ~3 ft.
(adjustment above or below this height only increases swr), here the swr is
~1.7:1. I cannot find a configuration on the gamma which brings the swr
under that figure... lengthing/shorting monopole +2 to -2 inches has
negligible effect and not for the better.

Lenght of coax from rf source to ant seems critical, when coax is shortened
or lengthened, gamma must be adjusted (but is always around 3 ft)

The gamma rod length seems to be quite above what the figures you gave me
would suggest (from what you suggested, 1/20 wave (~20 inches or do I have
that correct?)--what am I too blind to see to see here, or what I am I
ignorant of?

Your continued help and advice would be most appreciated...

Warmest regards,
John
--
Hay, if'n ya'll cun't konstructivly partecipete in this har disscusion, haw
aboot speel-checkin it fer me?


"Richard Clark" wrote in message
...
On Sun, 3 Apr 2005 08:17:48 -0700, "John Smith"
wrote:

I am looking for "Everything you wanted to know about a gamma-match--in a
nutshell."
In other words, what set of formulas would give you length, conductor
spacing, gamma capacitor value, ratio of gamma rod to driven element
diameter, and a starting measurement for the shorting bar between
conductors-- for a given frequency?

Hi Brett,

That question rather goes beyond the nutshell lead-in. However, for
the nutshell:
1/20th wave gamma rod;
capacitance about 5 to 8pF/Meter-of-wavelength;
gamma rod roughly half diameter as the radiator and spaced
roughly 1/100th wavelength from it.

With all the "roughlies" (a product of nutshell precision) it pays to
make the capacitor a variable, or the gamma loop length variable. All
such roughlies are also contingent upon the radiator's size WRT
wavelength.

To translate the capacitor characteristic:
for 20M band it would be 100 to 160pF

73's
Richard Clark, KB7QHC