[Antennas] Gamma Match

Wed May 16 01:24:49 EDT 2007

Can anyone suggest what I may have set up wrong.
I have a homebrew 4 el Yagi for 10 metres which appears to be working 
well, however I do not seem to be able to get the swr down below about 2 
or 3 to 1.
The set up is, the driven element is one inch Diameter, the gamma rod is 
half inch diameter
and the spacing is approx 3 inches. I have a 100 pf variable capacitor 
which is fully meshed
and turning for less capacity makes the SWR worse. From books that I 
have read, 100pf
sounds to be very much on the high side. I have adjusted the shorting 
bar but do not seem to be able to improve the SWR.
I Might add that my situation is such that when the antenna is swung 
over it is very close to a metal sided garage and therefore I have to 
swing it back up to check out what if anything has happened
which in itself is kinda frustrating but you put up with what you can 
have hi.
Would changing the diameter of the gamma rod maybe help by changing the 
range of
impedance(I think I have that right).
Almost to the stage of considering changing to a Beta Match to see if I 
can get the SWR
better, I am sure as good as it is working now ity would be even better 
with a decent match.
Any helpfull ideas would be appreciated.
Alan ZL3KR