The Gamma match is the most used matching device used for yagi beams.
What it does is:
A Yagi almost never has an impedance of 50 ohms. In other chapters i told that Gain, bandwith, F/B etc. all relate to eachother these figures are never all high at one point. A well designed yagi has for that reson an impedance around 20..25 ohms.
A Gamma-match can match impedance below 50 ohms right up to that 50 ohms wich your tranceiver wants to see.
The thickness of the rod should be around 1/2 part of the radiating element, The lenght in the order of 0.05 wavelenght long.
This comesdown to
The desgribed Gamma-match is used for 11 meter Yagi’s with an aluminim element thickness around 25mm !!!!!!!!
I am however convident that with slight adjustments it will work for other diameters.
For the dimensions I took the outside diamter of the radiating element (F) in the order of 2,5 CM.
F is an aluminum plate and should be about 0,5 cm thick and wide enough to hold a N-connector female or
the equivelent PL version. Preferbly in an L version so you can attach it to one of the U-bolts holding the
radiating element to the boom. The hart of the connector should be 10 cm from the hart of the radiating element
A the N- connector female or the PL version
!!! is between the two aluminium tubes B and C must be NON-electrical guiding material for example:
the “plastic” used in coax-cable.
The length of it must be a bit longer then the lenght given “G” !!!
C The long aluminum tube about 1,3 cm thick and 70 cm long.
D An aluminium plate drilled with three holes 1) the driving element
2) the tube D
3) on top a screw to hold it in place.
the holes should be from center to center 10 cm separated
E the radiating element also called driven element.
B Aluminum tube with a length of 13,5 CM diameter 1,8 CM (C and D goes into it)
By adjusting the aluminum plate left or right, you should be able to get a low SWR.
This Gamma-match can handle up to a couple KW’s.
Article originally available at http://dx-antennas.com/Gamma_match.htm