Gamma match


John Cline:
What is a gamma match, how does it work, and what is its purpose?

Steve Katz:
It's an adjustable device used for feeding and matching an antenna, usually the driven element of a beam, and usually to 50 Ohm coaxial cable.

Its advantage over some other matching systems is that it may be used with the driven element of a beam antenna, when the center of that driven element is directly grounded to the antenna boom.  Most other feed systems require that the driven element be isolated from the boom.

Using a gamma match eliminates the need for a balun, as it provides an unbalanced feed to the radiator, so the system that results is unbalanced-to-unbalanced (unbalanced coaxial cable to unbalanced driven element).  On the HF bands, the gamma match works very well because its component losses can be maintained very low.  On the VHF bands, gamma matches can often be lossy as component Qs are lower, and on the UHF bands, they usually don't work well at all -- too much loss in the components.  There are better, less lossy matching systems for the "very short" wave bands.


Doug Daniels:
There are some good explanations of this in the Extra Class test manuals.

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Larry J. Rolewic:
Also, do a Google Search for "Wayne Overbeck" and "Quagi."  Wayne developed the Quagi antenna (a cubical quad driven element and reflector combined with standard Yagi directors) to get around the problems at VHF and above, that Steve describes.  The gamma match doesn't work well at VHF and above.


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