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What are the real losses associated with a typical gamma match at a set frequency? Furthermore, are there good designs or dimensions to minimise these losses?

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  • $\begingroup$ Hello Francis, and welcome to ham.stackexchange.com! $\endgroup$
    – rclocher3
    Oct 29, 2020 at 21:26

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There are no resistive components in a gamma match, so with idealized components the loss is theoretically zero.

In practice, I'd expect if we could somehow measure the heat coming off the match we'd find it's less than 1 dB.

The sources of loss will include resistive losses in the conductor, and dielectric losses in the coaxial capacitor. To minimize these, you'll want to use highly conductive metals, of the biggest practical size, and a low-loss dielectric.

Practically speaking, the gamma match is there because it's solving a problem: the antenna (often, a Yagi) is mismatched. The problems associated with driving such a mismatched load are more significant than the small loss introduced by the match. So comparing a gamma match with a realistic alternative, the losses are negative: it's a gain.

A gamma match also steps up common-mode impedance of the feedline. While this doesn't affect efficiency, it is important to preserving the directivity of the antenna. It still doesn't hurt to have a choke, but the effects are cumulative: if the gamma match has a 4x step-up then it makes the choke 4x more effective.

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