So you follow the tutorial article on how to make the 3 Element Yagi on this page. You’ve even watched the tutorial video on how I build the 3 element yagi and wanted to duplicate it. You’re all set with all the materials at hand and most importantly you’ve got the perfect time to do it now. So you proceeded with the project, you cut the elements, marked the spacing, mounted the elements holder and things are looking good. Except for the last part the diagram seems too complicated to follow. So worry not this is the tutorial video on how I build the gamma match for my antenna build.
So to recap:
The gamma accomplishes 3 things:
1. Usually it’s a small diameter wire parallel and in close vicinity with the main radiating element, it will carry only a fraction of the main element current while being exposed to the same electrical field strength. This turns it in an effective up-transformer of the antenna input impedance. A sort of folded dipole performing an impedance step up.
2. It forms together with the main radiating element a closed wire stub, adding inductance to the antenna input impedance. If it is not required for matching, this additional inductance can be cancelled out with a lumped capacitor in series. A parallel shorted transmission line stub, adding shunt inductance.
3. The sheath of the coaxial feed-line (braid) is connected to the center of the main radiating element. When properly connected, a gamma-match also serves as a balanced to unbalanced converter or balun.
Here’s the how to video:
If you want a more in depth discussion and mathematics behind the gamma match read and download the gamma match document below.