Gamma matches are used in antenna construction to match the antenna's main coaxial cable to its parasitic beams, which are the horizontal struts attached to the main beam. The gamma match works as a balun, or transformer, to reduce common-mode noise and connect lines of differing impedance. There are several design types you can choose from when designing and building your gamma match.
Cut a 5-inch section of aluminum tubing. Flatten one side of the tubing by inserting it in a vice and squeezing.
Cut an 8-inch section of coaxial cable. Strip the outer shell of the coaxial cable, but leave the plastic insulation. Strip 3 inches of plastic insulation.
Drill a hole into the antenna's driven element. Bolt the L-bracket to the antenna's driven element. The type and size of the bolt will depend on the diameter of the antenna.
Bolt the flattened end of aluminum tube to the L-bracket. There should be a 1 1/2-inch gap between the aluminum tubing and the antenna's driven element.
Insert the coaxial cable into the aluminum tubing. The insulated end of the cable should go in first, leaving the 3-inch stripped section outside of the aluminum tubing. Attach a sliding bracket to the driven element and solder it to the stripped coaxial cable.