A Yagi antenna uses a gamma match. The variable capacitor connects to the:

A gamma match is commonly used to match an unbalanced coaxial feedline to a continuous, grounded driven element on a Yagi antenna. It creates a parallel resonant circuit using a rod placed parallel to the driven element, which inherently introduces inductive reactance. To cancel out this inductive reactance and achieve a perfect 50-ohm match, a variable capacitor is placed in series with the gamma rod. Therefore, the variable capacitor connects directly to the adjustable gamma rod, while the coaxial braid connects to the center of the driven element or the boom.