Chapter 6: Antennas and Feed Lines #

One of radio’s best-known rules of thumb is to cut a dipole to half a wavelength. The rule works, but a dipole cut to exactly half a wavelength usually resonates a little low in frequency, and its feed-point impedance shifts with its height above ground.

Explaining rules like that one is part of a larger skill: predicting how much of your power an antenna system radiates and in which directions. Along the way, you’ll see what the feed line and matching network do to the signal. That lets you compare antennas by more than their advertised gain, fix a mismatch with confidence, and choose a receiving antenna that hears better even though it loses signal.