[Elecraft] Common mode current

[Earl W Cunningham]

If you're talking about common mode currents in a low gain receive
antenna like a Pennant, K9AY loop, EWE, etc., common mode currents are of
great concern because any signal picked up by the coax is very
significant compared to the desired signal picked up by the antenna.

Common mode currents are of much less concern on a transmit antenna such
as a coax-fed dipole or inverted vee, where the received signal (and
noise) is much stronger.

For the above-mentioned receive antennas, a choke balun is the easiest
way to combat common mode currents. It can be made by coiling up the last
38' of coax at the antenna feedpoint into 12 turns, 12 inches in
diameter.

For transmit antennas, the same method may be used, or a 1:1 balun may be
installed at the feedpoint.

73, de Earl, K6SE