Q: If RF is a high frequency AC signal, why are there plus and minus signs on a balun?
A: Keep in mind that we are usually connecting a ‘BALanced’ antenna to the ‘UN-balanced’ coaxial cable, hence the term BALUN. So, for most regular applications on a single antenna that is ground independent, such as a beam, dipole and many other wire antennas, the balun polarity doesn’t matter. However, polarity markings on baluns become very important for matching phase on multiple antennas in a phased array, such as stacked Yagis. Also, on most 1:1 baluns, the minus side is connected to the coax shield. So, for an antenna that is ground dependent, such as a vertical, Inverted-L or long wire that uses a ground radial system, the positive terminal must be connected to the radiating element and the negative terminal must be connected to the radial system.