Abstract: A television broadcasting system uses an antenna diplexer to combine signals generated from visual and aural power amplifiers. The diplexer comprises first and second hybrids coupled together by transmission lines which have aural-frequency cavities for reflecting aural energy from an aural input port to an antenna output port of the second hybrid. In the event that the visual power amplifier fails, it is desirable to revert to multiplexed operation, in which the aural power amplifier amplifies a combined visual and aural signal. This mode of operation is accomplished by combining the low-level aural signal with the low-level visual signal, by putting the combined visual-with-aural multiplexed signal through the aural power amplifier, and by simultaneously shorting the transmission lines between the second hybrid and the aural cavities.

Abstract: A feed system for a helical CP antenna features folded belt or phasing lines to reduce space. This reduces icing and wind loading problems. If two belt lines are used, they can be placed diametrically opposite each other to reduce mutual coupling.