Abstract: A noncontact switch couples power from A and B radio frequency sources to a load and an antenna in three modes. Mode I couples the A source to the antenna and the B source to the load; Mode III is B to antenna and A to load, and Mode II couples both A and B sources to the antenna. The structure includes a first 3dB, 90.degree. coupler coupled to the sources and a second 3db, 90.degree. coupler coupled to the load and the antenna. A third 3dB, 90.degree. coupler is coupled in a first path between the first and second couplers. A pair of reflective terminations coupled to ports of the third coupler are mechanically controllable to one of three phase-shift conditions; 0.degree. for mode I, 90.degree. for mode II and 180.degree. for mode III. A fixed phase shifter couples the first and second 3dB, 90.degree. couplers by a second path. Each reflective phase shifter is a coaxial circuit including the parallel combination of first and second series inductance-capacitance circuits.

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 television broadcast transmitter includes two power amplifiers or transmitters, a dummy load and an antenna. A noncontacting switching arrangement includes directional couplers or hybrids operated as controllable phase-shifters under the control of pairs of variable reactive terminations. Signals arriving at the antenna or load port by two paths combine in-phase to couple signal to that port, or combine out-of-phase to cancel signal. If the out-of-phase condition is inaccurate, cancellation may be incomplete, resulting in crosstalk. To avoid the need for accurate positioners to position the variable reactive termination at the position providing the desired phase-shift, a particular structure of the reactive termination is used. The reactive termination is a short-circuited coaxial line with an axial gap in the center conductor at a position less than one quarter operating frequency wavelength from the short circuit.

Abstract: A television transmitter uses a diplexer to combine the signals from a visual power amplifier and an aural power amplifier. The diplexer uses hybrids coupled together by transmission lines, and the transmission-lines have aural-frequency cavities which reflect the aural energy from the aural input port to the antenna output port. In the event that the aural power amplifier fails, it is desirable to revert to multiplexed operation, in which the visual amplifier amplifies combined visual and aural signals. This mode of operation is accomplished by switching the low-level aural signal for combining with the low-level visual signal and by simultaneously switching the tuning of the aural cavities.