Abstract: A device for monitoring the performance of a transmitter, comprising a first input connected to receive a signal representative of transmitter output current, a second input connected to receive a signal representative of transmitter output voltage, a multiplier, a comparator connected to the output of the multiplier, and a switch controllable either to connect the first and second inputs to the multiplier such that the multiplier output is representative of the transmitter output power, or to connect one of the two inputs to the multiplier and the other to the comparator and to connect the comparator output to the multiplier such that the comparator remains in balance and the comparator output is representative of the transmitter output impedance. The first input may be connected directly to the multiplier and the second input can be selectively connected to either the multiplier or the comparator by the switching means.

Abstract: A switching system is described for use in for example AM transmitters comprising at least one pair of semi-conductor output switches connected in series across an AM modulated D.C. supply and arranged to be operated sequentially by a series of "on" and "off" command signals to energize a load, such as an antenna. The circuitry provides a delay interval between the "off" command to any one switch and the "on" command to the next switch in the sequence. Means are provided for detecting when two successive switches in the sequence conduct simultaneously, and means are provided for increasing the duration of the delay interval when such simultaneous conduction is detected.

Abstract: This invention relates to an amplifier system comprising two or more Class D amplifiers the outputs of which are associated with a common system output in a known manner. To avoid the appearance of spurious sidebands in the system output which are associated with the switching process of the amplifiers, separate clock pulse trains are applied to the Class D amplifiers, the separate clock pulse trains being interlaced to obtain cancellation of switching frequency ripple at the common system output.