The TH Radio Microwave Carrier Supply System

As described briefly in a preceding paper, 1 the common microwave carrier supply system supplies all the carrier frequencies (often called beat oscillator, or BO, frequencies) needed for a fully equipped repeater station. The major portion of the system is in three sliding-rack bays 2 which house regular and standby frequency generators, together with switching and control circuits. This equipment supplies four harmonically related frequencies (29.7 mc, 59.3 mc, G301 mc and 6049 me). Other parts of the carrier supply system are the carrier distribution networks which carry these frequencies as needed to the various transmitters and receivers, where carrier supply modulators 3 produce the specific frequencies desired. Frequency stability and over-all reliability are prime objectives for the microwave carrier supply. Frequency stability is given by a crystalcontrolled, thermistor-compensated oscillator with a long term stability of better than 10 ppm over operating temperatures of 40°F to 140°F. Reliability is obtained by the regular-standby arrangement. This requires various detectors, control circuits, and switches of a reliable nature to identify a failure quickly and replace the failed regular carrier 1569