Modern trends in high-frequency transmitter design

The operating costs of a transmitting station can be substantially reduced if the equipment is automatically tuned and all services are directly controlled from a central point. This is due to the reduction of operating staff covering three shifts, and to the saving in `off the air¿ time made possible by rapid change of frequency. The paper describes a range of transmitters with output powers up to 85kW which have completely automatic control of tuning, coupling and gain. The transmitters are of the linear-amplifier type, and hence are suitable for all forms of service used in h.f. communication, when associated with the appropriate signal source. In particular, the paper describes the automatic control system of the transmitter. Various aspects of performance are discussed, including the design requirements for low distortion and for the reduction of spurious and harmonic emissions. If the saving in operating costs is to be fully realized, a high standard of reliability is necessary. The types of components used are described. They include variable vacuum capacitors, variable inductors, silicon rectifiers and vapour-cooled valves.