Frequency-modulated v.h.f. transmitter technique, with particular reference to the B.B.C. United Kingdom service

Equipment and performance requirements for frequency-modulated broadcasting transmission are given, with particular reference to the British Broadcasting Corporation´s recently introduced network of v.h.f. transmitters. The general planning and design of the complete transmitting equipment used at the new high-power v.h.f. sites is surveyed, including problems of unattended operation, automatic phasing of paralleled amplifiers and 3-programme common-aerial working, to indicate the progress made in this new field of broadcasting. The design features of a current 10kW f.m. transmitter operating in Band II (87.5¿100Mc/s are described, with special mention of the method of generating the frequency-modulated carrier, its automatic centre-frequency control and means for automatic phasing of the high-power amplifiers operated in parallel. Details are given of a newly introduced system of transmitter control designed to increase the service reliability, thus reducing the demands on the time of visiting maintenance personnel. Reference is made to the B.B.C.´s requirement of combining three independent 10kW f.m. carriers spaced 2.2Mc/s apart to feed one half of a wideband horizontally polarized aerial, the other half being fed with an identical set of transmitters kept in phase within a few degrees. The necessary filter circuits, giving sensibly zero coupling between transmitters and negligible crosstalk, are described. Overall performance figures are quoted.