The factors involved in the planning and construction of the IBA's u.h.f. fourth channel network and the overall technical design requirements of the main transmitting stations are discussed in terms of the environmental, reliability and performance requirements. Transmitter configurations and the philosophy adopted for the control and monitoring systems are presented. The decision to introduce a new type of klystron which results in savings in both cost and building space is contrasted against the other available options of tetrodes or older type klystrons. Unattended operation is used at all sites and consequently a major goal is reliability, both in terms of failure rate and stability of performance and the results obtained discussed. Stringent filtering is required of the lower sideband transmitted at high-power transmitter sites using Ch. 21. The station supervisory system uses microprocessor-based control and monitoring techniques. The programme input equipment arrangements are also discussed. The decision was made to use all solid-state transposers up to the 200 W power level, at u.h.f. relay stations.