Design of tube power amplifiers for optimum FM transmitter performance

Tube amplifiers are extensively used in modern high-power FM broadcast transmitters. The power amplifier bandwidth affects not only the modulation performance, but also the transmitter's immunity to RF intermodulation. The tradeoffs involved and the choice of bandwidth are discussed. The design of tube power amplifiers for optimum FM performance requires careful considerations in the selection of input-matching and output-coupling circuit topologies, due to their effects on the transmitter amplitude and group delay responses. Results of computer circuit analysis and of measured amplitude and group delay responses are compared for different circuit topologies. Modulation performance data of a typical 20 kW FM transmitter are also presented to illustrate the effects of tube power amplifier input and output circuits.<
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