ABSTRACT

This chapter discusses the theory of all stages of the frequency modulation (FM) broadcast transmitter, as well as the evolution of each. It provides an overview of Radio Transmitter. In FM broadcasting, the radiofrequency carrier should have frequency deviation that is proportional to the amplitude of the modulating signal but independent of the frequency of the modulating waveform. In FM broadcasting, 100% modulation results in a peak frequency deviation of ±75 kHz of the RF carrier. One of the methods of combining individual amplifiers in solid state FM transmitters was the 60-degree combiner, used to combine multiple 50-ohm power amplifier outputs into one coherent 50-ohm output. A typical transmitter will have multiple amplifiers packaged in a power module, with a hybrid combiner for each pair of amplifiers, and additional combiners for combining multiple pairs in some cases. One of the more common ways of combining multiple amplifiers at very high frequencies is the Wilkinson combiner, or variations thereof.