ABSTRACT
This chapter provides conventional analog frequency modulation (FM) technology as well as digital HD Radio transmission technology. In FM broadcasting, the RF 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. FM broadcasting with pre-emphasis really becomes a mixture of FM at low modulating frequencies and PM at high modulating frequencies. On January 29, 2010, the Federal Communications Commission Media Bureau adopted an order to modify the FM digital audio broadcasting rules to expand digital coverage. Almost all FM broadcast transmitters require forced air cooling to remove heat from the output stage and other assemblies within the cabinet. Many broadcast facility operators are finding that the cost of purchasing and operating air-conditioning systems is increasing.
