Radio broadcasting has been around for a long time. Amplitude modulation (AM) was the first system that permitted voice communications to take place. In this scheme, the magnitude of the carrier wave is varied in accordance with the amplitude and frequency of the applied audio input. The magnitude of the incoming signal determines the magnitude of the carrier wave, while the frequency of the modulating signal determines the rate at which the carrier wave is varied. This simple modulation system was predominant throughout the 1920s and 1930s. Frequency modulation (FM) came into regular broadcast service during the 1940s.

These two basic approaches to communicating over long distances have served the broadcast industry well. While the basic modulating schemes still exist today, numerous enhancements have been made, including stereo operation and subcarrier programming. New technologies have given radio broadcasters new ways to serve their listeners.

Technology has also changed the rules by which the AM and FM broadcasting systems developed. AM radio, as a technical system, offered limited audio fidelity but provided design engineers with a system that allowed uncomplicated transmitters and simple, inexpensive receivers. FM radio, on the other hand, offered excellent audio fidelity but required a more complex and unstable transmitter (in the early days) and complex, expensive receivers. It is, therefore, no wonder that AM radio flourished and FM...