ABSTRACT
Although the mathematical principles explaining frequency modulation (FM) have been known for many years, the advantages and practical application to radio broadcasting were not realized until the 1930s, when Major Edwin H. Armstrong conducted extensive developmental work proving that FM radio transmissions were possible and practical. Many theoreticians claimed to have proof that Armstrong’s experiments were impossible based on mathematical models claiming that an infinite transmission bandwidth would be required. He never received proper credit for his many contributions to the radio communications industry during his lifetime [1]. The advantages of FM include freedom from static, wide audio bandwidth, and the ability of an FM receiver to capture the stronger of two signals transmitted on the same carrier frequency. More recently, an in-band, onchannel (IBOC) digital radio system, also known as “HD Radio™,” has been added to many FM broadcast stations [26,33,34]. This chapter will cover conventional analog FM technology, as well as digital, HD Radio transmission technology.
