[../../../_private/magazine_tmp.htm]AM & FM: Why Radio Has Two Sexes

BY JOHN BRY
   You might have noticed that the radio in your car, in your house or on your head probably has a switch that says "AM-FM." And you know that if you listen to AM you'll find Rush Limbaugh chattering or the Padres and Gulls playing. If you want music, you switch to FM. Besides, you may remember everybody insisting that FM is vastly superior to AM: "no static at all." Actually, nothing about radio is so simple. And not everything you may have heard about radio from your friends was entirely accurate.
   But back to AM and FM. Those two broadcast bands get their name from the way the audio information is coded into the radio wave. AM stands for amplitude modulation. As the entire radio wave gets stronger or weaker, you hear it as louder or softer. Not counting Morse code, AM is almost the simplest way to encode information on any radio wave. It also means that anything that interferes with the basic wave itself - like lightning - will shoot its noise right into your speaker. (Static City during a thunderstorm.)
   FM, on the other hand, refers to frequency modulation. You hear louder or softer sounds as the radio signal slides up or down past your receiver. You don't hear the actual wave itself, so the wave distortion is imperceptible. (No static.) FM also sounds better because the receiver can be made to sound better. AM stations are scrunched together on the dial, while FM stations have more elbowroom. If your receiver opened as wide a window on the AM band as it does on FM, you'd hear nothing but the clashing squeals of crowded signals.
   Back in the ancient days - in the 1940s - the government decided that AM stations would be 20 kilohertz (20 thousand cycles per second) apart. This limits the quality of the audio you can expect. By the beginning of the '60s, technology was beginning to improve, and FM became a commercial reality. The government pushed the somewhat experimental FM broadcast band way up to 100 megahertz (100 million cycles per second), which was like new frontier then. They spread the stations much farther apart. Receivers could provide better quality audio. They even had enough space to give you two channels - stereo. It's really the separation between stations - channel spacing - that makes AM sound worse than FM (if you don't count the static). It's not AM's fault; it's the government's.
It was natural that FM radio stations, with their superior sound, begin programming a lot of music. In the '60s and '70s, it became hip to listen to FM. Rebellious youths would do anything to be different from their parents. The word spread: "FM is better than AM." An eighth-grade kid in 1970 would rather lie down on the new freeway than admit to his friends that he heard anything on AM radio.
   Today we have a whole generation that only tunes in to a station if it has a decimal point in its dial position. No wonder AM stations spent the '80s contorting the electronic sciences to prove that "AM is not dead" in order to produce "AM Stereo." But that's another society/government story that we'll talk about another time.
John Bry is the news director at WCUZ AM-FM in Grand Rapids, Mich. He has been in radio for 20 years and is a licensed ham radio operator.

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