Radio can be broadcast on the AM or FM bands. What do AM and FM stand for?

All radio broadcasts begin with a basic, constant signal known as a carrier wave. To transmit audio, this wave must be altered, or "modulated," to carry the information. In an Amplitude Modulation (AM) broadcast, the amplitude—the overall strength or height of the carrier wave—is varied in sync with the sound waves of the original audio. This was the earliest and simplest method for broadcasting. While AM signals can travel impressive distances by bouncing off the atmosphere, especially at night, they are highly susceptible to interference from lightning and electrical noise, which manifests as static.

Frequency Modulation (FM) takes a different approach. It keeps the amplitude of the carrier wave constant and instead varies its frequency—the number of times the wave oscillates per second. This subtle change in frequency encodes the audio information. Because most natural and man-made interference (like static) primarily affects a wave's amplitude, FM signals are largely immune to it. This results in the clearer, higher-fidelity sound we associate with FM radio, making it ideal for music. The trade-off is that FM waves travel in a straight line, limiting their range to the line of sight.