Radio waves: AM vs. FM

by techtiptom

Originally posted on on 03/29/2010:

When WIBC switched from AM to FM, many of my friends asked what the real difference was, besides sound quality. Being a former radio communicator in the Marines; I knew the difference between Amplitude Modulation (AM), and Frequency Modulation (FM). I promised I would write something addressing this. Sorry I took so long; honestly, I forgot!

Ok, here it is…

The difference is in how the carrier wave is modulated, or altered. With AM radio, the amplitude, or overall strength, of the signal is varied to incorporate the sound information. With FM, the frequency (the number of times each second that the current changes direction) of the carrier signal is varied.

FM signals have a great advantage over AM signals. Both signals are susceptible to slight changes in amplitude. With an AM broadcast, these changes result in static. With an FM broadcast, slight changes in amplitude don’t matter — since the audio signal is conveyed through changes in frequency, the FM receiver can just ignore changes in amplitude. The result: no static at all.

FM frequencies, the numbers on your dial; are much higher that AM frequencies.

The AM range runs from 535 kHz (KiloHertz) to 1,605 kHz and is in the MF (Medium Frequency) range. MF is from 300 kHz to 3,000 kHz.

FM runs from 88 MHz (MegaHertz) to 108 MHz and is in the VHF (Very High Frequency) range. VHF is from 30 MHz to 300 MHz.

If you want to learn more about radio waves and how they are used, check out: