Does anyone know why FM radio seems to have better reception than AM? AM get lots of static during thunderstorms, or other interference, whereas FM stays clear?

In both AM and FM a steady carrier wave is modulated (changed in some way) by a signal such as voice, music, or code. All waves have amplitude and frequency. In AM (amplitude modulation) the signal varies the carrier's amplitude, while in FM (frequency modulation) the signal varies the carrier's frequency.

Lightning, electrical sparks inside motors, automotive ignitions, etc. generate broadband radio waves. These waves will interfere, by adding and subtracting energy, with the carrier wave being broadcast by a radio station. In fact lightning typically interferes with every radio station at once! It temporarily varies the waves' amplitudes.

The AM receiver can't tell the difference between signal and noise, however, because they both vary the amplitude. The noise gets through and you hear crackles.

The added noise doesn't change the carrier's frequency, however, so an FM signal isn't affected.

quote:

The AM receiver can't tell the difference between signal and noise, however, because they both vary the amplitude. The noise gets through and you hear crackles.

The added noise doesn't change the carrier's frequency, however, so an FM signal isn't affected.

Thanks so much Professor. That's a perfect answer, and is exactly what I wanted to know.