• For the same reason FM sounds better than AM. Lightning releases broadband radio frequency (RF) noise, easily picked up by your radio antenna, which adds the noise's voltage to the tuned-in carrier frequency. With AM radio the audio signal -- what you're supposed to hear -- is added to the carrier, modulating its amplitude (voltage). When RF noise is received from lightning, it mixes its amplitude with the radio signal (voltages add) and can thus be heard when the signal is extracted by the radio. With FM radio the audio signal is represented by the carrier's frequency. You can add all the RF noise you want -- the added voltage will affect the carrier's amplitude but not its frequency. Thus the radio ignores noise on the carrier while extracting the signal. FM typically has way better noise rejection than AM, & its larger bandwidth allows hi-fidelity stereo. However FM radio (unlike AM) suffers from shorter range & a tuning problem called multipath interference.
  • Xprofesor, I agree. I'll add one simple concept though. FM stands for "frequency modulation." Think of the ripples in the water when you toss a pebble in. FM changes by making more of the little ripples. AM stands for "amplitude modulation." Think of a small stone making taller ripples or even waves. When you change stations on an FM radio, you are really changing the "frequency" of what the radio is looking for. When you change stations on a AM radio, you change the "strength" of what your radio is listening to. Realize this is a very simple way of looking at it.

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