Why does AM radio transmit over a longer distance than FM and why is AM disrupted easier than FM by things like underground carparks or tunnels?
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AM stands for Amplitude Modulated which means the frequency of the waves never changes but the relative strength does to denote changes in the broadcast. Waves with a lower frequency, like very low sounds, just travel distances better because the waveform is so long that it takes a lot to disrupt it. Where as a shorter waveform, like a high screeching sound, is piercing but doesn’t travel that far because the short waveform is easier to disrupt
Conversely though, low frequency/long waveforms, don’t have the penetrating power that shorter/higher frequency waveforms do.
FM stands for Frequency Modulated. So the amplitude, or “height,” of the waveform doesn’t change but the frequency, or “length,” does. Because the overall energy of the wave remains the same (amplitude) this allows for a much cleaner and broader range of data you can transmit. This is why music sounds better on FM than it does on AM.
FM bandwidth is a much much higher range of frequencies than its AM counterpart. So as I mentioned above, higher frequency allows for greater penetration but a lower overall distance the waves can travel. That’s why FM radio stations aren’t as affected by physical barriers but do have a pretty limited range
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