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?

Question

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?

In: 2

Answer 1

AM radio uses lower frequencies. About 1/100 the frequency of FM. This means that it is more capable of bouncing off of the upper atmosphere and curving around obstacles.

This isn’t *necessarily* true for all AM broadcasts, but it happens that public AM broadcasting frequencies are in this lower range.

AM sends information based on the strength of the radio waves, which makes it fairly easy to confuse if some other source exists for waves of a similar frequency. FM sends information based on the frequency, and so unless you have another nearby source that sends a slightly-changing frequency, there is much less interference.