What generates all of the static on the AM frequency band?

Question

If you use an analog radio frequency adjuster on a radio (the one that is actually a dial or a wheel, and is not digital) and move through all of the AM frequencies that are not used you end up hearing a lot of very different sounding interference and noise. Some of them have a thump-thump-thump and another has a shimmy-shimmy-shwaaa and yet another is just kwisshhshhiwahshsh.

So my question is, where do these sounds come from, and why are they different on the different frequencies? If you listen to FM it's all the same universal static at any frequency that is unused. What makes AM different from this?

Answer 1

I'm not sure about all of the noise that comes on the am dial, but I do know that a lot of it is background static created here on earth.

First, the am band is a lot lower frequency than the fm band. Every time a lightning strike occurs, your radio will pick that up. The closer it is the louder the interference.
Also, I believe that a some of the noise may be white noise receieved from different radio signals that originate in space. Not intelligent life, just as a function of naturally occuring processes.

Answer 2

AM has the intelligence on the peaks of the radio waves. so the back ground noise is detected with the intelligence. A FM radio the intelligence is in the shifting of the frequencies. It is amplified and run through a limiter which cuts off the tops and bottoms . The limiter has eliminated the back ground noise.

Answer 3

The static is mainly coming from lightening. It doesn't have to be close by. It can be hundreds of miles away.

This is very common in Central Florida where we have a lot of thunder and lightening storms.

I remember when I was a kid and FM radio became available how amazed at how static free it was.

Answer 4

AM static is caused by electrical discharges- lightning discharges, most of them so minute that you don't even hear or see them.