Totally Rad Explanation, Bro

Kent from Sacramento, CA gave us a little info on some waves you can’t surf.

On your June 11 show you asked what was the difference between AM and FM radio. And although your players came up with a couple of good analogies, I would like to submit mine. As a former fifth grade teacher, I would demonstrate the difference using a slinky stretched between two students. AM waves would be shown by one student raising and lowering her hand causing an amplitude wave. FM waves were shown by the student pushing her hand forward, then pulling the slinky back. This would cause a frequency wave to transmit down the toy. This gave the class a concrete visual.

2 replies
  1. Jamie Ide
    Jamie Ide says:

    I think the Slinky demonstration gets the point across but what it’s really demonstrating is longitudinal (parallel to the direction of wave travel, i.e. back and forth) vs. transverse (perpendicular to the direction of wave travel, i.e. up and down) physical waves. Radio starts with two electronic waves, a carrier wave at a fixed frequency such as 107.9 MHz which is my local Burlington, Vermont NPR station, and the signal to be transmitted such as the mellow gravitas of Barry Nolan’s voice. The voice wave is superimposed on the carrier wave by altering the carrier wave using amplitude or frequency modulation, AM or FM. In AM, the amplitude of the carrier wave changes in response to Barry’s voice; in FM the frequency changes. The frequency changes in FM are small compared to the carrier frequency but do take up some room called bandwidth which is why FM radio stations are spaced apart on the dial in a listening area. In both methods, the now modulated carrier wave is converted to an electromagnetic wave by a broadcast antenna and propagates through the ether to a radio receiver which reverses the process using, of course, demodulation. This gets us back to Barry’s voice signal which is then amplified and converted to a physical sound pressure wave by a speaker for our listening pleasure. The next time a pun falls flat on Says You!, just think of all the wasted effort. The mind boggles.


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