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Did You Know??

Posted by radio On March - 27 - 2012

Why do some radio stations get received better at night?

Radio waves naturally travel in straight lines. Because of the curvature of the earth, no ground-based radio station transmits farther than 30 or 40 miles. Certain radio stations, however, especially in the short-wave and AM bands, can actually travel much farther than they transmit.

Short-wave can circle the globe, and AM stations travel hundreds of miles at night. This is because of the atmospheric layer called the ionosphere, which reflects certain frequencies of radio waves, allowing them to bounce between the ground and the ionosphere, making their way around the planet. The composition of the ionosphere is different between night and day due to the presence (or absence) of the sun. The composition at night allows for better reflection characteristics, hence the better reception at night.

Why do all FM radio stations end in an odd number?

First off, the FCC has allocated different frequencies to different activities in the U.S. For example, cell phones have their own assigned frequencies, baby monitors have their own frequencies, CB radios have their own, and so on.

FM radio stations all transmit in a band between 88 megahertz (millions of cycles per second) and 108 megahertz.

This band of frequencies is completely arbitrary and is based, frankly, mostly on history and whim: it doesn’t have to be that way, but it is, and it works, so it probably won’t be changed. Inside that band, each station occupies a 200 kilohertz slice, and all of the slices start on odd number boundaries. So there can be a station at 88.1 megahertz, 88.3 megahertz, 88.5 megahertz, and so on.

The 200 kilohertz spacing, and the fact that they all on odd boundaries is, once again, completely arbitrary and was decided by the FCC. For example, in Europe the FM stations are spaced 100 kilohertz apart instead of 200 kilohertz apart, and they can be even or odd. Neither way is right or wrong, so long as everybody follows the same rules in a given area. As to not following the rules – that way lies chaos.

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4 Responses to “Did You Know??”

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  3. some really interesting information, well written and generally user pleasant.

  4. Johana says:

    thanks for the insights your post gave me 🙂

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