Channel Separation/Spacing for FM and AM Stations

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Channel Separation/Spacing for FM and AM Stations

Post by sarmau » Wed Dec 24, 2014 7:01 pm

Hi! Can someone explain why is it essential to have a 3 channel spacing in FM or AM radio stations in a particular city? Can the spacing be reduced to 2 instead of three? If it can, would there be a problem? Thank you everyone,. Please I need help. happy holidays!

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Re: Channel Separation/Spacing for FM and AM Stations

Post by w9wi » Wed Dec 24, 2014 8:26 pm

You mean particularly in the U.S.? In some other countries smaller spacings are already in use. (for example, there are 100,000-watt stations in Regina, Saskatchewan on 92.1 and 92.7. Their transmitters are only 4.9km apart.) Low-powered stations may be separated by only one blank channel even in the U.S. -- we have low-powered stations here in Nashville on 98.3 and 103.7 vs. high-powered operations on 97.9 and 103.3.

I'd suggest only a single blank channel between overlapping stations is absolutely necessary to avoid interference. Any spacing beyond that is a tradeoff; how cheap of a receiver do we want to protect? I would suggest most car radios can handle one blank channel between stations in all cases. Cheap clock radios or the old "Walkman" sets require more. To some degree the current rules protect receivers of a (poor) quality that are no longer sold.
Doug Smith W9WI
Pleasant View, TN EM66

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Re: Channel Separation/Spacing for FM and AM Stations

Post by BroadcastDoc » Thu Dec 25, 2014 2:51 pm

The answer from a technical standpoint is that it could probably work just fine. The legal answer is no - the FCC won't allow it.
Christopher "Doc" Tarr CSRE, DRB, AMD, CBNE
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