How did large metropolitan cities (New York, Los Angeles, Chicago, Detroit, Washington DC, Portland OR, Salt Lake City etc) end up with the FM dial like this 92.3, 93.1, 93.9, 94.7, 95.5, 96.3, 97.1 97.9 etc. while secondary large metro cities adjacent to big metro cities (Seattle, Philadelphia, San Diego, etc.) have FM dial spacing like this 92.5, 93.3, 94.1, 94.9, 95.7, 96.5 etc. ?
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FM Radio Dial
- Thread starter e-dawg
- Start date
I think the reason Portland ended up with the same general spacing as Los Angeles is because it's the first major city after San Francisco. It isn't the same though. We didn't used to have 93.1, 93.9, 94.7, 96.3, 97.9 etc. 93.1, 96.3 and 97.9 are move-ins, as are some other stations further up the dial. 93.9 moved from 93.7, to accommodate 93.1 and 94.7 came from the 80-90 docket.
Could it have something to do with the TV channels in use in each market, so any harmonics from FM radio wouldn't interfere with TV and vice versa?
In a nutshell: The Commission broke the U.S. out into Regions. Channel allocations depend on things like geographic distance from one class allocation to another between regions; C to C, B to B, A to A, A to B, A to C, etc. Also, channel allocations in Northern regions include distance separations based on treaties negotiated between Canada, and Southern channel allocations in Mexico.
No, except in the NCE band where there are protections from TV 6. TV 2's (54 to 60MHz) 2nd harmonic is above the FM broadcast band.
Although it has no bearing today with all of the new stations introduced in Docket 80-90, it used to be that certain frequencies were reserved for only "Class A" FM's that were limited to 3kw at 300 feet. This is from memory, but I think those channels were 92.1, 92.7, 93.5, 94.3, 95.3, 95.9, 96.7, 97.7, 98.3, 99.3, 100.1, 100.9, 101.7, 102.3, 103.1, 103.9, 104.9, 105.5, 106.3, and 107.1. So in the larger metros where the FM dial filled up early those frequencies had lower-power stations. In addition, all high-power stations had to be 800 KHz apart to be in the same metro, but 400 KHz spacing was allowed between the Class-B or Class-C stations in the cities ;vs. the Class-A stations in the suburbs. I realize all of these allocations were done early on without the use of computers, and the it must have been a real strain on the brain for whoever worked on it at first. But you can see where metros with 92.3, 93.1, 93.9, etc. left room for 92.7, 93.5, 94.3, etc. in the outlying areas. The metros with 92.5, 93.3, 94.1, 94.9, 95.7, etc. did not have as many class A stations in between, allowing higher-power stations on 2nd adjacent channels in markets some distance away. I'd like to think that maybe there were some serious thoughts about this in the beginning - maybe that's why San Francisco has 98.1 and 98.9 while San Jose and Sacramento have 98.5. Again - it must have been a serious what-if game to allocate those first channels. But the big city channel plans were undoubtedly done early, and it would be interesting to know the methodology. Hey - is there a retired FCC engineer on this board?
Dave B.
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