Why are radio signals broadcast on odd numbered frequencies? Its always 101.1 101.3 102.7 or something along those lines. Always ends in an odd number. Anyone know why?
Sala, can’t you count?!? I said NO camels! That’s FIVE camels!
WAG: The station is assigned a frequency range. To make it easy to divide up the frequencies, FCC uses even numbers. The odd number puts the station’s “aim” frequency in the middle of the range.
In Europe, assigned radio frequencies are even.
starfish is correct, although the way this question is posed, I assume we are talking about FM stations in North America, because other countries use a slightly different system.
In the U.S., when a station says it is at “94.5 on the dial”, technically 94.5 refers to the “center frequency” for the FM channel on which they operate. The U.S. FM broadcast band runs from 88.0 to 108.0 megahertz, and is divided into 100 separate non-overlapping channels, which are each 200 kilohertz wide, and run from channels 201 (88.1) to 300 (107.9). (There is also a channel 200 on the books, but I don’t think it has ever been assigned to a station, because of interference considerations. The sound for TV channel 6 is centered at 87.75 if I remember correctly, which is why you can hear channel 6 audio on many FM receivers).
To recap, in the U.S. 94.5 is the center frequency for channel 233, which in turn occupies the frequency range from 94.4 to 94.6 megahertz.
In other countries, particularly Europe, they handle things somewhat differently, so you have FM stations with both odd and even ending fractions.
The FCC also prohibits stations from broadcasting on adjacent “aim” frequencies–this is why you seldom see 101.3 and 101.5 in the same metro area. That is done, of course, to limit interference between stations.
However, the FCC is going through the process of allowing mini-station licsenses (sp?). They will be giving away tons of low-power permits to community groups, not-for-profits, and maybe individuals. These, with a maximum broadcast range of something like 20 or 30 miles, will be allowed adjacent frequencies to the big stations. And that has the big guys up in a real snit.
The “tons” of licenses potentially granted to LPFM stations may soon be reduced by an order of magnitude, esswedl; no less a heavyweight than NPR has weighed in against allowing low-power stations to broadcast on the first OR second adjacent frequency.
LPFM BILL PASSES HOUSE IN VETO-PROOF 274-110 VOTE [edited for length/copyright purposes]
04/17/2000
COMMUNICATIONS DAILY
© Copyright 2000 Warren Publishing, Inc. All Rights Reserved.
Bipartisan compromise language restricting low-power FM adopted in House Commerce Committee helped Telecom Subcommittee Vice Chmn. Oxley (R-O.) draw support of 85 Democrats in House floor vote on HR-3439 late April 13. Approval of bill by 274-110 gave supporters more than 2/3 necessary to override Presidential veto, and in fact bill already had been approved by voice vote when Oxley called for roll-call vote. “Special interests triumphed over community interests today,” Kennard said in statement released after vote. He continued his criticism of NPR and said bill was intended to put up “roadblocks” to FCC’s implementation of LPFM . Telecom Subcommittee Chmn. Tauzin (R-La.) began debate by accusing FCC of illegal lobbying and saying he would refer matter to Dept. of Justice (DoJ) for investigation.
Modified from original Oxley language calling for ban on LPFM , compromise language approved in Commerce Committee markup and on House floor would allow 70 or so LPFM licenses that can operate within existing interference standards to proceed, while field tests would be conducted by independent agency in 9 markets to ascertain whether relaxed interference standards caused problems with existing stations. Compromise, sponsored by Rep. Wilson (R-N.M.) and Commerce Committee ranking Democrat Dingell (Mich.), was touted at markup by Tauzin as way to get veto-proof vote.
Kennard took issue with House vote: “While it appears on the face to simply be about requiring the FCC to conduct more tests to protect existing broadcasters from interference, its practical effect is to set roadblocks and hurdles for the FCC… that may never be met and that only can serve to protect incumbent broadcasters from competition.” He repeated his criticism of NPR for its support of HR-3439 after passage of Wilson-Dingell amendment: “I’m particularly disappointed that National Public Radio joined with commercial interests to stifle greater diversity of voices on the airwaves. I can only wonder how an organization that excels in national programming could fear competition from local programming by these tiny stations operated by churches, schools, community groups and public safety agencies.” NPR leaders have told us issue has nothing to do with competition, but rather with interference concerns that are particularly worrisome in noncommercial band, and Kennard never showed any inclination to work with NPR about interference concerns. Comr. Tristani expressed regret that NAB had “flexed its considerable lobbying muscle,” and hoped for better luck on other side of Capitol: “I hope the Senate will help us give a voice to the voiceless.”
Here is the page from the FCC about low power FM stations.
Maximum range: 3.5 miles
Frequency assignment: a little more complicated than I stated before.
Wow, great job everyone. More than answers my question. Now if I could just get this tin foil bent juuuust the right way…