View Full Version : What's the most commonly used FM radio frequency in the US?
06-11-2004, 12:44 PM
Example: Here in Seattle, 94.9 FM is a public radio station. Drive far enough out of the region and the frequency fades to static. Travel beyond that and at some point 94.9 will turn up again as a different radio station.
Question: Which FM frequency -- such as 94.9 or 101.5 or 107.7 -- is most commonly used in the US? I can think of three ways to consider this quesition:
1) The frequency that reaches the largest population. This isn't really what I'm looking for, because that gives a Manhattan station a big advantage over one in Nebraska.
2) The frequency that's available over the greatest geographical area. Not exactly what I'm looking for, but closer.
3) The frequency used by the greatest number of radio stations. I think this is what I want to know.
Or are all available frequencies parceled out approximately equally?
06-11-2004, 01:14 PM
I don't have the cites here to back me up, so I'll have to go by memory.
FM frequencies are "line of sight." How far they go depends on the height of the transmission tower and the strength of transmission. The FCC has geographical limitations on how close FM stations that share the same frequency can be located.
AM frequencies can be affected by a lot of different factors. AM transmission can also be "tuned" somewhat by using different arrays of transmission towers. Signals also travel farther during nighttime than when the sun is up.
If I recall, the most commonly used FM frequencies are in the 88-92 mhz range, which are reserved for non-commercial stations. There are a lot of low-power, limited range stations in there.
The most commonly used AM frequency stations are in the 1300-1400 khz range. They're primarily reserved for "local" stations.
The frequency hard over the largest geographical area would be the AM "clear channel" stations. They're licensed to operate at maximum power. Some can be heard in 30 or more states at night. Mexican clear channel stations transmit at even higher power and can be heard across huge parts of North America.
There's an old legend that WLW-AM 700 in Cincinnatti had a permit to broadcast at 10 times the normal power during national emergencies. Supposedly they cranked up the transmitter for a test once and it blocked out every other AM station anywhere on the dial within a 50-mile radius.
As for the single FM station that can be heard over the longest distance, I believe there are several in North Dakota that hang their antennas off a huge TV tower. It's pretty flat there, and they can be picked up more than 100 miles away.
06-11-2004, 01:17 PM
This information is from my days in radio. FM frequencies are passed out by the FCC who keeps track of the "footprint" of the signal based on signal strength and trys to ensure that the same frequency does not overlap. Signals end in odd numbers only (97.1, 97.3, 97.5) to ensure no bleedover. FM signals are "line of sight" and can be stopped by buildings or natural barriers such as mountains, and FM signals are weaker in general than AM. In addition, i think 88.1 through 91.9 are reserved for public radio. The same frequency can go to any number of stations as long as the signals don't overlap.
06-11-2004, 01:26 PM
Here's a page that lets you query the FM database. If you set the upper and lower range frequencies to the same value, you can get all the US stations at a given frequency.
99.9 - 572 stations
100.3 - 535
101.5 - 530
94.9 - 422
They also have a link to the source data, so someone who felt like doing some programming could actually figure out the most common frequency.
06-11-2004, 02:08 PM
Oops, those totals included a lot of stuff that wasn't full service. You have to set the service type to exclude those.
Stories I've read about WLW state that it first operated as 500,000 watt station, but later had to go down to "only" 50,000 watts.
But while it was a 500,000 watt station, it was heard widely which is likely how Red Barber, who was the Cincinnati Reds announcer at the time, was noticed by New Yorkers and moved over to the Brooklyn Dodgers.
That and the Cincinnati Reds president Larry McPhail moved over as well.
06-11-2004, 04:05 PM
I know the OP is looking for FM broadcast stations, but there are a lot of ~47MHz baby monitors, walkie talkies, and old cordless phones out there...
Airports without towers are assigned a Common Traffic Advisory Frequency (CTAF).
The most popular might be 122.9 MHz. Multiply the number of airports that use a CTAF by the number of airplanes that use those airports and you could get a pretty high number.
Every airplane in the US is required to have a ELT (Emergency Location Transponder). Most work on 121.5 MHz. Tho they are only supposed to transmit after a crash...
06-11-2004, 04:10 PM
Before anyone jumps all over me yes I know that aviation uses AM, not FM.
(tho the wavelengs are closer to FM brodcast freqs than to AM broadcast freqs)
How many garage door openers or radio contraled models are there (tho I'm not sure how many of tose use FM)
06-11-2004, 10:52 PM
"" Un-officially "", I would have to say 88. 1 3 5 7 9 get the most "use". I understand the spirit of the question, but the word of the question pushes 88 up pretty high.
For starters, the Belkin Tunecast transmits audio from any headphone jack to 88 1 - 7 (selectable per user, for best reception).
IIRC, The Oscar Meyer Weiner Mobile uses 88.3 for its tranmissions, and advises fellow drivers to tune in for their special (advertising) programing.
I think a few Drive-in Theatres (those that you can find) use Radio transmission for Movie audio, and I would assume this as well is "down" around 88.
In a related note, Drive through Christmas Light scenes also use radio frequencies.
Here in Atlanta, Public Broadcasting, College and similiar low budget stations air around 88.
I think since transmissions on 88 are relatively cheap to produce, this proves why it is offten used.
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