I stayed at a resort in the U.S. recently that is located in an unpopulated area with virtually no radio reception. To fill the gap, the resort has its own FM station that can be heard only within the resort (about a minute after you drive off the resort, it fades away completely). When you tune to the station, all you hear is one pop song after another, with fade/overlap between the songs. There is no station identification, commercials, or any other content.

The only resort employee I could find that knew any details about it said that he was the one who selects the playlist, using a desktop computer application but he didn't know anything about the radio transmission technology.

Does anyone have any information about this type of station? How does the transmitter connect to the software? What kind of equipment (antenna, etc) would it use? What is the software he's using? Where does it fit legally (FCC, etc)? How the heck are they able to keep the coverage area so tightly defined?

• Was the resort in the US? – Phil Frost - W8II Sep 5 '17 at 21:45
• Yes (as I indicated in the question :) ) I will add a U.S. tag – JoelFan Sep 5 '17 at 21:52
• Oh sorry, I never read the first sentences of things :) – Phil Frost - W8II Sep 5 '17 at 21:58
• Interesting info, but according to fcc.gov/media/radio/low-power-radio-general-information , Part 15 is limited to a 200 foot range. The resort is much bigger than that. – JoelFan Sep 6 '17 at 0:32
• My guess is that the resort is operating that station illegally. If they are unlicensed, they probably have too much power output, but nobody noticed since they're so remote. If they are licensed, they should be identifying. – PhilippNagel Oct 18 '17 at 19:33

I believe you have encountered a Part 15 radio station.

United States Code of Federal Regulations, Title 47, Part 15 (47 CFR 15) covers such things as garage door openers and the like. As such, and due to the fact that they are unlicensed by definition, there is no station-identification requirement. Note that this section covers both intentional and unintentional radiators.

According to the FCC, in OET Bulletin 63: (October 1993), page 15, operation on the FM broadcast band is limited to an effective radiated output of

250 uV/M as measured at 3 Meters distance


This was originally intended to provide roughly a 200-foot transmission range. And you can have as many transmitter as needed to cover a larger area.

A typical Part 15 FM radio transmitter is the Ramsey FM100B.

Note that there is no limit to the number of transmitters that can be operated, so it is possible to cover an entire city block or more if you have enough transmitters.

(The Ramsey FM100B was also offered for overseas buyers as a 1 Watt transmitter through the addition of a secondary power amplifier board)

For longer distances, Part 15 AM is often a better choice because of the availability of radios like the Chezradio Procaster, which is FCC type-certified when operated with the integrated antenna.

Part 15 AM is limited to 100mW power output and a 10-foot antenna-to-ground length.

This opens many possibilities especially in terms of range. For instance, a Procaster on a rooftop with a 20-wire radial system (a counterpoise, or artificial ground) can often reach more than a half mile in radius.

The particular FM transmitter shown above has 2 RCA input jacks for each Line, and a 1/8" (3.5mm) jack for Mic Input. In other words, it has an internal mixer.

The only cable required to connect to a Line input from a PC is a generic one like this:

New 3.5mm 1/8" Stereo Male to 2 RCA Male AUX Audio Stereo Adapter Y Cable Cord

As with all things FCC, the cardinal rule is that the station operator bears full responsibility to avoid interfering with any other licensed service.

There is an active Part 15 community presence on the WWW. There are many types of antennas in use, including carrier-current where powerlines are the primary radiators.

If you are interested in setting something up yourself it is worth the time to search around and learn from the experience of others.

• Excellent answer!! A couple questions... what if you want the transmitter at a bit of a distance from the PC (e.g. the next room)? And... it seems that this station has about a 1000 foot range. Could it still be Part 15. If the main concern is interference, I think they have no problem, since there is literally nothing around for miles and there is no reception from other stations, on any frequency. Finally... it seems like they exactly tailored the range for the size of the resort. Does the transmitter have such a fine adjustment of power? – JoelFan Sep 6 '17 at 16:20
• If you want the transmitter a distance from the PC, run a 1/8" extension cable. Interference: Since there isn't other reception in that area it gives them a lot of flexibility in choosing their own frequency without worry. Power: The short range nature of these is such that the signal would fall off rapidly as you drive away. 1000 ft range: Either they are exceeding the limits or have set up a network of transmitters. If they are not causing interference then nobody would complain about it either way, and it sounds like they are providing a welcome service to their guests. – SDsolar Sep 6 '17 at 18:19
• One more question... what about the legality of the pop song playing (i.e. music licensing)? – JoelFan Sep 7 '17 at 0:36
• Licensing only applies for commercial use. These stations are not licensed commercially - and even more importantly there seems not to be any cases against part 15 stations. There have been cases of pirate stations, though, like PirateCatRadio in San Francisco that was operating an unlicensed 50-Watt station in a cafe. You could drink your coffee and watch them through glass as they did interviews and such. It was a nice place when I was last there, and still operating the transmitter. I suspect they are just streaming now. But they definitely got both sued and had the FCC issue fines. – SDsolar Sep 7 '17 at 1:32
• You can find them at piratecatradio.com - Back less than 10 years ago they were the in-your-face place to be. Their engineer is named Monkey and he enjoys talking about taking on the FCC. Well worth an email, if it is like it used to be. – SDsolar Sep 24 '17 at 7:49

Of interest here: in the areas under the jurisdiction of the U.S. FCC, legal unlicensed operation in the FM broadcast band is limited to systems producing a maximum field intensity of 250 µV/m at a distance 3 meters in every direction from the transmit antenna. The applicable Rule is found in 47 CFR §15.239.

That maximum free-space field of 250 µV/m @ 3 meters will be produced by a simple, linear, 1/2-wave, center-fed dipole radiating an r-f power of 11.43 nanowatts (0.000 000 011 43 watts).

However most of the "Part 15 FM" transmitters commercially available are rated for output powers of 10 milliwatts or more.

It is up to the transmit equipment user to comply with the law, but probably few users of Part 15 FM systems know what that requires, or how to achieve it.

The FCC is active in finding and citing unlicensed operators who do not comply with §15.239.

Licensing does NOT only apply to commercial use. Generally, any copyrighted material that is intended for the general public needs to be licensed (i.e., played in bars, restaurants, even Part 15 stations). However, BMI is currently the only licensing agency that requires a license for Part 15 broadcasters. Both SESAC and ASCAP have stated in writing that they do not require licensing.

Note that radio broadcasters only have to worry about the copyright of the song (composer, lyricist, etc.). Performances, at least right now, do not require licensing for over-the-air broadcasting. That is something that the music industry is fighting to change.

If you are streaming over the Internet, however, you require a license from Sound Exchange (which covers the song and the performance).

• Interesting info. Do you have references on this so I can check it out? Nitpick: using it in a bar or restaurant is commercial, but Part 15 is not a licensed commercial station any more than your garage door opener is. – SDsolar Oct 16 '17 at 3:08
• It seems you are mixing the term "licensing" between the license required to use a certain part of the radio frequency spectrum, and licensing to use other's work in certain ways. – PhilippNagel Oct 30 '17 at 17:07