FM Modulators are HOT!
FM modulators–those devices that allow your iPod or your XM Radio receiver to play through your car radio–are hot! Not only are they hot in the sense of being popular, but they're also hot in the RF sense, transmitting with illegally high power levels. And there are some that want even higher power!
These devices are low-power unlicensed transmitters, operating under the technical rules of FCC Part 15. The rules specify a maximum power limit. Some devices have the ability to select from a limited number of FM channels; others can select from all FM channels. An off-air FM station signal is so much stronger than one of these modulators that a user will select a channel not being used by an off-air station. Otherwise, the station will cause interference to the modulator. But off-air FM stations can also interfere with FM modulators set to adjacent channels. And so, to overcome the signal strength of the off-air FM stations, manufacturers have been building RF modulators with more transmitter power than is legal. And that results in interference to off-air reception.
One 88.1 MHz FM broadcaster, WYPR, is telling its listeners, "If you are listening to WYPR, but begin hearing something else, you may be within range of a car utilizing the Sirius transmitter and receiving a Sirius broadcast. You can remedy the problem by simply moving away from the adjacent car. We thought you should be aware and thank you for listening to 88.1 WYPR."
North Country Public Radio just moved its WXLU-FM station transmitter frequency to 88.1 MHz, long after many FM modulator users set their devices to 88.1 MHz because it was a vacant channel. They now have to tell their listeners, "If you're driving around listening happily to 'The Eight O'clock Hour' on NCPR, you might find yourself listening to Howard Stern instead, because of interference from another vehicle's FM modulator."
Howard Stern is on Sirius Satellite Radio. Earlier this year, the FCC investigated both Sirius and XM Radio car receivers that have FM modulators incorporated in them. These aftermarket products are popular because no rewiring of the car audio system is needed. According to press reports, the FCC found products that did not comply with FCC technical rules. Three XM radios–the Audiovox Xpress, Delphi RoadyXT and XM Sportscaster–failed the FCC tests and were pulled off the market, but they finally passed FCC compliance tests and should be available at retail for the holidays. And Sirius recently said it was finally cleared to resume distributing the Xact Visor, Sirius One and Sportster Replay radios.
Earlier this year, the broadcasters commissioned a study of 17 FM modulators and found that only four complied with FCC power limits. The ones that passed came from Monster, Griffin, Crane and Dynex. Those that failed were from Belkin, Akron, iRiver, RCA, Sirius and others. The worst violator, from Hobbytron, was about 50 dB above FCC limits. Of the 13 that failed, six were less than 20 dB above FCC limits, and seven were more than 20 dB too hot. The study found that a car attenuates the signal by only about 11 dB, so it's easy to understand how a signal could leak from one car into another in the next lane.
The broadcasters' motivation may not be entirely technical. Don't forget that they strongly resent the competitive successes of XM and Sirius. But there is evidence of interference, so the technical battle between the broadcast industry and the folks that make and use FM modulators isn't over. It is not clear what the FCC will do if it continues to find over-powered devices.
And meanwhile, a new company, The Rail Network, has stepped right into the middle. To The Rail Network, the existing FCC Part 15 limits are too low, and it wants a 40 dB increase in power–because, you see, The Rail Network intends to install these FM modulators in metropolitan subway trains to broadcast news, weather, music, talk shows and emergency alerts to subway riders. No, I'm not kidding. I couldn't make this up. The Rail Network claims to have a deal with the subway system in Atlanta, and it plans to expand to Boston, New York, Washington and the Bay area.
If it were not for the Sirius and XM Radio compliance problems, The Rail Network might have had a slim chance to get its rule waiver. After all, subway cars are made of metal, which shields the RF emissions...but only by about 11 dB, if the car measurements are applicable. And they run underground...except when they run above ground. Well, even without the controversy, it was a long shot.
So this is a controversy that could end with a bang. The FCC could simply ban RF modulators, making XM, Sirius and iPod users furious. Or it could end with a whimper. Future FM modulators would have to comply with the FCC limits, they would not work as well as the illegally hot devices, and the FCC will devote a lot of resources to enforcement. I'd bet on the whimper.
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