So it would appear that various models of mobile satellite radio receivers are indeed little pirate stations that can intermittently and over short ranges jam other FM radio stations as their owner/listeners drive around. A Securities and Exchange Commission filing made by XM this week discloses that XM and at least one receiver manufacturer have been contacted by the FCC about bringing certain models of mobile satellite receiver “into compliance” with “FCC emission standards.”
Aftermarket, add-on mobile receivers contain small FM transmitters that take the satellite signal and relay it to a car stereo tuned to a certain FM frequency. Similar kits are available to allow people to listen to other audio devices on the road. The National Association of Broadcasters says some models of these transceivers contain FM transmitters that are too powerful, and thus technically require licenses to operate. Interestingly, the NAB report suggests some of these devices may also interfere with the reception of digital “HD” radio signals, since these, in the words of its report, occupy
“vacant” adjacent channels, it is likely that these are the exact channels a user would choose upon which to operate one of these devices. To the user, the “noise” like HD Radio carrier appears to be a vacant channel. However, with the wide modulation capability and strong signal levels emitted by these devices, it is likely that significant interference to the much lower power HD Radio signals would be caused.
XM and Sirius previously tried to pass off this problem as one of improper installation, not design.
Some Sirius receivers also apparently have over-beefy FM transmitters onboard, and this week the company discontinued production of select models. No word on whether Sirius is also in correspondence with the FCC.
It would be interesting to know just how much wattage these transceivers are throwing. Roughly speaking, the FCC’s limit for FM transmission power under Part 15 is less than a quarter of a watt, but past coverage of the interference caused by these transceivers suggested they generated signals that could be heard as far as a quarter-mile away. Considering that a transceiver’s antenna could be no bigger than the antenna of the vehicle in which it travels, that suggests a watt or more of power.
XM proposed a change to transceiver design that would “reduce emissions through the antenna or cigarette lighter adapter,” but the FCC just nixed that fix, no explanation given.
XM is quick to note that “no health or safety issues are involved with these wireless XM radios,” though if you, as an individual, were to run a stand-alone FM transmitter of that amount of power and pump your own programming through it, you risk a $10,000 fine or worse. No single microradio station ever caused this much widespread consternation about interference. Care to place bets on whether the FCC’s inquiry will lead to any sort of penalty for XM, Sirius, or any affected receiver manufacturers?
This news has affected both companies’ stock prices, which emphasizes the relative youth of this newcomer to the radio space.
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