NAB and the Association for Maximum Service Television (MSTV) filed comments this week with the FCC, [PDF] expressing concern that opening the TV band to unlicensed, untraceable wireless audio devices may "result in substantial interference for digital television service."
In January, the commission banned [PDF] wireless microphones and other low power auxiliary service devices from 698-806 MHz effective June 12, 2010, and allowed unlicensed users of wireless audio devices on these frequencies to operate in current TV bands at power levels not exceeding 50 mW until final rules were adopted. (See my Jan. 22, 2010 RF Report for more details.)
MSTV argued that these unlicensed devices were banned from the 700 MHz band because they could produce substantial harmful interference to the new commercial wireless services that will be using the band.
"Digital television service in the TV band is no less vulnerable to interference from such wireless audio devices and wireless microphones than the new wireless services in the 700 MHz band," the association said.
The organization argued that there was "no technical reason for such disparate treatment and that access to potentially life-saving information" might be in jeopardy. It stated further that there was no need to permit unlicensed operations in the core TV band, as they could operate on an unlicensed basis under Part 15 in less congested bands.
MSTV said that allowing unlicensed wireless microphones in the TV band would produce "an influx of new wireless devices that are wholly unsuitable for the TV band." These could include baby monitors, home intercom, and voice-activated, remote-controlled toys.
Current wireless microphone use in the TV band takes place in controlled settings and at locations "sufficiently distant" from residential TV viewing. Broadcasters are concerned that unlicensed wireless audio devices could be of poorer quality than licensed wireless mics, and would not be "installed, monitored or maintained by professional engineers or technicians, thereby raising the risk of interference due to faulty operations."
MSTV explained that the power limits and out-of-band emissions levels the FCC is proposing for unlicensed wireless audio devices in the TV band were inadequate to prevent interference to DTV service.
Rather than allow unlicensed wireless audio devices in the TV band, MSTV recommends a more conservative expansion of Part 74 eligibility for licenses to include groups such as theaters, live music productions, government bodies, and houses of worship using the devices in professional facilities sufficiently distant from residential areas. By virtue of being licensed, the operators would be identifiable and could coordinate use in the TV band with other services.
Comments from the FCC Chairman and FCC Commissioners have made it clear that the FCC is working to maximize the use of spectrum, including the TV bands. This includes allowing the use of vacant TV channels for low-power wireless broadband ("white space devices" or "TV band devices").
The National Broadband Plan is likely to include a provision allowing TV broadcasters to return spectrum in exchange for a portion of auction proceeds. This spectrum would then be auctioned to commercial wireless services. Even if the FCC ignores the potential for unlicensed wireless microphones to interfere with broadcast TV, I would expect them to be concerned about the interference to the other services, auctioned, licensed and unlicensed, that could share this spectrum with broadcasters.
Doug Lung is one of America's foremost authorities on broadcast RF technology. He has been with NBC since 1985 and is currently vice president of broadcast technology for NBC/Telemundo stations.
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