Where Wireless Mics Go Next

No place to call their own
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WASHINGTON—Wireless microphones will have a spectrum home after the incentive auction, but the neighborhood will be more crowded. The Federal Communications Commission published its rules pertaining to wireless mics this week after having approved them in the Aug.6 regular meeting. Wireless mics will be relegated to shared frequencies between wireless up- and downlink spectrum, and unoccupied TV channels. The move leaves wireless mics without dedicated spectrum for the first time. The FCC tried to mitigate the impact by loosening up the rules for operations.

“We revise our rules to provide more opportunities to access spectrum by allowing greater use of the VHF channels and more co-channel operations without the need for coordination where use would not cause harmful interference to TV service,” the Report & Order stated.

The R&O, along with a Procedures Public Notice also adopted last Thursday, officially opened up the “duplex gap” to wireless mics. The duplex gap will comprise an 11 MHz swath of spectrum separating wireless up- and downlink bands. It will also be open to unlicensed devices and used by TV stations in markets where there are more stations than channels after the repack.

With regard to unoccupied TV channels, or “white spaces,” the commission recognized there would be fewer such frequencies in a reduced TV band, and a greater chance of interference. New wireless mic systems operating in “TV bands and certain other bands” will have to meet the standards set forth by the European Telecommunications Standards Institute, the R&O said.

It also opened up frequencies between 941 and 960 MHz; 1,435 and 1,525 MHz; and 6,875 and 7,125 MHz for sharing with licensed wireless mics.

Sharing—now done with unlicensed devices in TV white spaces—involves registration in one of several databases that are supposed to direct the unlicensed devices to unoccupied frequencies. Bruce Franca of the National Association of Broadcasters found multiple anomalies and misinformation in the databases earlier this year, and the organization petitioned to have them shut down until the system could be fixed.

The FCC, in its wireless mic R&O, said it was “taking steps… to make improvements to the registration system in the TV bands databases to enable more timely and effective reservation of channels that would be protected from unlicensed white space device operations.”

With regard to operation in the VHF channels, current rules allow a power level of 50 mW for wireless mics, versus 250 mW in shorter-waved, UHF frequencies. Following a recommendation from Shure, a wireless mic maker in Niles, Ill., the commission changed the power level metric for VHF operation to 50 mW EIRP rather than conducted power. This helps manufacturers overcome the lower antenna efficiency of the longer-waved VHF frequencies.

The R&O also allows co-channel operations by licensed mic users within a TV channel where the signals falls below a threshold of -84 dBM “over the entire TV channel, provided certain conditions are met.” These include operations limited to indoor locations, and not in an “itinerant fashion where the signal threshold could be ever-changing, and the location is not being used for over-the-air television viewing.”

The 84-page R&O outlines many more technical parameters, including transition periods for moving, and is available online. TV Techology will follow up in the weeks to come with information from mic manufacturers and users.