In November, the Federal Communications Commission released the full text of its Second Report and Order approving the use of the “white spaces” – the TV channels that are not actually occupied by a broadcast station – by unlicensed consumer wireless devices.
The FCC now refers to these as “TV Band Devices” or “TVBD’s”. The 130-page document provides details of the technical, operational, and regulatory requirements that the new devices will be subject to.
The FCC’s attention to the needs of wireless microphone users is clearly evident throughout the ruling; in fact, the term “wireless microphone” is used 162 times – more than once per page.
The FCC recognizes that some wireless microphone use is pre-planned and occurs at scheduled events (think concerts, plays, sports events, or business meetings), while some is “itinerant”, meaning that it occurs at random times and places (think TV news crews covering a breaking story).
Accordingly, they have established multiple interference avoidance measures designed to protect the broadest possible range of wireless mic users.
The Order defines two different types of TV Band Devices, which will have slightly different operating characteristics.
Personal/Portable TV Band Devices could include next-generation mobile phones and mobile broadband cards for laptop computers – in other words, devices that move around. These will be limited to 100 milliwatts of transmit power on most TV channels, but will be further restricted to just 40 milliwatts when operating on a TV channel that is adjacent to one occupied by a TV station.
Fixed TV Band Devices could include equipment installed at a home or business (with an outdoor antenna at least 10 meters above the ground) that could transmit or receive wireless broadband internet service or other data.
Fixed TVBD’s will be permitted to operate on TV channels 2, 5-13, 14-36, and 38-51, while Portable units will be limited to channels 21-36 and 38-51 only. (Channel 37 is reserved for radio telescopes and medical telemetry systems; TV stations, wireless microphones, and other devices aren’t allowed.)
Because Fixed TVBD’s will be allowed to transmit at up to four watts of power, they will not be allowed to operate on the ‘adjacent’ channels at all.
TV Band Devices are allowed to go on sale after the DTV transition on February 18, 2009. Considering the mandatory certification testing required for each new product (which the FCC hopes will take less than 6 months), it will probably be early 2010 before any products reach the market.
The Order makes it very clear that TV Band Devices are not allowed to operate on TV channels that are being used by other ‘authorized users’ at or near the same location.
These include TV stations, Public Safety and municipal agencies (who are allowed to operate two-way radio systems on selected TV channels in 13 U.S. metropolitan areas), and ‘low power auxiliary stations’ (which includes wireless microphones, in-ear monitors, and production intercom systems that operate in the TV band).
To prevent interference, the FCC has devised a clever triple-layer protection scheme that serves both small and large users, who may use wireless mics at scheduled events or operate randomly. People who only need a moderate number of wireless mics or who use them at random times can operate on the channels that will be ‘off-limits’ to TV Band Devices.
Since the Portable TVBD’s aren’t allowed below channel 21, and the Fixed TVBD’s aren’t allowed to use the channels on either side of one occupied by a TV station, there will be (in many cities) a few TV channels between channel 14 and channel 20 that are entirely clear.
In the 13 metro areas where a few of those channels are designated for Public Safety use, the FCC is reserving two additional TV channels for wireless microphone use. These will be the first available channels on each side of channel 37.
So in Chicago, for example, TV channels 16, 18, 20, 35, and 39 will be clear, which would accommodate up to 30 professional-grade wireless mics.