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 [now June 12, 2009 -your fearless editor]. 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.
But what about large touring shows that need dozens of wireless mics, in-ear monitors, and intercoms? And what about special events like the Super Bowl, where hundreds of wireless audio, video, and control devices are in use?
To accommodate this kind of use, the FCC will require all TVBD’s to determine their location within 50 meters (using GPS or some other method) and then consult an online database.
The database will send the TVBD a list of available TV channels that are safe to use at that particular location; the device can’t transmit until it receives this list.
A wireless mic user just needs to register the date, time, and location (in latitude and longitude) of their event along with the TV channels being used by their wireless gear in the database, and any TVBD within one kilometer will stay off of those channels.
The Order is quite liberal in defining who will be able to register in the database, referring to “sites with significant wireless microphone use at well defined times and locations.” This is further defined as “instances where one or more microphones are in operation for a period of time not less than one hour.”
For outdoor events that cover a large area such as a race track or golf course, multiple sets of coordinates can be registered in the database to create a larger protected zone.
The database will be created and maintained by a third party, after proposals are solicited and reviewed by the FCC. There could even be multiple providers, but the FCC will require them to synchronize their data every day.
The database administrator can charge TVBD’s a fee to access the database – after all, someone has got to pay for this, right? – but the Order does not mention any fee for a wireless mic user to register.
The Order also requires a “remote kill switch” that can be used against devices that are determined by the FCC to be causing interference. The database administrator would be instructed to send a message of “no channels available” to a single device or to all devices of a particular make and model.
As a third layer of interference prevention, all TVBD’s must utilize spectrum sensing to detect and avoid wireless microphones, TV stations, and other authorized users nearby, whether or not they are registered in the database.
A TV Band Device must scan the spectrum for at least 30 seconds every time it is powered on, and then re-check the channel it is operating on every 60 seconds to make sure that no new microphones have been turned on. If a new mic is detected, the TVBD must cease transmitting on that TV channel within two seconds.
A couple of important issues were not covered in the ‘White Spaces’ Order. The question of when wireless microphones must cease operating in the 700 MHz Band (actually covering 698-806 MHz, or TV channels 52-69) was not addressed.
In August, the FCC proposed that this should occur as of the DTV transition date on February 18, 2009. Given that some wireless microphone users will need to replace significant amounts of equipment in order to comply, many consider this to be an unreasonable – if not impossible – timeline.
The next logical date for the FCC to announce a final decision on this issue would have been at their December 18th meeting, but the 700 MHz matter was not on the meeting agenda.
Nevertheless, wireless mic manufacturers have rapidly created programs to help wireless mic users to comply with the transition, which will occur sooner or later.
The White Spaces Order also does not deal with what some users consider to be the most worrisome issue still hanging: licensing. As most readers are probably aware, the FCC Part 74 Rules created in the 1970’s required wireless microphone users to have a license, and limited eligibility to broadcast stations, TV and film production companies, and cable TV networks.
Decades of problem-free operation with no record of complaints may have allowed the FCC to miss the rapidly expanding use of wireless audio equipment, as well as the fact that most users did not attempt to navigate the incredibly complex 26-page licensing form.
The fact that the FCC intends to allow very liberal access to the database of registered users – with no stated requirement for a license – would seem to indicate that the licensing topic will continue to lay dormant. A final decision in the 700 MHz issue could give the FCC an opportunity to address the licensing issue, but there have not been any announcements of this so far.
There’s no question that using wireless mics will become more complicated as new types of devices begin sharing the television band. Here are some operating tips that will help live sound engineers to maintain stellar performance:
Know the terrain. Before working at any venue, find out what RF transmitters are operating in the TV band nearby. his includes TV stations, Public Safety radios, and Fixed TV Band Devices.
Most major manufacturers offer an online Frequency Finder as well as free software that can help to identify these users. A high-quality scanner that interfaces with a laptop can also help to analyze the real conditions inside a venue, whose steel and concrete may reduce the strength of signals coming from outside.
Get registered. Once the new database is up and running, use it. TV Band Devices need to download the database every day, but that means the need to select TV channels (although not the exact frequencies) at least two days before the show.
Take inventory. Make sure that the wireless gear to be used covers the TV channels that you need to be in. Virtually all professional wireless mics are now frequency agile, but having the widest possible tuning range gives the most flexibility to take advantage of clear channels.
If renting gear, make sure that the provider knows that it may not be okay to substitute the same product in a different frequency range.
The good news is that wireless microphone users have become an important blip on the FCC’s radar. The cultural and financial importance of live entertainment content helped to emphasize the importance of protecting wireless audio systems from interference.
Working together, wireless manufacturers and live sound engineers have ensured the ability for wireless microphones to continue as the reliable, great-sounding tools for live sound.by Christopher Lyons
From Live Sound International