The upcoming incentive auction process will further squeeze an industry already short of needed capacity.

Wireless microphone users are fighting for spectrum. Here is why – and what the FCC is doing about it.

Anyone who watches TV or attends live shows knows about wireless microphones: those black or silver things the performer holds, plus a lot more equipment backstage. Until recently, few people gave these devices much thought – not even the FCC. Not until the 2009 digital TV transition that transferred 108 MHz of TV spectrum to other uses.

Most wireless microphones operate in vacant TV channels. The old analog TV rules required certain TV stations to be spaced far apart – not just those on the same or adjacent channels, but also some that operated many channels apart. That left plenty of room for microphones. But digital TV stations can safely be squeezed more closely together. That made possible the 2009 TV spectrum repacking, which cut the numbers of empty channels and left microphone users scrambling for spectrum, especially in microphone-dense areas like the Broadway theater district, while manufacturers struggled to squeeze more microphones into less spectrum.

The FCC added a complication by allowing unlicensed “TV white space” (TVWS) data devices into most of the same vacant TV channels that wireless microphones use. Until the digital repacking there would have been room for both, but the subsequent shortage set off acrimonious disputes at the FCC.

There was another complication. Back then many wireless microphones operated illegally. FCC rules required a license, but limited license eligibility to certain narrow classes of users: broadcast stations and networks, TV and film producers, cable companies, and a very few others. Lots of other people used wireless microphones anyway, including Broadway theaters, outdoor concerts, churches, high-school performers, and – famously – the FCC’s own meeting room.

Rather than enforce against the violators, the FCC instead took steps to make most of the violations go away. A 2010 order granted a blanket waiver allowing unlicensed use of wireless microphones up to 50 milliwatts – plenty for most churches and high-school auditoriums (and the FCC meeting room). Later in 2010, the FCC identified two vacant TV channels in each market for wireless microphone use, closed these to TVWS devices, and clarified how both licensed and unlicensed microphones users could temporarily lock out TVWS devices from other channels, if needed, to protect certain performances.

An uneasy truce prevailed – until the FCC proposed a second TV spectrum repacking.

This one comes about because the same 6 MHz TV channel that used to carry one analog program can now carry multiple digital programs simultaneously. The FCC plans an “incentive auction” that will invite broadcasters to accept cash for sharing a TV channel or, if they prefer, for leaving the business altogether. Spectrum thus freed up will be auctioned for wireless broadband use, with some of the proceeds earmarked to pay off cooperating broadcasters. The result will be still fewer vacant channels for wireless microphones and TVWS.

The FCC’s recent incentive auction order further divides up the ever-smaller pie:

  • The two channels now reserved for wireless microphones will become one, shared between wireless microphones and TVWS devices.
  • The new wireless broadband spectrum will include a “duplex gap” 11 MHz wide between base and mobile frequencies. The FCC will set aside 6 MHz of this for TVWS and 4 MHz for licensed wireless microphones, primarily for covering breaking news events.
  • Unlicensed wireless microphones may be permitted to use a guard band between 7 to 11 MHz wide that will separate TV from wireless operations, and possibly also channel 37 and additional guard bands around channel 37, at some locations. (Channel 37, used by radio astronomy at a limited number of sites and for medical telemetry, has never carried TV programming.) Rules for this operation have not yet been adopted.
  • Wireless microphones will be allowed to operate in closer geographic proximity to a TV station using the same channel, so long as they stay at least 4 km from the station’s predicted service contour – or even closer, if they coordinate with the TV station.
  • The FCC has promised to improve the performance of the TVWS database, possibly allowing wireless microphone users to register events for protection on short notice. Details will follow in a later proceeding.

In a separate order, the FCC expanded licensing eligibility for wireless microphones, now to include venues and professional sound companies that routinely use 50 or more wireless microphones. A production company that provides its own audio services would qualify. The FCC’s examples include indoor and outdoor seated facilities such as auditoriums, amphitheaters, arenas, stadiums, theaters, and houses of worship, as well as venues without fixed seating such as convention centers, conference locations, amusement parks, fairgrounds, entertainment complexes, athletic facilities, educational centers, and government locations. The venue does not have to own or operate the wireless microphones itself to qualify, but must routinely host large-scale productions that require 50 or more of these devices. A venue that includes multiple stages can count microphones by combining all stages at the same location.

Large productions typically use wireless microphone gear the audience does not see, including in-ear monitors for performers, “interruptible fold-back” for communicating with performers on air or on stage, and backstage intercoms – the iconic production person wearing a headset. All of these count toward the required minimum of 50. The FCC order also continues in force the waiver that allows unlicensed microphones to operate at 50 milliwatts or less, so that venues failing to make the minimum of 50 microphones still have the option of unlicensed use.

A later proceeding, not yet begun, will fill in a lot of the details. But even now, it is clear that users will have to replace equipment and adjust operations to work in a lot less spectrum than they had just a few years ago.