For all the recent hype about the FCC’s white space ruling disrupting the use of wireless microphones in sports applications, Sennheiser — a major manufacturer of wireless microphone systems — said customers should understand the new FCC ruling regarding the use of wireless spectrum.
The company said the FCC implemented a variety of safeguards to help prevent interference between the unlicensed consumer devices and RF wireless microphones. Most importantly, Sennheiser said, licensed operation of wireless mics takes precedence over TV band devices, formerly referred to as white space devices. TV band devices must coordinate around active licensed wireless mic systems.
TV band devices must include the spectrum sensing capability to listen to the airwaves and detect wireless microphones (in addition to TV stations). Until they can demonstrate through “proof of performance” that they can reliably sense wireless mics and avoid causing interference through this method alone, they must also use a geolocation database system.
The database will include a table of registered broadcast license assignments. It will also include a list of protected areas that use wireless microphones such as entertainment venues and sporting events. TV band devices must first access the database to obtain a list of permitted channels in the area before operating. A TV band device that lacks this capability can operate only under the direct control of a TV band device that has it.
The FCC ruling accommodates for at least two channels available for wireless mics. This ensures that a minimum of 16 wireless mic systems — eight in each TV channel — may be used simultaneously in any venue. Equipment with high linearity (extreme suppression of harmonic distortion known as intermodulation) will support at least 20 systems, or 10 in each TV channel. Specific areas protected by the FCC ruling will enable the operation of many more channels.
Multistage and studio properties may also increase the number of systems in use through physical distance and transmitter output power management. Techniques such as shifted coordinated frequency sets, zone isolation (natural or enhanced shielding between rooms), directional antennas and filtered distribution systems as well as time multiplexing (using systems in different rooms at different times) may also be used.
TV band devices categorized as fixed devices are allowed to operate with effective radiating power of up to 4W on Channels 2-51, with the exceptions of Channels 3, 4 and 37. Those classified as personal/portable are restricted to Channels 21–51 and are also not allowed in Channel 37. In addition, in 13 major markets where certain channels between 14 and 20 are used for land mobile (municipal and public safety) operations, two channels between 21 and 51 will be reserved and available for wireless microphones. These will be the first open (non-TV) channels above and below Channel 37.
Furthermore, the unlicensed consumer devices are limited to 100mW operating power or 40mW if operating in a channel adjacent to an active station. This moderate power will reduce their range and the possibility to cause interference.
Sennheiser said it is launching enhanced customer service and support programs for the wireless microphone issue.
For more information, visit http://www.sennheiserusa.com/spectrumreallocation/.
