Wireless microphones, both high-band VHF (174-216MHz, TV Channels 7-13)  and UHF (470-806MHz, TV channels 14-69),  have always had to operate on frequencies (channels) not used by nearby TV stations in order to avoid interference from TV transmissions. Channels not used by your local TV station are referred to as “white spaces” because they appear blank on charts of TV channels used in various geographic areas. The Federal Communications Commission (FCC) has now opened up the wireless microphone white space channels to other types of wireless transmitters for broadband access use, e.g., telephones and laptop computers. These additional wireless transmitters (referred to by the FCC as TVBDs—short for Television Band Devices) are prohibited from interfering with wireless microphone use in the digital TV band—channels 2 through 51.

Various measures have been taken to ensure that TVBDs will not interfere with your wireless microphone use in white spaces:

• TVBDs must incorporate “spectrum sensing” technology that checks for channels being used by wireless microphones. TVBDs must avoid transmitting on those channels.
  
  
• Spectrum Sensing Technology is still being developed and prototypes are still being tested. The technology is expected to function as follows: The TVBD will check 30 seconds prior to transmitting to make sure the channel is free from wireless microphone use. After starting to transmit, it must check at least once every minute and cease transmitting on that channel within 2 seconds of detecting a wireless microphone transmission.  How (and if) this currently mandated technology is actually workable on a practical basis is not yet fully understood. If not, the viability of TVBDs may be re-evaluated and requirements may change. The timetable for this process is still unclear.

• In the meantime, certain channels will be prohibited to TVBDs and are therefore safe for wireless microphone use.

  Two “safe” channels are in each of the 13 major metropolitan TV markets (Boston, Chicago, Cleveland, Dallas/Ft. Worth, Detroit, Houston, Los Angeles, Miami, New York/NE NJ, Philadelphia, Pittsburgh, San Francisco/Oakland, and Washington D.C./MD/VA) where certain other wireless services operate on channels 14 through 20 (470-512MHz). The “safe” channels are the first channels not used by TV broadcasting in the particular market on each side of channel 37 (608-614MHz): channel 36(602-608MHz) and channel 38 (614-622MHz). For example, if channel 36 is used for TV but channels 38 and 35 are not, the “safe” channels would be channel 35 (596-602MHz) and 38.

  Wireless microphone users may register for free with an internet database (to be established), noting the geographic location, dates, times (minimum one hour) and channel of the intended use.  Registration must take place at least 24 hours before use and may be for temporary or permanent use. TVBDs must check the database daily and avoid transmitting within one kilometer of the designated location and times on the “safe” channel.

  There are two types of TVBDs: Fixed devices that are required to use an outdoor antenna, and personal portable devices. Fixed devices operate at higher power than personal portable devices.  Because personal portable TVBDs are prohibited from using channels 2 through 20, and fixed TVBDs are prohibited from using channels 14-20 in geographic areas where other specified  wireless services are used and also prohibited from using channels adjacent to those used by your local TV stations (including stations using channels within the range 2 through 20), wireless microphones should have several “safe” channels in the 2 through 20 range that are not used by TV or other wireless service operations.

TVBDs must pass a lengthy FCC certification process before they may be marketed, and are not expected to reach the market before the end of 2009 at the earliest. There are still considerable technical hurdles to overcome before these devices are approved for use within the designated guidelines.

TVBDs are prohibited from using channels 52 through 69 (698-806MHz)—channels currently still available for wireless microphone use. None of these channels will be used for TV after the expected June 12, 2009 nationwide transition from analog to all-digital TV. However, those channels will be used by other yet-to-be developed and marketed wireless devices. The FCC has not yet announced guidelines for all of these uses. Currently it is legal to sell and to operate wireless mic systems in these frequencies, although this may change in the future. Further information about this will be forthcoming on this site when available.

Existing Systems at 794-806MHz

It is anticipated that current wireless operation between 794-806MHz will continue to be viable for at least several more years—perhaps even longer—since these applications, for the most part, are not really in competition for the same transmission "air space". Although this frequency range has also been used for public safety applications since 2005, we are not aware of any interference issues in this band.  This band is also free of DTV frequencies and will remain so into the future. 

Frequency Bands for Wireless Mics Going Forward

Wireless microphones offering user-select frequencies over a broad band (e.g., 20-36MHz or more), vs fixed frequency units, will have the most flexibility of use.  Flexibility will be limited more in some areas than others based on the tunability of  frequency synthesized PLL systems to open bands. However it is anticipated that fixed frequency VHF systems (170-172MHz and 174-216MHz) and UHF systems in the band 470-512MHz and 596-622MHZ (with geographic restrictions noted above) will also be viable for quite some time. Fixed frequency units are also usable in the bands 902-928MHz and 944-952Mhz. Although both of these bands are primarily intended for other uses, wireless mics are permitted at these frequencies since they are low-power transmitters. As a practical matter, wireless mics rarely, if ever, encounter interference from other devices sharing these bands.  All Nady frequency-agile and fixed frequency systems are on one or more of the allowed, designated bands as appropriate and will remain so into the future. 

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