What This Means For Wireless Microphone Users
November 18, 2008

The FCC has finally released its rules allowing a new class of unlicensed consumer electronic products to operate in locally unused TV channels. These have previously been referred to as white space devices (WSD) but are now called TV Band Devices (TVBDs). They will mainly be used as broadband access devices.
TVBD are categorized as:

1) Fixed
These are allowed to operate with effective radiating power up to 4W on channels 2-51, with the exceptions of channels 3, 4, and 37.

2) Personal/Portable
They are restricted to channels 21-51, and are also not allowed in channel 37 (reserved channel for radio astronomy and medical telemetry). They are limited to 100mW operating power or 40 mW if operating in a channel adjacent to an active station. This moderate power will reduce their range and therefore the possibility to cause interference.

Licensed operation of wireless mics takes precedence over TVBD. TVBD must coordinate around active licensed wireless mic systems.

The rules include several safeguards to avoid interference to wireless microphones:

  • Spectrum Sensing
TVBDs must include the ability to listen to the airwaves to sense 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 they must also use a:
  • Geolocation/Database system
TVBDs must use location sensing in conjunction with a database of registered broadcast license assignments. The database will also include a list of protected areas for wireless microphones such as entertainment venues and sporting events. TVBDs must first access the database to obtain a list of permitted channels in the area before operating. A TVBD that lacks this capability can operate only under the direct control of a TVBD that has it.
  • Reserved channels
Personal/ Portable devices will be barred from channels 14-20 (470 – 512 MHz). 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.

This means, at minimum, 16 wireless systems (8 in each TV channel) can be used simultaneously in any venue. When using our equipment with high linearity (extreme suppression of harmonic distortion known as intermodulation) such as our 3000 and 5000 series equipment, the number increases to at least 20 systems (10 in each TV channel). Protected areas will be able to operate many more channels.

Multi stage and studio properties can also effectively increase the number of systems in use through:

1) Physical distance and transmitter output power management

This can be augmented by a balance of other techniques such as shif
ted coordinated frequency sets, zone isolation (natural or enhanced shielding between rooms), directional antennas, and filtered distribution systems.

2) Time multiplexing:

Using systems in different rooms at different times

The anticipation of these changes has caused a great deal of anxiety for many customers. However, when you choose Sennheiser, you not only get great hardware, you get service and support. To help manage customers through this transition and assure they can purchase with confidence, we will be introducing several new service and support programs. In the meantime, we invite you to register at our website, www.sennheiserusa.com/spectrumreallocation, for a free initial consultation. A Sennheiser representative will contact you, assess your current list of equipment and make recommendations to ensure reliable operation of all your wireless audio equipment.

Feel free to contact me with any questions. Thank you for your continued support.

Joe Ciaudelli
Sennheiser Electronic Corp.
One Enterprise Drive
Old Lyme, CT 06371
860-434-9190, ext. 508