Boston AES Meeting
May 2010
with Tim Vear
On Tues. May 11th, 2010 the Boston Section of the Audio Engineering featured Tim Vear who presented "Wireless Microphones in the New RF Landscape" Practical Wireless Techniques in the Post-DTV Era. The talk covered three main topics; Spectrum Changes, Frequency Coordination and Antenna Selection and Installation.
The DTV Transition - The UHF broadcast spectrum is broken into 6 MHz chunks, one for each TV channel: DTV uses the entire 6 MHz whereas analog TV channels only needed some of the bandwidth. This left areas in the 6 MHz analog TV channel that could be used for a few wireless microphones if necessary (although not technically legal). In addition, analog TV could not operate on adjacent channels. DTV channels do not have this restriction, allowing a more densely packed spectrum when all channels are digital.
On June 12, 2009, most analog broadcast ended. All full-power broadcast TV was consolidated into TV channels 2-51 and required to be fully digital. The spectrum between 698-806 MHz (formerly TV channels 51-69 and referred to as the "700 MHz band") was reallocated for other uses. Most of this spectrum was auctioned off to telecommunications companies such as AT&T for new wireless broadband services, while other parts were set aside for new Public Safety Operations (Police, Fire, etc.). Although Public Safety has had operations in TV Channels 14-20 in some large cities, they have never been required to allow communication between different agencies, as evident at Ground Zero on 9/11. The new Public Safety bands will allow complete interoperability. Many wireless manufacturers have offered rebate programs and other incentives for people to trade in their old 700 MHz stuff to operate in a legal band.
In addition to TV channels, a potential source of interference may be future White Space Devices (TVBD's). This proposed technology would allow unlicensed consumer wireless devices to operate in the same "unused" television channels where wireless microphones now exist. Fortunately, the FCC has mandated technical requirements for TVBD's that should protect wireless microphone operations when and if these devices come into use. Historically, wireless microphones were classified as "licensed" devices. Recently, the FCC has removed the requirement for licensing if the device is operated at 50mW or less.
Band Selection and Frequency Coordination — Shure's Wireless Frequency Finder can give you a list of TV channels in your area and can give you suggested frequencies to use. Applications such as Shure's Wireless Work Bench program (Mac, PC) can be used to calculate a set of frequencies to be used for a show, making it possible to calculate compatible sets of frequencies for any type of radio equipment.
Antenna Selection and Installation — Pickup patterns of the different antenna are dependent on proper directional positioning and proximity to obstructing materials. Tim gave poor antenna placement examples and showed how intermodulation is caused when multiple units are in operation, making selecting frequencies a bit more confusing.
Tim outlined the setup and described the configuration of the wireless systems used for the Rolling Stones Big Bang Tour at Fenway Park August 21, 2005. Several sets of antennae were needed due to the distance of the large stage from the back stage area in addition to covering the two hundred foot width. Each guitarist had only two frequencies (A and B). Since bands do not normally tour with an RF Coordinator, it was lucky for the opening act The Black-Eyed Peas, that Tim was on hand to coordinate which wireless bands were to be used for their set in such a short amount of time.
Tim Vear is Senior Applications Engineer for Shure Inc., Niles IL., where he has served in a technical support and training capacity for several departments since 1984. He holds a BS degree in Aeronautical and Astronautical Engineering, with a minor in Electrical Engineering, from the University of Illinois, Urbana-Champaign. He has provided specific applications assistance to various performing artists including the Rolling Stones and U2, for theme parks such as Disney and Universal Studios, and performance groups such as Cirque du Soleil. While at Shure, Tim has authored several educational booklets including "Selection and Operation of Wireless Microphone Systems" and "Audio Systems Guide for Houses of Worship." His articles have also appeared in Recording Engineer Producer, Live Sound Magazine, Pro AV, Technologies for Worship, and
