Wireless microphone
In another type the transmitter is contained within a separate unit called a "bodypack", usually clipped to the user's belt or concealed under their clothes.
Wireless microphones usually use the VHF or UHF radio frequency bands since they allow the transmitter to use a small unobtrusive antenna.
A few low cost (or specialist) models use infrared light, although these require a direct line of sight between microphone and receiver.
[1][2] Figure skater and Royal Air Force flight engineer Reg Moores developed a radio microphone in 1947 that he first used in the Tom Arnold production "Aladdin on Ice" at Brighton's sports stadium from September 1949 through the Christmas season.
[8] At about the same time, Donald[9] E. Thomas at Bell Labs described an experimental transmitter that used a single point-contact transistor as both oscillator and modulator and whose signal could be picked up by any commercial FM receiver.
[11] The first recorded patent for a wireless microphone was filed by Raymond A. Litke, an American electrical engineer with Educational Media Resources and San Jose State College, who invented a wireless microphone in 1957 to meet the multimedia needs for television, radio, and classroom instruction.
The main transmitter module was a cigar-sized device that weighed 7 ounces (200 g), contained the microphone and circuitry including four junction transistors (a two-transistor audio amplifier, a one-transistor oscillator/modulator similar to the one described by Thomas, and a final RF amplifier), and was suspended around the user's neck in lavalier fashion by a cord that also carried the antenna wire.
It allowed television reporters to roam the floor of the convention to interview participants, including presidential candidates John F. Kennedy and Richard Nixon.
Radio Shack offered a microphone/transmitter module that proved to be vulnerable to capacitive detuning as a user moved around and mingled with crowds.
One solution was to build on a final RF amplifier stage, which the module lacked,[19] though Litke had already anticipated the problem and included one in his patent.
For her Tour of Life in 1979 she had a compact microphone combined with a self-made construction of wire clothes hangers, to free her hands for expressionist dance performances.
[20] Nady joined CBS, Sennheiser and Vega in 1996 to receive a joint Emmy Award for "pioneering [the] development of the broadcast wireless microphone".
Some models have adjustable gain on the microphone itself to be able to accommodate different level sources, such as loud instruments or quiet voices.
Some models have adjustable squelch, which silences the output when the receiver does not get a strong or quality signal from the microphone, instead of reproducing noise.
For example, a television, or film, sound production engineer may use a plug-in transmitter to enable wireless transmission of a highly directional rifle (or "shotgun") microphone, removing the safety hazard of a cable connection and permitting the production engineer greater freedom to follow the action.
This is useful where a vintage microphone is needed for visual or other artistic reasons, and the absence of cables allows for rapid scene changes and reducing trip hazards.
Small true diversity receivers which slot into a special housing on many professional broadcast standard video cameras are produced by manufacturers including Sennheiser, Lectrosonics and Sony.
The 6 GHz band has problems of range (requires line of sight) due to the extremely short transmission carrier wavelengths.
Manufacturers currently offering digital wireless microphone systems include AKG-Acoustics, Alteros, Audio-Technica, Lectrosonics, Line 6, MIPRO, Shure, Sony, Sennheiser and Zaxcom.
[23][24][25] Licenses are required to use wireless microphones on vacant TV channels in the United States as they are a part of the Broadcast Auxiliary Service (BAS).
Beginning in 2017, the amount of TV band spectrum available for wireless microphone use is decreasing as a result of the incentive auction, which was completed on April 13, 2017.
[26] There is a move to allow the operation of personal unlicensed wideband digital devices using the UHF television spectrum in the United States.
These 'white space' devices (WSDs) would be required to have GPS and access to a location database to avoid interfering with other users of the band.
Initial tests performed by the FCC showed that, in some cases, prototypes of these devices were unable to correctly identify frequencies that were in use, and might therefore accidentally transmit on top of these users.
[27] This did not reduce the opposition by broadcasters who might also have been concerned by the possibility of entertainment delivery competition from high-speed mobile Internet access delivered in the white spaces.
On September 23, 2010, the FCC released a Memorandum Opinion and Order that determined the final rules for the use of white space for unlicensed wireless devices.
While the WSD situation in the US is being closely watched by interested parties in the UK and elsewhere, early in 2009 Ofcom launched research and a public consultation on Cognitive Access to the UHF interleaved spectrum.
[30] The outcome of this consultation and the related WSD activities in the US could have far reaching implications for users of UHF radio microphones in the UK and around the world.
