The range of frequencies in the VHF band from 169 to 172 MHz designated for radio devices that are not assigned to any particular use. Frequencies above this are used for television but different cities use different television frequencies (channels). Therefore, a wireless microphone can use a television frequency that's not being used by a local TV station. However, a performance group that travels from city to city can not use any of those frequencies since they would only work in half the cities. Therefore, they use a "traveling" frequency hat will work in any city depending on who else is using that frequency near them.

Source: [ Church Audio & Acoustics Glossary] [[Category: Acoustics]]