In the 1970s and 1980s wireless microphone manufacturers referred to frequencies in the VHF band (150 - 174 MHz) as "travelling frequencies".  As wireless microphone technology advanced into the 1990s these frequencies were used less and less as wireless mics moved into the unused TV channels in the UHF band between channels 14 and 68 (470 MHz - 800 MHz).
The169-172 range is most commonly referred to as the “Traveling Band” and is usedprimarily for wireless microphones. In recent years this range has become verycongested due to the sheer number of users, and in many areas these frequenciesmay be too congested to get reliable performance. Since wireless microphonesoperate with 50 mW or less, systems operating in this range are commonlyaffected by high power hydrological transmitters and radio frequencyinterference generated by computers and lighting control systems. In spite ofthis, the 169-172 MHz “traveling frequencies” are the only legally licensableVHF frequencies available to a non-broadcaster user.  Use in the entirerange is subject to FCC rules part 90.