The UHF spectrum between 470 MHz and 800 MHz is particularly valuable for wireless microphone systems. This UHF range offers technical properties which allow portable systems to operate with a good balance of required RF output power, RF propagation (good both indoors and out), and small antennae size. Wireless microphone systems operating in the 470 MHz to 800 MHz spectrum share it with over-the-air television broadcasters. Wireless microphones operate in unused frequency spaces between broadcasting television stations and specific licensed bands authorized for wireless microphone use in certain regions of the world.
The technological transition from analogue to digital television broadcasting started in early 2000 throughout the world. It was done in large part because digital television broadcasting is a more efficient use of spectrum than analogue television broadcasting. The result has been a worldwide change in the use of UHF spectrum, intended to free it for more television channels and new mobile wireless devices.
In 2009 the United States Federal Communications Commission (FCC) auctioned the 700 MHz band to telecommunications companies for mobile broadband, eliminating that band from use by wireless microphone systems. Ofcom in the UK announced that the UK would similarly require users to vacate 700 MHz by May 2020. In April of 2017 the FCC licensed much of the 600 MHz spectrum to telecommunications companies, requiring users of wireless microphone systems to vacate that band by 2020.
Just as with digital television, digital wireless microphone systems are more efficient with spectrum for a given system performance than analogue wireless systems. This results in more systems being operational in a given frequency range.