Sennheiser SKM 9000 Wireless Microphone.

Frequency: UHF 510MHz – 570MHz . 300 meters Backlit LCD display showing RF level, AF level, Channel Frequency and mute status, battery level display. 100 Selectable frequencies on each channel, up to 20 units can be used simultaneously Built-In Tone Lock Squelch circuit protection from RF interference Automatic transmitter setup, the channel of the transmitter and receiver can easily synchronize