Wireless microphone
FM modulation is usually used , although some models use digital modulation to prevent unauthorized reception by scanner radio receivers; these operate in the 900 MHz , 2 . 4 GHz or 6 GHz ISM bands . 
<triplet> FM <subj> modulation <obj> subclass of <triplet> modulation <subj> FM <obj> has part <triplet> digital modulation <subj> FM <obj> has part