EXMAX ATG-100T 72-76MHz Wireless Tour Guide Monitoring System Microphone Earphone Headset for Church Simultaneous Interpreting Teaching Conference Travel Museum Translation(1 Transmitter 8 Receivers) 117 channels; 72MHz-76MHz,40 IDs allow 40 groups to use simultaneously,Avoid the interference of other frequencies automatically. The smallest and lightest,The cleanest voice transmission. The wire of the microphone and earphone has the antenna function, so please unfold the wire of the microphone and the wire of the earphone to make sure the voice signal transportation when using this system or testing. NOTE before Buying: Please DONT buy many or large quantity sets/units one time if you never operated this system before or dont know what it is for . Strongly advise customers just to buy one set/unit to test this system and completely understand its functions and know its advantages and disadvantages. If you like it after testing, you could buy many sets/units one time. Once a customer bought many sets/units of this system but immediately request returning right after he received the package due to he didnt like it and he realized that its not what he want. This raised too much costs and waste to the transaction, your kind understanding would be highly appreciated.