The S4.04 UHF range may be switched between four frequency channels,  The systems consists of a belt pack transmitter, a lapel microphone and a receiver.  
 
Since only four frequencies are available for use, only four S4.04 series transmitters can be used at once (if all are programmed to the same four frequencies) so the S4.04 range is appropriate for a site with up to four systems in use at one time or for where the likelihood of other users trying to use the same frequencies is considered acceptable.