Simplex Radio Channel 1 : A radio channel using a single frequency that, at any one time, allows either transmission or reception, but not both, by a particular radio
NFPA 1221 Standard for the Installation, Maintenance, and Use of Emergency Services Communications Systems, 2007 ed. (Std: Install, Maint, and Use of Emr Srvc Commun - Amer) {391 NFC}