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Chapter 7. Radio/Wireless > What Is a Radio Wave Anyway? - Pg. 150

150 Electronics Explained: The New Systems Approach to Learning Electronics Simplex Simplex is one-way communications. Examples are radio broadcasting, pag- ing, and remote control. A radio telescope is also one-way: there is a transmit- ter at one end and a receiver at the other. Half Duplex Duplex means two-way, and most radio communications are really two-way affairs. There is a transmitter and a receiver at both ends of the communica- tions system. Both parties can send and receive. And there are two types of duplex systems, half duplex and full duplex. In half-duplex systems, only one party can transmit at a time. Those com- municating with one another take turns talking. This is the kind of radio where you have to say "over" or "come back" after you finish speaking to let the other party know that it is time for her or him to talk. CB radio is like this. Most two-way communications services (police, fire, taxi, aircraft, marine, etc.) use this method because it is cheap and simple. Fax machines are half duplex. Most computer modems are half duplex.