Which term describes a radio system that uses only one frequency for both outgoing and incoming messages?

A simplex radio system is defined as a communication system that operates on a single frequency for both sending and receiving messages. This means that the communication can only occur in one direction at a time. In practical terms, once a transmission is made, the system cannot receive until the transmission is completed, making it efficient for certain applications where bidirectional communication is not necessary.

For example, traditional walkie-talkies often function as simplex systems where one party speaks while the other listens, but only one can transmit at any given moment. This is in contrast to duplex systems, which allow simultaneous two-way communication over different frequencies. The simplex system's design is straightforward and economical, making it suitable for specific circumstances and environments where duplex capabilities may not be essential.