In a simplex radio system, what is true about transmissions?

In a simplex radio system, the characteristic feature is that only one party can transmit at a time. This means that when one user is speaking or sending information, the other user must listen and cannot transmit simultaneously. This mode is often used in simple communication systems where full-duplex communication (simultaneous sending and receiving) is not necessary. Simplex communication is efficient for situations like broadcasting where only one party, often a speaker or a broadcaster, needs to convey information to multiple listeners.

Understanding simplex systems helps clarify why the other statements do not apply; for instance, while full-duplex systems allow for simultaneous transmission and reception, simplex does not. The notion of messages being transmitted clearly is not a defining feature of simplex systems—clarity depends on various factors like signal strength and environment, not the mode of communication itself. Lastly, simplex systems typically operate on a single frequency for communication, rather than multiple frequencies, which makes the assertion regarding multiple frequencies inaccurate.