At the close of a radio transmission, which word is used when a response is not expected?

In radio communication, the word used at the close of a transmission when no response is expected is "OVER." This term indicates that the speaker has finished their message and is waiting for a response, but when it specifically denotes that a response is not expected, it signifies that the communication is complete and the other party does not need to reply.

Using "OVER" communicates clarity and ensures that all parties understand the exchange has concluded, allowing for efficient communication, particularly in operational environments like transportation or emergency services where clarity is paramount. This practice is important because it minimizes misunderstandings and maintains effective communication protocols.

The other options don't fit this context as effectively. For instance, "DONE" is not a standard term used in radio communications, and "CLOSE" could imply a closing of the channel rather than the end of a message. "WAIT" suggests a pause or delay in communication, which would not align with indicating that a response is not expected.