What word should be used when ending a radio transmission if a response is required?

The term "Over" is the appropriate word to use when ending a radio transmission when a response is required. This word indicates to the receiving party that the transmission has concluded, and the sender is awaiting a reply. It signifies that the channel is open for the recipient to respond. In radio communication, clarity and brevity are crucial, and using "Over" serves to clearly communicate to the other operator that they are expected to respond.

In contrast, terms like "Out," "Clear," and "End" are generally used in different contexts. "Out" typically signals the end of communication without the expectation of a reply; it's a way for the sender to indicate they are done speaking and will not be waiting for acknowledgment. "Clear" may indicate that the frequency is available for use, but doesn't imply that a response is needed. "End" is not a standard term in radio protocol and may cause confusion regarding whether a response is anticipated. Thus, using "Over" ensures effective communication and operational efficiency in radio exchanges.