The DIRTLX command should be given to a coast station at what point in time?

Correct Answer: Option D — After receipt of the Go Ahead indication following the automatic exchange of answerbacks.

The DIRTLX command must be sent only after the 'Go Ahead' (GA) signal is received. This signal indicates that the initial handshake and answerback exchange are complete, and the coast station is ready to accept routing instructions for the subsequent telex message.