Which statement about SITOR communications is true?

• A. In the ARQ mode each character is transmitted twice.
• B. Two-way communication with the coast radio station using FEC is not necessary to be able to receive the broadcasts.
• C. Weather broadcasts cannot be made in FEC because sending each character twice would be prohibitively long.
• D. Communication is established on the working channel and answerbacks are exchanged before FEC broadcasts can be received.

Answer: (B)

SITOR uses two modes: ARQ, which is two-way with possible retransmission, and FEC, which is a one-way broadcast with error correction built in. In FEC, the transmitter adds redundancy that lets the receiver correct many errors without asking for data to be resent. Because of that redundancy, you don’t need a return link or any answerbacks to receive the broadcasts. Two-way communication is not required for FEC broadcasts to be received.

The other statements mix up how the modes work: ARQ isn’t defined by duplicating every character, weather broadcasts can be sent with FEC, and you don’t have to establish a working channel or exchange answerbacks before receiving FEC transmissions.