🔍 Key Concepts

• ARQ (Automatic Repeat reQuest) and FEC (Forward Error Correction) are digital text-transmission modes used in some maritime radio systems • The difference between radio-telex / data broadcast services and search-and-rescue locating devices • Which systems are used for Maritime Safety Information (MSI) broadcasts

💭 Think About

• First, identify which options are primarily used for digital text communications or data broadcast and which are used for locating or homing in an emergency • Ask yourself: ARQ and FEC are modes of error-controlled text/data transmission. Which option is not mainly about transmitting written messages over radio? • Consider which of these systems would be displayed as text on a receiver, versus which one works by interacting with another ship’s equipment (like radar) to make you visible.

✅ Before You Answer

• For each choice, decide: is this a text/data broadcast system or a radar/locating device? • Verify which systems are explicitly linked with NBDP/SITOR radiotelex and thus use ARQ and/or FEC modes • Double-check which one of the four is not designed to send MSI or radiotelex messages, but instead is used to help rescuers find a vessel or survival craft.