Explanation: "TLX" displayed on a MF/HF transceiver typically refers to Telex, which is the commercial counterpart of SITOR (SImplex Teletype Over Radio) or NBDP (Narrow-Band Direct-Printing telegraphy). SITOR is a robust digital mode designed for reliable text communication over long distances, often employing error detection and correction (such as ARQ or FEC) to ensure message integrity through varying propagation conditions. The other options are incorrect because: * **SSB (Single Sideband)** is an analog voice mode. * **DSC (Digital Selective Calling)** is a digital signaling protocol used primarily for automated distress, urgency, and safety calls, and for initiating contact, not for general text communication. * **AM (Amplitude Modulation)** is an analog voice or broadcast mode.