HF radio marine telex

The system of maritime mobile communications utilizing HF radio narrow-band direct-printing telegraph (HF marine telex) is expected to see expanded use during the next several years. Experience has shown the necessity for the system to embody both automatic error correction techniques and effective means of selective calling. Use of SITOR error correction has demonstrated that error rates in the order of 10
^-5
is a realistic expectation. Two selective calling methods, the sequential single frequency code (SSFC) and the digital selective calling (SELCAL), have been adopted internationally, although the latter is still subject to final definition of technical characteristics. HF marine telex avoids most of the problems encountered with manual Morse radiotelegraph. It is tried and proven, efficient and economical. Equipment is readily available. Indications are for a rapid expansion of this system's use.