Constant-Ratio Code and Automatic-RQ on Transoceanic HF Radio Services

Historical development, of present-day commercial teleprinter services, is briefly tabulated according to dates of significant advances. The 7-unit form of basic constant-ratio code is given, and its advantages explained; indicative values of improvement are tabulated. A general description of the Automatic-RQ method and system-rather than specific designs-is given. Commercial application and growth, in the international services, is illustrated by that of TEX (Overseas Teleprinter Exchange) service. Improvement in error probability and reliability, by use of 7-unit ARQ on such services, is given in terms of character-transposition probability, net channel speed in words per minute, and practical operating experience.