ARQ-E

ARQ-E is a radio transmission method used to send data over short wave radio. ARQ-E is a full duplex synchronous data communications system that requests repeats if data is not received correctly. It uses an alphabet that can detect errors. Another name for this is ARQ-1000 duplex or ARQ-1000D.

Alphabet

The alphabet used in the ARQ-E protocol is an extension of the CCITT Telegraph Alphabet No. 2 more commonly known as Baudot. This alphabet has five bits, and therefore has 2⁵ or 32 different possible symbols. The ARQ-M alphabet being synchronous always has to send data and does not have gaps between characters. It does not include start and stop bits that would be used in asynchronous transmissions. In asynchronous transmissions a steady stop signal indicates that there is nothing to send.

The ARQ-E characters are extended with an identification bit or signal element at the start to indicate whether it is a normal character or a function signal. This would add another possible 32 combinations to the code. But of the 32 only three are used.