SITOR

SITOR (SImplex Teletype Over Radio) is a system for transmitting text messages.

Although it uses the same frequency-shift keying (FSK) modulation used by regular RTTY, SITOR uses error detection, redundancy, and/or retransmission to improve reliability.

[1] SITOR is used commonly on shortwave bands, where it is used to transmit maritime-related information such as weather forecasts and storm warnings.

[citation needed] NAVTEX marine weather and safety messages are broadcast using SITOR-B.

[3] In 1991, an AMTOR extension was described that includes lower case and other printable ASCII characters.

Consequently, the CCIR 476 alphabet is guaranteed to detect all single bit errors within a character.

SITOR uses the additional code points for idle, phasing, and repeat requests.

[8] Idle signal α Transmission in synchronous frames of 450 ms. Three characters are transmitted by the Information Sending Station (ISS), which takes 210 ms.

Every few sync bursts, a Morse identifier of three letters is transmitted (for example NMO in Honolulu).