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Re: Navtex

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  • Kok
    In addition to what Brad mentioned, please be aware also that unlike RTTY and PSK31, to not expect SITOR-B decoding to start right away. SITOR-B (which is
    Message 1 of 3 , Jun 24, 2012
      In addition to what Brad mentioned, please be aware also that unlike RTTY and PSK31, to not expect SITOR-B decoding to start right away.

      SITOR-B (which is directly related to Amtor FEC receive) has a very neat FEC as a countermeasure against long and deep flat fading. Characters are cleverly reinserted into the data stream 35 bits after it is first sent. Decoding appears on the screen only after this latency (at least one third of a second).

      SITOR-B uses the same Baudot code as Amateur RTTY. However, instead of start and stop bits per character, the transmission is synchronous and finding character clocks depends on looking for a sync pattern (from a pair of idle and phasing characters) -- there is also no decoding until that particular transmission pattern is found,

      Amateur RTTY adds a start bit and a stop bit to form a 7 bit per character (or 8 bits if two stop bits are used). SITOR-B also uses 7 bits per character, but the two extra bits are part of the FEC that allows any single random error bit within a character to be perfectly corrected.

      - chen
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