it’s a world-wide system which allows the transmission of navigational
and meteorological warnings, and urgent information through coastal
stations. Transmissions take place on 518 kHz or 490 kHZ in AMTOR FEC
mode with special specificities of the message.
The user will set his receiver on USB at 517 or 489 khz. The
transmissions are done at fixed time, for example for NITON (GB): 7h00
and 19h00 UTC on 518 khz in English, 5h20 and 17h20 on 490 kHz in
English, 7h10 and 19h10 on 490 kHz in French.
The character set of SITOR A and SITOR B/AMTOR FEC is the same of the one used for RTTY.
On SITOR A, the reception of the "un-perforated tape" is used by
Russians ships to pass in traffic on Cyrillic. In that case, MULTIPSK
passes to "letters".
The character set of AMTOR ARQ is an extended character set which
allows the transmission of ASCII characters (32 to 128) thanks to the
use of the "un-perforated tape".
Go and see the page on l'AMTOR for more informations.