1 October 2014

CIS Navy Broadcast BEE36-50 (T-600)

BEE-36-50, also known as CIS 36-50 or T600, is a synchronous system with 1 stop bit used by the Russian navy. Usually a 36 baud idle sequence is transmitted, followed by 50 baud encrypted traffic with no apparent ACF. Common shifts are 200, 250 and sometimes 500Hz.
When idling at 36 bd it shows an ACF=2 and as it switches from 36bd to 50bd a preamble can be detected running with ACF=70.

A message begins with a bit synch sequence and a start-of-message preamble. Message data is sent with a 7 bit 3:4 ratio alphabet and ending with an end of transmission sequence containing at least 4 end-of-transmission characters.
The length of a message is variable. If a transmission contains more than one message, the start of message sequence is left out between messages.  


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