RTTY is a communication system that was previously the main mode of the Russian diplomatic service. At present, it may be heard only in training sessions involving the Russian embassies in Havana and New Delhi.

On RTTY links, operator chatter is transmitted in hand-keyed Morse code, while RTTY itself is used only for messages. The RTTY shift is always 500 Hz, while the typical symbol rates are 75 Bd, 100 Bd, and 200 Bd. The RTTY portion begins with the test sequence 464646..., followed by the individual 5-letter and 5-digit group messages like so:

4646464646464646464646464646464646464646464646464646464646464646464646464646

11177 30022 45013 20882 00549

KDRUG ALMIV LPTAT EACKS YBVPF LSCXG AFJII XDAHJ RQMXY JJXFV
HAJME EJKMA XMXLE ADMSE DSYHQ ZVAIZ ORANL PEBPI EHPGZ LTYFU
OSBBX DBWRM EKOOB NOZVX UPPPW ZVXHC OAETV DQJBR ABQFD TCILT
...

RTTY was introduced on the then Soviet diplomatic links in the mid 1980s; prior to that, the links used only Morse code. The X06 system was added in 1994; unlike today, the X06 calls on RTTY links were immediately followed by traffic on the same frequency. RTTY was gradually replaced by Serdolik during the late 1990s to the early 2000s.