This article describes the current version of Serdolik, introduced in 2018. For the previous version, see Serdolik (pre-2018).
Serdolik (Russian: Сердолик, English: Carnelian) is a proprietary communication system, used exclusively by the Russian diplomatic service. As of March 2020, the updated version of this system is deployed at the Russian embassies in Sofia, Dar es Salaam, and Nairobi.
Links are established by scanning 3 duplex channels in a loop, for 30 seconds each, until a timely response is received. On each frequency, a sequence of two tones is transmitted, representing the calling station's numeric address.
By default, an established link is in the command state, using 35-tone 40 Bd MFSK modulation. This state is used only briefly to switch between the different traffic speeds.
In the traffic state, 9 different speeds are supported. 200 to 1200 bit/s use MFSK modulation, while 2400 bit/s and up use OFDM instead. The symbol rate of all waveforms is 40 Bd.