Editing Category:Serdolik

[[File:Serdolik.png|550x550px|thumb|right|200 bit/sec mode, the most common used]]
[[File:Serdolikhigh.png|322x322px|thumb|right|800 and 1200 bit/sec mode, two of the higher speeds]]
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.

== Example recordings: ==
[https://drive.google.com/file/d/101SINLk2kkHoSQ_iyHu6tg8aXGkpjxRq/view?usp=sharing 200 bit/sec mode transmission from Moscow]

[https://drive.google.com/file/d/1McMfO1J68Nr8PfTrRclG4MZbQp4MNBoS/view?usp=sharing 800 and 1200 bit/second modes test]

== Frequencies ==
{| class="wikitable sortable"
|+
!'''bit/s'''
!'''Tones per symbol'''
!'''Spectrogram'''
!Note
|-
|200
|1
|[[File:200bps.png|300x300px]]
|The most common mode
|-
|400
|2
|[[File:400bps.png|300x300px]]
|Testing mode
|-
|600
|4
|[[File:600bps.png|300x300px]]
|One of the most common medium speed modes
|-
|800
|7
|[[File:800bps.png|300x300px]]
|One of the most common high speed modes
|-
|1200
|15
|[[File:1200bps.png|300x300px]]
|One of the most common high speed modes
|-
|2400
|60xBPSK
|[[File:60ofdm.png|300x300px]]
|Rarely used
|-
|3600
|45xQPSK
|[[File:45ofdm.png|300x300px]]
|Rarely used
|-
|4800
|60xQPSK
|Same as 2400 bit/s
|Rarely used
|-
|7200
|60x8PSK
|Same as 2400 bit/s
|Rarely used
|}
[[Category:Diplomatic]]
[[Category:Modems]]