Just a few unpretending notes as a result of web searches regarding the datalink signal, we have currently been monitoring, in particular about the format (69,48), where 48 bits are data, that for example can be heard on 6123.5 kHz, USB during daytime. The information below refers mostly to the AI-011 (АИ-011) device [1]: a DCE (Data Communication Equipment) for mobile systems designed to protect and transmit telecode data(the generic Russian term for radar data) over standard channels of wired, cable, radio relay, tropospheric and HF communication lines. The data transfer rate is 600 or 1200 bits/s FSK.
Please note that translating from Russian is never easy, I relied on Yandex Translate tool and the acronyms highlighted in orange are just their English translation.
AI-011 (S23) provides operation in duplex, half-duplex and simplex modes. In duplex mode, data blocks are transmitted and received simultaneously also using ARQ. In half-duplex mode the correspondents take turns in transmitting and receiving. In simplex mode the device provides either transmission or reception of data blocks. When exchanging radar information with external subscribers, it ensures the implementation of the exchange protocols:
* AKKORD-SS-PD (АККОРД-СС-ПД) in blocks of length (165, 144) and (69, 48) bits - equipment 55Ts6; in blocks of length (165, 144), (117, 96) and (69, 48) bits - equipment R-050 ;
* IRTYSH (ИРТЫШ) in blocks of length (69, 48) bits - equipment T-235-1L.
When data transmission is carried out in blocks with a length of 69 (or 117) bits, 5 of them are service bits (m,C), 16 (I) are used for error detection and correction and the remaining 48/96 bits (K) are used for data:
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| Fig. 1 - 69 (117) bit format |
The information is transmitted to the communication channel by three types of messages with the following priority:
1. Coordinates of the radar station and information about its operating modes.
2. The coordinates of the targets and bearings on the directors of the ASP.
3. Coordinates and signs of goals and a sign of the ROLE removal channel (automatic or PASS).
Messages of the first priority are issued three times.
I only found the format of the of the third priority message (figure 2): according to a web source [2] it should be the T-235-1L equipment and thus the IRTYSH (69,48) algorithm... but it could be wrong or misleading.
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| Fig. 2 - structure of the 3rd priority message (69,48) |
b) consequently, we are neither able to determine synchronization nor the correct polarity of the bit stream which in turn involves the parsing of bits m and C (and - obviously - the meaning of the 48-bit data block)
c) we do not know the way the three types of messages are signaled (if any) and therefore we do not know which 48-bit structure we are analyzing: i.e. it may be that the data fields of messages we observe have a different format an consequently a different interpretation than the one shown in figure 2.
0101 001 1 1 00 0 10011110 11101010 1 00110111111 0 01110000111 1
0101 111 1 0 10 1 10011110 01011111 1 11110011110 1 11011011010 1
0101 001 1 1 10 0 11111010 11101011 1 00010101011 1 01100001100 1
0101 111 1 0 10 1 11111010 11101111 1 11110011100 1 01111111001 1
0101 001 1 1 00 0 10011111 11101011 1 00010100111 1 01100001100 1
0101 111 1 0 10 1 10011111 01011111 1 11110011100 1 01111111010 1
0101 111 1 0 10 1 11111011 11111111 1 11110111111 1 11011101011 1
0101 001 1 1 00 0 10011110 11101010 1 00110111111 0 01110000111 1
0101 111 1 0 10 1 10011110 01011111 1 11110011110 1 11011011010 1
0101 001 1 1 10 0 11111010 11101011 1 00010101011 1 01100001100 1
0101 111 1 0 10 1 11111010 11101111 1 11110011100 1 01111111001 1
0101 001 1 1 00 0 10011111 11101011 1 00010100111 1 01100001100 1
0101 111 1 0 10 1 10011111 01011111 1 11110011100 1 01111111010 1
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| Fig. 3 |
001010101010101010101010101010101010101010101010101011101000101000000
Don't know if it's used as phasing/sync between messages or in absence of messages to be sent.
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| Fig. 4 |
That is not the only repeated sequence that is used: indeed, long periods of absence of traffic (sometimes more than one minute) are characterized by the sending at regular intervals (5.4 sec) of the sequence:
101011110110000000011110100001110010111111101110001110110100011111100
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| Fig. 5 |
The same sequence is also inserted within the messages stream, apparently without a precise criterion:
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| Fig. 6 |
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| Fig. 7 |
[1] https://vunivere.ru/work3160/page51
[2] https://disk.yandex.com/i/foPNyfiDpCHGPw
[3] https://disk.yandex.com/d/NjiybR9nwwUE9g
[4] https://studizba.com/files/show/doc/209357-4-1.html AKKORD-SS-PD (AKKORD-165)
[5] https://studbooks.net/1194685/bzhd/razrabotka_funktsionalnoy_shemy_peredayuschey_chasti