CIS-1200 SDPSK 1200Bd („Machowik”, T-230-1A)

i56578-swl.blogspot.com 1 miesiąc temu

This transmission, along with a most likely spurius emanation 600 Hz above, was recorded on 13002.5 KHz (cf) thanks to the distant KiwiSDR located in Azumino-city Nagano, Japan [1].

Fig. 1 - main signal and its spurius

The signal that I presume is the "actual" 1 and that I analyzed is characterized by a SDPSK (Simmetrical Differential PSK) modulation at a velocity of 1200 Baud. Indeed SDPSK is equivalent to π/2 DBPSK or PSK2 with phase rotation: ie, as shown by the transitions in absolute mode, SDPSK assumes that the phase is rotated by +π/2 for bit “0” and by -π/2 for bit “1” thus there is not a 180° turn (transitions do not pass through 0). The information transmitted is encoded in the transition and not in the state. The signal can be demodulated utilizing the differential mode (diff=1).

Fig. 2 - SDPSK modulation

The transmission consists of any segments that disagree by the presence or absence of an first preamble (signals A and B in Figure 3) which consists of a repeated 511-bit dimension pseudo-random series generated by the polynomial x^9+x^5+1 (1) as for the ITU advice O.153 [2] (188-110B "39-tone parallel mode" besides uses that sequences).

Fig. 3

Fig. 4 - 511 bits dimension sequence

The presence of specified sequences is 1 of the features of the alleged Makhovik (aka the "flywheel"), a well known Soviet-Mil crypto system. Although individual classifies Makhovik as vocoder, it can can be utilized for time-multiplexed encryption of both voice and data up to 9600 bps. It's authoritative name is "T-230 bundle ciphering device for teleprinter and data connections" and was designed to operate in UHF but very frequently is found in LF and in HF.
After the removal of the first preamble, the following data block consists of a "common" sequence:

110101100100011110101100100011

followed by 240-bit Initialization Vectors that are sent in 8x30-bit groups, each group repeted 3 times (Figure 5): these 30-bit groups are also peculiar feature of the Makhovik system.


Fig. 5

Segments sent w/out the first preamble (type B in Figure 3) show precisely the same structure: note as the Initialization Vectors slightly disagree (Figure 6): this feature should be further studied (it is most likely someway related to the presence/absence of the first preamble) but it is essential to get respective more recordings.

010000111011001110010100001110
011101100101000011001010000111
110010100001110010000111011001
001110110010100000111011001010
001110110010100011001010000111
111111111111111000011101100101
001110110010100111011001010000
101100101000011011101100101000

010000111011001110010100001110
011101100101000011001010000111
011001010000111100001110110010
111011001010000110010100001110
010100001110110110110010100001
100101000011101001010000111011
111011001010000111111111111111
011101100101000100001110110010


Fig. 6

It's worth noting that in any erstwhile Makhovik recordings I saw differential encoded data & BPSK, while this ones consist of plain encoded data & SDPSK [3].

https://disk.yandex.com/d/Vg5XruORhd8_5A

(1) the usage of the polynomial x^9+x^5+1 is rather common in CIS waveforms,see http://i56578-swl.blogspot.com/p/polynomials.html

[1] http://jf0fumkiwi.ddns.net:8073/
[2] https://www.itu.int/rec/T-REC-O.153/en
[3] https://i56578-swl.blogspot.com/search/label/Makhovik

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