Since in the last few weeks I have encountered mostly FSK2 signals (mostly from the East), I decided to take a slightly deeper look at "old" FSK2 modes such as CIS-81-81 and CIS-11 (the latter in a next post).
CIS-81-81 (81-81), T206-M 3M1 device, is the dual channel version of CIS-40.5 mode, hence the designation 81-81; "Moroz" ("FROST" in English) is just an old nickname for the mode [1]. Most likely, when operating in two channels the data are transmitted using time division multiplexing. Both 40.5 and 81 are quite "old" systems, most likely also in use by some ex USSR republic. Speculation is that this older 81-81 system, as defined above, is no longer in use and that the newer 81-81 system is most likely to be derived from CIS-14 or CIS-27 system (81-29 designation?) [2]. Some old reports from WUN logs indicate different users of these systems [2].
Shift Common User
-------------------------------
125 Navy
500 Railway Authority
200,250,500, Military
1000,1500
So far, I have at my disposal CIS-81 samples in two different shift patterns:CIS-81-81 (81-81), T206-M 3M1 device, is the dual channel version of CIS-40.5 mode, hence the designation 81-81; "Moroz" ("FROST" in English) is just an old nickname for the mode [1]. Most likely, when operating in two channels the data are transmitted using time division multiplexing. Both 40.5 and 81 are quite "old" systems, most likely also in use by some ex USSR republic. Speculation is that this older 81-81 system, as defined above, is no longer in use and that the newer 81-81 system is most likely to be derived from CIS-14 or CIS-27 system (81-29 designation?) [2]. Some old reports from WUN logs indicate different users of these systems [2].
Shift Common User
-------------------------------
125 Navy
500 Railway Authority
200,250,500, Military
1000,1500
81Bd 250
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| Fig. 1 |
It's the 81-81 most interesting waveform since its demodulated stream exhibits a 24-bit pattern due to the length of the idle signal which consists of 12 mark and 12 space bits (notice that CIS-40.5 250 uses 12-bit idle signal consisting of 6 mark and 6 space bits).The polynomial x^11+x^9+1 is used to scramble to the following data block which consists of 12-bit frames; then the idle signal is repeated in opposite polarity (Fig. 3). Traffic in the channels is encrypted. It's worth noting that the scrambler polynomial and the idle signal "format" are the same in the 250Hz shift patterns of CIS 40.5 and 81 Baud.
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| Fig. 2 - CIS-81-81 250 |
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| Fig.3 |
81Bd 500
Although the lack of the idle signals (at least in this recording), the demodulated stream is very interesting since it too can be descrambled using the polynomial x^11+x^9+1 (Fig. 5).
T-206 MT "WESNA" (T-206 MT, T-206 2MT, T-206 3M und T-206 3M1)
T-206 is a Soviet teletype and data encryption family devices (not a modem!) used in stationary and mobile operation [3].
https://yadi.sk/d/WQikSYo77Z6oBA (250Hz shift, #1)
https://yadi.sk/d/bd81CpHyBFDuCQ (250Hz shift, #2)
https://yadi.sk/d/-Q-4JagM1eeBHw (500Hz shift)
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| Fig.4 |
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| Fig.5 |
T-206 MT "WESNA" (T-206 MT, T-206 2MT, T-206 3M und T-206 3M1)
T-206 is a Soviet teletype and data encryption family devices (not a modem!) used in stationary and mobile operation [3].
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| Fig. 5 - T206 MT [3] |
https://yadi.sk/d/WQikSYo77Z6oBA (250Hz shift, #1)
https://yadi.sk/d/bd81CpHyBFDuCQ (250Hz shift, #2)
https://yadi.sk/d/-Q-4JagM1eeBHw (500Hz shift)
[2] http://xoomer.virgilio.it/.../Digitalsignalsfaq.htmlDigital Signals FAQ V5.0 (2001)
[3] http://scz.bplaced.net/t206mt.html