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| F7B signal, apparently a "classic" MFSK-4 |
F7B.exe can be downloaded from here:
Warning: F7B.exe is coded to run under win/32-bit systems so you may encounter a comdlg32.ocx error (component not correctly registered) when try to run it under x64 systems, here is how to resolve comdlg32.ocx missing error:
https://www.swisssalary.ch/.../register-comdlg32.ocx-on-x64-win7
F7B.exe needs as input file the raw MFSK-4 stream produced by the demodulator of SA and output two ASCII-Bit files CH1.txt and CH2.txt in the same directory of the input file:
Moreover, the Octave script T207_detect.m has been used for the check of T207/CIS-14 mode [1]: it can be freely downloaded from here (you will need GNU Octave package [2] to run the script):
https://github.com/hcab14/.../T207_detect.m
the Octave script T207_detect_e.m also extracts the two world and bit interleaved channels:
F7B.exe needs as input file the raw MFSK-4 stream produced by the demodulator of SA and output two ASCII-Bit files CH1.txt and CH2.txt in the same directory of the input file:
Moreover, the Octave script T207_detect.m has been used for the check of T207/CIS-14 mode [1]: it can be freely downloaded from here (you will need GNU Octave package [2] to run the script):
https://github.com/hcab14/.../T207_detect.m
the Octave script T207_detect_e.m also extracts the two world and bit interleaved channels:
https://yadi.sk/d/zsCD73C9DZpHPQ
I tested the demodulator on the two F7B modes 100Bd/1000 and 96Bd/500, both actively used by Ukrainian Nets; by the way, two preliminary observations:
1) usually, the two F7B channels CH1 CH2 are T-207 secured according to the CIS-14 mode [1]. Since CIS-14 consists of two independent 5-bit MTK-2 channels (transmitted in 14-bit frames), it turns out that those F7B transmissions may carry up to four independent 5-bit channels (CH1a, CH1b, CH2a, CH2b);
2) both those F7B waveforms have their FSK2 counterparts.
I also tested F7B.exe on the Rockwell TE-204, a "special" time-frequency diversity FSK4 mode most commonly used by Allied Air Forces as an air-to-ground messaging system as well as in ground and naval applications.
100Bd/1000 F7B
100Bd/1000 F7B transmissions occupies about 3000Hz bandwidth with the four tones at -1500, -500, +500, +1500 Hz respect to the center frequency. As said above, 100Bd/1000 F7B transmissions may carry up to four independent 5-bit channels. In this regard, it's worth noting in figure 2 that - at least in this sample - the two F7B channels adopt different CIS-14 checksums: mode 20 (0312) in channel CH1 and mode 3 (3120) in channel CH2: who knows, maybe the two F7B channels carry the same data but with different checksums just to increase the redundancy of the system. Note that CIS-14 100Bd/1000 (the FSK2 counterpart) uses the checksum mode 20.
96Bd/500 F7B
96Bd/500 F7B transmissions occupies about 1500Hz bandwidth with the four tones at -750, -250, +250, + 750 Hz respect to the center frequency. The same earlier conclusion applies: that is since CIS-14 consists of two independent channels, 96Bd/500 F7B transmissions too may carry up to four independent 5-bit channels.
In this transmission the two channels use different EOT signaling sequences (figure 6)
Rockwell TE-204 FSK4
Although TE-204 does not definitely use the F7B mode, I decided to check it since regards two FSK2 channels. Indeed, TE-204 transmits the "mark" on 935 Hz for 6.67 msec period followed by a replicated 6.67 msec "mark" at 1815 Hz. Similarly, the "space" is transmitted at 1375 Hz for 6.67 msec followed by a replicated 6.67 msec "space" at 2255 Hz (figure 6). This "mode" provides an in-band frequency and time diversity function (thus the speed is the half of the measured one). As for above, from the perspective of the data-transfer, the modem works as a 75Bd/880Hz FSK2 modem.
Well, decoding separately the two FSK2 channels (935-1375, 1815-2255) we get obviously two time-shifted similar streams (figure 7)
Demodulating it as if it were an F7B signal we get "01" sequences in channel CH1 and (expected) duplicated data in channel CH2 (figure 8)
https://yadi.sk/d/f0U80pRg3F58iA (F7B signals)
[1] https://i56578-swl.blogspot.com/.../redefining-t-207-checksums.html
[2] https://www.gnu.org/software/octave/
I tested the demodulator on the two F7B modes 100Bd/1000 and 96Bd/500, both actively used by Ukrainian Nets; by the way, two preliminary observations:
1) usually, the two F7B channels CH1 CH2 are T-207 secured according to the CIS-14 mode [1]. Since CIS-14 consists of two independent 5-bit MTK-2 channels (transmitted in 14-bit frames), it turns out that those F7B transmissions may carry up to four independent 5-bit channels (CH1a, CH1b, CH2a, CH2b);
2) both those F7B waveforms have their FSK2 counterparts.
I also tested F7B.exe on the Rockwell TE-204, a "special" time-frequency diversity FSK4 mode most commonly used by Allied Air Forces as an air-to-ground messaging system as well as in ground and naval applications.
100Bd/1000 F7B
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| Fig. 1 - 100Bd/1000 F7B |
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| Fig. 2 - two 100Bd/1000 F7B channels, each transporting two CIS-14 channels (CH1a, CH1b, CH2a, CH2b) |
96Bd/500 F7B
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| Fig. 3 - 96Bd/500 F7B |
I don't know if it's a mere coincidence, anyway it's interesting to note in figures 4,5 that only one channel transports data, as well as the CIS-14 96Bd/500 (the FSK2 counterpart) does: i.e., either 96Bd/500 F7B either 96Bd/500 FSK2 use only one of their two "available" channels. Both the waveforms use the CIS-14 checksum mode 20.
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| Fig. 4 - two 96Bd/500 F7B channels, only one of the two available CIS-14 channels is used |
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| Fig. 5 - CIS-14 96Bd/500 FSK2 channels, only one of the two available 5-bit channels is used |
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| Fig. 5 |
Rockwell TE-204 FSK4
Although TE-204 does not definitely use the F7B mode, I decided to check it since regards two FSK2 channels. Indeed, TE-204 transmits the "mark" on 935 Hz for 6.67 msec period followed by a replicated 6.67 msec "mark" at 1815 Hz. Similarly, the "space" is transmitted at 1375 Hz for 6.67 msec followed by a replicated 6.67 msec "space" at 2255 Hz (figure 6). This "mode" provides an in-band frequency and time diversity function (thus the speed is the half of the measured one). As for above, from the perspective of the data-transfer, the modem works as a 75Bd/880Hz FSK2 modem.
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| Fig. 6 |
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| Fig. 7 - the two TE-204 demodulated FSK2 streams |
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| Fig. 8 |
https://yadi.sk/d/f0U80pRg3F58iA (F7B signals)
[1] https://i56578-swl.blogspot.com/.../redefining-t-207-checksums.html
[2] https://www.gnu.org/software/octave/
Very nice explanation. Thanks a lot!
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