Some days ago my friend cryptomaster sent me an interesting recording dated December 4, 2025 about a test of new communications equipment conducted in the Russian Federation. The signal was recorded at the frequency of 15014.0 KHz/USB kHz and its external modulation parameters are similar to NATO standards used for serial waveforms, namely the symbol rate is 2400 Baud and the transmission mode is PSK8 (Figure 1).
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| Fig. 1 - serial waevorms main parameters |
The analysis of the ACF is very interesting (Figure 2). I think that the real structure of the frame is 106.66 ms which - at the speed of 2400 Bd - corresponds to a frame length of 256 tribit symbols (or 768 bits): a length quite usual in such PSK8 waveforms. In my opinion the strong 1173.33 ms spikes (corresponding to 2816 tribit symbols) could be caused by the interleaver length: in this case 8448 bits. As you know, an interleaver is deterministic and periodic and because of that, it can introduce hidden periodic structures into the signal, even if the original data looks random. When you compute the ACF, those periodicities may show up as spikes at specific lags. In this case 8448 is not a "casual" number but it's a quite structured one corresponding to 1056 bytes and it is exactly a multiple of the length of a single frame, ie 768 × 11 = 8448 (as you can see in Figure 2).
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| Fig. 2 - ACF analysis |
Something similar happens in MS-110A at low data rates (<1200 bps): in those cases, one group of four frames count 160 symbols (4×40) and it's just "in sync" with the scrambler length (160 symbols) causing the strong 66.67 ms ACF spikes rather tha the expected 16.67 ms [1].
About the interleaver, in the Russian MIL context the interleaver lengths are usually specified explicitly in bits or symbols (quantitatively), not categorized as “short,” “medium,” or “long” (qualitatively) like NATO documentation sometimes does, so if I'm right it could be a 8448-bit block interleaver, 1.17 s depth.
Now, why I talk about a Russian waveform? The analyzed signal is actually a segment of a longer recording which also includes some op-chats which are clearly in Russian language (Figure 3).
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Fig. 3 - spectrum of the entire recording |
My friend cryptomaster kindly provided me with a transcript of the chat. I didn't translate it, as the possible use of military jargon would have distorted the translation. The full transcript is available as a "transcript note" at the bottom of the post. Anyway, the .wav file you can download contains the entire recording (op-chat + signal).
The analysis of a 8448-bit slice of the PSK8 demodulated bitstream (only a conversion of phase positions), reshaped to a 768-bit period, doesn't help to detect/identify some sort of structured framing. Although repeating blocks of data are easily identifiable, the "usual" structure of Known/UnKnown data as we are used to seeing in similar waveforms is missing (Figure 4). Given the "experimental" nature of the transmission, it's possible that the same structures are being sent... but this is just pure speculation.
A more in-depth study of the code is certainly necessary, as is the need for further "captures" of this waveform.
Comments are welcome.
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| Fig. 4 - 768-bit period |
https://disk.yandex.com/d/oRognr-CGqxbgg
[1] https://i56578-swl.blogspot.com/2021/06/188-110a-acf-lengths-and-interleaved.html
transcript note
- 121, парусу.
- Парус, я 121, вы принимали от меня телекод? Квитанцию отдал, но вы не приняли по всему. После этого свой телекод отправил, но не принял от вас квитанцию.
- Мы отправку делали, получили на неё квитанцию и ваше сообщение получили и тоже дали квитанцию. Приём.
- Принято, отправьте в нашу сторону ещё одно сообщение.
- отправляем.
(передача сообщения)
- 121 парусу.
- у меня нет приёма. Приёмник не работает.
- (непонятно) или нет приёма, всё-таки?
- "Бозон" работает, а "чинара", у меня приёмник не работает на неё. Дайте счёт до двадцати, я послушаю на приёмнике.
- Ну, канал, может быть, немного ушёл, но эти "ноги" снять сегодня не успеем, как поняли? Прём.
- Хорошо, да, ладно.
- Даю счёт (передаёт счёт до 20), приём.
- Парус, я принимал от вас на четыре бала, наверное, но с прерываниями.
- Может, на другой канал перейдём? Повыше? Приём.
- Давайте, перейдём на другой канал.
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