CIS MFSK-33 (here:15+∅+17), likely a "Serdolik" multimode waveform

Fig. 1 - "Serdolik" multimode waveform

The MFSK segments have the usual 40Bd and 40Hz (channels separation) values which are typical of the Serdolik waveforms family: a long-range radio system used by the Russian and CIS countries Diplomatic Service, possibly Serdolik V2. It's worth noting in Figure 2 - at least in this sample - that although the system provides a 33 channels grid, only 32 are the effective (used) ones: specifically, the first 15 lower channels plus the 17 higher ones (the 16th channel is not used).

Fig. 2 - MFSK segments

The FSK inserts too have usual Serdolik values, ie 40Bd/680Hz in this sample, and consist of short "01"s sequences (Figure 3).

Fig. 3 - FSK segments

This sample has been recorded on 20.8155 MHz/USB using a remote AirSpy server located in UK.

CIS MFSK-33 waveform is not the only one that does not always use all the available channels of the frequency grid: CIS MFSK-34 (aka Crowd-36) is another example in this regard (Figure 4).

Fig. 4 - frequency grid of some CIS MFSK-34 samples

https://disk.yandex.com/d/wgskeCZfRcz6Ow

SDPSK 40Bd 50Hz OFDM-60 (60-out-of-61 + pilot tone)

OFDM signal heard on 5767.0 KHz (cf) and consisting of 61 channels plus a pilot tone located at the lowest frequency (thus 62 channels in all). The modulator actually uses 60 of the 61 available channels (60-out-of-61) since the position #34 is empty (figure 1).

Fig. 1

For what concerns the OFDM formation, the channels have a 50 Hz spacing and are modulated using SDPSK - also called π/2-DPSK (1) - at the rate of 40 symbol/sec (2400Bd as "aggregate" speed).

 

Fig. 2

Fig. 3

The pilot tone at its lowest position, rather than at the usual highest frequency of 3300 Hz, leds to think of a Russian "Serdolik" waveform, indeed it's similar to the Serdolik OFDM-60 [1]: same speed (40Bd) and spacing (50 Hz) but PSK4 modulation. Some friends of mine (Karaputz, linkz,...) confirmed the idea, likely an enhanced waveform.
Reception and recording thanks to the "Tambov" KiwiSDR [2].

 

(1) In SA Phase-Plane using n-Ary = 4 and absolute mode (diff=0) the transitions between states are similar to QPSK but without diagonal paths (no "zero" crossings); in differential mode (diff=1) we see transitions between two states (Fig. 3) thus it's a Differential-PSK or DPSK. DPSK is called Conventional DPSK (or CDPSK) if the phase differences is in the set of [0,π] and Symmetrical DPSK (SDPSK, also called π/2-DPSK) if the phase difference is in the set of [π/2,-π/2].  As you see in Figure 3, the transitions in differential mode (diff=1) are in the set of [π/2,-π/2].
 

https://disk.yandex.com/d/qq37H3KwwaJn9w 

 

[1] https://i56578-swl.blogspot.com/2015/04/serdolik-crowd-36-ofdm-mode-61-tone.html?m=0

[2] http://sdr4.tambov.gq:8901/?f=5767.00iqz7

"Serdolik" 40Bd mixed mode: OFDM 45 and 60 tones, MFSK-31, and a pich of FSK

One of the numerous variant of the nicknamed "Serdolik" system heard on 11469.0 KHz on USB. Such composite signals are not frequent in the air but sometimes, and for a short period of days, they spring up like magic. Who knows?  maybe the Russian Academy of Communication students take graduate work :).

 

Most of the transfer is performed with OFDM with short MFSK/FSK inserts at irregular cadences: it's interesting to note that all these modulations are characterized by the same 40 symbols/sec data rate. 

The used OFDM are the 60 (60 +1 pilot) and 45 (45 +1 pilot) tones waveforms, both with channel separation of 50Hz and - as said - 40 Baud speed (figs 1,2). The MFSK/FSK inserts occur in both the two modes. The 60+1 tones waveform was already meet here.

fig. 1 - OFDM 60-tones (+ 1 Pilot)

fig. 2 - OFDM 45-tones (+ 1 Pilot)

The switch bewteen the two modes just occured after an MFSK/FSK insert (fig-3)

fig. 3 - switch between the two OFDM waveforms

The parameters of the MFSK/FSK inserts are easy to measure: MFSK-31 40BD speed and 40Hz separation, FSK 40Bd 200Hz and 600 Hz shifts. I only show the MFSK detection in figure 4.

fig. 4 - MFSK parameters

Trasmission was closed by a series of MFSK/FSK bursts as shown in fig. 5

fig. 5

Apart from the affinity to the Serdolik "family" (clues are the MFSK-31 and the OFDM waveforms), it's improbable to say something more precise since the lack of official documentation.

(prob.) new SERDOLIK MFSK burst waveforms

s1: MFSK-28 burst waveform

s2: MFSK-30 burst waveform

s3: MFSK-32 burst waveform

s4: MFSK-32 burst waveform

heard on 19 October:
- 16251.0 KHz USB 1425z MFSK-28 and MFSK-30 burst waveforms(s1, s2)
- 16257.0 KHz USB 0834z MFSK-32 burst waveform (s3)
and 21 October:
- 18203.0 KHz USB 0610z MFSK-32 burst waveform (s4)

The waveforms have different MFSK parameters such as tones, baudrate and shift: probably they not involve all code combinations but the signals are certainly very similar and probably sent by the same equipment.

These signals seem to be experiment/tests with a new Serdolik set of MFSK waveforms, something like a combination of a call (or perhaps ALE Selcall) and data-sending. The s4 MFSK-32 waveform is reported as "new" also in radioscanner.ru, but in that post is used with OFDM-60 as a starting combination while here is used also as 'stand-alone' in burst mode. 
Interestingly the lack of the CIS-60 pilot-tone at the usual 3300 Hz: this could indicate the preamble purposes of the initial MFSK-32 tones. Also in this case, the burst mode is used.

MFSK-32 used as sort of CIS-60 preamble

An interesting difference - at least in these samples - between s1, s2 and s4 are the directions of the two initial sweeps (s3 has a different initial structure): in s1 and s2 the initial sweeps are upward while s4 has downward sweeps. In these recordings s2 carries the same data.

Other than the above post (by my friend KarapuZ) in radioscanner.ru forum, I could not find any other info/report about these waveforms: if they are on-air just from a few days we'll probably have the chance to read other logs and info in next days or weeks.

s1: MFSK-28 burst waveform

s2: MFSK-30 burst waveform

s2: MFSK-30 burst waveform dump

s3: MFSK-32 burst waveform

s4: MFSK-32 burst waveform

summary
s1: grid MFSK-28 (09/28 used), speed 76Bd, shift 95Hz
s2: grid MFSK-30 (21/30 used), speed 76Bd, shift 95Hz
s3: grid MFSK-32 (21/32 used), speed 40Bd, shift 46.8Hz
s4: grid MFSK-32 (32/32 used), speed 83Bd, shift 96.7Hz

SERDOLIK OFDM 35-tone BPSK

Pic. 1 - Serdolik OFDM 35-tone

here a signal that is another variant of the Serdolik OFDM 35-tone: I had a similar waveform (40 Baud and 50 Hz channel separation) with PSK-4 modulation, this waveform shows the same values of speed and channel separation but the modulation in absolute/relative positions is BPSK (Pic. 2). Signal has been resampled at 8000 Hz. The same waveform is also reported in this discussion in radioscanner.ru forum. 

Pic.2 - OFDM parameters and modulation in channels

Moreover, phase in carriers #1-2-3 and #33-34-35 does not change in relative constellation then they are not modulated altough they could carry service informations. Looking deeper at the signal, in this case I used the software tools "baudline - signal analyzer" (http://www.baudline.com/), some channels in time change their modulation (Pic. 3) and it would take a much more in-depth analysis.

Pic. 3 - the same signal as seen in baudline

The signal was heard today (31 August) in the morning at 0750z and tuned on 16120.8 KHz on USB: the recording is available on request.

SERDOLIK Selcall

This waveform provides a 31 frequency grid, 40 Hz spaced, and 40 Baud rate (pic. 1). The signals has MFSK insertions into the sync-marker sequence. 
The call shown in pic. 2 ends into a sync-marker sequence and since no data follows, this could be a sort of null call. 
In pic.3 a complete session, 105 secs lasting, with the call followed by data sent in MFSK-34 mode (CROWD-36): difficult to state if this 'traffic' corresponds to user-data or to link-setup informations with the actual traffic sent in another frequency and/or mode.

The recording in pic. 4 is a more complete example: the call and the sync timing, the sending of link-setup information through MFSK-34 and then the transmission of data through the OFDM 35-tone BSPK waveform. It's interesting to note that the both the call and the MFSK-34 two initial tones exhibit a shift that is the half of the usual.

Pic. 1

Pic. 2

Pic. 3

Pic. 4

SERDOLIK OFDM 35-tone DQPSK

This signal, heard several times and just today on 14390.5 USB starting from 0810z, is one of the many waveforms of the so-called SERDOLIK, a complex system used by the Russian Intel and Diplo services. Despite an initial annoyng CIS 36-50 interference (and the heavy selective fading), there are clearly visible the MFSK-34 (Crowd 36) parts and the OFDM one in the middle: the MFSK-34 partes are characterized by 40 Baud speed and 40 Hz channel separation, as shown here http://signals.radioscanner.ru/base/signal36/

The interesting part of this signal is the one related to the OFDM: another variant of the Serdolik OFDM 35-tone waveform shown here: http://signals.radioscanner.ru/base/signal123/ although the baudrate is the same (40Bd) as well as the used modulation (PSK-4).

On there, the OFDM part is formed w/out the cyclic prefix (ie channel separation = Br = 40Hz) and has 34 channels (the second probably used as pilot). On here, the OFDM part exhibits same baudrate (40 Baud) but 35 channels (the lower probably acts as pilot) with a 40 samples lenght cyclic prefix, channel separation = 50 Hz and k (correlation triangle) =1/4 (Pic. 1); the used modulation DQPSK

Pic. 1 OFDM params and modulation in SERDOLIK 35 modem PSK-4

OFDM parameteres and channels modulation  are the same of the 61 tones modem as reported here Serdolik 61.
First channel from bottom has no modulation and according to my measurements this lower channel is plus 6dB compared to the others (Pic. 2) just like a pilot tone does.

Pic. 2

Interesting is the behavior of the 3rd channel that looks like an "hole": looking deeper, it's a BPSK at 40Bd speed and KarapuZ thinks it acts as an additional sync since it carries only binary strings of zeroes and ones (Pic. 3 and 4), thanks for the tips.

Pic. 3-a

Pic. 3-b

Pic. 4

Since the different gaps between MFSK and OFDM channels the two signals are more likely not formed at the same stage, it's my guess that the initial segment of the OFDM part just acts as syncronization  (Pic. 5)

Pic. 5

SERDOLIK sync marker (idling)

24/06/15 16047.0 --- Russian Gov 0918 Serdolik sync marker

The sync marker sequence is sent alone or after a Serdolik Selcall as shown below

Serdolik Selcall and Sync Marker (courtesy of KarapuZ)

Serdolik, as several time reported in this blog, is a complex system used by Russian Gov/Diplo and designed to connect embassies and diplomatic missions. The link below is a little story of this system:
http://www.sozvezdie.su/museum/sura__posolskaya_svyaz_dlya_sssr/ 
Thanks to KarapuZ for the link and the Sedolik Selcall waveform.

SERDOLIK OFDM 61-tone

the signal shows an OFDM part followed by the usual Serdolik MFSK-34: this is one of the several variants of the Russian system SERDOLIK.

As the 35-tone OFDM mode, this variant shows a 40-samples lenght for LG, 35 tones and spreads a about 3000 Hz bandwidth.
This mode has an easily distinguishable pilot tone at the lower channel so the used channels count to 60 and they are PSK-4 manipulated at 40 Hz (aggregate speed 2400 bps). Separation among channels is 50 Hz, since the presence of CP. The other parameters of the correlation triangle are Br-40, Sh-50 and 'magic K' = 1/4.

SERDOLIK MFSK-34 (CROWD-36)

Serdolik MFSK-34, aka CROWD-36,  is a MFSK-34 system with 40Hz spaced tones modulated at speed of 40Bd speed. The needed bandwidth is ~ 1500 Hz. This waveform is also known as CROWD-36 just because the grid of the tones clearly exhibits 2 empty places, so that the possible tones sums to 36 (34+2).

In the past CROWD.36 transmitted encrypted information in the form of 5 digit numbers then later moved to online encryption. These days the mode seems to be being used for link setup information with the actual traffic being sent in another mode such as OFDM if the conditions are suitable. So we'll have frequently a long MFSK-34 sequence repeating the same chars (cit. from Rivet decoder).