MFSK-32 & OFDM 60-tone, a new "Serdolik" waveform ?

Interesting transmissions centered on 7659.0 KHz (7657.0/usb as tuning frequency) and picked up with a  KiwiSDR located in Northen Norway (Kongsdr).

Transmissions consist of MFSK-32 87Bd/97Hz and OFDM 60-tone 40Bd BPSK bursts, start and initial bursts likely act as  SOM/EOM and use a QPSK/PSK-8 2400 Bd modulation with 20ms ACF (ie 48 symbols). Both MFSK and OFDM bursts  are separated by 1900 ms and last 6000ms; the occupied bandwidth is about 3200Hz.

The OFDM bursts use the same MFSK-32 waveform as preamble and exhibit a clear 100ms CCF. Note the lack  of the usual 3300 Hz pilot tone. 
Likely it's a new waveform belonging to "Serdolik" family.

Fig. 1- MFSK-32 burts

Fig. 2 - OFDM 60-tone bursts

Fig. 3 - initial/final burst (SOM/EOM?)

The OFDM segment was observed also using QPSK modulation with a 225ms ACF

Fig. 4

Run a TDoA multilateration which showed Moscow area as the origin.

Fig.5

↓ https://yadi.sk/d/MqRF9KKs3Z6QXP

5400 KHz (cf) 2380Bd mix-mode burst waveform(by: i56578, ANgazu, KarapuZ, Rapidbit)

This is a very strange burst waveform modem that can be heard on 5398.2 KHz/USB (the central tone is exactly at 4000.0 Khz) at different times and SNRs. As Karapuz sais, probably it is Chinese equipment, but ANgazu guess the transmitter is near Spain, perhaps in Algeria: it's worth noting that there are 3 Chinese made ships in Algerian Navy and probably they maintained the factory radio-equiment:
http://www.defenceweb.co.za...Sea&Itemid=106 are
http://news.xinhuanet.com/english...29326.htm

The analysis of the bursts is not simple since the results exibith four different modulations in each burst (GFSK, MFSK-4, PSK-4, PSK-2), anyway all the transmissions have two fixed points (fig. 1):

-  constant manipulation rate of ~2380 symbols/sec 
-  all the bursts end with a PSK-2 segment

Fig. 1

Some good recordings can be download from here:
i56578-23-September
i56578-10-October 
Rapidbit-rec05

1. i56578-23-September recording
A detailed analysis of the bursts reveals a mix of GFSK 2380Bd/1500 and PSK-2 in both the two groups A and B, as shown in Figures 2-4.

Fig. 2 - group A

Fig. 3 - group B

Fig. 4 - modulation used

2. i56578-10-October & Rapidbit-rec05 recordings
The analysis of these recording reveals the use of QPSK and PSK-2 modulations in the group A and MFSK-4 and PSK-2 modulations in the group B (Figures 5-8).

Fig. 5 - group A

Fig. 6 - group B

Fig. 7 - QPSK and PSK-2 modulations used in group A

Fig. 8 - MFSK-4 and PSK-2 modulations used in  group B

3. observations & oddities
Tx windows are 4 min alternating short and long runs: the short transmissions are about 86 sec and the long ones last about 172 sec (twice the short). ANgazu recorded about 6 hours of monitoring period and processed the files using SA raster: as you can see, time window is 4 m. There are 13 transmissions and a no Tx period, building up groups of 14 frames starting by long Tx (Fig. 9)

Fig. 9

Each transmission consists of two groups of bursts (here termed "A" and "B"), possibly the group B is a repetition of A using different modulation to improve the reliability of the system. Every group starts using a longer carrier and a wider burst (about 2 sec). Unless some little variations, burts have a duration of ~720 msec and are spaced by a 500 msec unmodulated 1800Hz tone. It seems that if QPSK is used in the group A then group B will use MFSK; as seen, all the bursts end with BPSK segments.

In this signal, there are transients when changing modulation even if all modulations are BPSK, so no phase continuity is in use (Fig. 10)

Fig. 10

Phase vector rotates in one or other sense avoiding continous rotation in one sense. In this sample it can rotate both senses, mostly CCW or mostly CW (Fig. 11)

Fig. 11

In most systems, sync sequences are placed at signal start. In this one, after demodulated some BPSK bursts Sync seems to be 256 bits at the end (Fig. 12). Perhaps the burst shoul be reversed?

Fig. 12

(to be continued)

unid QPSK PSK-8 4800/2400Bd & OFDM 15-tones

This is an example of a "teamgroup" analysis: the signals were originally spotted by KarapuZ, then analyzed together by me, cryptomaster and IK1YDE: the discussion can be read here ("ansanto" is my nickname in radioscanner.ru forum)

http://www.radioscanner.ru/forum/topic36750-165.html 

The signal show up in FEC burst and ARQ modes with symbol rates of 4800 Baud (6000Hz bandwidth) and 2400 Baud (3000Hz bandwidth). 

The first weirdness we saw is just related to the baudrate lines of the signal in both the two speeds. As shown in figure 1, each burst consists of the preamble segment followed by the data segment: a strong 4800Bd line is visible only in the firts segments of the bursts, preambles, while just weak nuances are visible in the second segments.

fig. 1 - strong 4800Bd lines for preamble segments

In order to understand the used modulation we have isolated a single burst and then tried its harmonics: results are another weirdness. As shown in figure 2, the signal exhibits a clear PSK-8 modulation in preamble segment "A" (as expected, since its baudrate line) followed by short PSK-2 insert but no signs of modulation in the second segment "B" (altough the weak baudrate lines in fig.1).

fig. 2 - modulation harmonics in a single burst

Other than the 4800 Baud 8-ary constellation (shown in fig. 3) the segments A are characterized by a 53.33ms ACF that matches a 256 bits frame structure (fig. 4).

fig. 3 - PSK-8 single tone modulation at 4800 Baud in segments A

fig. 4 - 53.33ms ACF in segments A

For what concerns the segments B I suggested to isolate each of them from the ARQ signal and merge them together to form one unique file and then use the OFDM approach to study just that file. Cryptomaster spotted OFDM 15-tones structure and also isolated a single channel, detecting the presence of QPSK modulation: figures 5 and 6 show my tests that confirm his OFDM-15 238Bd QPSK observations.

fig. 5 - OFDM 15-tones in segments B

fig. 6 - inspecting a single OFDM channel

What remains still unclear, other than the source/user of the transmissions, is the reason of the baudrate line in the segments B since OFDM normally does not cause such pattern in the modulation harmonics.

To be thorough, figs 7,8 show the same behaviors in the 2400Bd waveform.

fig. 7 - strong 2400Bd lines in segments A

fig.8 - PSK-8 modulation only in 2400Bd waveform segments A

 

Israeli Navy hybrid modem in DSB/ISB ?

This is the first time that I see the Israeli Hybrid OFDM/Serial modem running on both the two sidebands: I did not analyze the contents of the two signals so it could be a DSB or ISB modulation but in any case the presence of the "supposed" carrier (10164.0 Khz) is quite odd since DSB and ISB does not provide its transmission. So, what I may say about that carrier? does it belongs to the signal?

Although 10164.0 has been reported as belonging to 4XZ Israeli Navy some years ago (precisely in 2013) and the waveform definitely refers to Israeli Navy, this frequency is very often used by the Russian Navy in T600 mode: many logs report such transmissions just on this frequency.

The second interesting point is the offset of the two signals from this "supposed" carrier. The first preamble tone is located at carrier+1000 Hz in the upper band (d1) while it is at carrier-800 Hz in the lower band (d2): ie the two lateral bands are not symmetric with respect to the carrier and that's wrong in AM modulation, other than in dual and independent sidebands.

The strenght of the two signal is just the same, then it is not the case of "fake" signals.

Concluding, it may be that this is something like a test  or something wrong/failure in the transmitter. I will try to pay a look at that frequency, if possible at same time of reception (2135z).

Israeli Navy Hybrid HF Modem

This system is used by Israeli Navy, more likely from 4XZ station in Haifa, and it's quite easy to hear. The waveform is composed of  3 parts: a four tones (2 seconds length) preamble, the parallel-data part using QPSK modulation in channels at 75Bd speed and the final serial-data part according to the MIL 188-110 single tone (1800Hz carrier modulated with PSK-8 at 2400Bd). A variant with an added 230ms pre-tone at 1000Hz has been seen.
Since the low data-rate, the apparent ACF is 66.6 ms.