12 February 2020

Interesting MS-110D App.D (WBHF) traffic

Interesting traffic heard on 5750 KHz/USB and picked up thanks to the UK KiwiSDR owned by G8JNJ.
Most of the signals are definitely "110C Appendix D" 3 KHz BW waveform (WID 1 or 2, BPSK). The synchronization preamble has a framing of ~240ms length that makes 576 symbols @2400Bd speed (Fig. 1). From 188-110C App.D documentation, the orthogonal Walsh modulation is used in the synchronization section of the preamble and the length of the repeated super-frame is 18 channel-symbols, ie: 9 (fixed) + 4 (downcount) + 5 (waveform identification). Since in 3 KHz bandwidth waveforms the preamble channel-symbols are 32 symbol long, the length of each repeated superframe is: 18 (channel-symbols) x 32 (length of one channel-symbol) that just matches the measured 576 symbols length.
Data section has 40ms length frames (Fig. 2) i.e. each frame consists of 96 symbols: 48 unknown data + 48 known data (mini-probe). This framing meet the waveform IDs 1 and 2 of the 3KHz bandwidth set (BPSK modulated data).

Fig. 1 - Synchronization preamble superframes
Fig.2 - data section frames
Anyway, FLSU BW5 bursts and unid 2400Bd bursts are the most interesting aspects in this catch.
In my opinion the presence of (repeated) 3G-HF Fast Link SetUp (FLSU) BW5 bursts is rather strange also because the link seems to be terminated with a 188-141A 2G-ALE "TWS" sequence: a kind of "fall back" for 2G-ALE? Perhaps we're dealing with a STANAG-4538 "circuit-mode" service and I did not hear the BW5 PDUs sent by the other side of  the link, or perhaps BW5 PDUs are just used to signal the following traffic waveform.
The other 2400Bd bursts (Fig. 3) have a fixed duration of ~2840ms: unfortunately the poor SNR of the signals does not allow to get other significant parameters from their analysis.

Fig. 3
As said, the link was terminated using 2G-ALE: the TWS message was sent by the ALE callsign "AC7", It's to be noticed that during the monitoring period other ALE soundings from calls "AC7" and "AC9"  have been heard. According to recent UDXF logs, these calls refer to a unid Jordan network, although it sounds weird to me that they use WBHF technology. Maybe some WBHF trials... but it's just a guess.


4 February 2020

Israeli Navy running their proprietary PSK serial tone with Tadiran/Elbit DCS (Digital-Coded Squelch)

Reading radioscanner.ru I found an interesting post my friend Cryptomaster about Israeli Defense Force (IDF) Navy transmissions consisting of their proprietary PSK serial tone waveform sent along with the Tadiran/Elbit Digital Coded Squelch (DCS) signal activated. Since the Istraeli Ny transmissions are quite frequent and easy to receive and recognize, I decided to take a look at the frequency reported by Cryptomaster (13372.0 Khz/USB): the transmissions were picked up using the Italian KiwiSDR owned by IZ6BYY.

The DCS signal is sent continuously, starting when transmission begins, and transmitted on a frequency which is slightly higher than the one used by the data signal (i.e. "over" the data signal) by using an FSK waveform wich is modulated at the rate of 125 bit/sec and 290 Hz shifted (Fig. 1).

Fig. 1
Tadiran/Elbit DCS implementation is a 84 bit long string, while standard DCS [1] codewords consist of 23 bit long string (10 bit data + 3 fixed bits + 11 check bits): don't know if a similar framing is used here. Anyway, notice that at the end of each transmission the encoder changes the code to a pattern consisting of the same string sent in opposite polarity: most likely it's a "turn off" code that causes receiving decoders to mute (Fig. 2) and to signal the end of the data transmission.

Fig. 2 - Tadiran/Elbit DCS bitstream
Radios with DCS options are generally compatible, provided the radio's encoder-decoder will use the same code as radios in the existing network. indeed, the use of DCS has only been noted on this frequency: Fig. 3 shows contemporary transmissions on 13372 and 8070 KHz/USB. Notice that the two signals occupy the same bandwidth: it may be that before DCS were applied the PSK signal is subjected to a tighter filtering.

Fig. 3 - Isr-Ny contemporary transmissions
DCS support could be provided by Tadiran/Elbit devices such as the HF-6000 or HF-8000 [2]: I already met that signal coupled with the Nokia msg terminal.
Since a compatible radio ignores signals that do not include a bitstream with the specified code, DCS could also be used as a type of selective calling. Indeed, the Tadiran "Selective Calling" feature (that's not ALE) just uses an FSK waveform as DCS: perhaps the DCS words "open" the squelch of the addressed radios (all, group, individual) but it's only a my guess...

Fig. 4

25 January 2020

Unid FSK 35.5Bd/1000

Unid FSK 35.5Bd/1000 heard in idling mode on 10550 KHz (CF) and recorded using the KiwiSDR located in Kuopio, Finland.
The raster shows a distortion of the manipulation speed which is also visible in the phase detector (Fig. 2): most likely a native defect of the source modem/transmitter.

Fig. 1
Fig. 2
Although quite uncommon, the baud rate is 35.5 Bd, as shown in Figure 3 where I isolated and analyzed a "clean" signal segment. It's the first time for me I meet such speed in a FSK waveform (only in CIS-60 HDR modem) but it must be said that there is a possibility that the speed will change when switching from idle to traffic mode (as the old BEE 36/50 did), unfortunately during my listening the signal remained in idle mode.

Fig. 3
As for the source of the signal, it is reasonable to think of a Russian user since the shift of 1000 Hz is used in waveforms such as CIS-14, Vezha-S and also Akula as well as used by Rus-AF (1). Nevertheless, Indian Navy too (VTH9) uses 1000 Hz shift in their FSK 50Bd transmissions.  
Although I have been keeping an eye on that frequency, to date I have not yet had the opportunity to hear this signal again.


(1) REA4 Moscow AF HQ  uses FSK 50Bd/1000 in idling between skeds in FSK Morse (5FGs).

22 January 2020

SkyOFDM 28-tone 86Hz 65.6Bd PSK2 (2)

Just for background it might be helpful to read the previous post.

Most likely the signal that is continuously transmitted on 4150 KHz/usb is a modded or a new waveform of the Skysweep Technologies proprietary "SkyOFDM" family. SkyOFDM is a high speed modem based on the OFDM and turbo coding technologies.  It offers several baud  rates (300-9600  bps) and two different interleaving options (short and long). Also there are two bandwidth options: 2000Hz (OFDM 22 tones) and 2400 Hz (OFDM 28 tones).

Fig. 1 - SkySweeper running the SkyOFDM modem
I tried the SkyOFDM modes available in SkySweeper 5.13 (Fig. 1), a Windows based product for radio data decoding and signal analysis developed by SkySweep.  As expected, I could not synthesize the exact waveform running on 4158 KHz since the different speeds, modulations, and ACF:

params SkyOFDM 4150 Hz OFDM
bandwidth (Hz) 2000, 2400 2400
preamble 7 tones 7 tones
tones 22, 28 28
shift (Hz) 86 86
Baud rate 60.56, 64, 79 65.57x
modulations PSK2, PSK4, QAM PSK2/SDPSKx
ACF (ms) 78, 113.4 76.2x

A peculiar difference lies in the type of the used modulations: for example, if you filter out and look at the modulation used in the second channel, you will see that is not PSK2 but SDPSK (Simmetric Differential PSK), thus it seems that channels are mixed artfully (Fig. 2 ).

Fig. 2
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; in differential mode (diff=1) we see transitions between two states (Fig. 3) (1).

Fig. 3
According to some utility DXers, SkyOFDM waveforms were used by Finnish MFA and that's correct since SkySweep Technologies is a Finnish high tech company. Although there are still many references in the web to SkySweep, their official website is no longer online: this suggests a ceased activity or an incorporation into another company. Indeed, looking at waybackmachine.com, the site skysweep.com was crawled last time on 13 June 2017; by the way, SkySweeper software was discontinued on June 1st 2009.
That said, the permanence of this signal on 4150 KHz and its purpose are still unknown to me as well as other friends.

(1) PSK encodes the input data sequences in pahes (states), while Differential PSK (DPSK) encodes the input data in the phase difference (transitions) between successive bits or symbols. This means that there would be a phase change in the modulation signal if the two successive bits in the input data sequence are different (0 to 1 or 1 to 0), and no phase changes if the successive bits are the same. 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 Fig. 3 the transitions in differential mode (diff=1) are in the set of [π/2,-π/2] so most likely it's a SDPSK (π/2-DPSK). 

18 January 2020

unid SkyOFDM 28-tone 86Hz 65.6Bd PSK2

Continuous ofdm bursts transmission picked up on 4158 KHz/USB thanks to the "ArcticSDR" in Kongsfjord Arctic Norway: a KiwiSDR managed by my friend Bjarne Mjelde

Timings of the transmission and its spectrum are shown in Fig. 1 

Fig. 1 - timing and spectrum
The analysis of the OFDM signal clearly shows 28 channels and a frequency spacing of ~86 Hz, each channel is modulated using PSK2 at the symbol rate of 65.57 Bd (Fig. 2). The same results are obtained/verified by analyzing a single channel as shown in Fig. 3 (higher channel).
Fig. 2 - OFDM analysis
Fig. 3 - anlysis of the higher channel (#28)
As you see in Fig. 2, I did a further analysis after resampling the signal at 10109 Hz. Indeed, I used the tool OCG [1] in order to calculate and sythesize an OFDM waveform having the same parameters (channels, Br, Shift, modulation, width,...) and got 10109 Hz as one of the possible "native" sampling rate. The analysis of the synthesized OFDM is visible in fig. 4: notice the similarity between the PSK2 constellation of the synthesized signal and the one of the real signal (although resampled).

Fig. 4 - analysis of the synthesized OFdM-28 signal
The seven initial tones last 30 symbol periods and are derived from the OFDM generator as shown in Fig. 5; more precisely the used tones are: 2, 5, 6, 9, 13, 16, and 19.

Fig. 5 - initial seven unmodulated tones
The autocorrelation has a value of 76.2 ms (Fig. 6) that makes a 140 symbols length frame if considering an aggregate speed of ~1836 Bd (65.57 x 28).

Fig. 6 - autocorrelation
A similar OFDM waveform but with shorter and different bursts (Fig. 7) was reported on 2016.02.05 by my friend Cryptomaster [2] just on the same frequency of 4158 KHz/USB. In that case the modulation used was a form of PSK4, anyway number of tones, shift, Br, and ACF are the same; thus, that signal is on-air since several years.

Fig. 7
As regards the signal source, several TDoA tries always indicated an area north to Helsinki as probable Tx site (Fig. 8) although qrg.globaltuners.com reports exactly the same waveform/spectrum (and frequency too) indicating it as a signal sourced by the Spanish Navy [3].  In my opinion that's quite odd since the signal is fairly well received in the northern European countries such as Sweden, Norway, and Finland, while it is rather weak or inaudible at all in south Europe... I don't think of such a long skip.

Fig. 8 - TDoA reults

In my opinion it's an evolution of the original Skysweep Technologies proprietary waveform named "SkyOFDM", probably used by Finnish MFA (thanks to Roland Proesch for the hint). Indeed, the mentioned recording by my friend Cryptomaster just matches the features of the "original" SkyOFDM waveform (Fig. 9).

Fig. 9 - Skysweep Technologies OFDM-28

It's worth noting that SkySweeper Pro 5.13 software does not recognize the "new" OFDM-28 PSK2 that is analyzed  in this post.
(to be continued)


[1] OCG is a program for calculating and synthesizing OFDM signals, it can be downloaded from here
[2] http://www.radioscanner.ru/files/unknown/file19060/
[3] http://qrg.globaltuners.com/details.php?id=17420

13 January 2020

COMSEC transmissions using a S4285 variant (2)

Secured burst transmission using a modified S4285 waveform [1] spotted around midnight on 4015 KHz/usb, the S4285 mode is 600bps and short interleaver. 

Fig. 1
After demodulation, the COMSEC preamble resembles 188-220D std and consists of 3 parts (my guess):
1) 60-bit Frame Sync (110000100000111000101111001011011101101001001011111010101100)
2) 5 x 128-bit strings, encoded Message Indicator (five times repeated)
3) 64-bit idling sequence (time to load the key?)

Preamble is followed by the encrypted data block which ends with "01" sequences.
Fig. 2 - demodulated stream of bursts

Fig. 3 - COMSEC preamble (my guess)

https://yadi.sk/d/nY-DTuTz-ZWG8g  (2020-01-10T005300Z, 4.015 MHz, USB.wav)
https://yadi.sk/d/oIHVEWbUO0_few   (2020-01-10T010336Z, 4.015 MHz, USB.bin)

[1] The same modified S4285 waveform was met here on 6931 KHz/usb:

Speed distortion in an FSK signal

Most likely modem instability is the cause of the distortion in the manipulation speed (~42 bps), as it's evident in SA raster.


2 December 2019

Unid FSK 400 (401)Bd/800 bursts
(i56578, cryptomaster, KarapuZ)

Unid FSK 400Bd (401)/800 bursts spotted on 13224.0 Khz (cf + 1700), slight distorsion in the speed. ACF=0, no other results if demodulated using differential mode. Transmissions are not frequent and most often consist of a single burst, sometimes two (maybe two stations).

Fig. 1
Quoting my friend KarapuZ "Despite the good recording quality and SNR ratio, in my opinion, the transmitter modulator malfunctions in the frequency discriminator. As a result, we have a bitstream with many errors at the output".

Fig. 2
Comments by my friend cryptomaster follow.
The signal structure of the first burst is shown in Fig. 3, the transfer is considered without translating it into a relative form:
1. A meander with a frequency of 150 Hz (300bps);
2. The preamble is 31 bits (300bps) of the form 0101110001101000010010001010101;
3. Information transfer with a speed of 401.3 bps;
The preamble is marked in yellow:
Fig. 3

Other than the frequency discriminator, the signal is distorted by the imposition of a stray frequency of 800 Hz, the intensity increases by the end of the transmission (Fig. 4), perhaps this frequency (800 Hz) is somehow connected with the formation of the separation of the frequencies of manipulation.

Fig. 4
On a bitmap, it looks like the pattern in Fig. 5:

Fig. 5


19 November 2019

Indian Navy STANAG-4285 naval broadcasts (tentative)

Follwing a tip from my friend KarapuZ and his recent tweet, I started to monitor 16941.0 KHz to study the STANAG-4285 naval broadcasts from the Indian Navy [1]. They use the quite rare 2400bps/Long sub-mode and decoding produces a lot of errors just due to the high data rate and the huge QSB that sometimes affects the signals. By the way, I used the KiwiSDRs VU Hams located in Kottarakkara Kerala and colombo4s7vk located in Colombo Sri Lanka, the latter is a bit less recommendable.

Fig. 1 - one of the S4285 2400/L heard broadcasts
For what I could see, daily broadcasts starting around 1100 or 1200 Z are transmitted on that frequency. Broadcasts consist of clear-text weather bulletins and 4FG messages to VWGZ (VWGZ is the collective callsign for any/all the Indian Navy ships): indeed, they typically use a four FIG (off-line) encryption system. Either the bulletins and 4FG messages, are sent using the async ITA2 8N1 framing (Figs. 2, 3). 

Fig. 2- 8N1 bitstream after decoding
Fig. 3 - off-line decoding using Harris RF-5710A modem
It is interesting to take a look at some bulletin/message typical contents.

VND 677/16
-P- 160732
GR 158
6469 5315 6155 6433 5098 8353 7507 5237 5375 4271

8394 6708 1257 6554 6238 5987 3600 6023 9076 1083
4574 3021 1116 0342 6063 4300 2248 0008ALFA

GR 158




collective callsign for any/all Indian Navy ships

VND 677/16 
indicates the daily serial number of the message in that broadcast, i.e. message #677 of day 16 (indeed 16 november, date of my reception). Don't know what VND stands for.

most likely the daily encrypted callsigns for specific ships

precedence indicator of the message
-R- Routine
-P- Priority
-O- Immediate (Operational Immediate)
-Z- Flash

date time of origination, no time zone indicator (!)

GR 158
the number of 4FG in the message (158 in this case)

separation (break), as the usual Morse Code abbreviation 

The 4FG block is always preceeded by a 9 chars string, i.e.: 


I noted that this string is used to "signal" the last two 4FG in the block, respectively the last and the second-to-last:
2299 4827 3953 0701 6748 2577 4084 8109 5655 4999
5904 4854 4358 8628 9964 9687 9032 0282 4140 7567
5029 5582 1302 9724 1992ALFA
6469 5315 6155 6433 5098 8353 7507 5237 5375 4271
8394 6708 1257 6554 6238 5987 3600 6023 9076 1083
4574 3021 1116 0342 6063 4300 2248 0008ALFA
0822 9678 3021 3357 0524 0160 9645 0013 4927 1959
5457 3192 3301 5013 5856 9799 0272 2857 8727 9046
1854 5256 7000 0659 0399ALFA

The 4FG blocks usually end with the separation char (BT) folowed by the repetition of the number of encrypted groups in the message (GR nnn), the usual RTTY end-of-message (NNNN) and the strings: 



at present I do not know their scope/meaning, maybe test chars, but it makes some sense if they are read respectively as couples [0;1][M;V]:

FIN (=finish ?)

and [A;J][1;0]:


It's worth noting that  in each transmission the most recent message is sent as first (a kind of LIFO). Moreover, some of the messages that were sent in the previous broadcast are re-inserted in the current one, i.e. the broadcast of 1304 Z contains the last message (#679) and the twos (#678 and #677) sent in the previous broadcast of 1255 Z

[2019-11-16 1152Z]
VND 677/16
VND 676/16
VND 675/16
VND 674/16

[2019-11-16 1255Z]
VND 678/16
VND 677/16
VND 676/16

[2019-11-16 1304Z]
VND 679/16
VND 678/16
VND 677/16

Probably this method is used to improve the reliability of the system but it is not clear to me how the number of messages to be repeated is determined (precedence? duration?).
Sometimes it's possible to see short messages as:

VND 675/16
ZBQ 0805

VTH is listed as the callsign of Indian Navy Mumbai.
Note the Z codes ZFA (Following message has been received) and ZBQ (Message was received at).

Weather bulletins report Weather, Surface Wind, Visibility, Sea State, Swell, and Warnings for specific areas and period of validity (12 hours). The bulletins header indicates the originator of the message just after the precedence indicator: 

-P-  150320

-R-  141004Z

-P-  160900


FOCINC EAST: Flag Officer Commanding-in-Chief Eastern Naval Command. The Indian Navy operates three operational Commands, each headed by a Flag Officer Commanding-in-Chief (FOCINC): FOCINC East (Visakhapatnam HQ), FOCINC West (Mumbai HQ), FOCINC South (Kochi HQ).

NAVAREA VIII CO-ORDINATOR: the Chief Hydrographer to the Government of India.

CINCAN: Commander-in-Chief of the Andaman & Nicobar Command. The Andaman and Nicobar Command is the first and only Tri-service (army, navy, air force) theater command of the Indian Armed Forces.

Since some of the weather bulletins also report detailed "LOCAL WEATHER FORECAST FOR VISAKHAPATNAM", probably the broadcasts are transmitted from a COMCEN belonging to the Eastern Naval Command (ENC) HQ in Visakhapatnam [2]. In this respect it's noted that some logs in old WUN/UTNL newletters report "VTP Visakhapatnam" as Indian Navy station operating in CW and RTTY 50Bd/850, but not on 16941 KHz. Actually, I didn't find any "official" allocation for 16941.0 KHz but only a clue related to one of the frequecies that are used for HF communications in the Indian activities in Antarctica (IAP, Indian Antarctic Programme) [3].
Given the period of validity (12 hours, except for the forecast for Visakhapatnam which have 24 hours validity) it makes sense to expect similar broadcasts around 0000Z, likely on a lower HF band.
(to be continued)

[1] https://en.wikipedia.org/wiki/Indian_Navy
[2] https://www.indiannavy.nic.in/node/1399#
[3] inpre07e.doc 

4 November 2019

Baudot FSK 100Bd/500 (unid Rus Gov/Mil)

Interesting async ITA2 5N1.5 FSK 100Bd/500 tuned on 11019.0 Khz some days ago. Once demodulated, the content consists of (off-line) encrypted 5LGs groups. Note also the slight deviation of the speed.

The transmission ends with the FSK-MORSE op-chat "CFM QRQ 100 QBN K": almost surely Russian Gov/Mil users.

Same 5LGs format and 5N1.5 framing was found in the reception reported in this post, with the difference that the latter has a speed of 50 Baud.