STANAG-5030/MIL-188-140 VLF/LF multichannel broadcast to submarines (2)

(this is a follow-up of the post published here)

The narrow 200Hz bandwidth for VLF/LF submarine broadcast and the low efficiency of the aerials are limiting factors, but the use of MSK (a form of QPSK) can allow optimum use of that narrow bandwidth. Indeed, using MSK it is possible to transmit two 100 Baud channels X and Y, each on a pair of phase, and each channel can consists of 2x50 Baud multiplexed channels. Thus, MSK can provide a TDM multi-channel broadcast of  up to 4x50 Baud within the 200Hz assigned band. These transmissions are easy to hear, either locally or, better, using remote SDRs such as the ones provided by Kiwi and thanks to the MSK demodulator coded by my friend Christoph [1] it is possible to study the bitstreams and verify their characteristics. 
The vast majority of users transmit four VALLOR channels (X1, X2, Y1, Y2), i.e. four 50 Baud channels which use KW-46 encryption system. In each channel, data are arrangend in the format defined by STANAG-5065 in which frames are delimited by the pseudo-random sequence generated by the polynomial x^31+x^3+1 ("Fibonacci bits") which also serves to sync the receive KW-46 devices. Error Correction And Detection (EDAC) is performed using (13,12) Wagner coding.

One of the examples of four VALLOR broadcast is the DHO38 station (Fig. 1): a VLF transmitter on 24.3 KHz used by the German Navy to transmit orders to submarines and navies of Germany and other NATO countries. Figure 2 shows the four X1, X2, Y1, and Y2 14-bit streams: the marked columns are the Fibonacci bits generated by x^31+x^3+1.

Fig. 1 - DHO38 constellation

Fig. 1 - the four 14-bit streams from DHO38

The most interesting subComm station is FUE French-Ny on 65.8 KHz from Kerlouan.

Fig. 3 - FUE constellation

As shown in Fig. 4, X1 and X2 channels use the same format of the French-Ny FSK 50/850 broadcast [2]. That format exhibits a characteristic 21-bit frame and, in a way similar to STANAG-5065, two/three sub-frames which are delimited by the bits of two LFSR markers M1 and M2 and a logical "1" value bit (1-bit). The sequences for the two markers are generated by the polynomials x^6+x^5+1 and x^7+x^6+1.
The other two channels Y1 and Y2 are sent using the 14-bit frames with KW-46 encryption.

Fig. 4 - the four streams from FUE

Don't know if it is their normal way to operate or it's just a coincidence, perhaps they use two channels for the shore-to-sub broadcasts (Y1 Y2) while the other twos (X1 X2) are connected to the shore-to-ship broadcast, maybe to forward these messages to subs, who knows?

[1] https://github.com/hcab14/signal-analysis/blob/master/m/demod_msk.m 
[2] http://i56578-swl.blogspot.com/2015/06/french-navy-broadcast-fsk-50bd850.html 

unid signals from US KiwiSDRs by ANgazu & Rapidbit

This signal was recorded tuning 5308 Khz and using some KiwiSDRs from the northeast of the US, mainly the one owened by K3FEF in Milford (PA). Since its various operating modes and its uncommon parameters, we decided to study it a little more thoroughly, leaving out the transmission purposes and the hypothetical users. The duty cycle of the signal is quite low so it took several hours of recording to collect signals suitable to be analyzed.

In the spectrogram of a recording we can see the bandwidth of the modes (Fig. 1). When several consecutive segments are transmitted, the separation between them is about 3m30s and the duration of the segments ranges between 94 and 106 seconds.

Fig. 1

mode 1

This mode has a spectral occupation of one 1000 Hz. The modulation is QPSK although with a notable majority of the symbols 0 and 2 and a speed of 600 Baud (Fig. 2). The ACF can be 840ms or 800ms and does not seem to transmit information, but seems  to be idling. After demodulation, bits aligned in frames of 1008 bits for ACF of 840 ms and 960 bits for ACF of 800 ms (Fig. 3).

Fig. 2

Fig. 3

 

mode 2

Its spectral occupation is about 1600 Hz. The modulation is QPSK with the same structure of mode 1, with a speed of 1200 Baud and an ACF of 420ms or 400ms. Also this mode exhbits a 1008 bits (960) frame with a very similar structure (Fig. 4).

Fig.4

mode 3

The modulation speed is 1200 Baud with a spectral occupancy of about 1400Hz. It is a GFSK with a shift of about 800 Hz andACF of 840ms or 800ms. The binary frame has a 1008 or 960 bits length (Fig. 5).

Fig.5

mode 4

The modulation speed is 300 Baud with a spectral occupancy of about 600 Hz. The modulation is an FSK with a shift of 400 Hz and an ACF of 3.35  or 3.2 seconds. Once demodulated, the frame is still 1008 bits or 960 bits just like the previous ones (Fig. 6).

Fig. 6

 

 

odd signals picked-up using the Arctic KiwiSDR

7600 Hz wideband signals from (only!) Kiwi ArcticSDR and using single tone QAM-64 modulation at a symbol rate of 7200Bd. The signals seem to have specular positions of a "supposed" reference/pilot tone. Most likely, the signals "leak" out of wired high-voltage lines (PLC) running close the Bjarne's KiwiSDR.

https://yadi.sk/d/P_r6r69SqVf_3g

8-ary constellation bursts at 12800bps data rate (3)

This is a follow-up of the posts about the "clusters" of S4539 12800bps bursts, all posts including this one are grouped here.

Since a couple of days it's possible to hear both the peers, don't know if it's due to new test sites or increased powers but previously the "called" station was not heard (or maybe it did not even exist). As you see, the "called" listens on f2 while it simultaneously replies on f1 (the same for f2/f3 and in all the six clusters) as well as the "caller" station puts its call on f2 while it simultaneously listens on f1 (Fig. 1); the interval between the call and the reply is about 319 ms. Maybe they use staring and synched SDRs?

Fig. 1

This simultaneity is also noted between the lower frequency of a cluster and the higher frequency of the preceding one, as shown in Fig. 2. Particularly, Figure 3 shows the timings between the last and the first cluster (the different signal strengths in Fig. 3 depend on the different locations of the two used KiwiSDRs).

Fig. 2 - timings between two consecutive clusters

Fig. 3 - timings between the last and the first cluster

https://yadi.sk/d/BEJ8lEYRUC1TiQ

wideband operations on 4950 KHz, new Harris wideband HF waveforms

since few weeks me and my friend and colleague ANgazu are studying interesting wideband waveforms family spotted on 4950 KHz (central frequency), just in the middle of the 60 mt Broadcast band, these transmissions have been also reported here by our friend KarapuZ from radioscanner.  Monitoring was done thanks the KiwiSDR owned by WA2ZKD that can provide up to 20KHz IQ band http://rx.jimlill.com:8073/.

As shown in Fig. 1, they use Harris WB-ALE paradigm for call and link negotiation:

- STANAG-4538 FLSU initial call for link setup
- spectrum sensing to measure interference within the selected wideband channel
- new burst handshake exchanges spectrum sense measurements
- data exchange
- STANAG-4538 FLSU for link term

Fig. 1

The Harris wideband ALE approach and the 3G extensions for wideband have been previously discussed in this post.  

For what concerns tha data waveforms, we saw bandwiths from 3-24 Khz and modulations from PSK-8 to QAM-64 with a data rate from 75 to 120,000 bps.

Each transmission begins with a transmit level control (TLC) block to allow radio transmit gain control (TGC), transmitter automatic level control (ALC), and receiver automatic gain control (AGC) loops to settle before the actual preamble is sent/received. A variable length preamble for reliable synchronization and autobauding follows the TLC section and it's followed by ariable length frames of alternating data (unknown) and mini-probes (known) symbols: times vary depending on the combinations of speed and modulation.

Although the characteristics such as BWs, modulations and speeds are the same as those indicated in Appendix D of MIL-STD 188-110D (WBHF), these adaptive waveforms definitely do not belong to that standard. Indeed, as shown in the following figures (2-5), the waveforms exhibit a common structure consisting of a super frame which is formed of 8 frames probably related to the 8 different allowable bandwidths: a similar structure and the duration of the frames (i.e., the number of K and U symbols) are quite different from what is stated in the Appendix D.

Fig. 2 - 4800Bd/6KHz waveform

Fig. 3 - 7200Bd/9KHz waveform

Fig. 4 - 9600Bd/12KHz waveform

Fig. 5 - 16800Bd/18KHz waveform

The frames structures have been verified also by analyzing some streams after the demodulation of the signals: in figure 6 the result of the demodulation of a 9600Bd/12KHz chunk (in this case using PSK-8 modulation):

Fig. 6

When measuring  the symbole rate using the quadrature detector, an interesting pattern shows up: a repetitive 8 blocks group which are generated by miniprobes. Up to date, we know the "frequency" in these blocks is different for every speed, starting in lower freq and going upwards. In some modes a mirror image can be seen as in Fig. 7. This is an odd feature since it looks like miniprobes are not phase modulated as data are.

Fig. 7

The 8 different minprobes repeat in a particular series and are complicated to study, their structure point to a sequence (maybe using Walsh modulation?) that repeats 4 times: this pattern seems to be the same in all waveforms varying frequency/duration.

Fig. 8

We have other examples of such miniprobes but we prefer to postpone to a next post, if possible with more precise details. For this purpose, ANgazu and I would like to have some other better recordings (i.e., with IQ band > 20KHz) from friends in US so that we can gather more informations. Thanks!

https://yadi.sk/d/9Imj9tLkYZHGTQ
https://yadi.sk/d/cGzxKGCXHfUuFQ