23 June 2017

the beauty of grayline

188-141A calls copied this morning around 0455 UTC on 11111.0 KHz/USB (Fig. 1). The ALE addresses  belongs to the French Navy naval bases at overseas departments and territories Papeete and Noumea:
1OMFUM French Navy OMAR Net, Papeete OCE
1OMFUJ French Navy OMAR Net, Noumea NC
more than 16000 Km far from my antenna: reception has been possible thanks to a grayline-path (Fig. 2).

Fig. 1 - decoding
Fig. 2 - the grayline at the reception time

It's interesting to note that, at that same time, exploiting the same grayline path I also had a good copy of CHU Ottawa Canada (Fig. 3).

Fig. 3

Grayline observations and predictions can be read at the VOACAP (Voice of America Coverage Analysis Program) site:
as well as a lot of interesting and accurate services about about HF propagation:

French Navy OMAR (Organisation MARitime des transmissions haute fréquence) HF New-Generation program have the task to modernize all the High-Frequency transmissions media of about 80 assets of the Ocean forces of the French Navy, maintaining interoperability with other NATO Navy. The project was committed to Thomson-CSF (now THALES):

21 June 2017

THALES HFXL modem, "SALAMANDRE" tests go on

Likely another "SALAMANDRE" test session for the new Thales HFXL modem spotted this morning on the 7MHz band. This time the modem uses 12 non-contiguous 3 kHz channels from 7505.8 KHz up to 7656.1 KHz (~150 KHz bandwidth). The HF waveform is a modified STANAG-4539 with the extended preamble of 124 symbols added by Thales developers; further info about the modified waveform and the modem, as well as useful links, can be read in this post.

Fig. 1
It's interesting to note in Figure 2 the use of a double 188-141A 2G link setup exchange before the beginning of the HFXL session: the ALE exchanges happen just on the first and last channel of the next HFXL transmission as to negotiate/announce the used band; anyway, the HFXL session starts after the usual 2G 3-way handshake (as in Fig. 1). This initial link setup part is termed by Thales as the "3KHz phase" and it is illustrated in one of their presentations
By the way, the used ALE calls are XLA and XLB and almost surely they stand for (HF)XL modem-A and modem-B and belongs to French Forces network.

Fig. 2
The HFXL modem 12 channels have been tracked using SDR-Console v3 software configured for twelve simultaneous receivers, in this sample all the channels exhibit a PSK-8 modulation at 2400 symbols/sec (Figs. 3,4): the channel #4 is damaged by an adiacente FSK-2 transmission.

Fig. 3
Fig. 4

10 June 2017

STANAG-4539 in multichannel mode: Thales HF XL modem (likely "SALAMANDRE" tests)

This system has been copied on 9 different simultaneous channels from ~6200 to ~6400 KHz on USB during 9 June morning. The analysis reveals it's a STANAG-4539 modem (frame length is 287 PSK-8 symbols) running at different data signaling rates at constant 2400Bd data rate. The system uses bursts and (possibly) ARQ mode. My friend KarapuZ too copied this system but on a different HF segment.

Fig. 1
Fig. 2

The decisive contribution for the identification of the signal came from my friend ANgazu: he suggested that these transmissions could be the Thales HFXL modem, since they use up to 16 narrowband channels in 200 Khz bw just using 4539 waveforms. Most likely, the heard transmissions are tests related to the Thales /French MOD contract: PEA "SALAMANDRE".

Indeed, as depicted in Thales presentation of the HFXL modem:
they uses an evolution from the SANAG-4539 frame structure, mainly differing in the preamble parts as shown in Figure 3 

Fig. 3
Other than the long miniproble (32 symbols length rather than 31), they added a third 124 PSK-8 symbols part (termed "Extended") to the S-4539 initial synchronization preamble. The data block length (256 symbols) and the mini probe length (31 symbols) remain unchanged so that the period counts 287 symbols as in S-4539 (Figure 2).
The extended synchronization preamble is specific to  HF XL.  This part, not included when operating according to S-4539 or MS 188-110C ISB modes, is combined with the main preamble to carry all  information  necessary  to  the  HF XL  waveform, in particular information on modulation choice for each channel. Furthermore, a specific redundancy capability is introduced, that ensures resilience to the loss of a channel as long as the number of channels is greater or equal to 3.

A deeper look at the preamble of one heard transmission confirms the Thales HF XL modem, as depicted in Figures 4,5

Fig. 4 - the whole preamble
Fig. 5 - the 124 symbols (51.6 msec) added by Thales
As further confirm, ANgazu measured the parts of the preamble (Fig. 6) and time durations fit perfectly:

Fig. 6 - parts durations in HF XL preamble
A: syncronization preamble (76 ms)
B: initial sync 287 symbols (b1 of 184 and b2 of 103 symbols)
C: extended Thales preamble (124 symbols)

The adaptive wideband HF waveform termed “HF XL” relies on the usage of several non-contiguous 3 kHz channels spread over a 200 kHz wide sub-band.

Fig. 7
Expanding on the high performance of the serial tone modem technology standardized in STANAG 4539 for 3 kHz sideband to conjugate a plurality of channels in a multi narrow band (MNB) waveform, this approach can be seen as an extension of the US MIL-STD-188-110C appendix F “ISB”, with the addition of specific redundancy capabilities to provide resistance to the highly variable HF channel conditions.  As illustrated in Figure 7, these channels do not need to be contiguous, which allows to select only good quality and authorized channels. A 4G ALE alternate proposte ?
(continue in this post)

Thanks to ANgazu for the identification and collaboration.