Israeli Navy 6931 kHz USB 0016 UTC 10 AUG 2021

[~SIGINT~]

UNID 6931.0 kHz USB 00:16 10 AUGUST 2021

00:16 UTC - UNID with digital data transmission (unknown format);
00:31 UTC - UNID with digital data transmission (unknown format);
00:34 UTC - UNID with digital data transmission (unknown format);
01:00 UTC - UNID with digital data transmission (unknown format);
01:46 UTC - UNID data transmissions continue;
02:00 UTC - UNID with digital data transmission (unknown format);
02:30 UTC - UNID with digital data transmission (unknown format);
03:00 UTC - UNID with digital data transmission (unknown format);
03:30 UTC - UNID with digital data transmission (unknown format);
04:00 UTC - UNID with digital data transmission (unknown format);
04:08 UTC - Number of messages being transmitted have decreased.

Notes:
a.     The message is composed of a 2 second long, 4 tone preamble followed by the stream of data;
b.     The data segment following the preamble is +/- 15 seconds in duration;
c.     Transmissions appear to follow a consistent start at the top of the hour (00) and bottom of the hour (30) with additional messages interspersed throughout; and
d.     The signal is potentially European in origin. Signal strength was observed to be very high and loud and clear from the University of Twente Wide-band WebSDR. Also heard on UK and Barcelona Spain KiwiSDRs.

Figure 1: Image of preamble tones

Figure 2: University of Twente Wide-band WebSDR waterfall display

RSPduo | Barker & Williamson antenna | Toronto, Ontario Canada

[tiNG]

Hi.

I have Israeli Navy listed on the frequency with a modifies MIL-STD 188-110 modem.

Hope this helps.

[~SIGINT~]

Thank you Thomas, that certainly fits the profile and was confirmed by a user on the UDXF group as:

Israeli Navy Hybrid Modem 188-110 MOD
https://www.sigidwiki.com/wiki/Israeli_Navy_Hybrid_Modem_(188-110_MOD)

It will definitely be worth some additional monitoring and further research on the modem. I have kept an mp3 and I/Q recording for further analysis.

[~SIGINT~]

Related post: Israeli Navy 8780 kHz USB 0208 UTC 13 AUG 2021
https://www.hfunderground.com/board/index.php/topic,85009.0.html