This afternoon I spotted a STANAG-4285 1200bps/L transmission on 7937.0 KHz/usb carrying the 1536-bit TDM data protocol already seen in some previous records here and here. The most important thing is that the signal, with very a good reliabilityl, comes from the RNAS Rattray (Royal Naval Air Station) near Crimond, Aberdeenshire (UK) and I remembered that a transmission that had the same characteristics (STANAG-4285 1200bps/L, 1536-bit protocol) was identified as coming from Cyprus Island (Figure 1).
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| Fig. 1 |
Well, both the stations belong to the Defence High Frequency Communications Service (DHFCS), a British military beyond line-of-sight communication system operated by the Ministry of Defence (MOD) and used predominately by the Royal Air Force, Royal Navy and British Army, as well as other authorised users (Fig. 2).
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| Fig. 2 |
This being said, it's likely to assume that the 1536-bit TDMA format is a proprietary protocol of DHFCS, maybe developed by Rockwell Collins who deployed the system. Some interesting information about DHFCS can be read from some presentations held in HFIA meetings [1] [2] [3]. In particular, in the presentation slides of Rockwell Collins [1] - albeit a little dated - some screenshot related to the modem preset are shown where it is possible to see the setup of the waveform 4285 at 1200 bps/Long interleaver in async mode as well as the the TDM preset (Figs. 3,4).
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| Fig. 3 |
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| Fig. 4 |
It is noteworthy that these slides date back to 2006 when probably the TDM system managed up to 4 flows, currently it seems that the system is able to carry a greater number of flows as shown in Fig. 5
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| Fig. 5 |
I am quite positive that further catches from other DHFCS stations will confirm this guess.