29 September 2015

Australian MHFCS net

this is a transmission from the Australian MHFCS (Modernised High Frequency Communications System), an HF radio network providing communications services for the operational control of Australian Defence Forces (ADF) and allied aircraft, HF equipped marine craft, and land units.
The signal was heard on September,25 at 1357z on 14790.0 KHz on USB. Waveform is FSK-2: shift frequency of 340 hertz and manipulation speed of 600 baud, probably GFSK (or CPFSK). 

Fig. 1
Fig. 2
MHFCS is a managed, long-range strategic communications system that enables the secure exchange of information, such as voice, e-mail, facsimile, interactive data and organizational messages, between fixed and mobile stations using one integrated system.
MHFCS features automated priority messaging, an assured delivery system, extensive geographic coverage that includes 2,000 nautical miles offshore, and automated frequency-management and traditional-operator tasks.

The network  is controlled remotely by Defence Communications Station Canberra (DCSC) at the Network Management Facility (NMF) located in Canberra and consists of four TX/RX Nodes:
NORTH WEST CAPE, WA (S22.20 E114.30)
DARWIN, NT (S12.22 E130.59)
TOWNSVILLE, QLD (S19.28 E146.25)
RIVERINA, NSW (S35.01 E146.25)

DCSC is capable of operating Independent Side Band (ISB) or AM modes, however, the normal mode of operation is Upper Side Band (USB). Digital modes may be employed for encrypted transmissions. It is possible that one of these modes is 2G ALE, ANDVT, or Stanag 5066, however message content is encrypted and it is an offence to decrypt such transmissions. Registered frequencies available on the ADF MHFCS are listed here. As reported, remember to subtract the 1500Hz offset from the listed frequency to obtain proper dial frequencies (Fig. 3)
Fig. 3
Sometimes an FSK 50Bd/340Hz transmission has been seen within the 600Bd/340Hz signal so that it seems an ISB system (Fig. 3).

Fig. 3
Unless the simultaneity of the transmissions start/end  points (one of the two may begin before or after) I'm not so positive about the MHFCS source since they use a 1500 Hz offset so, in my opinion, the distance of the two CFs should be 3000 Hz and not ~2700 Hz as measured (Fig. 4).

Fig. 4

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