Quite good FSK 600Bd/850 signal centered on 10405 KHz, from Australian MHFCS, heard some days ago around 1630z using iw2nke KiwiSDR (center Italy). As reported in UDXF logs by Eddy Waters [1] [2], Australian Defence Force (ADF) has changed the previous dual channel system (ISB) to two single channel with 4 KHz spacings: the lower of the 2 frequencies has a speed of 600 baud, while the higher is 50 baud. The shift in both cases is 850 Hz. As in the waterfall above, I did not hear the 50bd FSK signal 4 KHz above (i.e. on 10409 KHz): maybe it's missing? Eddy also logged 10405 KHz frequency reporting ADF MHFCS Humpty Doo as location of the Tx.
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| Fig. 1 - main parameters |
After arranged the demodulated stream into a 7-bit format, it's possible to detect the presence of the sequence called "Fibonacci bits" originated by the polynomial x^31+x^3+1 and which reveals the use of KW-46 crypto device (Fig. 2) as per STANAG-5065 Annex-A.
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| Fig. 2 - 7-bit frame delimited by KW-46 sync bit |
Sometimes an
FSK 50Bd/340Hz transmission has been seen within the 600Bd/340Hz signal
so in these cases they operate in ISB mode: according Eddy Waters from
UDXF, the USB side is called "Rockwell 700B" while the LSB side is called "Rockwell CPU100" (Fig. 3).
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| Fig.3 |
Just a tip: in order to identify the MHFCS transmissions, in addition to
the dial frequencies listed here (remember that they use a 1500Hz
offset above the indicated carrier) and to the shift and speed
parameteres (tipically 600Bd/340Hz), think that these MSK signals
exhibit a quite unique sign when inspecting the harmonics using the SA
'involutions' tool. In this case, you will see the presence of several
spectral lines in the 7^ power (Fig. 4).
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Fig. 4
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