16 November 2021

4339.8 KHz, an occasional French-Ny fleet broadcast FSK channel ?

On Sunday evening I came across an FSK 50Bd/850 transmission on 4339.8 KHz (CF): first time I have ever seen a S-4481 on this frequency, usually occupied by French Navy fleet broadcast in STANAG-4285 from FUG Saissac on 4338.0 KHz (// 4325.0 Khz). The dozens of DF tests carried out have all indicated the same FUG site as the location of the transmitter, while the analysis of the bitstream revealed the use of KW-46 encryption which is normally used in NATO 50Bd/850 FSK fleet-broadcast.
Actually I expected to find the classic 21-bit pattern, typical of domestic broadcast, even if 4339.8 is not among the FSK channels used by the French navy (see here).  I thought about a new FSK channel, but in subsequent monitoring the frequency has always resulted to be occupied by STANAG-4285 transmissions.
It's interesting to note that the same frequency/mode appears only once in the UDXF logs, precisely on March 21  of this year and only nighttime: coincidentally this too during the night between Sunday and Monday.  

Fig. 1 - STANAG-4285 & 50Bd/850 FSK both KW-46 secured from FUG

Fig. 2 - 4339.0 KHz FSK Direction Findings (TDoA algorithm)


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