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)

https://disk.yandex.com/d/laasTSzeM0o7fQ

French Navy Broadcast, FSK 50Bd/850

Following the previous post, I decided to analyze the French FSK 50Bd/850 in order to replicate the results obtained by my friend Christoph Mayer in his blog: happy to say that the results coincide.

French-Ny FSK 50Bd/850 has a characteristic 21-bit period and, in a way similar to STANAG-5065, two/three sub-frames which are delimited by the bits of two LFSR markers M1 M2 and a logical "1" value bit (1-bit). The sequences for the two markers are generated by the LFSRs described by the polynomials x^6+x^5+1 and x^7+x^6+1.

Since the missing of an initial sync in the recording, the 1-bit can occur in any position within the 21-bit frame therefore markers' positions are reported as relative to the 1-bit. A possible more significative layout shows 2 possible sub-frames (5 and 13 bits length).

 

Obviously, the length of the markers' patterns match the length of the respective generator polynomials.

One of such transmissions  heard on 8516.8/usb (offset + 2000Hz) has DF'ed to "La Regine" (Saissac), callsign of the station is FUG