15 March 2021

dwell on STANAG-4481F is always interesting

Sometimes we overlook the usual STANAG-4481F or similar FSK signals, but they are precisely the ones that turn out to be the most interesting: just in these days I heard two STANAG-4481F transmissions that, one way or another, are both notable.
The first one is the Dutch Navy which operates at 6358.5 KHz (cf). That channel is normally used by PBBs for their well known Frequency Availability Broadcast (FAB, also known as CARB) but I was lucky enough to listen to them in "traffic" mode, more precisely using the waveform 50Bd/850 in secured mode (KW-46 device). Likely it was a Maritime Rear Link to communicate with a specific ship. 


Fig. 1

Fig. 2

The second one has been heard on 8994.0 KHz (cf) using the waveform 75Bd/850, it also secured with KW-46 encryption: Tx site is AJE Barford St. John (UK). Well, apart from the use of KW-46 with the 75Bd waveform, the transmission is interesting since the tuning frequency (8992.0 KHz/USB) is one of the primary channels of the HFGCS network. One can object that 8992.0 KHz is CRO - Croughton, actually  both sites (Croughton and Barford St. John) belong to the same communications complex, being just a few miles apart. One site is the receiving station, the other one the transmitting station.

Fig. 3

Fig. 4
It may happen (Figure 5) that the FSK transmission is momentarily suspended to make way for an EAM message which - as you know - has a higher priority ("Ubi maior minor cessat").
Fig. 5 - higher prority EAM breaks a STANAG-4481F broadcast



  1. The TDOAs aren't great for Barford St John, however hihi

    1. yes correct! although Barford/Chrougton is the only HFGCS complex in UK (AFAIK), I could not get better TDoAs than the ones I published.