12 January 2016

an RFSM network on 9050.0 KHz (almost surely Bulgarian Diplo)


I followed these signals on 9050.0 KHz USB mainly in the morning and during the last days, from 0700 to 1100 UTC. Looking at UDXF logs and talking with some friends of mine, the network using 9050.0 Khz is probably Bulgarian or  Romanian Diplo (since some ALE calls such as RETEA, FARAONRETEA, SC1DSRETEA), the QRX is visible on 9055 kHz but sometimes only one frequency may be used. Is not sure if also a similar signal heard on 9040.0 KHz belongs to the same net. My friend Kristian from Germany suggested to be Bulgarian Diplo net and kindly pointed a Monitoring Times issue (May 2011) talking about this mode and Bulgarian Diplo activity:

Transmissions on 9050.0 seem to be scheduled at 0830, 0900 and 0930 UTC Mon-Fri, almost all the sessions start with a ~ 15sec tone at 9051.8 KHz (sent about two minutes before) and they last the time necessary for interchanging/sending the messages, usually few minutes.
From previous recordings they used plain MIL-STD 188-110A and now they switched to RFSM (Radio Frequency Software Modem) with Data Masking (link protect) feature, an MS188-110 ST based software-modem by "RFSM-IDE Group". 
Carrier frequency (1800Hz), symbol speed (2400Bd) and modulation (PSK-8)  are the same as that standard (pic. 1) and may be misunderstood and wrongly identified as MS188-110 4800bps/uncoded (the RFSM 75bps/L) and 2400bps/voice (the RFSM 300bps/L), as it happens with both k500 and sorcerer; the 13ms ACF is a clue in favor of RFSM (pic. 2). The structure of the signal is quite complicated, the PSK-8 preamble is followed by the data transfer in PSK-8, QAM-32 or QAM-16 according to needed data-rate. Just as aside note, a sort of 2-ISB signal + carrier has been seen on 9050.0 as central frequency: signal is very week and is difficult to say it's nature.
The RFSM-2400/8000 is a software by "RFSM-IDE Group", it operates under standards MIL 188-110A / MIL 188-110B App. C, (also under a modified version) providing a maximum speed of 8000bps (standard mode), or 6670bps (non-standard "narrow" mode). Signal bandwidth: 0.3-3.3 kHz (standard mode) and 0.3-2.7 kHz (non-standard mode).