20 September 2021

unid 1200Bd/850 (G)FSK bursts recorded in Japan

This is an update of the January 9, 2019 post (see below)

Nicely, on the same day two friends of mine linkz (from France) and Eddy (from South Australia) signaled me about the presence of these 1200Bd FSK bursts on 19102.0 KHz (cf). Linkz also DF'ed the signal with good success, identifying the probable Tx site location in the city area of Busan, South Korea "still transmitting the same data over & over":
So, at present, these (still unid) transmissions have been heard on (KHz): 4584,4626,4756,7531, and 19102 (all cf).

9 January 2019
This 1200Bd/850 FSK signal was recorded at different periods using some the KiwiSDRs located in Japan ( http://kiwisdr-jp7fso.ddns.net:8073), it was observed, at least, in three frequencies: 4765, 4626 and 4584 KHz. During night-time good results are also obtained with the KiwiSDR at Irkutsk (Russia), so the origin of the signal seems to be Japan or surroundings. 
My Spanish friends ANgazu and Rapidbit (from radiofrecuencias group) did a brief analysis measuring the speed (1200Bd) and the shift between tones (825-890 KHz) and suggesting the GFSK mode. On my behalf, I veried their measurements and verified that the bursts are 26 secs spaced and carry the same (encrypted?) text sent in async 8N1 mode (Fig. 21), although there are some difference among old recordings and new ones. The stream obtained after removal the start/stop bits does not offer useful information (encryption? not-standard 8-bit alphabet?), same results after descrambled the stream using the polynomial x^3+x^2+x+1. 



  1. What software are you using?

  2. mostly SA (Signals Analyzer http://signals.radioscanner.ru/info/item21/) and a bit editor