10 June 2016

Unid MSK 1200Bd 800Hz

Yesterday (10 June) morning I spotted this weird signal on 20877.0 KHz/USB at 0725 UTC, unfortunatelly some statics due to a thunder storm ruin the reception.
The signal has a 1200 Hz bandwidth and is characterized by a strong tone at ~1400 Hz (1394) and two simmetical tones at +600 and -600 Hz which are transmitted at lower level than the central one. A sort of "marks" are transmitted each 137.5 ms (pic. 1)

pic. 1

FSK bursts are inserted in a seemingly random way, they have a shift of about 800Hz and manipulation speed of 1200Bd: curiously it's the same value of the bandwidth (pic. 2)

pic. 2
The 137.5ms marks make the period of the signal = 165 bits.

pic. 3


  1. i would be very surprised if this does not use a CRC-16 polynomial (specific mask?). It should be a Telecode (generic russian name for radar data modems) as the 165 frame format is described for AKKORD-SS-PD algorithm (other frame lenght= 69&117 bits). Very interesting.

  2. they should use the "telecode" mode in Air Defense, carrying command and technical data such as telemetry. Do you agree?

  3. Yes. The 1200Bd modem is rarely seen on HF, even less the 165 bit frame variant. Have you find the CRC MASK with BEE(not familiar enough with it to find it). Possibilities are from Kaliningrad, Syria or Algeria, do you have an idea?