30 August 2021

MFSK-16 100Bd/100 transmissions, likely adaptive tests

Interesting MFSK-16 100Bd/100 transmissions spotted on 15810.0 KHz (cf) on August 27th, in the following days I tried several times to monitor that frequency, and more generally the 15 MHz band, but I never had the opportunity to hear them again. 

Figure 1 - 100Bd/100Hz signal

Some salient features are the presence of series of bursts that have the same pattern and therefore carry the same data, I do not think they act as "calls" but rather idle signaling or test patterns. A second curious feature is a kind of FSK modulations (with different shifts but basically reversals) which are apparently inserted without a precise pattern or timing (figure 2). 

Figure 2 - FSK insertions

After demodulation, a plain hex to bin conversion (mapping: 0 -> 0000 ... F -> 1111) doesn't provide much help other than a fairly well defined 438-bit period (figure 3). Likely the signal is transmitted from Ukraine and it's related to test of an adaptive waveform, as my friend KarapuZ say.

Figure 3 - 438 bit length period after demodulation

 Something regular appears when syncing on 1111111111110111100, but it's only speculating (figure 4).

Figure 4


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