Thursday, June 21, 2018

Interesting signal (TDMA?)

Today a signal on 5099 kHz USB (5100.8 kHz center) was picked up on several KiwiSDRs in the Northwest of Europe.

This signal consists of a sequences of sharp pulses and of tones:



Zoom around the tone:



Aligning the signal in frequency to the beginning of the tone, it becomes visible that there are two tones in three intervals. It might be a coincidence but the length of the intervals is close to 6/128 seconds which may or may not be relate to the information (here or here):

It is interesting that some residual modulation is visible, i.e., the phase is not perfectly constant or linearly rising.

The next three plots show abs(z) assuming different frame lengths:
  1. 854 samples (9.11/128 sec):



  2. 844 samples (9/128 sec):



  3. 281 samples (3/128 sec):



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