CIS-128 is an OFDM 128-tone + 1 'off' tone in the middle of the grid (then 64+64 carriers), it spreads a 3000Hz bandwidth with a step between carriers of 23.5
Hz, manipulation speed of ~ 21 Baud and modulation QAM-16 (Pic. 1). The signal was heard at 0948z on 13399.0 KHz on USB. This waveform is discussed in radioscanner.ru here: http://signals.radioscanner.ru/base/signal250/
Analyzing the signal, is clearly visible that each 5 symbols a special symbol is sent (Pic. 2) and then the expected ACF value should be 5 symbols; but there is a discrepancy because ACF is effectively doubled, i.e. 10 symbols for a ~477 ms length (Pic. 2).
Analyzing the signal, is clearly visible that each 5 symbols a special symbol is sent (Pic. 2) and then the expected ACF value should be 5 symbols; but there is a discrepancy because ACF is effectively doubled, i.e. 10 symbols for a ~477 ms length (Pic. 2).
 |
| Pic 1 |
 |
| Pic. 2 - a "special symbol" is sent every 5 symbols |
 |
| Pic. 3 - 10 Symbols ACF |
It seems that during the special symbol, i.e. every 5 clocks, AM modulation is lost since the "shape" of these symbols are pretty the same.
In sync-mode are sent only the special symbols and each 5 symbols all the tones do not change their phase (Pic. 4). The ACF is always 10 symbols lenght but in this case the symbols markers are more evident (Pic. 5).
 |
| Pic. 4 |
 |
| Pic. 5 - ACF of sync mode |
No comments:
Post a Comment