Interesting and good quality recording sent me by my friend Ary from UDXF group, whom I thank. The initial so-called CIS-48 probes/markers, that presumably(!) act as "calls", are sent at regular intervals and consist of four 50Bd PSK2 tones: notice the typical violation of the bit reversal structure, a "1" is inserted instead of a "0", when the system transits to the traffic condition (figure 1).
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| Fig. 1 - the four PSK2 probes/markers |
The following OFDM blocks clearly consist of two different sets of channels: 36 and 48, both using PSK2 modulation. As shown in figure 2, the parameters are exactly the same (50 Bd speed, 62.5 Hz spacing, LG, LU) and this leads to think of the same OFDM modulator but with 12 channels suppressed (off). Maybe - at least in this cases - the correct definition should be OFDM-36/48...
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| Fig. 2 - OFDM blocks 36 (likely 48-12) & 48 |
Although the classic 3300 Hz pilot tone is missing, the system is attributed to some CIS mil/gov organization.
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