5 November 2015

MIL 188-110C App.D: BW24 KHz, SR19200 Bd, QAM-64


Cross Correlation Function returns 106.6 ms (Pic. 2) and highlighting a single frame it can be seen that the length of the mini-probe is worth 6.8 ms (Pic. 3): since the baudrate (19200 Bd), it makes ~130 symbols length. Now, looking at Table-D for 24KHz bandwidth waveforms (Pic. 4), this value (~130 symbols) can be assumed as 128 and consequently the data segment consists of 1920 symbols: this way we get (128 + 1920) 2048 symbols per frame that generate a 106.6ms ACF,  and 'salright (*). So, the waveform number may be 11 (64-QAM) or 12 (156-QA). The value of the carrier can be obtained in the fourth degree, wich is characteristic of QAM modulation (Pic. 5), and - althought it's not so clear - the typical 5 rings of QAM-64 are distinguished in the phase-plane constellation (Pic. 6).

Pic. 1 - 24 KHz bandwidth and 19200 Baud
Pic. 2 - CCF
Pic. 3 - Mini-Probe lenght
Pic. 4
Pic. 5 - detecting baudrate, carrier ad harmonics of the signal
Pic. 6 - the 5 rings (hardly distinguishable) correspond to QAM-64
(*) 'salright, it's all right, as Lennon sings here (Whatever Gets You Through The Night)

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