7 August 2016

unid QPSK 2400Bd burst (1)

the signal spreads 2800Hz bandwidth and consists of a "train" of packets, each consisting of an initial 200ms burst followed by four 425ms bursts; since the initial burst the signal looks like an ARQ mode transmission; a short preamble is visible in the initial burst and in the first of the following four bursts (fig. 1).

fig. 1 bursts
The waveform employs the QPSK modulation at 2400 symbols/sec on a single 1800Hz carrier as shown by the constellation of figure 2
fig. 2 - QPSK 2400Bd constellation
The signal exhibits a 112.5ms ACF, corresponding to a 540-bit period (270 QPSK symbols), that resembles the same value of the QPSK signal reported in this post although their relative frame structures are different (figs. 3,4)

fig. 3 - ACF of a single burst
fig. 4 - 540-bit period corresponding to 270 QPSK symbols

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