Wavecom W40PC Manual page 99

In ASYNCHRONOUS mode, the signal is not demodulated at all. Instead, the phase of the
signal is visually 'compared' with a reference signal. Providing the correct reference signal is
selected, this will result in a phase display that provides an indication of the type of PSK or
PAM signal. The points will trace the path taken as the signal phases change. At the nominal
signal mapping points, there is normally an accumulation of data points, providing a visual
clue the total signal mapping.
Multi-channel DPSK signals often have a very narrow channel signal bandwidth. This results
in the phase of the signal never remaining constant, and so the accumulation of signal points in
the phase plane is not visible. To quantify such signals use SYNC Mode.
The frequency of the reference signal is set using the "Ref I/Q: ..." option. Note that if the
reference frequency is incorrect, the display rotates at a rate that is the difference between the
reference frequency, and the true carrier frequency of the signal. When adjusting the reference
signal, the changes are 'live'. This means that changes you make have immediate effect, and
resulting change in the phase display is immediately visible on the display.
For ASYNCHRONOUS mode, the symbol rate measurement is not required. The sampling
rate is independent of symbol rate. Three sampling rates are selectable. For low baud rate
signals, better results are obtained with a lower sampling rate. The "Mode" menu item is
disabled in the "Demodulator" menu.
Several color schemes for both tools are available through the right-click menu.
In summary, the basic steps for analyzing a suspected (D)PSK signal is as follows:
Use the Real-time FFT tool to characterize the signal. Use the cursors to configure the
estimate of the center frequency and bandwidth.
Use the PSK Symbol Rate analysis tool to measure and select the symbol rate of the signal.
Advanced Topics • 91
WAVECOM Decoders v6.15 W40PC, W41PC, W51PC