Thomas Braunstorfinger und Martin Hisch, GbR

Change Big Display Mode to Mixer Frequency

Switch on Big Display Readout by pressing the appropriate button in the toolbar. The green ruler should be visible in the main spectrum display

Choose a PSK signal within the main spectrum display by clicking in the middle of the PSK signal (the green ruler should move to that position)

Activate the PSK demodulator by pressing the appropriate button in the toolbar. The mixer frequency changes automatically to the exact center frequency of the PSK signal.

The PSK demodulator is used to synchronize the mixer frequency of Analyzer2000to a PSK modulated signal. After synchronization is achived, the so called constallation display shows a stable picture of the phase states of the modulated signal.

This technique is called carrier recovery, because in all PSK modes, any demodulation is done in a coherent way. The above picture shows a QPSK signal with 4 phase states. The lines between the phase states (called state transitions) are produced from the pulse shaping used in the transmitter (here: square root cosine with rolloff factor 0.6).

The second constallation display shows an offset QPSK signal (OQPSK), which looks very similar to a normal QPSK signal, except there are no diagonal state transitions. That is the reason why the PSK demodulator of Analyzer2000 shows the complete signal within the constallation display. It helps to distinguish between the different variants of PSK modulated signals.

To see if the carrier recovery is working correctly, the "magic eye" display is used.

In fact the display shows the frequency spectrum after performing a nonlinear math operation with the signal. The red line shows the center frequency. The modulation control determines the math operation:

If the correct modulation is chosen, the "magic eye" shows one sharp peak at the center frequency with some side slopes around it.

The bandwidth of the signal can be determined in the main spectrum display of Analyzer2000. Set the bandwidth control in the PSK demodulator to the next higher value.

Bandwidth in the above example is appr. 1.8 kHz. 3 kHz should be chosen in the demodulator dialog.

The time domain display of the PSK demodulator dialog shows the phase of the signal between +pi and -pi.

The above picture is taken from an OQPSK signal. A BPSK signal is shown in the next picture.

All other demodulator sections are identical to the FSK demodulator dialog.

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Last Update: Jan 12