User Manual DDS200 Digital Demodulation System 070-9952-00

Manual OperationUsing the GATE TIME, GATE CNT, MAX HOLD and FREEZE keys, you mayadapt the constellation diagram to your special requirements. Operation in theconstellation analyzer mode is illustrated in Figure 2–44.Collection ofmeasured I/Qvalues withinGATE TIMEGraphicevaluation ofmeasured valuesand displayCollection ofmeasured I/Qvalues withinGATE TIMEGraphicevaluation ofmeasured valuesand displayCollection ofmeasured I/Qvalues withinGATE TIMEGraphicevaluation ofmeasured valuesand displayDisplay range for GATE CNT = 1Display range for GATE CNT = 2Display range for GATE CNT = 3Figure 2–44: Function of GATE TIME and GATE CNTUsing the GATE TIME key, a collection time between 2 ms and 1000 ms can beset. Within this period, the DDS200 stores the received I/Q value pairs every740 ns. Thus 1.351 million I/Q values are available every second. Subsequently,the data are read again from the memory and displayed. This procedure takesapproximately 250 ms. If GATE CNT = 1 has been selected, a new cycle withnew I/Q values is started when a cycle is completed independent of the previousvalues and is then displayed.With GATE CNT = 3 selected, a collected I/Q value remains in the display over3 complete cycles. During this time, new cycles are started the measured data ofwhich are again displayed for 3 cycles. This display is still being updated,although the integration time is now three times as long as before. The settingrange for GATE CNT is 1 to 99999.A special function is offered by the MAX HOLD key. In this case, the GATETIME is set to 1000 ms and the value of GATE CNT is set to infinite. Using thisfunction, long-term monitoring can be performed, since displayed I/Q values areonly cleared when the function is terminated.With the aid of the FREEZE key, the currently displayed constellation diagramcan be frozen. This function is useful when a particular event should be retainedon the screen for printing.DDS200 Digital Demodulation System User Manual 2–53