User Manual DDS200 Digital Demodulation System 070-9952-00

Manual OperationOperation as Demodulator for Quadrature-Amplitude-Modulated (QAM) SignalsThe DDS200 Digital Demodulation System measures QAM signals used indigital video broadcasting (DVB). A number of special characteristics formeasuring DVB signals make this instrument especially suitable for accurateanalysis and measurements of all main parameters (refer to MEASURE Menu onpage 2–46). Such characteristics are the newly developed steep-edge channelfilters, which were especially developed for use in cable channels, the powerfulequalizer, and the DVB-specific Nyquist filters.The input signal is processed in compliance with DVB specifications. Thisincludes demapping, the Reed-Solomon decoder, deinterleaving, and energydispersal. Decoded MPEG data is available in serial or parallel form.Extremely powerful digital signal processing provides accurate analysis of theapplied QAM signal. A newly-developed data storage technique allows a veryflexible and efficient collection of measurement results for all relevant signalparameters, providing valuable information on problems that may occur duringtransmission. In addition, the display of constellation diagrams on the LCD canbe individually configured, and variable result hold times (up to ∞) can be set.Thus signal events lasting an extended period of time can be displayed. Anotherbenefit is the automatic storage of messages in the alarm register.This powerful unit can be used any time for applications in developmentlaboratories, quality assurance, and production monitoring of TV consumerelectronics.This section presents and describes the different functions in their logical order.To take full advantage of the instrument capabilities, particular attention shouldbe paid to the characteristics mentioned in Examples of Application on page2–62. The following discussions of the DDS200 menus provide informationabout interpreting the measurement results obtained with the DDS200.OverviewFor users already familiar with basic DDS200 characteristics, the steps requiredfor the direct synchronization of a QAM signal are listed below in theirsequence:1. Switch on instrument and establish RF (IF) connection.2. Press PRESET.3. Select input frequency (RF) and input (INPUT).4. Select order of QAM (STATUS menu).5. Select symbol rate (STATUS: SYMBOL RATE menu).After the previous selections, the calculated parameters or the constellationdiagram can be displayed in the MEASURE menu.2–26 DDS200 Digital Demodulation System User Manual