User Manual DDS200 Digital Demodulation System 070-9952-00

Manual OperationBER Measurement with External Equipment. The DDS200 has an internal BERmeasurement function which does not require any interruption of the program,since the error control mechanisms of the DVB signal are used for calculatingthe BER (refer to Selection of Integration Time for BER Measurementpage onpage 2–79). This method has its limitations when very high bit error rates areinvolved (>10 -3 ). For measuring high bit error rates (or for checking the internalBER measurement function), the setup shown in Figure 2–60 can be used.Device under testNoisegenerator2715SpectrumanalyzerDDS200QAM modulatorDVT 200OUTINX6X5SerialclockSerialdataBERmeasurementunitFigure 2–60: Setup for external BER measurementEquipment settings:DVT 200 Digital Video Transmitter:Modulation with built-in PRBS generator(length of sequence: 2 23 – 1 bit)DDS200 Digital Demodulation System:SPECIAL FUNCTION: BER INTEGRATION:BER EXTSPECIAL FUNCTION: MPEG DATA OUTPUT:I/Q-INVERSION: NORMAL or INVERTED (notAUTO).Description of external BER measurement: The DVT 200 Digital VideoTransmitter provides a signal which is modulated by means of an internal PRBS(pseudo random bit sequence) generator. The QAM output signal is taken via anattenuator to a coupler, where a signal of the same frequency from a noisegenerator is added. The resulting signal can be displayed on a spectrum analyzer(for example, a 2715 Spectrum Analyzer) for determining the C/N value (seebelow). The signal is then taken to the DDS200 where it is demodulated. Of2–80 DDS200 Digital Demodulation System User Manual