User Manual DDS200 Digital Demodulation System 070-9952-00

Manual OperationQAM Parameters. When the QAM PARAMETERS key is pressed, the DDS200 isswitched to parameter calculation. The parameters selectable in the constellationanalyzer mode are now preset and can no longer be varied:GATE TIME = 750 ms,GATE CNT = 1.During the set gate time of 750 ms, approximately 840,000 I/Q values are storedin the internal data memory and used for statistical evaluation. A specified valueis completely independent of all others. Using suitable computation, a value canbe completely separated from the effects of other values. The signal to bemeasured should comprise a minimum of errors (phase error, amplitudeimbalance, carrier suppression) so that available margins are free for disturbances(for example, noise) that cannot be avoided.A list of parameters is given in Table 2–3. Provided the listed parameters do notoccur at the same time, the set limit values should not be exceeded to afforduseful transmission. In the case of combined parameters, limits are correspondinglyreduced. As the variety of combinations is almost infinite, no values can bespecified for such a case. Specified values are based on experience, simulation,and measurements on the QAM modulators.2–54 DDS200 Digital Demodulation System User Manual