User Manual DDS200 Digital Demodulation System 070-9952-00

Manual OperationIf the accurate symbol rate is not known, an automatic search routine can bestarted. To do so, set the search range with the aid of the UPPER / LOWERSEARCH LIMIT keys (the UPPER LIMIT must always be higher than theLOWER LIMIT).The search itself is started with START AUTO SEARCH. Since up to fiveminutes is needed to search through the whole range, it is advisable to set narrowrange limits so that the setting can be made quickly.A search run may be stopped any time with the STOP AUTO SEARCH key. Inthis case the previous, manually-set values will be used again. After the symbolrate of the modulator has been changed, a new search run must be started, sincethe search is only performed once.Information on the progress of the search is displayed in the SYMBOL RATEVALUE field where the current symbol rate is indicated at regular intervals(approximately every five seconds). Once the instrument has synchronized to thesymbol rate, no search is started when the START AUTO SEARCH key ispressed, even if the set search range limits are outside the actual symbol rate.NOTE. If the automatic symbol rate search is active, setting commands otherthan the STOP AUTO SEARCH command cannot be processed.Order of QAM. The order of QAM is determined in the modulator and must be setaccordingly in the QAM receiver. All common methods (4–, 16–, 32–, 64–, 128–and 256QAM) are available and can be selected by means of the ORDER OFQAM key (toggle function). 64QAM is the default value.BEEPER. The internal acoustic signal generator can be configured in theBEEPER... submenu. With the different kinds of error that may occur, thegenerator is active when the corresponding parameter has been set to EN-ABLED, or inactive when the corresponding parameter is set to DISABLED.The following errors may be acoustically signaled:1. Recovery of symbol clock rate not synchronized.2. Equalizer not synchronized.3. Carrier recovery not synchronized.4. Sync byte of MPEG frame not found.5. At least one faulty byte in the 188-byte MPEG frame could not be corrected.6. At least one faulty byte was corrected in the 188-byte MPEG frame.DDS200 Digital Demodulation System User Manual 2–33