User Manual DDS200 Digital Demodulation System 070-9952-00

Manual OperationFigure 2–24: INPUT: ATTENUATION menuWhen the AUTO, AUTO LOW NOISE, AUTO LOW DIST or AUTO LOWESTDIST key is pressed, the attenuator in the receiver input is set as follows:With AUTO LOW NOISE selected, the input attenuation is reduced by 5 dBbelow the setting under AUTO. This improves the signal-to-noise ratio of thereceiver.With AUTO LOW DIST selected, the input attenuation is increased by 5 dBabove the setting under AUTO. This improves the signal-to-intermodulationratio of the receiver.With AUTO LOWEST DIST selected, the input attenuation is increased by10 dB above the setting under AUTO. This is only useful if, for instance, thelevel in the adjacent channel is considerably higher than that of the signalchannel.With MANUAL selected, the attenuator can be set manually in 5 dB steps from0 to 55 dB. Settings can be made using the up and down cursor keys or bydirect entry via the numeric keypad and confirmation with ENTER. In the caseof direct entry, the entered numerals are rounded to a value that can be dividedby 5.With the 10 dB PREAMP key, a low-noise preamplifier can be switched into thesignal path to improve the noise figure of the receiver. This is useful whenlow-level signals are received. The attenuator is correctly set in automaticoperation. In the AUTO LOW DIST and AUTO LOWEST DIST modes, the10-dB preamplifier cannot be switched on as preamplification of the TV signalin these modes is not useful. In this case the label 10 dB PREAMP is in italics.2–28 DDS200 Digital Demodulation System User Manual