Variable gain stage

Pulser, T/R Switch, Variable Gain Stage (or TGC Amplification)... 

The transmitter chain consists, basically, on a signal generator and an amplifying stage composed of a Variable Gain Amplifier (VGA), a preamphfier and a power amphfier. 

A fairly useful stability analysis method is the Niederlinski index. It can be used to eliminate unworkable pairings of variables at an early stage in the design. The settings of the controllers do not have to be known, but it applies only when integral action is used in all loops. It uses only the steadystate gains of the process transfer function matrix. 

The densitometer uses a two beam comparator technique of measurement. A single lamp illuminates, through a variable neutral density filter, the emitter of an eleven stage photomultiplier tube. Because the frequency of measurement is five times the AC line frequency and the amplifiers are extremely high gain, the lamp must be operated from a regulated DC source, otherwise, 120 Hz brightness ripple of the lamp is recorded in the data. 

The application of QSAR to bioactive synthesis has always suffered from an unfortunate paradox. In order to develop a useful equation, it is necessary to first complete a substantial fraction of the synthesis. Only then can the derived equation assist in extending or optimizing the bioactive series. No help is available for the earliest or intermediate stages of synthesis which have already been passed. Nor is it certain that a useful equation can be gained from the first 10-20 members of a series. Poor selection of structural changes, variable biodata, differential metabolism of some members and the presence of unknown factors can all lead to poor correlations of little practical use. These problems are common to anyone who has attempted QSAR on novel bioactive series. 

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