FIG. 3 Receiver Control Unit
Each receiver on the telescope is connected to a control unit in the receiver room. All switching functions necessary for observations (Dicke switch, frequency switching, calibration signals etc.) can be remotely controlled from there. Even data logging occurs at the rate set by the control unit switching signals.
The control unit is essentially a programmable switching signal generator, which operates during observations under control of the process control computer. The observer can freely decide in which way the receiver is being used, e.g. he can define up to 16 different frontend switch settings, which are then cyclically repeated at a rate also determined by the user. The online computer stores this information as part of the data header on tape and the reduction software is capable of dealing with a wide variety of switching conditions.
To achieve operational flexibility and allow changes between different receivers in the secondary focus cabin within a few seconds, computer controlled Receiver Rack Multiplexers provide routing of all necessary signals. See Fig 4 for an overview and Fig. 5 for more details.
