The tuning of receivers, the equalization of cable lengths for multi-channel systems using polarimeters and the phase equalization of these systems are done by the Systems Group before the start of observations. The receivers contain swept frequency sources (VTO = voltage tuned oscillator) the signals from which can be injected through the input directional coupler. The display of the insertion curves is possible via dedicated monitor detectors or via the polarimeter.
Remotely controlled phase shifters are provided in one local oscillator arm of a number of receivers. The phase adjustment can be checked and if necessary corrected by the observer during observing.
Some receivers can be used over a wide signal frequency range and this can be accomplished by remote control from the receiver room. The 18 - 26 GHz maser is currently the only system, which has to be tuned. Other broadband systems use a set of different RF-filters to suppress the image frequencies.