Sideband measurement

The interferometer has the ability to separate the upper and lower sidebands of the receiver output. Accordingly, it is possible to measure the receivers'sideband ratios provided at least 3 antennas are available. (With 2 you get only the product of the sideband ratios). This is done using the OBS $\backslash$GAIN command, which simply does a cross-correlation. A continuum source must be observed (strong, but not necessarily point-like). Quasi real time data reduction is available within CLIC using the CLIC $\backslash$SOLVE GAIN command, and real-time reduction is done to give the result.

Because atmospheric calibration depends on the sideband ratio, and vice-versa if the optical depth is different in the two bands, it may be necessary to iterate between the OBS $\backslash$CALIBRATION and OBS $\backslash$GAIN commands. CLIC command CLIC $\backslash$SOLVE GAIN /PRINT produces a command procedure which can be used in OBS to enter the appropriate gain values. It also allows to set the LO1 and LO3 phases to obtain a zero phase on all baselines in both sidebands.