A 210-280 GHz sis heterodyne receiver for the James clerk Maxwell telescope .2. Calibration

The comparison of a 240 GHz SIS heterodyne receiver with a Schottky diode receiver at the Maxwell telescope revealed difficulties with its calibration using continuum loads. The difficulties arise from the fact that the local oscillator power is not hugely greater than the total load power incident across the RF and IR band. This broadband power influences the receiver gain, principally by varying the slope of the I-V characteristic, and hence the output matching as a result of the ac Josephson effect. Suppressing the Josephson effect with a magnetic field permits the standard calibration procedure, using hot/cold continuum loads, to be employed.