The cold-load calibration is used to calibrate the noise correction factor (b). in fact, this fine tunes the slope of the linear function which computes the atmospheric temperature from the radiometer raw reading.
To start a cold-load calibration, connect a cold-load to the test port of the radiometer channel to calibrate. Then, at the Calibration page select 'Switch channel 1 to cold-load' or 'Switch channel 2/3 to cold-load', depending on the channel where the cold-load is connected. This actuates the wave guide switch to the selected test port and changes the calculation of atmospheric temperature according to equation 5.16 to 5.20.
The radiometer returns to the Reading page and displays the cold-load temperature. The displayed temperature value is based on the actual calibration of the radiometer. You may now either select (ABORT) to return to normal mode (this switches the wave guide back to antenna) or (START CALIBRATION) in order to recalibrate the radiometer.
In the latter case the radiometer temporarily sets the noise correction factor (b) to 1.0 and takes the configured number of radiometer readings. From the average of these readings it calculates a new noise correction factor.
Instead of the normal reading page the radiometer shows a table presenting the nominal cold-load temperature, the measured temperature, the old noise correction factor and the new one.
Clicking to 'Cancel' abandons the calibration result, leaves the noise correction factor at it's old value. Clicking to 'OK' replaces the noise correction factor by the new one. In both cases the wave guide switch of the calibrated channel is reset to the antenna.
Please note the following: