The Institute of Applied Physics has developed a new ground-based radiometer for measurements of water vapour profiles in the stratosphere and mesosphere. The uncooled instrument, called MIAWARA, has a very good sensitivity and is calibrated using a combination of tipping curve and balancing calibration. Using this combination the instrument can operate as a self calibrating system without the need for routine maintenance. We present a validation technique for the tipping curve calibration and a new approach for the reference absorber design used in the balancing calibration. The uncommon design of the reference absorbers decreases standing wave artifacts and thus enhances the sensitivity of the instrument, leading to a very good altitude coverage in the range of 20 - 80 kilometres.