A modified approach to realise a cold reference for radiometer calibration is presented. A common problem with the cold references used in radiometer calibration is the temperature distribution of the connection cable between the load and the receiver. The introduced approach utilises the thermodynamical fact that the temperature distribution between two connected points is linear, when the connection is isolated from the surrounding environment. The level of liquid nitrogen is forced to stay at a certain level enabling high stability over a long period of measurement time. In this paper a principle for doing this is presented and a test setup for testing the linearity is introduced. When the linearity of the temperature distribution fulfils the given requirement the accuracy of the cold reference meets an adequate value. The essential benefit of the approach is the high stability and good accuracy compared to the complexity of the configuration.