LNF-VTL_WR28A is a precision cryogenic noise source with very high accuracy. It is based on a variable temperature waveguide termination with a WR-28 port. The termination is made of a crystal quartz chip with a resistive film, a 50 Ohm heater resistor and a precision temperature sensor. The chip is thermally isolated from the module and can thus be heated with minimal influence on the waveguide block temperature. However, the chip is thermally connected to the incoming wiring. Therefore, it is imperative that the incoming wires are properly grounded to the base temperature. The block has to be cooled down to 50 K or lower to ensure proper functionality. The temperature sensor is a Lakeshore DT-670A1 series which requires a suitable temperature monitor to supply a constant current of 10 μA, to measure the voltage and display the corresponding temperature. Typically, a temperature regulator is used to both monitor the temperature and regulate it by applying a voltage to the heater resistor.