Theory of three-level paramagnetic masers. Part 3: Output noise power spectrum

Noise in a maser amplifier is analysed by treating the paramagneticions quantum-mechanically and the electromagnetic field classically. The output noise temperature of a maser amplifier is equal to the `average¿ temperature of the various parts of the amplifier (including the impedance of the signal generator). The average temperature is obtained by weighting the temperature (actual or effective) of each part of the amplifier by the ratio of the power absorbed therein to the input power which obtains when the susceptibility tensors of the various parts of the amplifier are transposed and power is sent in through the output port.