  Radiometer experiments to detect 21-cm Hydrogen line emission from the Cosmic
Dawn and Epoch of Reionization rely upon precise absolute calibration. During
calibration, noise generated by amplifiers within the radiometer receiver must
be accounted for; however, it is difficult to measure as the noise power varies
with source impedance. In this letter, we introduce a convenient method to
measure the noise parameters of a receiver system, which is practical for
low-frequency receivers used in global 21-cm experiments.
