3HILL D A, HAWORTH D P. Accurate Measurement of Low Signal to Noise Ratios Using a Superheterodyne Spectrum Analyzer [ J ]. IEEE Transaction on Instrumentation and Measurement, 1990, 39 ( 2 ) : 432 - 435.
4HILL D A, HAWORTH D P. Accurate Measurement of Low Signal - to - noise Ratios Using a Superheterodyne Spectrum Analyzer[ J]. IEEE Trans. on Instrum. Meas. , 1990, 39(2) : 432 -434.