Those who have ever tried to manually measure an amplifier’s noise figure may have found that the numbers aren’t quite what was expected. This is most likely the result of the spectrum analyzer’s noise figure, which adds noise to the measurement. If an interfacing amplifier is needed to boost the device-under-test (DUT) output noise power above that of the spectrum analyzer’s noise floor, then it becomes even more likely that accuracy will suffer.
Additional components are sometimes necessary, but to accurately determine the noise figure of the DUT, one must know the gain and noise figure of the additional components so that the DUT characteristics can be de-embedded from the measured response. Although high-gain amplifiers are less susceptible to the analyzer’s noise figure, some analyzers can have extremely high noise figures at high frequency—on the order of 30 to 60 dB.