Relative merits of quadratic and linear detectors in the direct measurement of noise spectra

Initially a brief discussion is presented of the relative merits of quadratic and linear detectors as regards ease and convenience of use following narrow-band filters in the measurement of noise spectra. An analysis is then given of the noise content in the output signals of the two types of detector. The analysis uses results already available in the literature of the subject, but is presented here in a manner which allows a direct and ready comparison. The analysis is not restricted to any one type of narrow-band filter and it is concluded quite generally that neither type of detector has a significant advantage.