Аннотация:A theoretical analysis of approaches to standard-free calibration of the quantum efficiency of a wide class of analog detectors based on measurements of the statistical characteristics of fields generated by parametric downconversion is carried out. General expressions are obtained for the photocurrent noise reduction factor and photocurrent covariance in the signal and idler channels, which take into account the possibility of strong fluctuations in the amplitudes of single-photon responses of the applied detectors. It is shown that the measurement of the photocurrent noise reduction factor using detectors that are not capable of operating in the photon counting mode does not make it possible to directly characterize the degree of two-photon squeezing in the parametric downconversion field and determine the quantum efficiency of photosensitive elements without additional calibration procedures. To determine the quantum efficiency of such detectors, a method based on measuring the dependence of the normalized covariance of photocurrents on the parametric gain is proposed.