A method for calibrating a radiofrequency multichannel subsystem of a telecommunications payload includes a step of generating and injecting a calibration signal at one or more input access channel injection points; a step of tapping off the injected and propagated calibration signal at tapping-off points of an access channel at output; and then a step of estimating the amplitude and/or phase differences between the internal channels of the multichannel subsystem on the basis of the calibration signal injected at input, serving as a reference, and of the extracted calibration signal or signals; and then a step of correcting the amplitude and/or phase differences by way of correction means. The injected calibration signal is a chirp signal, formed of a chirp or of a sequence of at least two identical chirps. A calibration system implements the calibration method.