A complete injection signal is provided having a digital spectrum formed from components weighted by a set of coefficients, in a preliminary step, the coefficients of the components included within a frequency band are attenuated resulting in an incomplete digital spectrum being obtained; in a next step, the analog signal composed from the incomplete digital spectrum is injected into the electrical line; in a next step, the echo corresponding to the injected signal is measured; in a next step, the digital spectrum of the echo is calculated; in a next step, the digital spectrum of the echo of the complete analog signal if the latter had been injected is estimated, the kth component of the estimated complete digital spectrum being equal to the kth component of the digital spectrum of the echo received multiplied by the ratio between the kth component of the digital spectrum of the complete injection signal over the kth component of the incomplete digital spectrum; in a next step, the measurement of the reflectogram of the line is obtained based on the estimated complete digital spectrum.