Abstract: Process aimed at the extraction of electrical signals emanating from the two ends of a two wire link between two installations exchanging data, wherein a probe comprising an attenuation cell is plugged in on either side of a break point situated on the line pair, then the connections thus established are isolated in such a way as to transfer the signals to the attenuation cell, the attenuation cell is activated by progressive withdrawal of active components, high-impedance signals are tapped off at the two ends of the attenuation cell, and signals which are images of the electrical signals dispatched by one or other of the ends of the line pair are obtained as output from the attenuation cell, after analogue calculation based on subtraction of the signals and multiplication by a constant which is directly related to the value of the attenuation of the cell.