Abstract: A facsimile interface unit, which encodes signals from a facsimile terminal for transmission by satellite, can only encode signals which conform to the Group 3 standard. The interface unit intercepts signals which identify non-standard features supported by the terminal and replaces them by a modified signal of the same format which does not identify any non-standard features. Another facsimile terminal receiving the modified signal is prevented from enabling any non-standard features and signals to the first facsimile terminal that the Group 3 standard is to be followed. Therefore, the facsimile interface unit is able to encode and decode signals successfully during the subsequent transmission.