The Picturephone System: Baseband Video Transmission on Loops and Short-Haul Trunks

For Picturephone service, baseband video signals are being transmitted on customer loops and short-haul interoffice trunks along routes similar to the ones used for present telephone service. It is economicallyattractive to use ordinary pairs of wires in the existing cables for video transmission. One pair is used for each direction of video transmission in addition to the pair used for the audio signal. The basic element needed to provide video transmission is a cable equalizer, which provides shaped gain to compensate for cable loss. Present designs which are the subject of this paper are intended primarily for underground 22-, 24-, and 26-gauge paper pulp-insulated conductors. Underground cables are preferred since they are subject to less temperature variation and interference than aerial cables. Future systems now being designed will have temperature regulation and higher transmission levels, permitting the use of longer underground loops and trunks and the use of aerial facilities. 395