TELEVISION TELEPHONE SYSTEM

• US 3,723,653 A
• Filed: 10/21/1968
• Issued: 03/27/1973
• Est. Priority Date: 10/24/1967
• Status: Expired due to Term

• Current Assignee: Yoshinobu Tatsuzawa
• Original Assignee: Yoshinobu Tatsuzawa
• Inventors: Tatsuzawa, Yoshinobu
• Primary Examiner(s): Claffy, Kathleen H.
• Assistant Examiner(s): D'Amico, Thomas
• Application Number:
  US04/769,051
• Time in Patent Office: 1,618 Days
• Field of Search: 179/2TV 178/6.8,7,DIG.13 325/50
• US Class Current: 348/14.13
• CPC Class Codes: H04N 7/141 between two video terminals, e.g. videophone telephonic communication systems combined with television receiver for reception of entertainment or information matter H04M11/085
• CPC Class Codes: H04N 7/148 Interfacing a video terminal to a particular transmission medium, e.g. ISDN
• CPC Class Codes: H04N 7/15 Conference systems

Abstract

A television telephone system, wherein frequency-modulation with a low modulation index is effected by using a carrier wave of a slightly higher frequency than the maximum frequency of a video signal, and the video signal thus modulated is transmitted through a transmission line. With such system, a wide band video signal and audio signal can be transmitted without cross talk and distortion by using an ordinary telephone cable which is intended to be used only for the transmission of voice frequency signals, and communication can be achieved, with the image of the opposite party or drawing, document or the like being viewed.

Claims

1. A television-telephone system, comprising, in combination:

a conventional telephone transmission line having a narrow band transmission characteristic;

means for generating a video signal;

means for generating a carrier wave signal having a higher frequency than the maximum frequency of said video signal and having a frequency such that the upper side band portion thereof is substantially the only portion of said carrier wave which is not transmittable through said transmission line;

means for frequency modulating said carrier wave by said video signal with a low index of modulation;

means for transmitting said modulated carrier wave through said transmission line, except for said upper side band portion;

frequency demodulating means for demodulating said transmitted modulated carrier wave;

means connecting voice and video reception lines of at least three television-telephone instruments in parallel with each other;

means generating a tone burst signal and transmitting same through said transmission line;

means connected to said video transmission and reception lines for detecting said tone burst signal; and

means for preventing the switching of said video signal by the generation of said tone burst signal by a voice signal, said preventing means including means generating a continuous tone, whereby said video signal is transmitted through and reProduced from said conventional narrow band telephone transmission line.

2. A television-telephone system, comprising, in combination:

a conventional telephone transmission line having a narrow band transmission characteristic;

means for generating a video signal;

means for generating a carrier wave signal having a higher frequency than the maximum frequency of said video signal and having a frequency such that the upper side band portion thereof is substantially the only portion of said carrier wave which is not transmittable through said transmission line;

means for frequency modulating said carrier wave by said video signal with a low index of modulation;

means for transmitting said modulated carrier wave through said transmission line, except for said upper side band portion;

frequency demodulating means for demodulating said transmitted modulated carrier wave;

means to reverse polarity at the transmitting and receiving stations of said system upon completion of a polarity connection of a D.C. power source supplied from an exchange to a voice line;

means to view the image of a calling party prior to the completion of said connection; and

means to thereafter view the image of a called party, whereby said video signal is transmitted through and reproduced from said conventional narrow band telephone transmission line.

3. A television-telephone system, comprising, in combination:

a conventional telephone transmission line having a narrow band transmission characteristic;

means for generating a video signal;

means for generating a carrier wave signal having a higher frequency than the maximum frequency of said video signal and having a frequency such that the upper side band portion thereof is substantially the only portion of said carrier wave which is not transmittable through said transmission line;

means for frequency modulating said carrier wave by said video signal with a low index of modulation;

means for transmitting said modulated carrier wave through said transmission line, except for said upper side band portion;

frequency demodulating means for demodulating said transmitted modulated carrier wave;

separate two-wire telephone cables for each of two directions of transmission and reception of said video information and a further two-wire line for said voice signal;

means to reverse polarity at the transmitting and receiving stations of said system upon completion of a polarity connection to a D.C. power source supplied from an exchange to a voice line;

means to view the image of a calling party prior to the completion of said connection; and

means to thereafter view the image of a called party, whereby said video signal is transmitted through and reproduced from said conventional narrow band telephone transmission line.