IE38407B1 - Add-on tv system - Google Patents

Abstract

1384970 Television; multiplex systems HAZELTINE RESEARCH Inc 10 July 1973 [30 Oct 1972] 32840/73 Headings H4F and H4L A system for compatibly transmitting and receiving both a television signal (preferably colour television signal, e.g. NTSC or PAL type signal), and one (or more) additional information (add-on) signal within the same frequency band normally occupied by the television signal alone. wherein the additional information is transmitted preferably within the portion of the frequency band lying between the normal location of the luminance and chrominance carrier frequencies, the add-on signal information elements transmitted on each alternate line period being repeated in the adjacent intervening line period but with opposite polarity so that by processing (e.g. subtracting by inverting and integrating), successively received pairs of line signals the add-on signal information elements reinforce each other while the television video information tends to cancel. In addition when the composite received signal is displayed the opposite polarity add-on information tends to visually cancel. One or more elements of addition information may be transmitted during each pair of line intervals. Instead of inverting the polarity of the repeated add-on signals during the intervening lines, the add-on signals and repeated add-on signals may be phase modulated on a carrier having a frequency which is an odd multiple of one half of the frequency of the television line frequency. The additional information may comprise different language translations for multilanguage television transmissions, or answers to questions in educational television transmissions. [GB1384970A]