A HDTV system compatible with NTSC is accomplished by employing two channels for transmitting data. Since the channel I has low spatial definition+high time definition and the channel II has high spatial definition+low time definition, associating the channel I with the channel II produces high spatial...http://www.google.ca/patents/US5247351?utm_source=gb-gplus-sharePatent US5247351 - High definition television system compatible with NTSC system
