Scrambled video communication system

An encoder for a television communication system wherein a composite video signal is scrambled to prevent a stabilized picture from being displayed by a typical broadcast television set receiving the scrambled video signal, comprising

• means for offsetting the DC level of the reference color burst information in a composite video signal to a point nearly midway between the reference black and white levels of the video information;
• and for removing horizontal synchronizing pulses from the composite video signal to provide a scrambled video signal;
• a code word generator for generating a code word;
• and
• an insert circuit for inserting the code word in the scrambled video signal in regularly spaced positions that normally would be occupied by every nth one of the horizontal synchronizing pulses to thereby encode the scrambled video signal;
• wherein n is an integer greater than 1.

A decoder for a television communication system wherein a composite video signal is scrambled to prevent a stabilized picture from being displayed by a typical broadcast television set receiving the scrambled video signal by offsetting the DC level of the reference color burst information in a composite video signal to a point nearly midway between the reference black and white levels of the video information;

• and removing horizontal synchronizing pulses from the composite video signal and encoded to enable verification by generating a code word;
• and inserting the code word in the scrambled video signal in regularly spaced positions that normally would be occupied by every nth one of the horizontal synchronizing pulses to thereby encode the scrambled video signal, wherein n is an integer greater than 1;
• the decoder comprising
• a video detector for receiving the encoded scrambled video signal;
• a code module for storing a predetermined code word;
• a verification device for comparing the predetermined code word with code words in the received encoded scrambled video signal and for providing verification signals when the predetermined code word is detected in the encoded scrambled video signal;
• and
• means responsive to the verification signals for restoring horizontal synchronizing pulses in the received video signal, and for restoring the DC level of the reference color burst information in the received video signal to the back porch level of the restored synchronizing pulses, to thereby provide the decoded video signal, to thereby enable a stabilized picture to be displayed by a typical broadcast television set receiving the decoded video signal.

A television communication system wherein a composite video signal is scrambled to prevent a stabilized picture from being displayed by a typical broadcast television set receiving the scrambled video signal and encoded to enable verification, and wherein a received encoded scrambled video signal is verified and decoded to enable a stabilized picture to be displayed by a typical broadcast television set receiving the decoded video signal, comprising

• an encoder including
• a first circuit for offsetting the reference back porch level of the horizontal synchronizing pulses in a composite video signal to a point nearly midway between the reference black and white levels of the video information;
• and for removing horizontal synchronizing pulses from the composite video signal to provide a scrambled video signal;
• a code word generator for generating a code word;
• and
• an insert circuit for inserting the code word in the scrambled video signal in regularly spaced positions that normally would be occupied by every nth of one of the horizontal synchronizing pulses to thereby encode the scrambled video signal, wherein n is an integer greater than 1;
• a decoder including
• a video detector for receiving the encoded scrambled video signal;
• a code module for storing a predetermined code word;
• a verification device for comparing the predetermined code word with code words in the received encoded scrambled video signal and for providing verification signals when the predetermined code word is detected in the encode scrambled video signal;
• and
• a second circuit responsive to the verification signals for restoring horizontal synchronizing pulses in the received video signal, and for restoring the reference back porch level in the received video signal to the back porch level of the restored synchronizing pulses, to thereby provide the decoded video signal.

An encoder for a television communication system wherein a composite video signal is scrambled to prevent a stabilized picture from being displayed by a typical broadcast television set receiving the scrambled video signal, comprising

• means for offsetting the reference back porch level of the horizontal synchronizing pulses in a composite video signal to a point nearly midway between the reference black and white levels of the video information;
• and for removing horizontal synchronizing pulses from the composite video signal to provide a scrambled video signal;
• a code word generator for generating a code word;
• and
• an insert circuit for inserting the code word in the scrambled video signal in regularly spaced positions that normally would be occupied by every nth one of the horizontal synchronizing pulses to thereby encode the scrambled video signal, wherein n is an integer greater than 1.

A decoder for a television communication system wherein a composite video signal is scrambled to prevent a stabilized picture from being displayed by a typical broadcast television set receiving the scrambled video signal by offsetting the back porch level of the horizontal synchronizing pulses in a composite video signal to a point nearly midway between the reference black and white levels of the video information;

• and removing horizontal synchronizing pulses from the composite video signal and encoded to enable verification by generating a code word;
• and inserting the code word in the scrambled video signal in regularly spaced positions that normally would be occupied by every nth one of the horizontal synchronizing pulses to thereby encode the scrambled video signal, wherein n is an integer greater than 1;
• the decoder comprising
• a video detector for receiving the encoded scrambled video signal;
• a code module for storing a predetermined code word;
• a verification device for comparing the predetermined code word with code words in the received encoded scrambled video signal and for providing verification signals when the predetermined code word is detected in the encoded scrambled video signal;
• and
• means responsive to the verification signals for restoring horizontal synchronizing pulses in the received video signal, and for restoring the reference back porch level in the received video signal to the back porch level of the restored synchronizing pulses, to thereby provide the decoded video signal, to thereby enable a stabilized picture to be displayed by a typical broadcast television set receiving the decoded video signal.