Apparatus for processing modified NTSC television signals, with digital signals buried therewithin

A system for transmitting a video carrier the amplitude of which is modulated in accordance with a composite video signal descriptive of image frames scanned with successive scan lines occurring at a prescribed scan line frequency, said composite video signal comprising a baseband luminance signal and a color subcarrier modulated by color difference signal components, said system for transmitting being improved to further comprise:

• means for transmitting, together with said video carrier the amplitude of which is modulated in accordance with said composite video signal, digital information encoded in phase-shift keying of a PSK subcarrier of a suppressed carrier having the same frequency as said video carrier,
• wherein said means for transmitting digital information encoded in phase-shift keying of a PSK subcarrier of a suppressed carrier having the same frequency as said video carrier comprises:
• means for supplying said digital information as a succession of samples of a modulating signal, each having a respective value that is of a prescribed level respective to a zero level and that has a respective polarity;
• means for supplying respective carrier waves of first and second frequencies, the difference between which is an odd multiple of half said prescribed scan line frequency;
• a balanced modulator for modulating the amplitude of said carrier wave of said first frequency in accordance with the successive samples of said modulating signal, thereby generating a double-sideband phase-shift-keyed carrier wave of said first frequency;
• a sideband selection filter connected for receiving said double-sideband phase-shift-keyed carrier wave of said first frequency, the output signal of said sideband selection filter responding to only a single sideband of said double-sideband phase-shift-keyed carrier wave of said first frequency;
• a mixer for supplying a mixer output signal, said mixer output signal including a low-frequency band component containing frequencies that correspond to differences between the frequencies of said sideband selection filter output signal and said carrier wave of said second frequency received by said mixer as respective mixer input signals, and said mixer output signal further including a high-frequency band component containing frequencies that correspond to sums of the frequencies of said sideband selection filter output signal and said carrier wave of said second frequency received by said mixer as respective mixer input signal;
• a lowpass filter connected for receiving said mixer output signal and supplying response to said low-frequency band component thereof as said subcarrier;
• and
• means for modulating the amplitude of said suppressed carrier having the same frequency as said video carrier, in accordance with the response of said lowpass filter to said low-frequency band component of said mixer output signal.

A system for transmitting a video carrier the amplitude of which is modulated in accordance with a composite video signal descriptive of image frames scanned with successive scan lines occurring at a prescribed scan line frequency, said composite video signal comprising a baseband luminance signal and a color subcarrier modulated by color difference signal components, said system for transmitting being improved to further comprise:

• means for transmitting, together with said video carrier the amplitude of which is modulated in accordance with said composite video signal, digital information encoded in phase-shift keying of a PSK subcarrier of a suppressed carrier having the same frequency as said video carrier,
• wherein said means for transmitting digital information encoded in phase-shift keying of a PSK subcarrier of a suppressed carrier having the same frequency as said video carrier comprises:
• means for supplying said digital information as a succession of samples of a modulating signal, each having a respective value that is of a prescribed level respective to a zero level and that has a respective polarity;
• means for generating the Hilbert transform of said digital information;
• means for supplying respective carrier waves of first and second frequencies, the difference between which is an odd multiple of half said prescribed scan line frequency, including:
• means for supplying said first carrier wave of said first frequency in first and second phases that are in quadrature with each other;
• a first balanced modulator for modulating the amplitude of said carrier wave of said first frequency and said first phase, in accordance with the successive samples of said modulating signal, thereby generating a first double-sideband phase-shift-keyed carrier wave of said first frequency;
• a second balanced modulator for modulating the amplitude of said carrier wave of said first frequency and said second phase, in accordance with said Hilbert transform of said digital information, thereby generating a second double-sideband phase-shift-keyed carrier wave of said first frequency;
• means for combining said first and second double-sideband phase-shift-keyed carrier waves of said first frequency, thereby to obtain a single-sideband phase-shift-keyed carrier wave of said first frequency;
• a mixer for supplying a mixer output signal, said mixer output signal including a low-frequency band component containing frequencies that correspond to differences between the frequencies of said single-sideband phase-shift-keyed carrier wave of said first frequency and said carrier wave of said second frequency received by said mixer as respective mixer input signals, and said mixer output signal further including a high-frequency band component containing frequencies that correspond to sums of the frequencies of said single-sideband phase-shift-keyed carrier wave of said first frequency and said carrier wave of said second frequency received by said mixer as respective mixer input signal;
• a lowpass filter connected for receiving said mixer output signal and supplying response to said low-frequency band component thereof as said subcarrier;
• and
• means for modulating the amplitude of said suppressed carrier having the same frequency as said video carrier, in accordance with the response of said lowpass filter to said low-frequency band component of said mixer output signal.

A system for detecting symbols encoded in a PSK subcarrier buried in a composite video signal descriptive of image frames scanned with successive scan lines occurring at a prescribed scan line frequency and being repeated from time to time in a known pattern of repetition, said composite video signal comprising a baseband luminance signal and a color subcarrier modulated by color difference signal components, said system for detecting symbols encoded in a PSK subcarrier buried in a composite video signal comprising:

• means for detecting portions of said composite video signal in which said PSK subcarrier is buried, thereby to generate a first detected signal;
• a comb filter, responding to said first detected signal during a first set of time intervals in its response for enhancing said PSK subcarrier vis-a-vis remnant portions of said composite video signal in which said PSK subcarrier is buried, and responding to said first detected signal during a second set of time intervals in its response with extraneous comb filter response arising because of said repetition of the PSK carrier in accordance with said known pattern;
• rate buffering circuitry for converting response from said comb filter during said first set of time intervals to a continuous flow of rate-buffered PSK subcarrier, without said repetition in accordance with said known pattern;
• and
• means for synchronously detecting at symbol rate the phase-shift keying of said flow of rate-buffered PSK subcarrier, thereby generating a synchronous detection output signal.

A system for detecting symbols descriptive of digital data encoded in a digital subcarrier of a video carrier, the amplitude of said video carrier being modulated in accordance with a composite video signal descriptive of image frames scanned with successive scan lines occurring at a prescribed scan line rate, said composite video signal comprising a baseband luminance signal and a color subcarrier modulated by color difference signal components, said digital data being encoded with a symbol rate that is a multiple of said prescribed scan line rate and occurring in consecutive data lines occurring at said prescribed scan line rate, the symbols descriptive of data in each alternate one of said consecutive data lines repeating in opposite sense the symbols in the previous data line, said system for detecting symbols comprising:

• a detector generating a first detected signal by detecting an amplitude of portions of a frequency spectrum containing at least a portion of said composite video signal including said color subcarrier as modulated by said color difference signal components, which said frequency spectrum further contains said digital data encoded in said digital subcarrier of said video carrier;
• and
• a line-comb filter for differentially combining during said alternate data lines said first detected signal and that signal as delayed by the duration of one scan line, for recovering said symbols descriptive of data with reduction of accompanying said color subcarrier as modulated by said color difference signal components.