Receivers for digital signals buried within the trace and retrace intervals of NTSC television signals

A receiver for receiving a data signal transmitted simultaneously with a television signal through the same television transmission channel;

• said television signal comprising a video carrier the amplitude of which is modulated in accordance with a video signal descriptive of the scanning of a succession of image frames as scanned one scan line after another at a prescribed video line rate, said image frames occurring at a prescribed video frame rate;
• said data signal modulating at least a first phasing of a suppressed data carrier having a frequency differing from that of said video carrier by a prescribed offset frequency and having no image on the other side of said video carrier;
• said data signal having a symbol rate that is a multiple of said prescribed video line rate, and having data frames occurring at a data frame rate that is the same as said video frame rate;
• said receiver comprising:
• a tuner for selecting a television transmission channel and converting a data signal and a television signal transmitted simultaneously therethrough to an intermediate-frequency data signal and an intermediate-frequency television signal;
• intermediate-frequency amplifier circuitry for supplying amplified responses to said intermediate-frequency data signal and said intermediate-frequency television signal;
• a local oscillator having the frequency of its oscillations synchronized to an intermediate-frequency video carrier component of said intermediate-frequency television signal;
• a video detector responsive to said intermediate-frequency television signal for supplying a baseband video signal;
• a horizontal sync separator for separating horizontal scan synchronizing pulses from said baseband video signal;
• a vertical sync separator for separating vertical scan synchronizing pulses from said baseband video signal;
• a first locked oscillator for generating first oscillations at a frequency that is a multiple of the frequency of said horizontal scan synchronizing pulses separated by said horizontal sync separator;
• a symbol-per-row counter for counting selected average-axis crossings of said first oscillations to generate a symbol-per-row count, said symbol-per-row counter being reset to an initial symbol-per-row count responsive to each horizontal scan synchronizing pulse separated by said horizontal sync separator;
• an end-of-line decoder for determining when said symbol-per-row count reaches a value associated with the ends of horizontal scan lines to generate end-of-line indications;
• a data row counter for counting said end-of-line indications to generate a data row count;
• circuitry for determining when said symbol-per-row count reaches a value associated with the ends of horizontal scan lines at the same time that one of said vertical scan synchronizing pulses is separated by said vertical sync separator, to generate end-of-frame indications used to reset said data row counter to a prescribed data row count;
• a data frame counter for counting said end-of-frame indications to generate a data frame count having a bit indicative of whether data frames are odd or are even;
• a second locked oscillator for generating second oscillations at a frequency that is one-half an odd multiple of the frequency of said horizontal scan synchronizing pulses separated by said horizontal sync separator;
• a mixer for multiplicatively mixing said first oscillations and said second oscillations to generate a mixer output signal including as one of its components a regenerated data carrier;
• a data carrier separation filter for selecting said first phasing of said regenerated data carrier from the other components of said mixer output signal;
• a first synchronous detector for synchronously detecting said amplified response to said intermediate-frequency data signal in accordance with said first phasing of the regenerated data carrier separated by said data carrier separation filter, to generate a first synchronous detector response;
• first analog-to-digital conversion circuitry responsive to said first synchronous detector response to generate a digitized first synchronous detector response;
• and
• a first data separation filter responsive to said digitized first synchronous detector response to generate a first separated data response, said first data separation filter including a first highpass digital frame-comb filter for said digitized first synchronous detector response, a response from which first highpass digital frame-comb filter is used for providing said first separated data response.

A receiver for receiving a data signal transmitted simultaneously with a television signal through the same television transmission channel;

• said television signal comprising a video carrier the amplitude of which is modulated in accordance with a video signal descriptive of the scanning of a succession of image frames as scanned one scan line after another at a prescribed video line frequency and in accordance with line- and frame-synchronizing pulses for said scanning, said image frames occurring at a prescribed video frame rate;
• said data signal modulating at least a first phasing of a suppressed data carrier having a frequency differing from that of said video carrier by a prescribed offset frequency, and having no image on the other side of said video carrier, to generate amplitude-modulation sidebands of said suppressed data carrier;
• said data signal having a symbol rate that is a multiple of said prescribed video line rate, having data frames occurring at a data frame rate that is the same as said video frame rate, and being at all times relatively small in amplitude compared to the line- and field-synchronizing pulses of said television signal;
• said receiver comprising:
• amplitude detection circuitry for generating a digitized response to variations of amplitude within a portion of said same television transmission channel occupied by said suppressed data carrier and at least a portion of the frequency spectrum of said television signal, said generating performed without relying on video detection of said television signal, so said digitized response includes digitized data signal and digitized unwanted cross-products of said data carrier and said at least a portion of the frequency spectrum of said television signal;
• comb filter circuitry for receiving said digitized response to variations of amplitude within said portion of said same television transmission channel and generating a comb filter response thereto, which comb filter response is relatively sensitive to said digitized data signal and relatively insensitive to said digitized unwanted cross-products, and which comb filter response at least at times contains digitized data samples that are multiple-level in form with more levels than the digitized data signal component of said digitized response to variations of amplitude within said portion of said same television transmission channel received by said comb filter circuitry;
• symbol decision circuitry of a type for responding to said digitized data samples that are multiple-level in form, receiving said comb filter response and supplying a symbol stream in response thereto;
• and
• a partial response filter responsive to said symbol stream to reproduce said data signal, said partial response filter providing filtering complementary to the filtering of said digitized data signal done by said comb filter circuitry.

A receiver for receiving a data signal transmitted simultaneously with a television signal through the same television transmission channel;

• said television signal comprising a video carrier the amplitude of which is modulated in accordance with a video signal descriptive of the scanning of a succession of image frames as scanned one scan line after another at a prescribed video line frequency and in accordance with line- and frame-synchronizing pulses for said scanning, said image frames occurring at a prescribed video frame rate;
• said data signal modulating at least a first phasing of a suppressed data carrier having a frequency differing from that of said video carrier by a prescribed offset frequency, and having no image on the other side of said video carrier, to generate amplitude-modulation sidebands of said suppressed data carrier;
• said data signal having a symbol rate that is a multiple of said prescribed video line rate, having data frames occurring at a data frame rate that is the same as said video frame rate;
• said receiver comprising:
• amplitude detection circuitry for generating a digitized response to variations of amplitude within a portion of said same television transmission channel occupied by said suppressed data carrier and at least a portion of the frequency spectrum of said television signal, said generating performed without relying on video detection of said television signal, so said digitized response includes digitized data signal and digitized unwanted cross-products of said data carrier and said at least a portion of the frequency spectrum of said television signal;
• comb filter circuitry for receiving said digitized response to variations of amplitude within said portion of said same television transmission channel and generating a comb filter response thereto, which comb filter response is relatively sensitive to said digitized data signal and relatively insensitive to said digitized unwanted cross-products, said comb filter circuitry having a signal path therethrough which passes through a highpass line-comb filter and other comb filtering in consequence of which said comb filter response is multiple-level in form with more levels than the digitized data signal component of said digitized response to variations of amplitude within said portion of said same television transmission channel received by said comb filter circuitry;
• and
• decoder circuitry of a type for responding to said digitized data samples that are multiple-level in form with more levels than the digitized data signal component of said digitized response to variations of amplitude within said portion of said same television transmission channel received by said comb filter circuitry, receiving said comb filter response and reproducing said data signal in response thereto.

A receiver for receiving a data signal transmitted simultaneously with a television signal through the same television transmission channel;

• said television signal comprising a video carrier the amplitude of which is modulated in accordance with a video signal descriptive of the scanning of a succession of image frames as scanned one scan line after another at a prescribed video line rate and in accordance with line- and frame-synchronizing pulses for said scanning, said image frames occurring at a prescribed video frame rate;
• said data signal modulating at least a first phasing of a suppressed data carrier having a frequency differing from that of said video carrier by a prescribed offset frequency, and having no image on the other side of said video carrier, to generate amplitude-modulation sidebands of said suppressed data carrier;
• said data signal having a symbol rate that is a multiple of said prescribed video line rate, having data frames occurring at a data frame rate that is the same as said video frame rate;
• said receiver comprising:
• amplitude detection circuitry for generating a digitized response to variations of amplitude within a portion of said same television transmission channel occupied by said suppressed data carrier and at least a portion of the frequency spectrum of said television signal, said generating performed without relying on video detection of said television signal, so said digitized response includes digitized data signal and digitized unwanted cross-products of said data carrier and said at least a portion of the frequency spectrum of said television signal;
• comb filter circuitry for receiving said digitized response to variations of amplitude within said portion of said same television transmission channel and generating a comb filter response thereto, which comb filter response is relatively sensitive to said digitized data signal and relatively insensitive to said digitized unwanted cross-products, said comb filter circuitry having a signal path therethrough which passes through a highpass frame-comb filter and other comb filtering in consequence of which said comb filter response is multiple-level in form with more levels than the digitized data signal component of said digitized response to variations of amplitude within said portion of said same television transmission channel received by said comb filter circuitry;
• and
• decoder circuitry of a type for responding to said digitized data samples that are multiple-level in form with more levels than the digitized data signal component of said digitized response to variations of amplitude within said portion of said same television transmission channel received by said comb filter circuitry, receiving said comb filter response and reproducing said data signal in response thereto.