Transmitters for burying digital signals within the trace and retrace intervals of NTSC television signals

• US 5,555,024 A
• Filed: 09/07/1995
• Issued: 09/10/1996
• Est. Priority Date: 12/23/1994
• Status: Expired due to Term

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Limberg, Allen L.
• Primary Examiner(s): Kostak, Victor R.
• Assistant Examiner(s): Flynn, Nathan J.
• Application Number:
  US08/524,488
• Time in Patent Office: 369 Days
• Field of Search: 348/486, 348/478, 348/473, 348/436, 348/435, 348/434
• US Class Current: 348/473
• CPC Class Codes: H04H 20/31 using in-band signals, e.g. subsonic or cue signal
• CPC Class Codes: H04N 7/08 Systems for the simultaneous or sequential transmission of more than one television signal, e.g. additional information signals, the signals occupying wholly or partially the same frequency band , e.g. by time division H04N7/007 takes precedence
• CPC Class Codes: H04N 7/0803 using frequency interleaving, e.g. with precision offset

Abstract

An NTSC television signal transmitter also transmits through the same transmission channel a suppressed data carrier having a frequency differing from that of video carrier, having a symbol rate that is a multiple of horizontal scanning rate of video signal, having data frames occurring at a data frame rate that is the same as the video frame rate, and transmitting the symbols transmitted in each of alternate data frames in opposite phase during the next data frame. The data carrier has no image on the other side of the video carrier and preferably its modulation spectrum overlaps the video carrier. A digital-signal receiver can recover data from such a data carrier buried in an NTSC television signal, using frame-comb filtering to separate data from interfering video signal.

Claims

1. 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, or scan line frequency;

said image frames occurring at a prescribed video frame rate;

said data signal modulating a data carrier having a frequency differing from that of said video carrier by a prescribed frequency offset, 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, having data frames occurring at a data frame rate that is the same as said video frame rate, and customarily having each of the symbols in said data signal that are transmitted in each of alternate data frames being transmitted again but in opposite phase during the next data frame.

2. A data signal as set forth in claim 1, wherein said prescribed offset in frequency from said video carrier is one-half an odd multiple of said prescribed scan line frequency.

3. A method for operating a transmitter for transmitting a data signal and a television signal simultaneously through the same television transmission channel, said method comprising the steps of:

generating said television signal, which step includes substeps of

generating a video carrier and

modulating the amplitude of said video carrier 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, or scan line frequency, said image frames occurring at a prescribed video frame rate;

generating a suppressed data carrier, having a frequency differing from that of said video carrier by a prescribed frequency offset, and having no image on the other side of said video carrier;

generating amplitude modulation sidebands of said data carrier in response to said data signal; and

generating said data signal so as to have a symbol rate that is a multiple of said prescribed video line rate, so as to have data frames occurring at a data frame rate that is the same as said video frame rate, and so as customarily to have each of the symbols in said data signal that are transmitted in each of alternate data frames by modulation of said suppressed data carrier transmitted again but in opposite phase during the next data frame.

31. A method as set forth in claim 3, wherein said steps of generating a suppressed data carrier and generating amplitude modification sidebands of said data carrier are carried out by phase-shift keying of said data carrier in response to said data signal.

35. A method as set forth in claim 3, wherein said prescribed offset in frequency from said video carrier places said data carrier above said video carrier in frequency, and wherein said phase shift keying of said data carrier is binary phase shift keying in which said step of generating amplitude modulation sidebands of said data carrier in response to said data signal includes substeps of:

generating a lower sideband of the binary phase-shift-keyed data carrier, and

suppressing most of an upper sideband of said binary phase-shift-keyed data carrier.

36. A method as set forth in claim 35, wherein said step of generating said television signal includes the further substep of

generating a chroma subcarrier of said video carrier, which chroma subcarrier is subject to modulation by chrominance signals, and wherein said prescribed offset in frequency from said video carrier places said data carrier between said video carrier and said chroma subcarrier in frequency, at a frequency sufficiently removed from the frequency of said chroma subcarrier that most sideband energy of said data carrier arising from its modulation is below most of the sideband energy of said chroma subcarrier, to avoid interference with modulation of said chroma subcarrier by chrominance signals.

40. A method as set forth in any one of claims 31 and 32-39, wherein said prescribed offset in frequency from said video carrier is one-half an odd multiple of said prescribed scan line frequency.

4. A transmitter for transmitting a data signal and a television signal simultaneously 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, or scan line frequency;

said image flames occurring at a prescribed video frame rate;

said data signal modulating a suppressed data carrier having a frequency differing from that of said video carrier by a prescribed frequency offset, 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, having data frames occurring at a data frame rate that is the same as said video frame rate, and having each of the symbols of said data signal that are transmitted in each of alternate data frames being customarily transmitted in opposite phase during the next data frame;

said transmitter comprising;

a station sync generator for generating horizontal synchronizing pulses at a prescribed time in each scan line of said video signal and for generating vertical synchronizing pulses at a prescribed time in each field of said video signal;

an amplitude modulator for generating amplitude-modulation sidebands of said video carrier in accordance with said video signal, said horizontal synchronizing pulses, and said vertical synchronizing pulses;

a first symbol clocking signal generator receiving said horizontal synchronizing pulses as a control signal and generating first symbol clocking signals, which said first symbol clocking signals are supplied at a first symbol rate locked in frequency and phase to a multiple of said prescribed video line rate;

a modulo-two frame counter for counting selected ones of said vertical synchronizing pulses to provide a modulo-two frame count defining data frames as being odd or even;

a frame repeater receptive of bits of data for supplying in bit-serial format a data frame of said bits at said first symbol rate during each odd data frame and for supplying in bit-serial format an identical data frame of said bits at said first symbol rate during the next even data frame;

an exclusive-OR gate, receiving as a first input signal thereto the bits supplied at said first symbol rate from said frame repeater, receiving as a second input signal thereto said modulo-two frame count, and generating an exclusive-OR gate response;

phase shift keying circuitry for generating amplitude-modulation sidebands of said suppressed data carrier in accordance with exclusive-OR gate response; and

a frequency multiplexer, receiving at least a portion of the amplitude-modulation sidebands of said video carrier as a first input signal thereof, receiving at least a portion of the amplitude-modulation sidebands of said suppressed data carrier as a second input signal thereof, and supplying an output signal combining its first and second input signals for simultaneous transmission through the same television transmission channel.

5. A transmitter as set forth in claim 4 further comprising:

a forward error correction coder receptive of digital signal for generating data in forward error correction coded form; and

means for interleaving said data in forward error correction coded form for use by said frame repeater.

6. A transmitter as set forth in claim 5 wherein said frame repeater and said means for interleaving said data in forward error correction coded form for use by said frame repeater together comprise:

a second symbol clocking signal generator receiving said first symbol clocking signals as a control signal and generating second symbol clocking signals, which said second symbol clocking signals are supplied at a second symbol rate that is one-half said first symbol rate;

a symbol-per-column counter counting at said second symbol rate to generate a symbol-per-column count, reset at the beginning of each data frame and after every m^th count, where m is the number of scan lines of said video signal per frame thereof;

a data column counter, reset at the beginning of each data frame and counting the number of times said symbol-per-column counter is reset in each data frame to generate a data column count, said data column count and said symbol-per-column count together providing a write address signal;

a symbol-per-row counter counting at said first symbol rate to generate a symbol-per-row count, reset at the beginning of each data frame and after every n^th count, where n is the number of symbols per scan line of said video signal;

a data row counter, reset at the beginning of each data frame and counting the number of times said symbol-per-row counter is reset in each data frame to generate a data row count, said data row count and said symbol-per-row count together providing a read address signal;

a modulo-two frame-pair counter stage for counting successive non-overlapping pairs of frames to generate a modulo-two frame-pair count;

an address multiplexer controlled by said modulo-two frame-pair count for selecting as first and second output signals therefrom separate ones of said write address and said read address signals supplied as first and second input signals thereto, said address multiplexer responding to said modulo-two frame-pair count being a ONE for selecting said read address signal as said first output signal therefrom and said write address signal as said second output signal therefrom, and said address multiplexer responding to said modulo-two frame-pair count being a ZERO for selecting said write address signal as said first output signal therefrom and said read address signal as said second output signal therefrom;

a first framestore random-access memory addressed by the first output signal from said address multiplexer, conditioned for being written by said data in forward error correction coded form when said modulo-two frame-pair count is ZERO, and conditioned for reading said data in interleaved forward error correction coded form to said exclusive-OR gate as its said first input signal when said modulo-two frame-pair count is ONE; and

a second framestore random-access memory addressed by the first output signal from said address multiplexer, conditioned for being written by said data in forward error correction coded form when said modulo-two frame-pair count is ONE, and conditioned for reading said data in interleaved forward error correction coded form to said exclusive-OR gate as its said first input signal when said modulo-two frame-pair count is ZERO.

7. A transmitter as set forth in claim 4, 5 or 6, wherein said prescribed offset in frequency from said video carrier is one-half an odd multiple of said prescribed scan line frequency.

8. A transmitter as set forth in claim 4, 5 or 6, wherein said phase shift keying circuitry is of a type for generating amplitude-modulation sidebands of an in-phase data carrier for a first set of data symbols and amplitude-modulation sidebands of a quadrature-phase data carrier for a second set of data symbols.

9. A transmitter as set forth in claim 8, wherein said prescribed offset in frequency from said video carrier is one-half an odd multiple of said prescribed scan line frequency.

10. A transmitter as set forth in claim 9, wherein said video carrier has a chroma subcarrier subject to modulation by chrominance signals;

and wherein said prescribed offset in frequency from said video carrier places said data carrier between said video carrier and said chroma subcarrier in frequency, at a frequency sufficiently removed from the frequency of said chroma subcarrier that most sideband energy of said data carrier arising from its modulation is below most of the sideband energy of said chroma subcarrier to avoid interference with modulation of said chroma subcarrier by chrominance signals.

11. A transmitter as set forth in claim 9, wherein said video carrier has a chroma subcarrier subject to modulation by chrominance signals;

and wherein said prescribed offset in frequency from said video carrier places said data carrier between said video carrier and said chroma subcarrier in frequency, at a frequency sufficiently removed from the frequency of said chroma subcarrier that most sideband energy of said data carrier arising from its modulation is below most of the sideband energy of said chroma subcarrier to avoid interference with modulation of said chroma subcarrier by chrominance signals.

12. A transmitter as set forth in claim 4, 5 or 6, wherein said phase shift keying circuitry is of a type for generating an upper sideband of binary phase-shift-keyed data carrier and for suppressing most of a lower sideband of said binary phase-shift-keyed data carrier.

13. A transmitter as set forth in claim 12, wherein said prescribed offset in frequency from said video carrier is one-half an odd multiple of said prescribed scan line frequency.

14. A transmitter as set forth in claim 13, wherein said prescribed offset in frequency from said video carrier places said data carrier below said video carrier in frequency.

15. A transmitter as set forth in claim 12, wherein said prescribed offset in frequency from said video carrier places said data carrier below said video carrier in frequency.

16. A transmitter as set forth in claim 15, wherein said upper sideband of binary phase-shift-keyed data carrier occupies a frequency range extending above the frequency of said video carrier.

17. A transmitter as set forth in claim 4, 5 or 6, wherein said prescribed offset in frequency from said video carrier places said data carrier above said video carrier in frequency, and wherein said phase shift keying circuitry is of a type for generating a lower sideband of binary phase-shift-keyed data carrier and for suppressing most of an upper sideband of said binary phase-shift-keyed data carrier.

18. A transmitter as set forth in claim 17, wherein said prescribed offset in frequency from said video carrier is one-half an odd multiple of said prescribed scan line frequency.

19. A transmitter as set forth in claim 17, wherein said video carrier has a chroma subcarrier subject to modulation by chrominance signals;

and wherein said prescribed offset in frequency from said video carrier places said data carrier between said video carrier and said chroma subcarrier in frequency, at a frequency sufficiently removed from the frequency of said chroma subcarrier that most sideband energy of said data carrier arising from its modulation is below most of the sideband energy of said chroma subcarrier to avoid interference with modulation of said chroma subcarrier by chrominance signals, but at a frequency closer to the frequency of said chroma subcarrier than to the frequency of said video carrier.

41. A transmitter as set forth in claim 12, wherein the frequencies of a first set of said amplitude-modulation sidebands of said video carrier and the frequencies of a second set of said amplitude-modulation sidebands of said video carrier are on opposite sides of the frequency of said video carrier, wherein the frequencies of the second set of said amplitude-modulation sidebands of said video carrier more remote from the frequency of said video carrier are suppressed by filtering to leave vestigial sideband amplitude modulation, and wherein said prescribed offset in frequency from said video carrier places the frequency of said data carrier on the same side of the frequency of said video carrier as said second of said amplitude-modulation sidebands of said video carrier.

20. A system for transmitting a modulated video carrier and a modulated data carrier over a common transmission channel, 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 or scan line frequency, said composite video signal comprising a baseband luminance signal and a color subcarrier modulated by color difference signal components, each said image frame comprising a prescribed integral number at least one of image fields, said system comprising:

a sync generator for generating horizontal scan synchronization signals at a prescribed interval in each of said successive scan lines occurring at said prescribed scan line rate, for generating vertical synchronization signals at prescribed intervals in said image frames, for generating data frame synchronization signals, for generating first symbol clock signals at a first symbol clock rate that is a multiple over a hundred of said prescribed scan line rate, and for generating data column synchronization signals;

a video carrier generator for generating said video carrier;

a vestigial-sideband amplitude-modulation transmitter for modulating the amplitude of said video carrier in accordance with said composite video signal and supplying a resulting vestigial-sideband amplitude-modulated video carrier for transmission over said common transmission channel;

a data carrier generator for generating said data carrier with a prescribed offset in frequency from said video carrier;

phase shift keying circuitry for phase shift keying said data carrier in accordance with a processed data signal and supplying a resulting phase-shift-keyed data carrier for transmission over said common transmission channel;

a source of data with forward error correction coding, supplied in a bit stream;

a rate buffer for receiving said bit stream for temporary storage and clocking the bits of said bit stream out of said rate buffer during alternate image frames at said first symbol clock rate in response to said first symbol clock signals generated by said sync generator;

a frame repeater receptive of the bits of said bit stream clocked out of said rate buffer during alternate image frames at said first symbol clock rate, for repeating the bits of said bit stream clocked out of said rate buffer during alternate data frames during the respective frames immediately following each of said alternate data frames;

logic for bit-complementing the bits in every other data frame supplied from said frame repeater, thereby generating said processed data signal supplied to said phase shift keying circuitry.

21. A system for transmitting a modulated video carrier and a modulated data carrier over a common transmission channel, as set forth in claim 20, wherein said prescribed offset in frequency from said video carrier is one-half an odd multiple of said prescribed scan line frequency.

22. A transmitter as set forth in claim 20 or 21, wherein said phase shift keying circuitry is of a type for generating amplitude-modulation sidebands of an in-phase data carrier and amplitude-modulation sidebands of a quadrature-phase data carrier.

23. A transmitter as set forth in claim 22, wherein said prescribed offset in frequency from said video carrier places said data carrier between said video carrier and said chroma subcarrier in frequency, at a frequency sufficiently removed from said chroma subcarrier to avoid interference with its said modulation by chrominance signals.

24. A transmitter as set forth in claim 20 or 21, wherein said phase shift keying circuitry is of a type for generating an upper sideband of binary phase-shift-keyed data carrier and for suppressing most of a lower sideband of said binary phase-shift-keyed data carrier.

25. A transmitter as set forth in claim 24, wherein said prescribed offset in frequency from said video carrier places said data carrier below said video carrier in frequency.

26. A transmitter as set forth in claim 25, wherein said upper sideband of binary phase-shift-keyed data carrier occupies a frequency range extending above the frequency of said video carrier.

27. A transmitter as set forth in claim 20 or 21, wherein said prescribed offset in frequency from said video carrier places said data carrier above said video carrier in frequency, and wherein said phase shift keying circuitry is of a type for generating an lower sideband of binary phase-shift-keyed data carrier and for suppressing most of an upper sideband of said binary phase-shift-keyed data carrier.

28. A transmitter as set forth in claim 27, wherein said prescribed offset in frequency from said video carrier places said data carrier at a frequency sufficiently removed from said chroma subcarrier to avoid interference with its said modulation, but at a frequency closer to the frequency of said chroma subcarrier than to the frequency of said video carrier.

29. A system for transmitting a modulated video carrier and a modulated data carrier over a common transmission channel, the amplitude of said video carrier being modulated in accordance with a composite video signal descriptive of image frames scanned with successive video scan lines occurring at a prescribed video scan line frequency, said composite video signal comprising a baseband luminance signal and a color subcarrier modulated by color difference signal components, each said image frame comprising a prescribed integral number at least one of image fields, said system comprising:

a sync generator for generating horizontal scan synchronization signals at a prescribed interval in each of said successive video scan lines occurring at said prescribed video scan line rate, for generating vertical scan synchronization signals at a prescribed interval in each of said image fields, for generating data frame synchronization signals, for generating first symbol clock signals at a first symbol clock rate over a hundred times said prescribed video scan line rate, for generating second symbol clock signals at a second symbol clock rate that is one half said first symbol clock rate, and for generating data column synchronization signals at a rate that is a submultiple of said second symbol clock rate by a factor equal to the number of said successive scan lines in each frame, each of said data frame synchronization signals being generated concurrently with one of said horizontal scan synchronization signals and with one of said data column synchronization signals;

a video carrier generator for generating said video carrier;

a vestigial-sideband amplitude-modulation transmitter for modulating the amplitude of said video carrier in accordance with said composite video signal and supplying a resulting vestigial-sideband amplitude-modulated video carrier for transmission over said common transmission channel;

a data carrier generator for generating said data carrier with a prescribed offset in frequency from said video carrier;

phase shift keying circuitry for phase shift keying said data carrier in accordance with a processed data signal and supplying a resulting phase-shift-keyed data carrier for transmission over said common transmission channel;

a frame counter for counting said data frame synchronization signals to provide a modulo-four frame count, said modulo-four frame count having as a less significant bit thereof a modulo-two frame count defining image frames as being odd or even, and said modulo-four frame count having as a more significant bit thereof a modulo-two frame-pair count of successive non-overlapping pairs of frames;

a symbol-per-column counter, counting at said second symbol clock rate to generate a symbol-per-column count, and being reset to an initial count thereof in response to each of said data column synchronization signals;

a data column counter, counting said data column synchronization signals to generate a data column count, and being reset to an initial count thereof in response to each of said data frame synchronization signals, said data column count and said symbol-per-column count together providing a write address signal;

a symbol-per-row counter, counting at said first symbol rate to generate a symbol-per-row count, and being reset to an initial count thereof in response to each of said horizontal scan synchronization signals;

a data row counter, counting the number of said horizontal scan synchronization signals in each data frame to generate a data row count, and being reset to an initial count thereof in response to each of said data frame synchronization signals, said data row count and said symbol-per-row count together providing a read address signal;

a source of forward-error-correction-coded data, supplied in a first bit stream clocked at said second symbol clock rate;

an exclusive-OR gate connected for receiving as a first input signal thereto a second bit stream clocked at said first symbol clock rate, receiving as a second input signal thereto said modulo-two frame count, and supplying an exclusive-OR gate response to said phase shift keying circuitry as said processed data signal;

an address multiplexer controlled by said modulo-two frame-pair count for selecting as first and second output signals therefrom separate ones of said write address and said read address signals supplied as first and second input signals thereto, said address multiplexer responding to said modulo-two frame-pair count being a ONE for selecting said read address signal as said first output signal therefrom and said write address signal as said second output signal therefrom, and said address multiplexer responding to said modulo-two frame-pair count being a ZERO for selecting said write address signal as said first output signal therefrom and said read address signal as said second output signal therefrom;

a first framestore random-access memory addressed by the first output signal from said address multiplexer, conditioned when said modulo-two frame-pair count is ZERO for being written with said forward-error-correction-coded data supplied in said first bit stream, and conditioned when said modulo-two frame-pair count is ONE for reading said forward-error-correction-coded data clocked at said first symbol clock rate to said exclusive-OR gate as its said first input signal; and

a second framestore random-access memory addressed by the first output signal from said address multiplexer, conditioned when said modulo-two frame-pair count is ONE for being written with said forward-error-correction-coded data supplied in said first bit stream, and conditioned when said modulo-two frame-pair count is ZERO for reading said forward-error-correction-coded data docked at said first symbol clock rate to said exclusive-OR gate as its said first input signal.

30. A system for transmitting a modulated video carrier and a modulated data carrier over a common transmission channel, as set forth in claim 29, wherein said prescribed offset in frequency from said video carrier is one-half an odd multiple of said prescribed scan line frequency.

32. A method for operating a transmitter for transmitting a data signal and a television signal simultaneously through the same television transmission channel, said method comprising the steps of:

generating said television signal, which step includes substeps of

generating a video carrier and

modulating the amplitude of said video carrier 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, or scan line frequency, said image frames occurring at a prescribed video frame rate;

generating a suppressed data carrier, having a frequency differing from that of said video carrier by a prescribed frequency offset, and having no image on the other side of said video carrier;

generating amplitude modulation sidebands of said data carrier by binary phase shift keying thereof in response to said data signal, which step of generating amplitude modulation sidebands of said data carrier includes substeps of

generating an upper sideband of the binary phase-shift-keyed data carrier, and

suppressing most of a lower sideband of said binary phase-shift-keyed data carrier; and

generating said data signal so as to have a symbol rate that is a multiple of said prescribed video line rate, so as to have data frames occurring at a data frame rate that is the same as said video frame rate, and so as customarily to have each of the symbols in said data signal that are transmitted in each of alternate data frames by modulation of said suppressed data carrier transmitted in opposite phase during the next data frame.

33. A method as set forth in claim 32, wherein said prescribed offset in frequency from said video carrier places said data carrier below said video carrier in frequency.

34. A method as set forth in claim 33, wherein said upper sideband of binary phase-shift-keyed data carrier occupies a frequency range extending above the frequency of said video carrier.

37. A method for operating a transmitter for transmitting a data signal and a television signal simultaneously through the same television transmission channel, said method comprising the steps of:

generating said television signal, which step includes substeps of

generating a video carrier and

modulating the amplitude of said video carrier 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, or scan line frequency, said image frames occurring at a prescribed video frame rate;

generating a suppressed data carrier, having a frequency differing from that of said video carrier by a prescribed frequency offset, and having no image on the other side of said video carrier;

generating amplitude modulation sidebands of said data carrier, which step includes substeps of

generating amplitude-modulation sidebands of an in-phase component of said data carrier in response to its phase-shift keying in response to a first set of data symbols from said data signal, and

generating amplitude-modulation sidebands of a quadrature-phase component of said data carrier in response to its phase-shift keying in response to a second set of data symbols from said data signal; and

generating said data signal so as to have a symbol rate that is a multiple of said prescribed video line rate, so as to have data frames occurring at a data frame rate that is the same as said video frame rate, and so as customarily to have each of the symbols in said dater signal that are transmitted in each of alternate data frames by modulation of said suppressed data carrier transmitted in opposite phase during the next data frame.

38. A method as set forth in claim 37, wherein said step of generating said television signal includes the further substep of

generating a chroma subcarrier of said video carrier, which chroma subcarrier is subject to modulation by chrominance signals, and wherein said prescribed offset in frequency from said video carrier places said data carrier between said video carrier and said chroma subcarrier in frequency, at a frequency sufficiently removed from the frequency of said chroma subcarrier to avoid interference with its said modulation by chrominance signals.

39. A method for operating a transmitter for transmitting a data signal and a television signal simultaneously through the same television transmission channel, said method comprising the steps of:

generating said television signal, which step includes substeps of

generating a video carrier,

generating an audio carrier to accompany said video carrier to be frequency-modulated by an audio signal, and

modulating the amplitude of said video carrier 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, or scan line frequency, said image frames occurring at a prescribed video frame rate;

generating a suppressed data carrier, having a frequency differing from that of said video carrier by a prescribed frequency offset, and having no image on the other side of said video carrier, the frequency of said video carrier being between the frequency of said audio carrier and the frequency of said data carrier;

generating amplitude modulation sidebands of said data carrier in response to said data signal; and

generating said data signal so as to have a symbol rate that is a multiple of said prescribed video line rate, so as to have data frames occurring at a data frame rate that is the same as said video frame rate, and so as customarily to have each of the symbols in said data signal that are transmitted in each of alternate data frames by modulation of said suppressed data carrier transmitted in opposite phase during the next data frame.