Measurement of sc/h phase using a polar display

Claim 2

An instrument for use in indicating SC/H phase of a composite video signal, comprising a display device for providing a polar display, said display device including means (16, 18, 20, 24) for generating from the reference subcarrier burst of the video signal a first input signal for the display device such as to cause the display device to diplay an indication at a predetermined angular position of the polar display, and said instrument further comprising phase determining and indicating means (28, 30, 32; 46, 48, 50; 52, 54, 56; 58, 60, 62, 64) for determining the time difference between the sync point and that zero crossing of the extrapolated subcarrier wave which is closest to the sync point and for generating from said time difference a second input signal for the display device such as to cause the display device to display an indication at a position of the polar display that is angularly spaced from a predetermined axis of the polar display by an angle given by the fraction having as its denominator the period of the reference subcarrier wave and as its numerator the product of said time difference and 360 degrees.

Claim 3

An instrument according to claim 1, wherein said display device comprises a subcarrier regenerator (16) for regenerating from burst a continuous wave signal at subcarrier frequency and phase-locked to burst, and wherein the phase determining and indicating means comprise a sync detector (46) for generating a pulse at the sync point, a sampler (48) for sampling the regenerated subcarrier wave with the pulse generated by the sync detector and providing an output signal representative of the magnitude of the continuous wave at the sync point, and means (50) for converting said output signal into a signal representative of the angular position, within the reference subcarrier cycle, of the sync point.

Claim 4

An instrument according to claim 1, wherein the phase determining and indicating means comprise an oscillator (55) for generating a signal at subcarrier frequency and phase-locked to horizontal sync, and means (52, 54, 56) for determining the phase difference between burst and said signal at subcarrier frequency.

Claim 5

An instrument according to claim 1, wherein the phase determining and indicating means comprise an oscillator (55) for generating a signal at subcarrier frequency and phase-locked to horizontal sync, means (52) for generating a pulse at a predetermined zero crossing of burst, a sampler (54) for sampling said signal at subcarrier frequency with said sampling pulse and providing an output signal representative of the magnitude of the sampled signal at the sample point, and means (56) for converting said output signal into a signal representative of the angular position, within the reference subcarrier cycle, of the sync point.

Claim 6

An instrument according to claim 1, wherein the phase determining and indicating means comprise a first pulse generator (58) for generating a pulse at a predetermined time relative to the sync point, a second pulse generator (60) for generating a pulse at a predetermined time relative to the first positive-going zero crossing of burst, means (62) for determining the time difference between said pulses, and means (64) for converting said time difference into a signal representative of the angular position, within the referece subcarrier cycle, of the sync point.

Claim 7

A circuit for use with a vectorscope to indicate SC/H phase of a composite video signal, comprising oscillator means (28) for generating a continuous wave signal at subcarrier frequency and having its phase locked to the hoizontal sync point of the video signal, and switch means (30) for connection between the output terminal of the filter (24) of the vectorscope and the second inputs of the demodulators (18, 20) of the vectorscope and for connection also to the oscillator means, for alternately connecting the subcarrier burst from the filter of the vectorscope and the sync locked continuous wave from the oscillator means to the demodulators, so that when the subcarrier burst is connected to the demodulators the vectorscope provides an indication at a predetermined angle of the polar display of the vectorscope, whereas when the sync locked continuous wave signal is connected to the demodulators the vectorscope provides an indication at a position of the polar display that is angularly spaced from a predetermned axis of the polar display by an angle that depends on the difference in phase, within the subcarrier cycle, between the sync locked continuous wave signal and the subcarrier burst.

Claim 8

A circuit for use with a vectorscope to indicate SC/H phase of a composite video signal, comprising oscillator means (28) for generating a continuous wave signal at subcarrier frequency and having its phase locked to the hoizontal sync point of the video signal, and switch means (30) for connection between the output terminal of the filter (24) of the vectorscope and the second inputs of the demodulators (18, 20) of the vectorscope and for connection also to the oscillator means, for alternately connecting the subcarrier burst from the filter of the vectorscope and the sync locked continuous wave from the oscillator means to the demodulators, so that when the subcarrier burst is connected to the demodulators the vectorscope provides an indication at a predetermined angle of the polar display of the vectorscope, whereas when the sync locked continuous wave signal is connected to the demodulators the vectorscope provides an indication at a position of the polar display that is angularly spaced from a predetermned axis of the polar display by an angle that depends on the difference in phase, within the subcarrier cycle, between the sync locked continuous wave signal and the subcarrier burst.

Claim 9

An instrument for use in indicating SC/H phase of a composite video signal, comprising: an input terminal (12) for receiving the composite video signal, a display device for providing a polar display, said display device having a display sur - face, means for generating a visible dot on the display surface, X and Y deflection means for deflecting the position of the visible dot in mutually perpendicular rectilinear directions, a subcarrier regenerator (16) connected to the input terminal for generating a continuous wave signal at subcarrier frequency from, and phase-locked to, the reference subcarrier burst of the video signal, first and second demodulators (18, 20) having their outputs connected to the X and Y deflection means respectively and each having first and second inputs, means (24) connecting the output of the subcarrier regenerator to the first inputs of the first and second demodulators with a quarter-period relative phase difference, and a filter (14) which passes the subcarrier burst of the video signal; means (28) for generating a continuous wave signal at subcarrier frequency and having its phase locked to the sync point of the video signal, and a switch (30) for alternately connecting the sync locked continuous wave and the subcarrier burst to said second inputs of the demodulators, so that when the subcarrier burst is connected to the second inputs of the demodulators the display device displays an indication at a predetermined angular position of the polar dispaly, whereas when the sync locked continuous wave is connected to the second inputs of the demodulators the display device displays an indication at a position of the polar display that is angularly spaced from a predetermined axis of the polar display by an angle that depends on the phase difference, within the subcarrier cycle, between the reference subcarrier wave and the sync locked continuous wave.

Claim 10

An instrument for use in indicating SC/H phase of a composite video signal, comprising: an input terminal (12) for receiving the composite video signal, a display device for providing a polar display, said display device having a display sur - face, means for generating a visible dot on the display surface, X and Y deflection means for deflecting the position of the visible dot in mutually perpendicular rectilinear directions, a subcarrier regenerator (16) connected to the input terminal for generating a continuous wave signal at subcarrier frequency from, and phase-locked to, the reference subcarrier burst of the video signal, first and second demodulators (18, 20) having their outputs connected to the X and Y deflection means respectively and each having first and second inputs, means (24) connecting the output of the subcarrier regenerator to the first inputs of the first and second demodulators with a quarter-period relative phase difference, and a filter (14) which passes the subcarrier burst of the video signal; means (28) for generating a continuous wave signal at subcarrier frequency and having its phase locked to the sync point of the video signal, and a switch (30) for alternately connecting the sync locked continuous wave and the subcarrier burst to said second inputs of the demodulators, so that when the subcarrier burst is connected to the second inputs of the demodulators the display device displays an indication at a predetermined angular position of the polar dispaly, whereas when the sync locked continuous wave is connected to the second inputs of the demodulators the display device displays an indication at a position of the polar display that is angularly spaced from a predetermined axis of the polar display by an angle that depends on the phase difference, within the subcarrier cycle, between the reference subcarrier wave and the sync locked continuous wave.

Claim 11

An instrument for use in indicating SC/H phase of first and second video signals, comprising: first and second input terminals (46, 48) for receiving the first and second video signals respectively, a display device for providing a polar display, said display device having a display surface, means for generating a visible dot on the display surface, X and Y deflection means for deflecting the position of the visible dot in mutually perpendicular rectilinear directions, a subcarrier regenerator (16) connected to the first input terminal for generating a continuous wave signal at subcarrier frequency from, and phase-locked to, the subcarrier burst of the first video signal, first and second demodulators (18, 20) having their outputs connected to the X and Y deflection means respectively and each having first and second inputs, means (24) connecting the output of the subcarrier regenerator to the first inputs of the first and second demodulators with a quarter-period relative phase difference, and a filter (14) which is connected to the second input terminal for passing the subcarrier burst of the second video signal, first means (28a) connected to the first input terminal for generating a first continuous wave signal at subcarrier frequency and having its phase locked to the sync point of the first video signal, second means (28b) connected to the second input terminal for generating a second continuous wave signal at subcarrier frequency and having its phase locked to the sync point of the second video signal, and a switch (30') for successively connecting the first and second sync locked continuous waves and the subcarrier burst of the second video signal to said second inputs of the demodulators; so than when the subcarrier burst is connected to the second inputs of the demodulators the display device displays an indication at a predetermined angular position of the polar display, whereas when one of the sync locked continuous waves is connected to the second inputs of the demodulators the display device displays an indication at a position of the angular display that is angularly spaced from a predetermined axis of the polar display by an angle that depends on the phase difference, in the subcarrier cycle, between the reference subcarrier wave and said one sync locked continuous wave.

Claim 12

An instrument for use in indicating SC/H phase of first and second video signals, comprising: first and second input terminals (46, 48) for receiving the first and second video signals respectively, a display device for providing a polar display, said display device having a display surface, means for generating a visible dot on the display surface, X and Y deflection means for deflecting the position of the visible dot in mutually perpendicular rectilinear directions, a subcarrier regenerator (16) connected to the first input terminal for generating a continuous wave signal at subcarrier frequency from, and phase-locked to, the subcarrier burst of the first video signal, first and second demodulators (18, 20) having their outputs connected to the X and Y deflection means respectively and each having first and second inputs, means (24) connecting the output of the subcarrier regenerator to the first inputs of the first and second demodulators with a quarter-period relative phase difference, and a filter (14) which is connected to the second input terminal for passing the subcarrier burst of the second video signal, first means (28a) connected to the first input terminal for generating a first continuous wave signal at subcarrier frequency and having its phase locked to the sync point of the first video signal, second means (28b) connected to the second input terminal for generating a second continuous wave signal at subcarrier frequency and having its phase locked to the sync point of the second video signal, and a switch (30') for successively connecting the first and second sync locked continuous waves and the subcarrier burst of the second video signal to said second inputs of the demodulators; so than when the subcarrier burst is connected to the second inputs of the demodulators the display device displays an indication at a predetermined angular position of the polar display, whereas when one of the sync locked continuous waves is connected to the second inputs of the demodulators the display device displays an indication at a position of the angular display that is angularly spaced from a predetermined axis of the polar display by an angle that depends on the phase difference, in the subcarrier cycle, between the reference subcarrier wave and said one sync locked continuous wave.