CA1223955A - Television transmitter comprising a common klystron for the picture and sound - Google Patents
Television transmitter comprising a common klystron for the picture and soundInfo
- Publication number
- CA1223955A CA1223955A CA000472398A CA472398A CA1223955A CA 1223955 A CA1223955 A CA 1223955A CA 000472398 A CA000472398 A CA 000472398A CA 472398 A CA472398 A CA 472398A CA 1223955 A CA1223955 A CA 1223955A
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- Canada
- Prior art keywords
- signal
- klystron
- intermediate frequency
- amplitude
- output
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N5/00—Details of television systems
- H04N5/38—Transmitter circuitry for the transmission of television signals according to analogue transmission standards
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- Engineering & Computer Science (AREA)
- Multimedia (AREA)
- Signal Processing (AREA)
- Transmitters (AREA)
- Amplifiers (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
TELEVISION TRANSMITTER COMPRISING A COMMON KLYSTRON
FOR THE PICTURE AND SOUND
The klystron has a grid or another electrode for controlling the density of the electron beam, which receives a pulse signal, whose amplitude, duration and period are such that the klystron can supply a power equal to its peak power during the time intervals corresponding to the sync pulses of the picture signal and such that the klystron can only supply a predetermined fraction of its peak power for the remainder of the time, said fraction corresponding to the power to be supplied during the back porch of the picture signal. The variation of the klystron characteristic during the sync pulses leads to a variation in the amplitude and the group delay ofthe intercarrier signal frequency modulated by the sound and which itself modulates a UHF carrier. This is why correction means are provided on each sound channel, in order to compen-sate said amplitude variation and said group delay variation throughout the duration of the sync pulses.
TELEVISION TRANSMITTER COMPRISING A COMMON KLYSTRON
FOR THE PICTURE AND SOUND
The klystron has a grid or another electrode for controlling the density of the electron beam, which receives a pulse signal, whose amplitude, duration and period are such that the klystron can supply a power equal to its peak power during the time intervals corresponding to the sync pulses of the picture signal and such that the klystron can only supply a predetermined fraction of its peak power for the remainder of the time, said fraction corresponding to the power to be supplied during the back porch of the picture signal. The variation of the klystron characteristic during the sync pulses leads to a variation in the amplitude and the group delay ofthe intercarrier signal frequency modulated by the sound and which itself modulates a UHF carrier. This is why correction means are provided on each sound channel, in order to compen-sate said amplitude variation and said group delay variation throughout the duration of the sync pulses.
Description
issue BACKGROUND _ _ Ho IN NINA
The present invention relates to television transmitters using a single klystron for amplifying a carrier wave negatively amplitude modulated by a video signal and at least one carrier wave frequency modulated by an audio signal.
It is known to construct television transmitters comprising two separate power amplifiers for separately amplifying a picture signal and a sound signal, whilst respectively utilizing two klystrons3 whose electron beam density is modulated to obtain an improved efficiency. French Patent No. 1, 385,583 , filed on December Thea 1963 by the Compagnie Générale de Télégraphie Sans Film describes a television transmitter with separate amplification for the picture signal and a sound signal, in which a picture signal is applied to the input cavity of a klystron and in which the density of the electron beam of the klystron is modulated by applying to a modulation anode the sync pulses of the picture signal with a duration and an amplitude such that, during said sync pulses the klystron can supply its peak power, whereas during the remainder of the time it can only supply a power corresponding to 0.56 times its peak power.
Thus, the consumption of the picture signal amplifier is reduced by approximately 30% calipered with a picture signal amplifier comprising a klystron without beam density modulation.
,~:
,; I., 3~5 Moreover, it is known to modulate the density of the electron beam of an amplifier klystron of a picture signal by modulating the bias voltage of a Wehnelt grid or a grid placed in the vicinity of the klystron cathode. French Patent 1,457,632 filed on September sty 1965 by the Compagnie Générale de Télégraphie Sans Fit describes a television transmitter comprising a picture signal modulator incorporating a klystron, whose grid receives a video signal.
A klystron, whose efficiency is improved by a modulation of the beam density as a function of the video signal does not make it possible to simultaneously amplify a picture signal and a sound signal, because the variation of the transfer kirk-touristic of the klystron, when the density of the electron beam is modified, leads to a variation in the amplitude and the group delay of the sound signal.
The latter is constituted by a frequency modulated carrier converted into ultra-high frequency. Thus, the group delay variation leads to a parasitic phase modulation of the sound signal.
The object of the invention is to obviate this deficiency through providing a transmitter incorporating a single klystron for amplifying a picture signal and a sound signal, which is more economic than transmitters having two separate amplifiers, whilst retaining the improvement to the efficiency brought about by a modulation of the density of the electron beam The present invention therefore relates to a television transmitter comprising a common klystron for the picture and sound comprising a klystron having an output cavity coupled to the output of the transmitter an input cavity and an electrode for the control of the density of the electron beam; means for supplying to the control electrode a pulse signal having an amplitude, duration and period such that the klystron can swoop a power equal to its peak power during time intervals corresponding to the sync pulses of the picture signal and such that the klystron can only supply a given fraction of its peak power during the remainder of the time said fraction corresponding to the power to be supplied during the back porch of the picture signal; means for negatively modulating the amplitude of an intermediate frequency signal by a video signal; means for generating at least one second intermediate frequency signal frequency modulated by an audio signal correction means for correcting the group delay and amplitude of each intermediate frequency signal, in order to compensate the group delay variation and amplitude variation of the signal supplied by the output cavity of the klystron, said variations being caused by the density control of the electron beam; and means for adding the first intermediate signal and the second intermediate frequency signal corrected by correction means, converting the resulting signal to a very high I
frequency and applying it to an input cavity of the klystron.
The invention will be better understood and - further details will become more readily apparent from the study of the following description and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig 1 shows the transfer characteristic of a klystron for two biasing values of its grid.
Fig 2 shows the block diagram of a first embodiment of a television transmitter according to the invention.
Fig 3 is a more detailed block diagram of part of this embodiment.
Fig 4 shows the block diagram of a second embodiment of the television transmitter according to the invention DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Fig 1 shows the graph of I , PO being the output power of a klystron~ as a function of , Pi being the input power of said klystron~ The transfer characteristic of a klystron is dependent on the density of its electron beam, the latter more particularly determining the gain and peak power which can be supplied by the klystron. The electron density of the beam can be controlled by the bias of a grid or a Wehnelt grid close to the cathode.
Fig 1 shows a first characteristic curve C2 cores-pounding to a zero bias of the grid of a klystron with respect to its cathode together with a characteristic curve Of corresponding to a non-zero bias and such that the peak power which can be supplied by the klystron is reduced by approximately 25%.
The transmitter according to the invention comprises a single klystron, whose grid or Wehnelt grid is biased in such a way that the klystron functions according to characteristic C2 during sync pulses and according to characteristic Of throughout the remainder of the time. Fig l also shows the graph of a video signal corresponding to a picture, whose brightness progressively varies from white to black along a picture line. The dotted lines link points of this video signal with the corresponding operating points for the klystron.
For the duration of the sync pulse, the klystron functions with the characteristic curve C2, so that it can supply its peak power, which is distributed between the peak power of the picture signal and the peak power of the sound signal. For the remainder of the time, the klystron functions according to characteristic Of. When the brightness varies from white to black, the power supplied by the klystron varies from a value close to zero to a value closer to the peak power permitted by the characteristic Of. This peak power corresponds to the peak power of the sound signal, plus the power corresponding to the blanking level.
Fig 2 shows the block diagram of an embodiment of a television receiver with a single klystron power amplifier for the picture signal and for the sound signal, the latter corresponding to the transmission of two audio channels. This transmitter comprises input terminals I 2, 3 respectively receiving a video signal and two audio signals means 21 supplying an intermediate frequency picture signal, means 4, 5 supplying intermediate frequency sound signals, correction means 7, I means 6 supplying a very high frequency signal formed by adding and converting the picture signal and the sound signals at intermediate frequency, a klystron 10, means 9 for controlling the density of the electron beam of klystron 10, an antenna 22 radiating the output power of klystron lo and a power supply 20 supplying the bias stages of klystron lo The means 21 comprise a device 40 for processing the video signals, two delay lines 41! 42, a modulator 43, a band pass filter 44 and an oscillator OWE Input terminal 1 is connected to an input of device 40 in order to supply a video signal thereto. A first output of device 40 supplies a processed video signal to delay line 42 and the latter restores it at one input of modulator 43, which modulates an inter-mediate frequency carrier signal supplied by oscillator 45. The thus modulated carrier signal is filtered by the band pass filter 44 and constitutes an intermediate frequency signal applied to a first input of means 6, where it is added to the intermediate frequency signals carrying the two audio signals.
A second output of device 40 supplies a blanking level control signal to a second input of owe means 6. A third output of device 40 supplies sync pulses extracted I m the video signal, It is connected to a third output of means 21 by a direct connection and to a fourth output via the delay line 41. The said third output and the said fourth output are respectively connected to an input of means 9 and to an input of means 7, 8.
A fifth output of means 21, connected to the output of oscillator 45, is connected to one input of means 4 and to one input of means 5.
The delay line 42 delays the video signal supplied by the first output of device 40, with respect to the sync pulses supplied by the third output, in order more particularly to compensate the transit time of the electrons between the density control grid of the electron beam of klystron 10, to which are applied the sync pulses, and the input cavity of klystron 10, to which is applied an ultra-high frequency signal modulated by the video signal. Delay line 41 delays the sync signal controlling the correction means 7, 8, in order to more particularly compensate the transit time of the sound signals through means 4, I
The amplitude of the sync pulses of the video signal supplied by the first output of the device is reduced to 15% of the maximum amplitude of said video signal instead ox the usual 25%, in order to compensate the gain increase of klystron 10 for the duration of the sync pulses.
Means 4 comprise a modulator 46, a converter 47 ~3~55 and a band pass filter 48. An input and an output of modulator 46 are respectively connected to the input terminal 2 and to a first input of converter 47. A second input of converter 47 is connected to the fifth output of means 21, i.e. to the output of oscillator 45. An output of converter 47 is connected to an output of means 4 via band pass filter 48, whose center frequency is equal to the intermediate frequency.
The input terminal 2 receives an audio signal and supplies it to the input of modulator 46, where it brings about a frequency modulation of the so-called inter carrier signal Swede by a not shown oscillator. The modulated inter carrier signal is converted to an intermediate frequency (IF) by converter 47 receiving for local oscillation a signal supplied by oscillator 45 of means 21. The intermediate frequency signal supplied by converter 47 is filtered by filter 48 and is then transmitted to an input terminal 34 of correction means 7, where it is connected to the output of means 4.
The input terminal 3 receives a second audio signal, which is applied to means 5 and to means 8 which are respectively identical to means 4 and 7. An output terminal 36 of means 7 and an output terminal of means 8 are respectively connected to a third and a fourth input of means 6.
Means 6 comprise an oscillator 23, a frequency multiplier 24, a band pass filter 259 a converter 26, a linearity and phase corrector 27, an analog adder 28, a linearity corrector 29, an automatic gain control device 30 and an analog adder 31. The third and fourth inputs of means 6 are respectively connected to two inputs of the analog adder 31 and one output of the latter is connected to an input of the linearity corrector 29. Corrector 29 has a control input connected to an output of the automatic gain control device 30 and an output connected to a first input of adder 28. A second input of adder 28 is connected to the first input of means 6 and an output is connected to a first input of the linearity and phase corrector 27. A second input of corrector 27 is connected to the second input of means 6 for receiving the blanking level control signal.
A first input of converter 26 is connected to an output of filter 25~ a second input is connected to an output of corrector 27 and an output constitutes the output of means 6 and it connected to a first input of klystron 10. The output of oscillator 23 is connected to an input of multiplier 24 and an output of the latter is connected to an input of filter 25.
Adder 31 adds the intermediate frequency signals respectively carrying the first and second audio signals and supplies the resultant signal to the linearity corrector 29, in order to correct its amplitude variations. Corrector 29 supplies an intermediate frequency signal of constant amplitude and also carrying the two audio signals.
This signal is added by adder 28 to the intermediate frequency signal carrying the video signal. The signal supplied by the output of adder 28 undergoes linearity and phase correction by co rector 279 as a function of the control signal supplied by the video signal processing device devises 40) 27 and 29 are of a conventional nature in the field of television transmitters and fall within the scope of the Expert.
The intermediate frequency signal supplied by the output of corrector 27 carries the video signals and the inter carrier signals modulated by the two audio signals. This intermediate frequency signal is converted to an ultra-high frequency forming the transmission frequency by means of converter 27 which receives a local oscillation frequency supplied by oscillator 23, multiplier 24 and filter 25.
Klystron lo comprises a cathode lo an electron beam density control grid 12, an anode 13, an input cavity 14, two intermediate cavities 18, 19, an output cavity 16, a collector 17 and intermediate tubes 15 between the cavities. The supply generator 20 has a positive terminal connected to the reference potential of the transmitter and connected to collector 17 and to the intermediate tubes 15. It also has a negative terminal connected to cathode 11 and a terminal at intermediate potential connected to anode 13. The first input of klystron 10 it coupled to the input cavity 14 and supplies it with the output signal converter 26. A differential input connected to grid 12 and to cathode if is connected to a differential output of means 9.
One output of the klystron is coupled to the output cavity 16 and is connected to antenna 22.
The control means 9 comprise a beam density S control device 32 and an insulating device 33.
An input of means 9 is connected to the third output of the video signal processing device 40 for receiving sync pulses and is connected to an input of insulating device 33. The latter retransmits them to device 32, whilst ensuring the insulation of the latter, which is raised to the potential of the klystron cathode 11, i.e. 209000 Volts with respect to the reference potential. Two outputs of device 32 constitutes the differential output of means 9, which supplies voltage pulses which are synchronous with the sync pulses in order to control the potential of grid 12 with respect to cathode 11. Insulating device 33 can be realized by a transformer for a light-emitting diode 2G coupled to a photo diode by an optical fire.
Its construction is simple, because it is merely a question of transmitting a pulse of given duration and amplitude and not an analog signal.
Fig 3 shows an embodiment of the correction means 7, which are identical to correction means 8.
These correction means 7 comprise an analog switch 51, an amplifier 52, a group delay collector 53, a gain corrector 54 and an analog subtracter 55.
The input terminal 34 is connected on the one hand to an input of switch 51 and on the other to an input of amplifier 52. An output of the switch 51 and a control input are respectively connected to an input of corrector 53 and to the input terminal 35~ An output of corrector 53 is connected to a negative input of subtracter 55 by gain corrector 54. An output of amplifier 52 is connected to the positive input of subtracter 55 and the output of the latter is connected to output terminal 36. The intermediate frequency signal received by the input terminal 34 is amplified by amplifier 52 and is transmitted to the output terminal 36 by subtracter 55 without undergoing modification if switch 51 is open, id e. outside the time intervals corresponding to the sync pulses of the picture signal. When a sync pulse is applied to the input terminal 35~ it controls the closing of switch 51. The intermediate frequency signal transmitted by switch 51 undergoes a group delay correction and an attenuation in gain corrector 54 and is then subtracted from the signal supplied by the output of amplifier 52 by means of subtracter 55. The intermediate frequency signal supplied by subtracter 55 to output terminal 36 is consequently a reduced amplitude signal, whose phase is modified during the time intervals cores-pounding to the synchronization. The correctors 53, 54 are regulated in such a way as to compensate the effect of the variation of the group delay and the variation of the gain of the klystron during the time intervals corresponding to the sync pulses.
, The invention is not limited to the embodiment described herein before and numerous variants are possible thereto without passing beyond the scope of the invention. Thus 9 it is possible not to place the correction means 7 between the intermediate frequency filter 48 and adder 31 and instead position them between the output of modulator 46 and the intermediate frequency converter 47.
Fig 4 shows the block diagram of a second embodiment of the transmitter according to the invention. Its elements are identical to those of the first embodiment and carry the same references, with the exception of means and 7, which are replaced by means 4' and means 5 and 8 which are replaced by means 5'. Means 4' have correction means 7', as well as a modulator 46', a converter 47; and a band pass filter 48'~ which are respectively identical to modulator 46, converter 47 and filter 48.
The correction means 7' are identical to correction means 7 7 except that they operate at the inter carrier frequency instead of at the intermediate frequency and they are inserted between the output of modulator 46' and the input of converter 47'. The input of modulator 46' constitutes a first input of means 4' and is connected to input terminal
The present invention relates to television transmitters using a single klystron for amplifying a carrier wave negatively amplitude modulated by a video signal and at least one carrier wave frequency modulated by an audio signal.
It is known to construct television transmitters comprising two separate power amplifiers for separately amplifying a picture signal and a sound signal, whilst respectively utilizing two klystrons3 whose electron beam density is modulated to obtain an improved efficiency. French Patent No. 1, 385,583 , filed on December Thea 1963 by the Compagnie Générale de Télégraphie Sans Film describes a television transmitter with separate amplification for the picture signal and a sound signal, in which a picture signal is applied to the input cavity of a klystron and in which the density of the electron beam of the klystron is modulated by applying to a modulation anode the sync pulses of the picture signal with a duration and an amplitude such that, during said sync pulses the klystron can supply its peak power, whereas during the remainder of the time it can only supply a power corresponding to 0.56 times its peak power.
Thus, the consumption of the picture signal amplifier is reduced by approximately 30% calipered with a picture signal amplifier comprising a klystron without beam density modulation.
,~:
,; I., 3~5 Moreover, it is known to modulate the density of the electron beam of an amplifier klystron of a picture signal by modulating the bias voltage of a Wehnelt grid or a grid placed in the vicinity of the klystron cathode. French Patent 1,457,632 filed on September sty 1965 by the Compagnie Générale de Télégraphie Sans Fit describes a television transmitter comprising a picture signal modulator incorporating a klystron, whose grid receives a video signal.
A klystron, whose efficiency is improved by a modulation of the beam density as a function of the video signal does not make it possible to simultaneously amplify a picture signal and a sound signal, because the variation of the transfer kirk-touristic of the klystron, when the density of the electron beam is modified, leads to a variation in the amplitude and the group delay of the sound signal.
The latter is constituted by a frequency modulated carrier converted into ultra-high frequency. Thus, the group delay variation leads to a parasitic phase modulation of the sound signal.
The object of the invention is to obviate this deficiency through providing a transmitter incorporating a single klystron for amplifying a picture signal and a sound signal, which is more economic than transmitters having two separate amplifiers, whilst retaining the improvement to the efficiency brought about by a modulation of the density of the electron beam The present invention therefore relates to a television transmitter comprising a common klystron for the picture and sound comprising a klystron having an output cavity coupled to the output of the transmitter an input cavity and an electrode for the control of the density of the electron beam; means for supplying to the control electrode a pulse signal having an amplitude, duration and period such that the klystron can swoop a power equal to its peak power during time intervals corresponding to the sync pulses of the picture signal and such that the klystron can only supply a given fraction of its peak power during the remainder of the time said fraction corresponding to the power to be supplied during the back porch of the picture signal; means for negatively modulating the amplitude of an intermediate frequency signal by a video signal; means for generating at least one second intermediate frequency signal frequency modulated by an audio signal correction means for correcting the group delay and amplitude of each intermediate frequency signal, in order to compensate the group delay variation and amplitude variation of the signal supplied by the output cavity of the klystron, said variations being caused by the density control of the electron beam; and means for adding the first intermediate signal and the second intermediate frequency signal corrected by correction means, converting the resulting signal to a very high I
frequency and applying it to an input cavity of the klystron.
The invention will be better understood and - further details will become more readily apparent from the study of the following description and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig 1 shows the transfer characteristic of a klystron for two biasing values of its grid.
Fig 2 shows the block diagram of a first embodiment of a television transmitter according to the invention.
Fig 3 is a more detailed block diagram of part of this embodiment.
Fig 4 shows the block diagram of a second embodiment of the television transmitter according to the invention DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Fig 1 shows the graph of I , PO being the output power of a klystron~ as a function of , Pi being the input power of said klystron~ The transfer characteristic of a klystron is dependent on the density of its electron beam, the latter more particularly determining the gain and peak power which can be supplied by the klystron. The electron density of the beam can be controlled by the bias of a grid or a Wehnelt grid close to the cathode.
Fig 1 shows a first characteristic curve C2 cores-pounding to a zero bias of the grid of a klystron with respect to its cathode together with a characteristic curve Of corresponding to a non-zero bias and such that the peak power which can be supplied by the klystron is reduced by approximately 25%.
The transmitter according to the invention comprises a single klystron, whose grid or Wehnelt grid is biased in such a way that the klystron functions according to characteristic C2 during sync pulses and according to characteristic Of throughout the remainder of the time. Fig l also shows the graph of a video signal corresponding to a picture, whose brightness progressively varies from white to black along a picture line. The dotted lines link points of this video signal with the corresponding operating points for the klystron.
For the duration of the sync pulse, the klystron functions with the characteristic curve C2, so that it can supply its peak power, which is distributed between the peak power of the picture signal and the peak power of the sound signal. For the remainder of the time, the klystron functions according to characteristic Of. When the brightness varies from white to black, the power supplied by the klystron varies from a value close to zero to a value closer to the peak power permitted by the characteristic Of. This peak power corresponds to the peak power of the sound signal, plus the power corresponding to the blanking level.
Fig 2 shows the block diagram of an embodiment of a television receiver with a single klystron power amplifier for the picture signal and for the sound signal, the latter corresponding to the transmission of two audio channels. This transmitter comprises input terminals I 2, 3 respectively receiving a video signal and two audio signals means 21 supplying an intermediate frequency picture signal, means 4, 5 supplying intermediate frequency sound signals, correction means 7, I means 6 supplying a very high frequency signal formed by adding and converting the picture signal and the sound signals at intermediate frequency, a klystron 10, means 9 for controlling the density of the electron beam of klystron 10, an antenna 22 radiating the output power of klystron lo and a power supply 20 supplying the bias stages of klystron lo The means 21 comprise a device 40 for processing the video signals, two delay lines 41! 42, a modulator 43, a band pass filter 44 and an oscillator OWE Input terminal 1 is connected to an input of device 40 in order to supply a video signal thereto. A first output of device 40 supplies a processed video signal to delay line 42 and the latter restores it at one input of modulator 43, which modulates an inter-mediate frequency carrier signal supplied by oscillator 45. The thus modulated carrier signal is filtered by the band pass filter 44 and constitutes an intermediate frequency signal applied to a first input of means 6, where it is added to the intermediate frequency signals carrying the two audio signals.
A second output of device 40 supplies a blanking level control signal to a second input of owe means 6. A third output of device 40 supplies sync pulses extracted I m the video signal, It is connected to a third output of means 21 by a direct connection and to a fourth output via the delay line 41. The said third output and the said fourth output are respectively connected to an input of means 9 and to an input of means 7, 8.
A fifth output of means 21, connected to the output of oscillator 45, is connected to one input of means 4 and to one input of means 5.
The delay line 42 delays the video signal supplied by the first output of device 40, with respect to the sync pulses supplied by the third output, in order more particularly to compensate the transit time of the electrons between the density control grid of the electron beam of klystron 10, to which are applied the sync pulses, and the input cavity of klystron 10, to which is applied an ultra-high frequency signal modulated by the video signal. Delay line 41 delays the sync signal controlling the correction means 7, 8, in order to more particularly compensate the transit time of the sound signals through means 4, I
The amplitude of the sync pulses of the video signal supplied by the first output of the device is reduced to 15% of the maximum amplitude of said video signal instead ox the usual 25%, in order to compensate the gain increase of klystron 10 for the duration of the sync pulses.
Means 4 comprise a modulator 46, a converter 47 ~3~55 and a band pass filter 48. An input and an output of modulator 46 are respectively connected to the input terminal 2 and to a first input of converter 47. A second input of converter 47 is connected to the fifth output of means 21, i.e. to the output of oscillator 45. An output of converter 47 is connected to an output of means 4 via band pass filter 48, whose center frequency is equal to the intermediate frequency.
The input terminal 2 receives an audio signal and supplies it to the input of modulator 46, where it brings about a frequency modulation of the so-called inter carrier signal Swede by a not shown oscillator. The modulated inter carrier signal is converted to an intermediate frequency (IF) by converter 47 receiving for local oscillation a signal supplied by oscillator 45 of means 21. The intermediate frequency signal supplied by converter 47 is filtered by filter 48 and is then transmitted to an input terminal 34 of correction means 7, where it is connected to the output of means 4.
The input terminal 3 receives a second audio signal, which is applied to means 5 and to means 8 which are respectively identical to means 4 and 7. An output terminal 36 of means 7 and an output terminal of means 8 are respectively connected to a third and a fourth input of means 6.
Means 6 comprise an oscillator 23, a frequency multiplier 24, a band pass filter 259 a converter 26, a linearity and phase corrector 27, an analog adder 28, a linearity corrector 29, an automatic gain control device 30 and an analog adder 31. The third and fourth inputs of means 6 are respectively connected to two inputs of the analog adder 31 and one output of the latter is connected to an input of the linearity corrector 29. Corrector 29 has a control input connected to an output of the automatic gain control device 30 and an output connected to a first input of adder 28. A second input of adder 28 is connected to the first input of means 6 and an output is connected to a first input of the linearity and phase corrector 27. A second input of corrector 27 is connected to the second input of means 6 for receiving the blanking level control signal.
A first input of converter 26 is connected to an output of filter 25~ a second input is connected to an output of corrector 27 and an output constitutes the output of means 6 and it connected to a first input of klystron 10. The output of oscillator 23 is connected to an input of multiplier 24 and an output of the latter is connected to an input of filter 25.
Adder 31 adds the intermediate frequency signals respectively carrying the first and second audio signals and supplies the resultant signal to the linearity corrector 29, in order to correct its amplitude variations. Corrector 29 supplies an intermediate frequency signal of constant amplitude and also carrying the two audio signals.
This signal is added by adder 28 to the intermediate frequency signal carrying the video signal. The signal supplied by the output of adder 28 undergoes linearity and phase correction by co rector 279 as a function of the control signal supplied by the video signal processing device devises 40) 27 and 29 are of a conventional nature in the field of television transmitters and fall within the scope of the Expert.
The intermediate frequency signal supplied by the output of corrector 27 carries the video signals and the inter carrier signals modulated by the two audio signals. This intermediate frequency signal is converted to an ultra-high frequency forming the transmission frequency by means of converter 27 which receives a local oscillation frequency supplied by oscillator 23, multiplier 24 and filter 25.
Klystron lo comprises a cathode lo an electron beam density control grid 12, an anode 13, an input cavity 14, two intermediate cavities 18, 19, an output cavity 16, a collector 17 and intermediate tubes 15 between the cavities. The supply generator 20 has a positive terminal connected to the reference potential of the transmitter and connected to collector 17 and to the intermediate tubes 15. It also has a negative terminal connected to cathode 11 and a terminal at intermediate potential connected to anode 13. The first input of klystron 10 it coupled to the input cavity 14 and supplies it with the output signal converter 26. A differential input connected to grid 12 and to cathode if is connected to a differential output of means 9.
One output of the klystron is coupled to the output cavity 16 and is connected to antenna 22.
The control means 9 comprise a beam density S control device 32 and an insulating device 33.
An input of means 9 is connected to the third output of the video signal processing device 40 for receiving sync pulses and is connected to an input of insulating device 33. The latter retransmits them to device 32, whilst ensuring the insulation of the latter, which is raised to the potential of the klystron cathode 11, i.e. 209000 Volts with respect to the reference potential. Two outputs of device 32 constitutes the differential output of means 9, which supplies voltage pulses which are synchronous with the sync pulses in order to control the potential of grid 12 with respect to cathode 11. Insulating device 33 can be realized by a transformer for a light-emitting diode 2G coupled to a photo diode by an optical fire.
Its construction is simple, because it is merely a question of transmitting a pulse of given duration and amplitude and not an analog signal.
Fig 3 shows an embodiment of the correction means 7, which are identical to correction means 8.
These correction means 7 comprise an analog switch 51, an amplifier 52, a group delay collector 53, a gain corrector 54 and an analog subtracter 55.
The input terminal 34 is connected on the one hand to an input of switch 51 and on the other to an input of amplifier 52. An output of the switch 51 and a control input are respectively connected to an input of corrector 53 and to the input terminal 35~ An output of corrector 53 is connected to a negative input of subtracter 55 by gain corrector 54. An output of amplifier 52 is connected to the positive input of subtracter 55 and the output of the latter is connected to output terminal 36. The intermediate frequency signal received by the input terminal 34 is amplified by amplifier 52 and is transmitted to the output terminal 36 by subtracter 55 without undergoing modification if switch 51 is open, id e. outside the time intervals corresponding to the sync pulses of the picture signal. When a sync pulse is applied to the input terminal 35~ it controls the closing of switch 51. The intermediate frequency signal transmitted by switch 51 undergoes a group delay correction and an attenuation in gain corrector 54 and is then subtracted from the signal supplied by the output of amplifier 52 by means of subtracter 55. The intermediate frequency signal supplied by subtracter 55 to output terminal 36 is consequently a reduced amplitude signal, whose phase is modified during the time intervals cores-pounding to the synchronization. The correctors 53, 54 are regulated in such a way as to compensate the effect of the variation of the group delay and the variation of the gain of the klystron during the time intervals corresponding to the sync pulses.
, The invention is not limited to the embodiment described herein before and numerous variants are possible thereto without passing beyond the scope of the invention. Thus 9 it is possible not to place the correction means 7 between the intermediate frequency filter 48 and adder 31 and instead position them between the output of modulator 46 and the intermediate frequency converter 47.
Fig 4 shows the block diagram of a second embodiment of the transmitter according to the invention. Its elements are identical to those of the first embodiment and carry the same references, with the exception of means and 7, which are replaced by means 4' and means 5 and 8 which are replaced by means 5'. Means 4' have correction means 7', as well as a modulator 46', a converter 47; and a band pass filter 48'~ which are respectively identical to modulator 46, converter 47 and filter 48.
The correction means 7' are identical to correction means 7 7 except that they operate at the inter carrier frequency instead of at the intermediate frequency and they are inserted between the output of modulator 46' and the input of converter 47'. The input of modulator 46' constitutes a first input of means 4' and is connected to input terminal
2. The output of converter 47' is connected by filter 48' to an output of means 4', which is connected to the third input of means 6. Means 5' are identical to means 4'.
,.
The main advantage of the transmitter according to the invention is that it has a less costly construction than that of a conventional transmitter with a klystron power amplifier for the sound and a klystron power transmitter for the picture, whilst still having an excellent efficiency as a result of the electron beam density modulation process. This process makes it possible to obtain a klystron efficiency of approximately 30%, whereas when it is absent the efficiency is approximately 23%.
Jo
,.
The main advantage of the transmitter according to the invention is that it has a less costly construction than that of a conventional transmitter with a klystron power amplifier for the sound and a klystron power transmitter for the picture, whilst still having an excellent efficiency as a result of the electron beam density modulation process. This process makes it possible to obtain a klystron efficiency of approximately 30%, whereas when it is absent the efficiency is approximately 23%.
Jo
Claims (3)
1. A television transmitter comprising a common klystron for the picture and sound comprising a klystron having an output cavity coupled to the output of the transmitter, an input cavity and an electrode for the control of the density of the electron beam; means for supplying to the control electrode a pulse signal having an amplitude, duration and period such that the klystron can supply a power equal to its peak power during time intervals corresponding to the sync pulses of the picture signal and such that the klystron can only supply a given fraction of its peak power during the remainder of the time, said fraction corresponding to the power to be supplied during the back porch of the picture signal; means for negatively modulating the amplitude of the intermediate frequency signal by a video signal; means for generating at least one second intermediate frequency signal frequency modulated by an audio signal; correction means for correcting the group delay and amplitude of each intermediate frequency signal; in order to compensate the group delay variation and amplitude variation of the signal supplied by the output cavity of the klystron, said variations being caused by the density control of the electron beam; and means for adding the first intermediate signal and the second intermediate frequency signal corrected by correction means, converting the resulting signal to a very high frequency and applying it to an input cavity of the klystron.
-16- .
-16- .
2. A transmitter according to claim 1, wherein the correction means for each audio signal comprise a group delay corrector and a gain corrector correcting the corresponding intermediate frequency signal by modifying the group delay and amplitude of said second intermediate frequency signal.
3. A transmitter according to claim 1, wherein the means for generating at least one second intermediate frequency signal frequency modulated by an audio signal, comprise means for the frequency modulation of an intercarrier signal and means for converting the modulated intercarrier signal to an intermediate frequency and wherein the correction means for each audio signal comprise a group delay corrector and a gain corrector correcting the second corresponding intermediate frequency signal, by modifying the group delay and the amplitude of the intercarrier signal modulated by said audio signal, before the frequency conversion of said intercarrier signal.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR8400893A FR2558673B1 (en) | 1984-01-20 | 1984-01-20 | TELEVISION TRANSMITTER COMPRISING A COMMON KLYSTRON FOR IMAGE AND SOUND |
| FR8400893 | 1984-01-20 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1223955A true CA1223955A (en) | 1987-07-07 |
Family
ID=9300329
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000472398A Expired CA1223955A (en) | 1984-01-20 | 1985-01-18 | Television transmitter comprising a common klystron for the picture and sound |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0149950B1 (en) |
| CA (1) | CA1223955A (en) |
| DE (1) | DE3473551D1 (en) |
| FR (1) | FR2558673B1 (en) |
| ZA (1) | ZA85203B (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4821097A (en) * | 1987-03-05 | 1989-04-11 | General Instrument Corporation | Apparatus and method for providing digital audio on the sound carrier of a standard television signal |
| KR950005600B1 (en) * | 1992-06-29 | 1995-05-27 | 주식회사금성사 | Multi-sound receiving apparatus for vcr |
| EP0577899B1 (en) * | 1992-07-10 | 1997-10-08 | Thomcast | Aural carrier correction system and method |
| US5418578A (en) * | 1993-12-27 | 1995-05-23 | Harris Corporation | Precorrecting an aural carrier signal in a common amplifier system |
| FR2731576B1 (en) * | 1995-03-09 | 1997-05-23 | Telediffusion Fse | TELEVISION SIGNAL TRANSMISSION CHAIN COMPRISING A DATA CHANNEL |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR1385583A (en) * | 1963-12-04 | 1965-01-15 | Csf | Improvements to dual or multiple amplitude modulation transmitters |
| FR1457632A (en) * | 1965-09-21 | 1966-01-24 | Csf | Improvements to television transmitters |
| FR2392540A1 (en) * | 1977-05-27 | 1978-12-22 | Thomson Csf | VIDEO AND AUDIO-FREQUENCY SIGNAL AMPLIFICATION SYSTEM, AND TELEVISION TRANSMITTER USING SUCH A SYSTEM |
| FR2437117A1 (en) * | 1978-09-22 | 1980-04-18 | Lgt Lab Gen Telecomm | HIGH PERFORMANCE AMPLITUDE MODULATION TRANSMISSION SYSTEM AND TELEVISION TRANSMITTER AND TRANSMITTER COMPRISING SUCH A SYSTEM |
-
1984
- 1984-01-20 FR FR8400893A patent/FR2558673B1/en not_active Expired
- 1984-12-27 EP EP84402745A patent/EP0149950B1/en not_active Expired
- 1984-12-27 DE DE8484402745T patent/DE3473551D1/en not_active Expired
-
1985
- 1985-01-09 ZA ZA85203A patent/ZA85203B/en unknown
- 1985-01-18 CA CA000472398A patent/CA1223955A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| EP0149950A3 (en) | 1985-08-28 |
| EP0149950B1 (en) | 1988-08-17 |
| ZA85203B (en) | 1985-09-25 |
| FR2558673A1 (en) | 1985-07-26 |
| EP0149950A2 (en) | 1985-07-31 |
| FR2558673B1 (en) | 1986-04-25 |
| DE3473551D1 (en) | 1988-09-22 |
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| MKEX | Expiry |