US2178766A - Television apparatus - Google Patents

Television apparatus Download PDF

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Publication number
US2178766A
US2178766A US717715A US71771534A US2178766A US 2178766 A US2178766 A US 2178766A US 717715 A US717715 A US 717715A US 71771534 A US71771534 A US 71771534A US 2178766 A US2178766 A US 2178766A
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United States
Prior art keywords
synchronizing
tube
signals
picture
impulses
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Expired - Lifetime
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US717715A
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English (en)
Inventor
William A Tolson
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RCA Corp
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RCA Corp
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Filing date
Publication date
Priority to NL46316D priority Critical patent/NL46316C/xx
Application filed by RCA Corp filed Critical RCA Corp
Priority to US717715A priority patent/US2178766A/en
Application granted granted Critical
Publication of US2178766A publication Critical patent/US2178766A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00—Details of television systems
    • H04N5/04—Synchronising
    • H04N5/08—Separation of synchronising signals from picture signals

Definitions

  • My invention relates to television systems and particularly to apparatus for synchronizing the transmitters and receivers thereof.
  • both picture signals and synchronizing impulses are transmitted on the same carrier, the horizontal synchronizing impulses being transmitted at the end of each horizontal scanning line and the vertical synchronizing or framing impulses being transmitted at the end of each picture frame.
  • precautions must be taken at the receiver to prevent the picture signals from interfering with the synchronizing impulses in their control over the saw-tooth wave oscillators. This may be accomplished by producing, at the transmitter, synchronizing impulses which have a considerably larger amplitude than the amplitude of the picture signals, and, at the receiver, by utilizing the difference in amplitude to prevent the picture signals from having an undesired effect upon the synchronization of the system.
  • the picture signals and synchronizing impulses are separated at the receiver by utilizing a polarity difierence between the said signals and impulses.
  • This polarity difierence may be obtained, for example, by introducing the synchronizing impulse modulation into the carrier in the same direction as the modulation thereof by the dark portions of a view being transmitted.
  • this carrier wave is demodulated at the receiver and after amplification in alternating current amplifier having the proper number of stages, the picture signals and synchronizing impulses appear as an alternating current in which all or most of the picture signal component appears on the negative side of the zero axis while the synchronizing impulse component appears on the opposite side of the zero axis.
  • a system utilizing a tube biased beyond cutofi has been found fairly satisfactory although; 5 it has several objectionable features.
  • One of these is that, since the tube operates over a portion of its grid voltage-plate current curve which has a small slope, the amplification 'is rather low. This defect is accentuated by the fact that in 10 order to allow interchangeability of tubes, it is necessary to increase the bias considerably beyond the optimum value.
  • Another disadvantage is that any difference in the amplitude of the synchronizing signals will be increased by pass- 5 ing the signals through the separating tube.
  • Figure l is a partial circuit diagram of a television receiver constructed in accordance with one 40 embodiment of my invention.
  • Figs. 1a., 2,- 3, and 4 are diagrams which will be referred to in explaining the operation of the circuit shown in Fig. 1.
  • a television receiving sys- 5 ,tem is illustrated in which a cathode-ray receiver tube l of the type disclosed in the above-mentioned applications is supplied with picture and synchronizing signals from a radio channel.
  • a radio receiver 3 demodulates the modulated in- 5 coming carrier wave to impress picture and synchronizing signals upon the input circuit of any suitable amplifier 5, the output of which is impressed across the control grid 1 and cathode 9 of the cathode-ray tube
  • the control grid 1 ts may be maintained at a suitable negative bias by means of a biasing battery II.
  • both picture signals and synchronizing signals are impressed upon the control grid of the cathode-ray tube, there being no objection to this as the synchronizing impulses are utilized in blocking the tube during the return of the cathode-ray at the end of each scanning line and at the end of each picture frame.
  • the cathode-ray tube is provided with the customary deflecting devices for producing horizontal and vertical deflection of the cathode-ray beam, these devices being shown in the drawing as horizontal and vertical deflecting coils l3 and I5, respectively.
  • a saw-tooth wave oscillator or generator I! is provided for supplying a comparatively high frequency deflecting current to the horizontal deflecting coils
  • the incoming synchronizing impulses are impressed upon the saw-tooth wave oscillators l1 and I9 through a circuit which includes an electric discharge tube 2
  • be of the indirectly heated cathode type comprising a cathode 23, a control grid 25 and an anode 21.
  • is so designed that if picture and synchronization signals of opposite polarity are impressed thereon, with the synchronizing signals having a negative polarity, only the synchronizing signals or impulseswill appear in the output circuit of the tube.
  • is'provided with an input resistor 29 which is connected at one end through ground to the cathode 23 and which is connected at the other end through a resistor 3
  • may be given values varying within wide limits. It may be noted, however, that in one receiver embodying my invention excellent results were obtained by giving the resistor 29 a value of 500,000 ohms and I the resistor 3
  • the gridend of the input resistor 29 is connected through a coupling condenser 33 to the output circuit ofthe amplifier 5 whereby both picture and synchronizing signals are impressed 1 izing impulses, two filter circuits are connected to the output circuit of the separating tube 2
  • the filter circuit for selecting the vertical synchronizing impulses may consist of an inductance coil 39 connected in series with a resistor 4
  • 9- is connected
  • may across resistor 4
  • is preferably shunted by a condenser 43.
  • the filter circuit for selecting the horizontal synchronizing impulses may consist of a condenser 45 connected in series with a resistor 41.
  • This selecting circuit is connected across the output circuit of the selecting tube 2
  • the horizontal synchronizing impulses are taken off the resistor 47 and supplied spection of Fig. 2 and from an inspection of the circuit in Fig. 1 that the tube 2
  • is indicated at 59. It will be apparent that any picture signal appearing in the input circuit of the selecting tube 2
  • Fig. 1a where the input resistor 29 is represented as a signal generator 63 and the grid-cathode impedance of-the tube is represented as a variable resistor 65. It will be seen that the resistor 3
  • the picture signals 53 cause substantially no change in the plate current of the tube while the negative synchronizing impulses 55 and 51 cause a large reduction in the plate current.
  • the reduction in plate current by a synchronizing impulse results in a reduced IR drop in the plate resistor 35 whereby the plate voltage increases momentarily to a comparatively high value'to apply a Synchronizing impulse to one of the saw-tooth wave oscillators,
  • a separating tube accentuates any difference in the amplitude of synchronizing signals.
  • This action is illustrated in Fig. 3 where the control grid-plate current curve of a separating tube is indicated at 61.
  • the picture signals 69 and synchronizing impulses I! are shown along a vertical time axis. Since the tube is biased beyond the cut-01f point and the picture signals are negative, only the synchronizing impulses will appear in the output circuit of the separating tube as indicated by the plate current impulses 13.
  • the second synchronizing impulse H has been shown as having an amplitude twice that of the first synchronizing impulse. Referring to the resulting plate current impulses, it will be seen that the second impulse 13 has an amplitude which is more than twice that of the first ime pulse 13. In other words, the separating tube has increased the amplitude difference of the synchronizing impulses.
  • Fig. 4 where parts similar to those in Fig. 3 have like reference numerals, the action of a separating circuit designed in accordance with my invention is illustrated. It will be seen that although the second synchronizing impulse H has twice the amplitude of the first impulse H, just as in the case shown in Fig. 3, the second resulting plate current impulse 13 is less than twice the amplitude of the first impulse 13. This tendency to smooth out differences in amplitude of synchronizing impulses is of value in systems where the incoming synchronizing impulses are varying considerably in amplitude, since a more positive synchronizing action is obtained when synchronizing impulses of constant amplitude are applied to the sawtooth wave oscillators.
  • a still further advantage of my invention resides in the fact that the grid-cathode capacity of the separating tube 2
  • means for separating picture signals from synchronizing signals comprising an electric discharge tube having a cathode and a control electrode, an'input impedance unit upon which said picture and synchronizing signals may be impressed, one end of'saidimpedance unit being connected to said cathode, and a second impedance unit connected between the other end of said first impedance unit and said control electrode.
  • an oscillator and means for impressing said synchronizing signals only upon said oscillator, said means including an electric discharge tube having a cathode and a control electrode and having two resistor sections connected between said cathode and said control I electrode, said picture and synchronizing signals being impressed upon the resistor section ad,- J'acent said cathode.
  • a receiver tube of the cathode-ray type having a deflecting device, an oscillator connected to said deflecting device, and an electric discharge tube having an output circuit connected to said oscillator and an input circuit connected to receive picture and synchronizing signals of opposite polarity, said tube being operated at approximately zero bias whereby positive picture signals are transferred through said tube with low efficiency as compared with the transfer of negative synchronizing impulses.
  • a receiver including a saw-tooth wave generator, an electric discharge tube having an input circuit and an output circuit, means for connecting said output circuit to said generator, means for impressing said picture signals and said synchronizing signals through a condenser upon said input circuit with the synchronizing signals having a negative polarit and means for rendering said tube effective to transfer said negative polarity signals and substantially ineffective to transfer the positive polarity picture signals.
  • a receiver including a saw-tooth wave generator and also including an electric discharge tube having a input circuit'and an output circuit, means for impressing said signals and impulses upon said input circuit through a condenser with the said signals having a positive polarity with respect to said limiting value and the synchronizing impulses having a negative polarity with respect to said limiting value, means for connecting'said output circuit to said generator, and means for rendering said electric discharge tube effective to transfer said negative synchronizing impulses and substantially inefiective to transfer said positive picture signals.
  • a receiver including a saw-tooth wave generator and also including an electric discharge tube having an input circuit and an output circuit, means for impressing said signals and impulses upon said input circuit through a condenser with at least part of the said signals having a positive polarity with respect to a certain axis and the synchronizing impulses having a negative polarity with respect to said axis and having a greater amplitude than said signals, means for connecting said output circuit tosaid generator, and means for rendering said electric discharge tube effective to transfer said negative synchronizing impulses and substantially ineffective to transfer said positive picture signals.
  • a receiver comprising a cathoderay tube having a horizontal deflecting device and a vertical deflecting device, a saw-tooth wave generator coupled to said first device, a saw-tooth wave generator coupled to said second device, an electric discharge tube having input electrodes and an output circuit, means for coupling said output circuit to said generators, means for impressing said picture signals and said synchronizing signals upon said input electrodes through a condenser with said synchronizing signals having a negative polarity, and means for rendering said tube efiective to transfer said negative polarity signals and substantially ineffective to transfersaid positive polarity picture signals.
  • a receiver including a cathode-ray tube having deflecting devices and two saw-tooth wave generators coupled thereto, a vacuum tube having input electrodes and an output circuit, means for impressing said signals and impulses upon said input electrodes with at least part of the said signals having a positive polarity with respect to a certain axis and the synchronizing impulses having a-negative polarity-with respect to said axis, means for rendering said vacuum tube effective to transfer said negative synchronizing impulses and substantially inefi'ective to transfer said positive picture signals, and means for impressing the horizontal synchronizing impulses appearing in said output circuit upon one of said generators and for impressing the vertical synchronizing impulses appearing in said output circuit upon the other of said generators.
  • the input. circuit of said vacuum tube includes an input resistor unit upon which the picture signals and the synchronizing impulses may be impressed, one end of said unit being connected to the cathode input electrode, and further characterized in that a second resistor unit is. connected between the other end of said first resistor unit and the control grid input electrode.
  • means for separating picture signals from horizontal and vertical synchronizing impulses and means for separating the horizontal synchronizing impulses from said vertical'synchronizing impulses said first means preceding said second means and comprising a vacuum tube having a cathode and a control electrode, an input resistor upon which said picture signals and synchronizing impulses are impressed, one end of said resistor being connected to said cathode, and a second resistor connected between the other end of said first resistor and said control electrode.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Television Systems (AREA)
US717715A 1934-03-28 1934-03-28 Television apparatus Expired - Lifetime US2178766A (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
NL46316D NL46316C (enrdf_load_stackoverflow) 1934-03-28
US717715A US2178766A (en) 1934-03-28 1934-03-28 Television apparatus

Applications Claiming Priority (1)

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US717715A US2178766A (en) 1934-03-28 1934-03-28 Television apparatus

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US2178766A true US2178766A (en) 1939-11-07

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2426501A (en) * 1941-03-20 1947-08-26 Submarine Signal Co Method and apparatus for radio ranging
US2566763A (en) * 1946-09-28 1951-09-04 Motorola Inc Synchronizing signal separator and keyed automatic gain control
US2615978A (en) * 1947-10-14 1952-10-28 Motorola Inc Pulse width separation filter
US2631230A (en) * 1949-10-11 1953-03-10 Du Mont Allen B Lab Inc Circuit for minimizing the effects of noise in television signals
US2636939A (en) * 1949-06-30 1953-04-28 Avco Mfg Corp Keyed automatic gain control

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2426501A (en) * 1941-03-20 1947-08-26 Submarine Signal Co Method and apparatus for radio ranging
US2566763A (en) * 1946-09-28 1951-09-04 Motorola Inc Synchronizing signal separator and keyed automatic gain control
US2615978A (en) * 1947-10-14 1952-10-28 Motorola Inc Pulse width separation filter
US2636939A (en) * 1949-06-30 1953-04-28 Avco Mfg Corp Keyed automatic gain control
US2631230A (en) * 1949-10-11 1953-03-10 Du Mont Allen B Lab Inc Circuit for minimizing the effects of noise in television signals

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Publication number Publication date
NL46316C (enrdf_load_stackoverflow)

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