US1978684A - Television - Google Patents

Description

Oct. 30, 1934. H. J. MCCREARY TELEVISION Filed NOV. 9, 1928 HIGH TIME 55c.

Patented Oct. 30, 1934 UNITED STATES TELEVISION Harold J. McCi-e'ary, Chicago, Ill., assignor, by mesne assignments, to Associated Electric Laboratories, Inc., Chicago, 111., a

Delaware corporation of Application November 9, 1928, Serial No. 318,262

22 Claims.

The present invention relates in general to television and the object of the invention, broadly stated, is to provide a new and improved television receiver.

A special object of the invention is to provide a television receiver of the type which employs a cathode ray tube and which can be used to pick up television programs which are broadcasted by transmitting stations using the so-called disc w transmitter.

Other objects of the invention relate to various improvements in television receivers of the general character pointed out above and will be discussed hereinafter.

Referring to the drawing accompanying this specification, Fig. 1 shows a cathode ray television receiver using a neon tube oscillator for producing the scanning potentials; Fig. 2 shows a modified type of oscillator employing a motor-driven interrupting mechanism; Figs. 3 and 4 show the wave forms of the scanning potentials which are produced by the oscillators shown in Figs. 1 and 2; while Fig. 5 is a diagrammatic representation showing how the television frame in the cathode ray receiver of the instant case compares with the television frame in a disc type of receiver or transmitter.

Referring now to Fig. 1, the reference letter A refers generally to a cathode ray tube of the general type which is in common use and known as a cathode ray oscillograph tube. It comprises an evacuated glass vessel or tube within which is a filament or cathode 2, a perforated disc or shield 3, an anode 4, and two pairs of plates 5-6 and '78. The end of the tube opposite the filament is preferably flattened out somewhat and is coat-.

ed on the inside with some fluorescent material, such as willemite. The A" battery 10 is provided for the purpose of lighting the filament 2, while the so-called 13" battery 11 serves to place a positive potential on the anode 4. A C battery 12 is also provided for the purpose of maintaining a negative potential upon the shield 3. In series with the battery 12 is a high resistance grid leak 13. a

The reference letter B indicates generally the last stage of a resistance coupled amplifier. This amplifier may be any good type of radio receiver such as is used topick up ordinary radio broadcasts. The amplifier is coupled to the oathode ray receiver by means of condensers 14 and 15.

The reference letter C indicates a double neon tube oscillator which is provided for the purpose of impressing the necessary scanning potentials upon the plates 5 to 8, inclusive, of the cathode ray receiver. The low frequency oscillator comprises essentially the neon tube 25 shunted by variable condenser 27 and connected in series with the battery 31 through the high resistance 29. The high frequency oscillator is similar and comprises the neon tube 26 shunted by variable condenser 28 and connected in series with the same battery 31 through the high resistance 30. The voltage of the battery 31 is variable so that the frequency of the oscillators can be adjusted. One end of the battery may be tapped for rough adiustment, one cell at a time, while at the other end of the battery a potentiometer is provided shunted around one or two of the cells to provide for a finer adjustment. The positive pole of the battery is connected to common lead 42 which is connected to plates 5 and 8 of the cathode ray receiver. The low frequency conductor 40 is connected to scanning plate 6 of the receiver, while the high frequency conductor 41 is con nected to the scanning plate '7. The common lead 42 includes the potentiometer 33 which is shunted around the battery 32. This battery is connectedin opposition. to the battery 31 and is provided so that the cathode ray beam can be centered on the fluorescent screen 9 of the receiver. Battery 32, being connected in the common lead, provides only for a diagonal adjustment across the screen, which however, is ordinarily all that is required. Separate vertical and horizontal adjustments can be provided for by inserting a potentiometer and battery in each of the leads 40 and 41, omitting the potentiometer and battery in the common lead 42.

The leads 40, 41, and 42 are connected to the receiver through keys K1, K2, and K3. Key K1 reverses the connections to the low frequency scanningplates 5 and 6, while key K2 reverses the connections to the high frequency scanning plates '7 and 8. Key K3 reverses the high and low frequency conductors 40 and 41 with respect vto their connections in the receiver. These keys are provided so that any desired direction of scanning may be secured.

Assuming that the receiver is set up and connected as shown in the drawing, the filament 2 will be heated by the battery 10 and is thus caused to emit electrons. In the ordinary operation of a cathode ray tube of this type the potential on 105 the anode 4 is sumcient to pull a stream of electrons through the central opening in the shield 3, thus forming the well-known cathode ray or beam which passes through the cylindrical anode 4 and between the pairs of plates 5-6 and 7-8 110 andimpingesonthescreenDattheendofthe tube. The 6" battery 12 should have such a value that the negative potential on the shield 3 will very nearly prevent the e of anyelectrons when there is no incoming light signal; that is, with no incoming signal the cathode beam should be very nearly, if not quite, extinguished. m\n

The purpose of the two pairs of scan g plates 56 and 7-8 is, of course, to cause the cathode beam to scan or trace a path over the fluorescent screen 9 so as to display the picture being received. This operation is described in my co-pending application, Serial No. 705,413, filed April 10, 1924, which describes the use of approximately sine wave generators for producing the scanning potentials. When potentials having such a wave form are used, however, the beam will trace a zig-zag or Lissajous figure ori the fluorescent screen, and since this does not correspond to the method of scanning used in the disc transmitter, potentials having a different wave form must be used. The foregoing may be understood better by reference to Fig. 5. The dotted semi-rectangular frame abxu represents the area scanned by a disc transmitter, horizontal clockwise scanning being assumed. The first hole in the disc will trace a path across the frame as represented by the dotted line ab, the second hole will trace a path represented by the dotted line dc, etc. It will be understood from this that the frame is scanned from top to bottom and from left to right, or the same as one reads a page of English print. The problem is to cause the cathode ray beam to scan the frame in the cathode ray receiver in the same manner. This can be done by arranging for. generation of scanning potentials having a wave form such as is illustrated in Figs. 3 and 4, Fig.

3 showing the wave form of the high frequency scanning potential, while Fig. 4 shows the wave form of the low frequency scanning potential. It will be seen that in each case the voltage rises with approximately straight-line characteristics to a maximum and then suddenly, practically instantaneously, falls to zero. It will be understood that when the voltage across condenser 28,

for instance, is rising the voltage across the resistance 30 will be falling and vice versa, so that assuming positive values above the base line the curve, Fig. 3, represents the wave form of the potential across the condenser, while if negative values are assumed above the base line the curve shows the wave form of the potentials across the resistance 30.

The effect of these scanning potentials on the movement of the cathode beam will readily be perceived. Considering the rectangular frame shown by the solid lines in Fig. 5, we will assume that the scanning potentials both have a value of zero at a given instant and that at this partic- 4 ular instant the beam impinges at the point a in the upper left-hand comer of the frame, which will be true with the reversing switches K1, K2, and K3 in a particular position. As the voltage of the high frequency source rises, the beam will be pulled across the frame toward the point-b, but at the same time the voltage of the low frequency source is rising also, with the result that the beam will gradually be deflected downward so that it actually traces a path as indicated by the line ac. When the point e is reached the voltage'of the high frequency source drops suddenly to zero with the result that the beam instantly assumes a position at point (1 on the left of the screen, there being no visible path on the screen to denote the transition of the beam from c to d. The voltage of the high frequency source now rises gradually again with the result that the beam sweeps across the screen again from left to right following the path indicated by the line de until when e is reached the voltage again drops to zero and the beam instantly assumes its position at the leftof the screen at point 1. Thus, it will be seen that the beam traces lines from left to right across the screen, each line being a little lower down on the screen than its predecessor, until finally on the last movement across the frame the beam arrives at the point 1!. At this instant the voltage of the low frequency source drops to zero simultaneously with the voltage of the high frequency source and the beam thereupon instantly resumes its position at a in the upper left-hand corner of the frame. Thus, the beam has traversed the entire frame in a series of horizontal lines. It will be understood that the lines are much closer together in practice than are shown in Fig. 5, as this drawing is merely for the purpose of explaining the principle, and the displacement of the lines ac, de, etc., from the horizontal will be much less than appears on the drawing. While these lines do not coincide exactly with the-lines 'ab, dc, etc., the method of scanning is the same; that is, the cathode ray scans in a clockwise direction and from top to bottom, and the departure of the lines produced by the cathode ray beam from the paths followed by the holes in the disc is very small. It is so small as to produce merely a very slight distortion of the picture which is practically unno- 11o ticeable. Y

The neon tube oscillator C is so designed as to produce scanning currents having the requisite wave form, as pointed out in the foregoing. The frequencies of the two oscillators must, of course, correspond to the picture frequencies employed at the transmitting station whose broadcasted pictures it is desired to receive. Broadcasting stations are now in operation which transmit at the rate of fifteen pictures per second using a disc having forty-eight holes. To receive these programs the low frequency oscillator including the neon tube 25 must have a frequency of fifteen cycles persecond, while-the high frequency oscillator including the neon tube 26 must have a frequency of forty-eight times this or seven hundred twenty cycles per second. The desired frequencies can be obtained by using the proper values for the resistances 29 and 30 and for the condensers 2'1 and 28. It is desirable, however, that the resistances 29 and 30 both be comparatively high, on the order of 10 megohms, and it is preferable, therefore, to take care of the difference in frequencies largely by means of a difference in the capacities of the two condensers 27 and 28. It follows from this that the condenser 27 of the low frequency oscillator will have a very much higher capacity than the condenser 28. The approximate values can readily be calculated from the formula in which f=frequency in cycles per second; E=charging potential in volts (battery 31); e=breakdown voltage of neon tube; R=resistance in ohms (resistance 29) and C=capacity in farads (condenser 27).

In the operation of the oscillator, and considering the low frequency side, the condenser 27 will be charged by the battery 31 through the resistance 29 until the potential across the terminals 'of the condenser reaches the value at which the neon tube 25 flashes over. When this occurs, the condenser is short-circuited through the neon tube and is instantly discharged. The neon tube then becomes open-circuited and the condenser is again charged, the operation continuing in this manner at the rate of fifteen cycles per second. The exact frequency can be adjusted by adjusting the condenser 2'7. The breakdown potential of the neon tube may be in the neighborhood of volts and the battery 31 should have a voltage somewhat higher than this so that the condenser 27 will be worked on the lower portion of its charging curve which has nearly a straight-line characteristic.

The high frequency oscillator including the neon tube 26, of course, operates the same as the low frequency oscillator except that the condenser 28 charges and discharges exactly forty-eight times as fast as the condenser 27. The exact frequency is adjusted by adjusting the capacity of the variable condenser. When the two oscillators are separately adjusted to substantially the proper frequencies they tend to keep in step with each other, due to the inclusion of the resistance 35 in the negative lead from the battery 31, and can then be adjusted simultaneously by regulating the voltage of battery 31.

The high and low voltage leads 40 and 41 could be taken directly from the terminals of the condensers, if desired, common lead 42 being connected to the other terminal of the battery in this case, but it is better to connect these leads around the resistances 29 and 30 so that the oscillators will be independent of any extraneous circuits which might introduce variable capacity effects which would have a tendency to make it difiicult to maintain adjustment of the frequencies. The resistances 29 and 30 are preferably constructed in the form of potentiometers so that the impressed voltages on conductors 40 and 41 can be varied for the purpose of varying the amplitude of movement of the cathode ray beam as it traverses the fluorescent screen in the receiver. By adjusting the potentiometers toward the outside terminals of the resistances the voltages on the conductors 40 and 41 will, of course, be increased and the amplitude of the beam will be increased also. Thus the beam can be made to cover as large or small a frame as is desired within the limits of the apparatus.

It will be understood now that with the oscillator in operation? connected up as shown the cathode ray bea in the receiver A will be caused to traverse a path across an imaginary picture frame such as is shown in Fig. 5 on the fluorescent screen 9 at the end of the tube, viewing the tube from the outside, or from the right of the drawing. With no incoming signal this frame will be practically invisible. When light signals are received, however, the potential of the shield 3 will be made more positive so that more electrons are permitted to pass through, and the intensity of the beam is thus greatly increased, the amount of increase, of course, depending on the strength of the received signal at any given instant. It follows, therefore, that as the beam traverses the frame its intensity will change in accordance with the change in the incoming light currents so that certain portions of the frame will be more or less brightly illumisystems of transmission.

nated while other portions of the frame will be left dark, all in accordance with the illumination of the picture which is being transmitted.

The modified form of oscillator shown in Fig. 2 may be used in place of the neon tube oscillator in circumstances where a motor is available and where the use of moving parts is not objection able. The motor-driven oscillator is somewhat simpler to operate than the neon tube oscillator, as there are less adjustments, but ordinarily it will not be as desirable as the latter in which all moving or rotating parts of the ordinary kind are eliminated. 7

Referring to the drawing, the reference letter M indicates the driving motor which may be a synchronous motor running in step with the motor at the transmitting station or it may be an ordinary shunt field motor arranged to be adjusted by hand to the required speed, for instance 900 R. P. M. On the shaft of the motor is mounted an interrupting mechanism which comprises the slip ring 52 and the short- circuiting commutators 51 and 53. The slip ring 52 serves to connect the negative pole of the battery 31' with the active segments of the two commutators. The brush of commutator 51 is connected to the far side of condenser 27' while the brush of commutator 53 is connected to the far side of condenser 28'. The commutator 53 has one active segment while the commutator 51 has forty-eight active segments. Assuming a motor speed of 900 R. P. M., commutator 53 will shortcircuit the condenser 28 fifteen times per second, while commutator 51 will short-circuit the condenser 27' seven hundred twenty times per second. This produces the proper scanning frequencies for receiving programs transmitted at the rate of fifteen pictures per second with a forty-eight-hole scanning disc. The apparatus can, of course, be adjusted for other rates of transmission, although if the ratio between the number of pictures per second and the number of holes in the scanning disc is different from that assumed, then one or both of the commutators will have to be changed. The neon tube oscillator possesses an advantage in this respect in that the frequency of the oscillators can be independently adjusted and thus the same physical apparatus can be used on a number of different The rest of the apparatus in. Fig. 2 is similar to the corresponding apparatus shown in Fig. 1, except that the conductors 40', 41, and 42' are connected to the receiver through condensers, which prevents displacement of the ray by the battery 31', and renders it unnecessary to provide a compensating battery such as 32, Fig. 1. The condensers are indicated by reference characters 80, 81, and 82, and should be of large capacity, on the order of 2 m. f. High resistance leaks 83 and-84 should also be used, connected from leads 40' and 41' to the common lead 42'. It will be understood that the condenser method of coupling can also beused with the oscillator shown in Fig. 1.

Having described my invention, what I consider to be new and desire to have protected by Letters Patent will be pointed out in the appended claims.

What is claimed is: 145

1. In a television receiver, a cathode ray device, said device including a target and two pairs of deflecting plates, two sources of potential connected to said pairs of plates, respectively, to cause the beam to scan the target, and a-revers- 15,

ing switch included in said connections for reversing the direction of scanning.

2. In a television receiver, a screen, means for.

producing a cathode ray, means for causing the ray to scan the screen in a series of disconnected lines, and means for changing the direction of the lines.

3. In a television receiver, a screen, means for producing a cathode ray, means for causing the ray to scan the screeen in a series of disconnected lines, and means for changing the order in which consecutive lines are produced on the screen.

4. In a television receiver, a cathode ray device, said device including a target and beam deflecting plates, means for producing deflecting potentials on said plates including a current source having one pole conductively connected to one or more of said plates, and an opposed current source included in the conductive connection to aid in centering the beam on said target.

5. In a television "receiver, a cathode ray device, said device including a screen on which the ray impinges, an oscillator for producing electrostatic fields to cause the ray to scan the screen, and adjustable means for causing the ray to scan any limited desired fractional portion of said screen.

6. In a television receiver, a screen, means for producing a cathode ray, means for causing said ray to scan the screen in a series of disconnected lines, and means for reversing the direction of scanning and the order in which consecutive lines are produced on the screen.

7. In a television receiver, a screen, means for producing a cathode ray, means for causing said ray to scan the screen in a series of disconnected lines, and means for reversing the direction of scanning and for changing the direction of said lines.

8. In a television receiver, a screen, means for producing a cathode ray, means for causing said ray to scan the screen in aseries of disconnected lines, and means for changing the direction of said lines and the order in which consecutive lines are produced on the screen.

9. In a television receiver, a screen, means for producing a cathode ray, means for causing said ray to scan the screen in a series of disconnected lines, and means for changing the direction of said lines, for reversing the direction of scanning, and for changing the order in which consecutive lines are produced on the screen.

10. In a television receiver, a cathode ray device including a screen and two pairs of deflecting plates, two sources of potential connected to said pairs of plates, respectively, to cause the beam to scan the target in a series of disconnected lines extending from left to right, said lines being produced consecutively from top to bottom, and means for changing said connections, so that said lines extend from right to left.

11. In a television receiver, a cathode ray device including a screen and two pairs of deflecting plates, two sources of potential connected to said pairs of plates, respectively, to cause the beam to scan the target in a series of disconnected lines extending from left to right, said lines being produced consecutively from top to bottom, and means for changing said connections so that said lines are produced consecutively from bottom to top.

12. In a television receiver, a cathode ray device including a screen and two pairs of deflecting plates. two sources of potential connected to said pairs of plates, respectively, to cause the beam to scan the target in a series of disconnected lines extending from left to right, said lines being produced consecutively from top to bottom, and means for changing said connections to cause the beam to scan-the target in a series;, of disconnected lines extending from top to bottom, said lines being produced consecutively from left to right.

13. In a television receiver, a cathode ray device including a screen and two pairs of deflecting plates, two sources of potential connected to said pairs of plates, respectively, to cause the beam to scan the target in a series of disconnected lines extending from left to right, said lines being produced consecutively from top to bottom, and means for changing said connections to cause the beam to scan the target in a series of disconnected lines extending from bottom to top, said lines being produced consecutively from right to left.

14. In a television receiver, a cathode ray device including a target and two pairs of beam deflecting plates, means for producing deflecting potentials on said plates, said means including a source of current having one pole conductively connected to one plate in each of said pairs, and adjustable means included in said connection for varying the potential on the two connected plates so that the point of impact of said beam may be shifted diagonally across said target.

15. In a television receiver, a cathode ray device including a screen and two pairs of beam deflecting plates, a source of potential connected in multiple to one plate in each pair, an oscillator for producing two fluctuating potentials connected to the other two plates, respectively, to produce deflections of the beam to cause it to scan said screen, and means for causing said beam to scan any desired portion of said screen, said means including adjustable means in said common connection for shifting the point of im-- pact of said beam diagonally across said screen and adjustable means in each of said individual connections for varying the amplitudes of the deflections of said beam.

16. In a television receiver, a cathode ray device including a screen and two pairs of beam deflecting plates, a neon tube oscillator for producing high and low frequency scanning potentials of a wave form having a substantially vertical component on one side, a common lead from said oscillator to one plate in each pair, a biasing battery in said common lead for normally maintaining the beam in contact with one corner of said screen, a low frequency output lead from said oscillator connected to the other plate of one of said pairs for slowly deflecting said beam in one direction across said screen, and a high frequency output lead from said oscillator connected to the other plate in the other pair for rapidly deflecting said beam across said screen in a direction at right angles to said first direction.

1'7. In a television receiver, a cathode ray device including a screen and two pairs of beam deflecting plates, a differential oscillator comprising two neon tube oscillating circuits coupled by a common branch including a source of current, means for adjusting the frequency of each oscillating circuit separately, a resistance in said common branch for causing said oscillating circuits to tend to keep in step when oscillating at multiple frequencies, and connections from said oscillator to sai d deflecting plates such that said beam is caused to scan said screen in a series 01' disconnected lines.

18. In a television receiver, a cathode ray device including a screen and two pairs of beam deflecting plates, a differential oscillator comprising two oscillating circuits each including a resistance and a neon tubeshunted by a condenser connected in series with a source of current common to both circuits, and connections from said oscillator to said deflecting plates such that the beam is caused to scan said screen in a series of disconnected lines, said connections including a multiple connection from one pole of said current source to one plate in each pair and adjustable connections from said resistances to the other two plates, respectively.

' 19.- In a television receiver, a cathode ray device including a screen and two pairs of beam deflecting plates, an oscillator comprising two neon tube oscillating circuits coupled by a common branch including a source of current, means for adjusting. each circuit separately so that one oscillates at a frequency'having a definite multiple relationship to the frequency of the other, connections from said oscillator to said deflecting I plates such that the beam is caused to scan the is caused to scan said screen in a series of disconnected lines, means for adjusting the irequency of each oscillating circuit separately so that the two frequencies have a deflnite multiple relationship governed by the mtmber of holes in the transmitting disc, means in said common branch for simultaneously adjusting said frequencies to correspond to the speed of rotation' of the disc at the transmitting station, and means for maintaining said multiple relationship between said frequencies during said adjustment.

21. In a television receiver, a screen, means for producing a cathode ray impinging on said screen, two pairs of deflecting plates, means for impressing on each pair of plates successive potentials of only one polarity, thereby causing movement of the ray in two directions from normal, and means for impressing on said pairs of plates a constant potential of opposite polarity to alter the normal position of said ray from which said movements begin.

22. In a television receiver, a screen, means for producing a cathode ray which normally impinges on said screen at a flxed point, two pairs of deflecting plates, means for impressing varying potentials of only one polarity but of two different frequencies on said pairs of plates, respectively, to cause the ray to scan a rectangular area on said screen extending in two directions from said fixed point, and means common to both pairs of plates for placing a constant-biasing potential on said plates to shift the point at which the ray impinges on the screen, whereby the deflecting potentials cause the my to scan a rectangular area on a different portion of said screen.

HAROLD J. MCCREARY.

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