US2178758A - Television system - Google Patents

Description

Nov. 7, 1939. R. D. KELL TELEVISION SYSTEM Original Filed Sept. 30, 1951 2 Sheets-Sheet 1 Fig.1.

E E W H M M A m m w U M E E T h MV 3 N w T /m m m P AMPLIFIER 15 A T'I'ORNEY.

Nov. 7, 1939 R. D. KELL TELEVISION SYSTEM Original Filed Sept. 30, 1931 2 Sheets-Sheet 2 TIME i g. 3. 1% F TIME MES-SALEM K r. AT L B WHITE lama Fig. 6. 40

LEAD! REEEIVEE i1 A TTORNEY.

Patented Nov. 7, 1939 UNITED STATES TELEVISION SYSTEM Ray D. Kell, Haddonfleld,

Corporation of America,

aware N. J., assignor to Radio a corporation oi. Del- Application September 30, 1931, Serial No. 565,953 Renewed November 19, 1937 6 Claims.

My invention relates to improvements in television systems, and more particularly to the method and means for synchronization.

In television systems of the general type disclosed in Arthur W. Vance Patent 2,137,039, issued Nov. 15, 1938, and assigned to the Radio Corporation of America, wherein the picture signals and the horizontal and vertical synchronizing impulses are transmitted in the same channel, these signals and impulses are separated by a method commonly known as amplitude selection, that is, the transmitted synchronizing impulses are substantially greater in amplitude than the picture signals so that the synchronizing apparatus at the receiving station, which is adjusted to be responsive only to the synchronizing impulses of greater amplitude, can readily distinguish the latter from the received picture signals.

In these systems proposed heretofore, the vertical impulses are distinguished or separated from the horizontal impulses also by amplitude selection, the amplitude of the transmitted vertical impulses being substantially greater than that of the horizontal impulses.

With this arrangement, the percentage of modulation of the radio transmitter by the picture signals has, of necessity, been limited to a relatively low value.

With the foregoing in mind, it is one of the objects of my invention to provide an improved television system of the character referred to, wherein it is possible to obtain greater percentage of modulation of the radio transmitter by the picture signals than has been possible in sys tems of this type proposed heretofore.

Other objects and advantages will hereinafter appear.

In accordance with my invention, both the horizontal and vertical impulses are transmitted at the same amplitude, but are of different shapes, so that these impulses have substantially different steepness of wave fronts, and the synchronizing apparatus at the receiving station is so adjusted and arranged as to readily distinguish between these impulses by reason of the difference in steepness of their respective wave fronts.

Further, in accordance with my invention, in a television system of the character described, the received picture signals are distinguished from the horizontal and vertical synchronizing impulses by amplitude selection, and the vertical impulses are distinguished from the horizontal impulses by wave-shape selection.

More particularly, in accordance with my invention, the horizontal and vertical synchronizing impulses are transmitted at the same amplitude, which is substantially greater than the amplitude of the peak picture sinals, the horizontal and vertical synchronizing apparatus at the re- 5 ceiving station is adjusted to be responsive only to the synchronizing impulses at the higher amplitude, and the vertical synchronizing apparatus at the receiving station is adjusted to be responsive only to the received vertical synchronizing 10 impulses which are of substantially less steepness of wave front than the received horizontal synchronizing impulses.

My invention resides in the features of connection, arrangement and method of operation, l5 as hereinafter described and claimed.

For the purpose of illustrating my invention, an embodiment thereof is shown in the drawings, wherein;

Figure 1 is a diagrammatic view of a television 20 transmitting system embodying my invention;

Fig. 2 is an enlarged fragmentary view, in elevation, of the scanning disc shown in Fig. 1;

Figs. 3, 4 and 5 are graphical illustrations of the principle of operation of the system shown in 25 Fig. l; and

Fig. 6 is a diagrammatic view of a television receiving station embodying my invention.

With reference to Figs. 1 and 2, the picture signals are developed by the so-called spot-scan- 30 ning method, employing a photoelectric cell 10 and a scanning disc I I provided with square apertures l2 arranged on a spiral, as usual. The photo-electric cell If! is connected to the input circuit of a suitable amplifier l3, which, in turn, 35 supplies an amplifier unit M. The amplifier i4 is connected, as indicated, to a suitable modulator connected to and controlling a radio transmitter E6.

The horizontal synchronizing impulses are de- 40 veloped by causing light from a source I! to shine through rectangular apertures, such as the apertures Ina to l5a shown in Fig. 2 circularly disposed inwardly from the scanning apertures I2 and concentric with the axis of revolution of the 5 disc H. The light shining through these apertures falls upon a photoelectric cell [8 supplying a suitable amplifier l9 connected to the input circuit of the amplifier unit l4. As indicated in Fig.

2, there is a horizontal synchronizing aperture 5 for each of the picture apertures 12, these synchronizing apertures being uniformly spaced around the peripheral edge of the disc I I.

For the purpose of developing a single vertical synchronizing impulse upon each revolution of 5 the disc H, or, in other words, for each picture frame, the disc is provided with an aperture having a shape similar to that of half a sine wave, and provided with a tail portion 2| for the purpose hereinafter explained.

In operation, the horizontal synchronizing impulses, such as those designated by reference characters lllb to i5b, which have a very steep wave front, as shown in Fig. 3, are developed and transmitted as the synchronizing apertures pass between the light source l1 and the photoelectric cell l8. These impulses occur at the end of each scanning line, the periods of time too, t1, i2, is, and t4, for example, elapsing between the occurrence of the successive horizontal impulses, being substantially equal to the period of time during which the light spot is caused to scan once across the object horizontally. For the purpose of illustration, it is assumed that the transmitted picture has sixty lines horizontally.

The aperture 20 is arranged to move between the light source I1 and the photoelectric cell l8 at the end of the picture frame, or substantially during the time that the last picture aperture I2 is effective.

On account of the characteristic shape of the aperture 20, an impulse 22, of the general shape shown in Fig. 4, is developed and transmitted, it being noted that this impulse has a steepness of wave front substantially less than that of the horizontal synchronizing impulses. The width of the aperture 20, at the middle thereof, is such that the amplitude of the developed vertical synchronizing impulse is substantially equal to that of the horizontal synchronizing impulses.

Fig. 5 shows graphically the manner in which the picture signals and the horizontal and vertical synchronizing impulses are transmitted in the same channel. The picture signals are designated by the reference numeral 23. The amplitiers l3 and is are so constructed and adjusted that the level of the horizontal and vertical synchronizing impulses, indicated by the broken line 24, is substantially greater than the level of the peak picture signals, indicated by the broken line 25. Both the horizontal and vertical synchronizing impulses, which are of the same amplitude, are made to modulate the radio transmitter l6 substantially This accounts for the fact that upon simultaneous occurrence of the horizontal synchronizing impulses, llb, l2b, I312, Nb and l5b, with the impulse caused by the vertical aperture 20 and its tail portion 2|, the tips 26 of these horizontal impulses rise only a relatively small amount above the level 24. This action, in other words, is caused by the fact that the radio transmitter is already working at substantially saturation at conditions as indicated in Figs. 3 and 4.

The construction and adjustment of the ampliflers and associated parts are such that the received picture and synchronizing impulses above the horizontal time line are in the black direction and accordingly operate to increase the negative bias on the control grid of the cathode ray receiving tube, hereinafter referred to. On the other hand, the picture signals below the horizontal time line are in the white direction, and operate to decrease the negative bias on the control grid of the cathode ray tube,

When the vertical impulse 22 has risen to the point 21, it is at the level 25 of the peak picture signals in the black direction, and is accordingly effective to cut oil the cathode ray at the receiving station. On account of th cha act tall portion 2| being correct to provide for this action. With the vertical impulse then at the level 28, it is still eil'ective, as received at the receiving station, to cut oil the cathode ray during the vertical return line period. The length of the tail 2| is made suilicient to insure that the vertical return line is entirely eliminated. By causing the vertical impulse to drop suddenly from the level 24 to the level 28, the load on the radio transmitter l6, after the strong vertical synchronizing impulse has been transmitted and served its purpose, is substantially decreased to such point as is only necessary to maintain the impulse at the level 28 for the purpose of effectively eliminating the vertical return line, as explained.

The level 24 is sufllciently above the level 25 to insure that the synchronizing apparatus at the receiving station will be capable, without critical adjustment, to be non-responsive to the picture signals and to readily distinguish between the latter and the horizontal and vertical synchronizing impulses.

As indicated in Fig. 5, the entire vertical impulse, including that caused by the tail portion 2|, occurs during the time period substantially equal to the periods for five picture lines. That is, this impulse occurs during the period in for the last picture line and the periods ii to it for the first four picture lines.

The horizontal synchronizing impulses are made to have as steep a wave front as is practical. In this connection, itis proposed that they be about five picture elements in width and of such shape that they may be represented by a single loop of a sine wave having a frequency of approximately 10,000 cycles.

With regard to the vertical synchronizing impulse, it is proposed to make the same of such shape that it may be represented by a single loop or a sine wave having a frequency of approximately 1,200 cycles.

Coming now to the receiving station, the same is disclosed as being of the same general type described in detail in the Vance patent referred to, and comprises a resistance 29 connected across the output of a suitable radio receiver 30 and supplied by the latter with picture signals and the horizontal and vertical synchronizing impulses. The control grid 3| of a suitable cathode ray tube receiver 32 is supplied with these signals and impulses through a connection 33. The various electrodes of the tube 32 are supplied with suitable operating potentials, as indicated.

For the purpose of causing the cathode ray 34 to scan the usual fluorescent screen structure 25 at the large end of the tube, electromagnetic coils 36 operate to deflect the ray vertically, while electromagnetic coils 31 operate to deflect the ray horizontally, A suitable electrical system 38 operates to force a current wave of the proper shape through the coils 36, while a suitable electrical system 39 operates to force a current wave of the proper shape through the coils 31.

Both of the systems 38 and 39, are constructed and adjusted so that the same are non-responsive to an electrical impulse at substantially the level 25 of the peak picture signals in the black direction, but are responsive to electrical impulses at the height of the substantially the level 24 of the received horizontal and vertical synchronizin impulses.

For the purpose of supplying the vertical and horizontal deflection systems 38 and 39 with the received synchronizing impulses and separating the latter so that only the vertical synchronizing impulses operate to drive the system 38, the grid circuit of a suitable amplifier tube 48 is connected across the output of the radio receiver 30. A battery 4| and an associated resistance 42 supply suiiicient negative bias to the tube 48 to cut off all picture signals, and permit only the synchronizing impulses to pass. A simple filter, comprising a resistance 43 and a condenser 44, is connected as shown in the plate circuit of the tube 48. The input circuit of the horizontal deflection system 39 is connected across both the resistance 43 and the condenser 44, while the input circuit of the vertical deflection system 38 is connected across only the condenser 44. The filter circuit 43-44, as is well known, depends upon the steepness of the wave fronts of the impulses for this action, and the horizontal synchronizing impulses at the higher frequency are, accordingly, permitted to pass to the horizontal deflection system 39, but only the vertical synchronizing impulses at the lower frequency are permitted to pass to the vertical deflection system 38 connected across the condenser 44.

With regard more particularly to the step forward in the art which my present improved system represents, it is important to understand first that in the prior art systems, of the general type disclosed in the co-pending application referred to, the vertical synchronizing impulses are distinguished from the horizontal synchronizing impulses by developing the former at a substantially greater amplitude than the latter, the picture m'gnals being distinguished from the synchronizing impulses by keeping the peak picture signals at an amplitude substantially lower than that of the horizontal synchronizing impulses. In these systems, therefore, the percentages of modulation of the radio transmitter by the synchronizing impulses and the picture signals are different, according to the respective amplitudes, the percentage for the picture signals being the lowest. In my present improved system, however, the vertical and horizontal synchronizing impulses are developed at the same amplitude and are distinguished from each other by reason of their having different steepness of wave fronts. The percentage of modulation of the radio transmitter by the horizontal synchronizing impulses is therefore the same as that by the vertical synchronizing impulses. The synchronizing impulses each being of the same amplitude, it is possible to develop the picture signals at a higher voltage level than has been possible heretofore, and still distinguish between the picture signals and synchronizing impulses. The percentage of modulation of the radio transmitter by the picture signals may therefore be correspondingly higher, and the efiective range of the transmitter is accordingly greater than in the prior art systems.

In other words, in my present improved system, there is amplitude selection of the horizontal and vertical synchronizing impulses from the picture signals, and frequency or wave-shape selection of the vertical impulses from the horizontal impulses. This makes possible, at the receiving station, a faithful separation of the synchronizing impulses from the picture signals and faithful separation of the vertical from the horizontal synchronizing impulses with a simple circuit or connection effective to maintain itself in operation without any critical adjustments.

While but one embodiment of my invention has been described, various changes within the conception of those skilled in the art may be made without departing from the spirit of my invention or the scope of the claims. I claim as my invention:

1. In a television system, means for developing electrical effects for framing purposes, said means including a rotatable member provided for such purposes with an aperture having a configuration similar to that of half a sine wave and pro vided with a slit-like opening extending from said aperture to constitute a tail portion thereof.

2. In a television system, means for developing and transmitting picture signals, a cathode my device comprising screen structure, means for developing a cathode ray, means for causing the ray to scan said structure for a picture frame, means for controlling the intensity of the ray in accordance with the received picture signals, and means for causing said ray to scan said structure along a return line at the end of each pictureframe period; and means for developing and transmitting an electrical effect during the return-line period, said last-named means including a rotatable member having an aperture shaped to have a tail portion and arranged so that the tail portion is effective during the return-line period, said ray-controlling means being responsive to said electrical effect as received to render the ray substantially non-effective with respect to said structure, said electrical effect as received being effective-to synchronize operating action of said fifth-named means with operating action of said first-named means.

3. In a television system, means for developing electrical effects for framing purposes, said means including a rotatable member provided for such purposes with an aperture having a certain width and a slit-like opening having less width than said certain width extending from said aperture to constitute a tail portion thereof.

4. In a television receiving system for the reception of a composite signal comprising picture signals, synchronizing signals occurring at a comparatively high frequency and synchronizing signals occurring at a comparatively low frequency, all of said synchronizing signals being of substantially the same amplitude and being of greater amplitude than peak picture signals of like polarity, each of said low frequency synchronizing signals being of greater duration than each of said high frequency synchronizing signals, said receiving system being of the type comprising a scanning device comprising a cathode ray tube provided with screen structure and with means for developing a ray of electrons and directing the same at said structure, said picture signals being supplied to said cathode ray tube, and also being of the type including means for deflecting the ray in a given direction at a relatively high frequency and means for defleeting the ray in a direction substantially perpendicular to said first-named direction at a relatively low frequency and including means for intercepting said composite signal, a separating circuit comprising a synchronizing channel connected between said intercepting means and said two ray deflecting means, said channel including amplitude separating means for removing said picture signals, said amplitude separating means being followed by a non-resonant filter circuit consisting of resistor and capacitor elements, said elements having such impedance values with respect to the characteristics of the said synchronizing signals that only one group 01' said synchronizing signals appears across one of said elements, one of said ray deflecting means being coupled across said one element.

5. In a television receiver for the reception of a composite signal comprising picture signals, synchronizing signals occurring at a high frequency and synchronizing signals occurring at a low frequency, said two groups of synchronizing signalsvbeing 01' substantially the same amplitude and being of greater amplitude than picture signals 01' like polarity, each of said low frequency synchronizing signals being of greater duration than each of said high frequency synchronizing signals, said receiver being of the type comprising a cathode ray tube having a cathode ray modulating electrode, horizontal deflecting means and vertical deflecting means, and including means for supplying received picture signals to said horizontal deflecting means after said picture signal has been removed.

6. In a television receiver for the reception or" a composite signal comprising picture lignais. synchronizing signals occurring at a comparatively high frequency and synchro occurring at a comparatively low frequency, said two groups 01' synchronizing signals being of substantially the same amplitude and being of signals of like of greater duration than each of said high frequency synchronizing signals. said receiver being of the type comprising a tube, and comprising generator means for supplying a saw-tooth wave fleeting means and generator means for supplying a saw-tooth wave to said vertical d means, a separating circuit comprising a fllter circuit, means for supplying only said synchronizseries, the values of said resistor and condenser being so chosen with respect to the frequency and duration 01' said synchronizing signals that substantially only said low frequency synchronizing signals appear across said condenser. means for supplying the signal appearing across said condenser to said second generator means, and means for supplying said high frequency synchronizing signals to said first generator means.

RAY D. KELL.

Images