US2401384A - Television system - Google Patents

Description

June 4, 1946. N. H. YOUNG, JR 2,401,384

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June 4, 1946.

Filed July 17, 1944 N. H. YOUNG, .JR

TELEVISION SYSTEM 4 Sheets-Sheet 3 To SHA/ER (9J) f INVENTOR.

, .4 TTORNEY June 4, 1946. N. H. YOUNG, JR 2,401,384

TELEVISION SYSTEM Filed July 17, 1944 4 Sheets-Sheet 4 Hop/2mm. BLANK/Nc; PULSE moo/105k) 5,45 ways OUTPUT C OM POS TE wn v5 q IN VEN TOR. NORMA/v H. you/ve JR.

TTORNE'Y Fatented .lune 4, i946 TELEVISION SYSTEM .if T y OF Fl il.; L

Application July 17, 1944, Serial No. 545,291

l This invention relates to television systems and more particularly to transmission of picture signals, synchronizing signals and sound signals over a common transmission medium.

It has been proposed heretofore to transmit sound signals represented by pulses modulated either in amplitude or width during the blanking intervals between lines of picture signals. Such systems, however, have several disadvantages. Where sound is transmitted by amplitude modulated pulses, it is necessary that the transmitter and receiver circuits have accurate linear characteristics to avoid distortion. Because of the amplitude modulation feature of such systems limiters cannot be used for minimizing interference, and the maximum signals-to-noise ratio 14 Claims. (Cl. 1785.6)

usually obtainable for the expenditure in band width cannot be realized. Furthermore the average power required varies according to the modulating signal. In the case of distant transmission, the eiects of fading as well as other distorting eects are amplified through all or part of the repeaters that may be used in the transmission system thereby necessitating the use of A. V. C. circuits. As for width modulation of pulses, here again the average power required varies directly in proportion to the sound signals.

It is an object of the present invention to provide a method and means for transmitting sound signals with picture signals over the same transmission medium without the above-mentioned disadvantages. Another object is to produce an improved composite video signal in which the horizontal, vertical and equalizing components are easily distinguished one from the other; and wherein sound modulated pulses are time modulated relative to one form of synchronizing pulses for demodulation at receivers.

Another object of the invention is to provide a television transmission system with sound transmitting equipment for transmission of sound signals in the same channel with the picture signals wherein such equipment is of relatively simple construction and has negligible power consumption.

According to a feature of my invention the horizontal synchronizing pulses as well as the sound pulses are made of very narrow width with the sound pulses timed to occur during the blanking intervals which contain the horizontal synchronizing pulses. To convey sound intelligence, the sound pulses are time modulated preferably relative to the horizontal synchronizing pulses, although the modulation in time may follow some other principle. For example, the sound pulses may be modulated in time accordingto the pushpull type of pulse modulation whereby successive sound pulses are displaced toward and away from each other according to the instantaneous values of the sound signals. The time displacements of the sound pulses where made relative to the horizontal synchronizing pulses may be demodulated at the receiver according to the principles of my invention disclosed in my copending application for Receiver system, Serial No. 539,882, filed June 12, 1944.

For a further understanding of the above and other objects and features of my invention reference is had to the following detailed description to be read in connection with the accompanying drawings in which: l

Fig. 1 is a block diagram of a television transmitting system incorporating the subject matter of this invention;

Fig. 2 is a graphical illustration used in explaining the production of the horizontal blanking, horizontal synchronizing and sound signals according to the system of Fig. 1;

Fig. 3 is a schematic wiring diagram of a form of time modulator that may be employed in the system of Fig. l;

Fig. 4 is a graphical illustration of a composite television signal according to the principles of my invention;

Figs. 5 and are block diagrams of modifications of the invention; and

Fig. 7 is a graphical illustration used in explaining the form shown in' Fig. 6.

In the vtelevision transmitting system of Fig. 1 I show as a base wave source an oscillator l which may be of any known type capable of producing a stable oscillatory wave. For the present disclosure let the frequency of the oscillatory wave 2 of graph a, Fig. 2, of the oscillator l be equal to 2f. The Wave 2 controls the production of horizontal, vertical and equalizing synchronizing signals,blanking pulses for the horizontal retraced intervals, blanking pulses for the frame retraced intervals and the sound signals. The vertical and equalizer synchronizing pulse producer 3 may be of conventional form including means for producing the frame retrace blanking wave. 'I'he horizontal synchronizing and blanking signals are produced by applying the wave 2 of oscillator I to a multi-vibrator d which is preferably a1'- ranged to operate at one mode of operation in response to a given point on the Wave 2 which operation continues for substantially two cycles of the wave 2 until the grid vbias of one of-the multi-vibrator tubes decreases to such a value that the wave 2 causes the multi-vibrator to change its mode of operation. The change of operation defines, as indicated by wave 5 graph b, a trailing edge 6. This change conditions the circuit for triggering actuation into a new period of operation as indicated by the leading edge 'I caused by a given valve of the wave 2. The wave 5 of the multi-vibrator 4 is applied to a horizontal synchronizing pulse shaper 8 which may comprise the usual series of differentiator and clipper circuits whereby a series of narrow Width pulses 9 of frequency f is produced corresponding to the leading edges 1 of the wave 5. The output wave 5 of multi-vibrator 4 is also applied to horizontal blanking pulse shaper I which may include the usual differentiating and clipping circuits and if desired, a multi-vibrator, for producing a series of pulses I I of the proper width for the horizontal blanking periods.

The wave 2 of the oscillator I may also be used as hereinbefore stated for controlling the timing of.sound signals. This is accomplished by ap plying the wave through a phase shifter I2 to obtain if necessary, the proper phase relation necessary for the sound signals to a time modulator I3. The time modulator may be of any known form of pulse modulator whereby the pulses are displaced in time according to the instantaneous value of an audio signal such as may be applied thereto from source I4. For purposes of illustrating one form of time modulator that maybe employed, I show in Fig. 8 a cusper type of modulator whereby the pulses are time modulated in push-pull manner. This type of modulator may be symmetrically biased or it may be unequally biased as indicated in Fig. 3.

The modulator is shown in Fig. 3 as including a transformer I5 having a primary coil I6 to which is applied wave 2 of frequency 2f. The audio signals are applied from a microphone Il through audio amplifier I 8 to input coils Ita on transformer I5. Secondary coils I9 and 2D are connected respectively to the control grids of vacuum tubes 2I and 22 respectively. Coil I9 has its opposite end connected to a source of energy 23 and thence to ground 24. The coil 20 has its opposite end connected to a source of energy 25 and thence to ground 24. The two coils are interconnected by a by-pass condenser 26. The cathodes of the tubes 2l and 22 are connected to ground While the anodes thereof are interconnected and provided with' a source of anode potential through resistor 2l.' The outn put of the circuit is taken across resistor 27 and pplied to the shaping amplifier 28 as shown in Referring to graphs e, f and g. of Fig. 2 the base wave 2 is shown in graph e and represents the Wave energy applied to primary coil I6. The potential difference of sources 23 and 25 is so chosen as to effect an offset relation between the wave 2 and the biased relationship of the tubes 2l and 22. The push-pull operation of the tubes rectifies, in effect, the wave 2 about an offset axis 29 thereby producing a. cusper wave 30 as indicated by graph f. The shaping amplifier 28 of Fig. 1 is arranged to clip the cusps of the Wave 30 along a level such as indicated at 3l thereby producing a series of narrow width pulses 32 as indicated by graph g.

The modulation of the pulses 32 is produced by the audio wave applied to the transformer I5 through coils I8 and I9. The audio wave affects the offset relationship of the wave 2 with respect to the axis 29. The extreme swings of modulation are indicated by limits 33 and 34. It will be noted that for the upper "limit 33 the displacement of the pulse 35 is to the right as indicated by the limit 36 in graph y and that the pulse 3l is displaced to the left as indicated by limit 38. Likewise a modulating wave corresponding to limit 34 will displace the pulses 35 and 31 in the opposite direction as indicated by limits 39 and 40 respectively. For a further understanding of this type of pulse time modulation reference may be had to the copending application of E. Labin and D. D. Grieg, Serial No. 455,897, filed August 24, 1942.

According to the present embodiment only every fourth pulse of the series 32 is necessary for conveying the audio signals. The surplus of pulses in this series ls caused by the choice of a high frequency for the wave 2. It will be understood that a. frequency divider may be used to reduce the frequency of the wave 2 but this is not necessary since the unwanted pulses may be suppressed on keyed amplifier 4 I. The keyed amplier may be of any known form to which the pulse energy II is applied from shaper I0. The key-in and key-out operation of the amplifier 4I is indicated by curve 42 of graph g, the output of the amplifier being indicated by the pulse series of graph h.

The picture signal source 43 may comprise any known scanning circuit synchronized by the vertical and horizontal synchronizing pulses from producer 3 and shaper 8 by way of connections 3a and 8a, respectively. The output of the picture signal source 43 is applied together with the horizontal synchronizing pulses of Shaper 8, vertical and equalizer synchronizer pulses and frame retrace blanking pulses, the latter from producer 3 over connection 3b, horizontal blanking pulses from Shaper IU and the time modulated output pulses of amplier 4I to mixer 44. 'I'h'e mixer 44 may comprise more than one mixer stage but for simplicity of illustration a single mixer block is shown.

If desired, the mixer 44 or one of the stages thereof may be provided with a bias to provide a threshold clipping operation for the removal of the unwanted time modulated pulses of graph g, thereby replacing the keyed amplifier 4 I.

The composite video signal output of mixer 44 is applied to a known form of transmitter 45 for transmission at a given carrier frequency over omni-directional antenna 48.

The video signal applied to the transmitter 45 indicated by graph i has the same time base as the preceding graphs of Fig. 2. The horizontal blanking pulses I I are shown to separate the lines 41 of picture signals. superimposed on the blanking pulses II are two narrow width pulses, the first of which is a horizontal synchronizing pulse ofl series 9 and the second of which is a time modulated pulse of series 32. It will be noted that the synchronizing pulses occur shortly after the occurrence of the leading edge of the blanking pulse and since the horizontal synchronizing pulses are in synchronism with the blanking pulses they will always have the xed relationship shown. The time modulated pulses 32, however, vary in time displacement from the position indicated in graph i between the limits 36 and 39. This displacement, it will be observed, is relative to the horizontal synchronizing pulses 9. It is on this relationship that I base the principles of operation of a receiving circuit disclosed in my aforesaid copending application Serial No. 539,882. The receiver disclosed in my copending application includes a clipper circuit for removing the horizontal and time modulated pulses from the video signal. The horizontal synchronizing pulses are used to synchronize a sawtooth generator, the saw-tooth wave vof which is used for controlling the line scanning of the picture signals and for translating the time displacements of the time modulated pulses into pulses having corresponding amplitude displacements. The amplitude modulated pulses thus obtained are applied to a low-pass filter and audio reproducer as is commonly practiced in A. M. receivers.

To give a further understanding of the television transmitter I show in Fig. 4 a composite video wave including the different' signal components. The portion of the wave shown in graph i of Fig. 2 is shown to the left of Fig.` 4, the components thereof being identified with like referenced characters. The frame tracing interval is sh'own broken, but the components thereof are all represented in the part shown. The horizontal and time modulated pulses 9 and 32 eX- tend above the blanking level as do equalizer pulses d and vertical synchronizing pulses 50. The equalizer4 pulses 59 are preferably wider than the horizontal pulses and the vertical synchronizing pulses are of still greater Width than the equalizer pulses so that they may be separated by width selection from the horizontal synchronizing and time modulated pulses and from each other. The energy of an equalizer pulse is preferably equal to the combined energy of one horizontal synchronizing pulse and one sound pulse. It will be noted that the vertical synchronizing pulses are so shaped as not to require any transmission of energy during the horizontal blanking interval containing the horizontal synchronizing and time modulated pulses.

Referring back to Fig. l, the time modulator i3 may follow any one of several diierent principles of time modulation. Where the time modulator operates on a base wave such as wave 2 of oscillator i, the modulator may be placed in the position indicated in Fig. 1. If the modulator is of the type operated from a pulse source it may be desired to utilize the horizontal synchronizing pulses of shaper as the source of pulses for the modulator. may be modied as shown in Fig. 5. Fig. 5 only shows that portion of Fig. l that is pertinent to this modification. The pulses from Shaper 8 are applied over connection 5l to time modulator 52 which, in this'case, may be of the character including a multi vibrator diferentiator clipper principle of operation such as set forth in Fig. 6 hereinafter described, or it might include the pulse shaping and gate clipping-differentiating principles of the conding application of Emile Labin and D. D. Grieg, Serial No. 455,898, iled August 2li, 1942, or any other suitable pulse time modulator.

Where a multi-vibrator-diferentiator-clipper principle of modulation is employed, the circuit of Fig. 5 may oe modied, if desired, according to the circuit diagram of Fig. A6. The base wave 2 of graph m, Fig. 7. applied Afrom oscillator i vthrough phase shifter 5i to pulse producer 52 is In such case, the circuit of Fig. 1

56 arranged to receive wave 2 and produce a wave" n 51 of the character shown in graph o. The audio signal wave from source I4 is applied to one of the tube circuits of the multi-vibrator 56 so as to modulate the period thereof by varying the occurrence of the trailing edge 58 of the output wave thereof. This modulation is indicated as progressively increasing the period of the pulses 51 as indicated by the delayed occurrence of traillng edges 58h and 58e. When the wave 51 is differentiated by diierentiator 59, the output pulses El! of positive polarity, graph p, correspond to the leading edges of the wave 51 while the output pulses 6| of negative polarity correspond into the time positions of the trailing edges 58. The pulses 6B are clipped ci as indicated at 52 and shaped by shaper 63 to produce horizontal synchronizing pulses a, 60h, 60e etc. while the pulses 5l are likewise clipped at level 64 and shaped by shaper 65 to produce signal pulses Bla, Bib, Blc etc. For further variations in multivibrator types of time modulation reference is made to U. S. Patents Nos. 2,262,838 and No. 2,266,401.

It will be noted that in this embodiment of the invention horizontal synchronizing and signal pulses are obtained by the same multi-vibratordifferentiator circuit, the two series of pulses being segregated by suitable shaping circuits. The horizontal synchronizing pulses 60a, 60h, 60o etc. occur at a given timing and when mixed with the horizontal blanking pulses in mixer M are superimposed on the blanking pulses 55 directly following the leading edges of the blankingpulses as shown by graph q. The signal pulses Sla, Glb, Slc etc are also superimposed by mixer 44 on the pulses 55 but they vary in time position relative to the horizontal synchronizing pulses. The

horizontal synchronizing and signal pulses 60a, 6ta; Bb, Sib; 60e, Sic; etc. are segregated from the composite video signal in the manner hereinbefore referred to and the time modulation represented thereby translated into amplitude modulated output as set forth in my aforesaid copending application Serial No. 539,882.

While I have shown and described particular forms and variations of the television transmitter system of my invention it should be understood that the forms hereinI shown and described are given by wayfof illustration of the invention only and not as restricting the invention as set forth in the object and the appending claims.

I claim:

1. A method of .producing television signals including picture signals and sound'signals com/ prising producing lines of picture signals wit intervals between the successive lines, time d placing pulses according to instantaneous values of said sound signals, and interleaving pulses produced by the time displacing operation between said lines of picture signals. d I.

2. In" an intelligence transmission system, means for producing lines of picture signals with intervals between said lines, means fpr producing a pair of pulses variably spaced according to instantaneous values of a sound signal wave, and

' means for causing said variably spaced pulses to shifted in phase as indicated at 2a. The pulse f producer 52 may include, for example, a multivibrator 53 and a clipper 5d for production from energy of wave 2a a wave of substantially rectangularly-shaped horizontal blanking pulses 55, graph n. For time modulation of theaudio signals from source it I provide a multi-vibrator occur insald intervals.

3. A method of producing television signal/s including picture signals, synchronizing signals and sound signals, comprising producing lines of picture signals with intervals between the successive lines, producing synchronizing pulses occurring during said intervals, time modulating pulses relative to said synchronizing pulses according to instantaneous values of said sound signals, and causing pulses produced by the time modulating operation to occur during said intervals.

4. In television transmission wherein picture signals are separated by horizontal blanking intervals containing horizontal synchronizing signals; a method of producing sound signals for transmission with said picture signals comprising producing pulses time modulated relative to said horizontal synchronizing signals according to instantaneous values of a sound signal wave, and causing pulses produced by the time modulating operation to occur during said blanking intervals.

5. In television transmission wherein picture signals are separated by horizontal blanking intervals; a method of producing horizontal synchronizing signals and sound signals during said blanking intervals comprising producing a base wave of a frequency having a given relation to the repetition frequency of said blanking intervals, producing horizontal synchronizing pulses from said base wave timed to occur during said blanking intervals, producing from said base wave pulses time modulated relative to said horizontal pulses according to the instantaneous values of a sound signal wave, and causing pulses produced by the time modulating operation to occur during said blanking intervals.

6. In television transmission wherein the composite video television signal includes producing lines of picture signals separated by horizontal retrace b'lanking intervals and frame retrace blanking intervals; a method of producing horizontal synchronizing pulses, vertical synchronizing pulses and sound pulses for the video television signal comprising producing horizontal synchronizing pulses to occur at a rate corresponding to the repetition rate of said horizontal blanking intervals, producing pulses time modulated relative to said horizontal synchronizing pulses according to instantaneous values of sound signals, timing said horizontal and time modulated pulses to occur during said blanking intervals, producing vertical synchronized pulses timed to occur during the frame retrace intervals in interleaved relation with said horizontal and time modulated pulses.

7. A method according to claim 6 further including the steps of producing equalizer pulses to occur during the frame retrace blanking intervals interleaved with said horizontal and time modulated pulses, and shaping the equalizer and vertical synchronizing pulses differently from each other and differently with respect to the shape of said horizontal and time modulated pulses.

8. In a system for producing television signals including picture signals, horizontal synchronizing signals and sound signals; means for producing horizontal blanking signals to provide intervals between lines of picture signals, means for said intervals in time displaced relation to said horizontal synchronizing pulses.

9. In a television system, means for producing a base wave, means 'to produce horizontal blanking pulses from said base wave, means for further producing from energy of said base wave horizontal synchronizing and signal pulses timed for super-position on said blanking pulses, means to time modulate the signal pulses according to in.. stantaneous values of a signal wave, and means for mixing said horizontal synchronizing pulses and said time modulated signal pulses-with said blanking pulses.

10. A system according to claim 9 wherein the means for producing horizontal synchronizing and signal pulses includes means for producing horizontal synchronizing pulses having a repetition frequency equal to one-half the frequency of said base wave, a modulator for producing signal pulses having a repetition frequency equal to twice the frequency of said wave, and means for blocking all said signal pulses except those timed to occur in super-position on said b lanking pulses.

1l. A system according to claim 9 wherein the means for producing horizontal synchronizing and signal pulses includes means for producing horizontal synchronizing pulses having a repetition frequency equal to one-half the frequency of said base wave, a modulator for producing signal pulses having a repetition frequency equal to twice the frequency of said wave, means to unbalance the operation of said modulator to cause the pulses produced thereby to occur in time displaced relation relative to said horizontal synchronizing pulses, and means for blocking all said signal pulses except those timed to occur in super-position on said blanking pulses.

12. A system according to claim 9 wherein the means for producing horizontal synchronizing and signal pulses includes means for producing horizontal synchronizing pulses having a repetition frequency equal to one-half the frequency of said base wave, means for shifting the phase of the base wave a desired amount, a modulator for producing signal pulses from energy of the phaseshifted wave, the pulse repetition rate of which is equal to twice the frequency of said wave, and means for blocking all of said signal pulses except those timed to occur in super-position on said blanking pulses.

13. A system according to claim 9 wherein the means for producing horizontal synchronizing and signal pulses includes means to generate horizontal synchronizing pulses for producing signal pulses time displaced with respect to said horizontal synchronizing pulses,

14. A system according to claim 9 wherein the means for producing horizontal synchronizing and signal pulses includes a multi-vibrator for producing a rectangular wave having distinct leading and trailing edges for each period thereof, the. means for time modulating signal pulses being arranged to vary the operation of said multi-vibrator to cause the occurrence of one of said edges to vary in time relation relative to the other edge of the wave period according to the instantaneous values of saidsignal wave, means to derive signal pulses from the edge, the position of which varies from period to period according to signal value, and means to derive horizontal synchronizing pulses from the other edges of said rectangular wave. u

NORMAN H. YOUNG, JR.

Disclaimer 2,401,384.Nmmm H. Y 01mg, Jr., Jackson Heights, N. Y. TELnvIsIoN Srs- TEM. Pate-11tdated J une 4, 1946. Disclaimer filed Dec. 8, 1951, by

the assignee, Federal Teephone amd Radio 00mm-ation. Hereby enters this disclaimer to claims 1, 3, and 4 of said patentf [Oficial Gazette Janna-wy 75, 7.952.]

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