US2258943A - Synchronizing signal generator - Google Patents

Description

A. v. BEDFORD sYNcHRoNIZING SIGNAL GENERATOR Oct. 14, 1941.

'7 Sheets-Sheet 1 Filed Nov. 5o, 19:58

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SYNCHRONIZING SKIGNAL GENERATOR Filed Nov. 30, 1938 '7 Sheets-Sheet 2 7 ShetS-Sheet 3 Filed Nov. 50, 1938 WRR u@ "mm, A

Oct. 14, 1941. A. v. BEDFORD I 2,258,943

SYNCHRONIIZING SIGNAL GENERATOR Filed Nov. so, 1958 7 sheets-sheet 4 .-/Zld 1.7 0 d n ram/fr Oct. 14, 1941. A. v. BEDFORD SYNCHRONIZING SIGNAL GENERATOR Oct- 14, 1941- A. v. BEDFORD 25258943 SYNCHRONIZING SIGNAL GENERATOR Filed Nov. .'50, 1938 '7 Sheets-Sheet 6 Oct. 14, 1941. A, v. BEDFORD SYNCHRONI-ZING SIGNAL GENERATOR v '7 Sheets-Shea*I 7 Filed NOV. 30, 1938 Liuu'uuuu'uuu LILILIUULI L I| l LI- v mijn;

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Patented Oct. 14, 1941 UNITED STATE s PATENT oFFlcE I SYNCHRONIZIN G SIGNAL GENERATORl Alda V. Bedford, Collingswood, N. J., assignor to i' Radio Corporation of America, a corporation oi' Delaware Application November 30, v|.9:'8,.Sel'la.l N0. 243,238

(ci. 17a-69.5)

A a corresponding displacement of their front 19 Claims.

My invention relates to television transmitters and particularly to a method of and means for producing synchronizing signals or impulses. More specifically, my invention relates to' a synchronizing signal generator of the general type described in Patent No. 2,132,655, issued October l1, 1938, to J. P. Smith and assigned to the Radio Corporation of America.

Ideflection period. While the Smith patent describes a signal wherein the double frequency impulses are set into these slots, it is preferred at the present time that the front edge of a slot be utilized for maintaining horizontal synchroni-1 zation.

' The specic synchronizing signal produced by the generator which is described by way of example in this application is the signal disclosed.

in my copending application Serial No. 222,081, illed July 30,1938, entitled Television systems and assigned to the Radio Corporation of America. As described in this application, the

preparatory double frequency impulses have onehalf the width of the horizontal synchronizing impulses. Q I

From the foregoing. it will be understood that the synchronizing signal consists of several groups of impulsesr namely, horizontal synchronizing impulses, double frequency preparatory impulses vand vertical synchronlzing'impulses.

xSince the front edges ofl these various impulses produce synchronizing voltage kick or sharp impulse that is applied to the horizontal deflecting circuit, it is essential that there be a iixed time interval between these front edges if there of these oscillators will cause a -slight displaceedges.

The vprincipal object of the present invention is to provide a synchronizing signal generator of the electronic type, as distinguished from the rotating disc type, in which all edges of the signal which determine horizontal synchronization have a fixed time relation. In the preferred embodiment, these edges are the front edges.

States more broadly, an object of my invention is to provide an improved method of and means for producing a synchronizing signal.

My invention is based on the idea that impulses -derived from a single oscillator may be utilized to provide the front edges for the impulses of all the above-mentioned groups of impulses.

Briefly, this may be accomplished, for example, by generating one-half width double frequency impulses, the -front edges of which, in the n nal signal, are the front edges of all impulses. In the region of the synchronizing signal where the regular horizontal synchronizing impulses are desired, alternate double frequency impulses are removed by means of impulses occurringI at the horizontal scanning or line frequency. The

remaining one-half width impulses in this region are widened to full width by adding line frequency impulses -to their back side.

Inthe region where the slotted vertical synchronizing impulse is to appear, comparatively wide double frequency impulses are added to the back sides of the one-half width impulses to produce the vertical synchronizing impulse.

Thus, .four signals are added together to produce a synchronizing signal which will be the final signal after it has been "clipped oil" at both top and bottom, these four signals being (1) the doublev frequency one-half width impulses, (2) line frequency impulses which occur outside the region oi' the preparatory impulses and which remove alternate double frequency impulses, (3) line frequency impulses which also occuroutside the region of the preparatoryim- Figure 1 is a block diagram of a synchronizing 'I ment of the dlnerent groups of impulses with 55- sisnal generator embodying my invention.

Figure 2 is a group of curves which are referred to in explaining the invention, the dotted lines and arrows indicating the waves which are combined to produce a new wave,

Figures 3a, 3b, 3c and 3d together are a circuit diagram of the generator shown in Figure 1, and

Figures 4 and 5 are groups of curves illususe in an odd-line interlaced scanning system. The desired whole number plus 1/2 relation between the scanning line frequency and the frame frequency/is obtained by utilizing a main or master oscillator I operating at double the line frequency, in this particular case at 26,460 cycles per second, by dividing this frequency by two by means of a frequency divider 2 to produce the horizontall deflecting or line scanning frequency of 13.230 per second and by dividing the double frequency by odd numbers by means of frequency dividers 3, 4 and 6 to produce the vertical deflecting or frame frequency of 60l per second. This method of obtaining the synchronizing impulses for interlaced scanning is described in my British Patent 434,469, issued September 2, 1935.

Since the oscillator l is a sine wave oscillator in the present design. its output is passed through a limiter or clippercircuit 1 for the purpose of producing rectangular impulses, these impulses being impressed upon the frequency dividers.

zontal and vertical synchronizing impulses are derived, is locked in with the 60 cycle power line by means of a suitable lock-in circuit indicated at 8 to which is supplied 60 cycle impulses from frequency divider 6 and sine wave voltage from the 60 cycle power line, the sine wave voltagey passing through a phase shifter 6 which determines the phase relation of the synchronizing impulses with respect to the power line supply. l

The generator of Fig. 1 produces tive signals as follows:

First, and of the most interest, the video synsignal is built. Specifically. the front edges of the impulses d are the front edges of ail impulses comprising the final signal shown at o in Fig. 2.

The 26,460 cycle impulses d are obtained by taking impulses from the limiter circuit 1, delaying them a suitable amount by a delay network D to make the front edges of the impulses start at proper time, impressing them upon a multivibrator II which may be adjusted to make the impulses d ofthe proper width, passing the tion, in the specific design illustrated, is for resulting impulses through a limiter or clipping circuit I2 which supplies the final impulses d to a mixing portion of the circuit indicated at I3 where the impulses d. h. j and m are to be mixed or added.

It may be noted that in the actual circuit, which is hereinafter described, there is no specific unit I3 since the addition of signals is accomplished by means of a' common plate circuit for the limiter I2 and the limiters for the other three signals h, i and m.

The impulses h, which are for the purpose of removing alternate impulses d in the region where double frequency impulses are not desiredfare obtained by taking impulses froma 13.230 cycle multivibrator I8 which feeds into a limiter-mixer circuit I1. To eliminate the ixnpulses h for the period during which double frequency impulses are desired, cycle impulses are also fed into the limiter-mixer I1, the 60 cycle impulses being taken from a multivibrator I8 through a limiter circuit I9. The two groups of impulses which are fed into circuit I1 are shown at j and e in Fig. 2.

The technique for removing an undesired group oi' impulses by means of the circuit I1 may bethe same as that described in the abovementioned Smith patent. For example, a group The main oscillator I, from which the horiw of 13'230 cycle impulses may be depressed below a certain voltage level by the 60 cycle impulse and then only the impulses above this level passed through a limiter or clipping circuit 2i following the mixer I1. Thus the final signal 15 h may be produced. In the specific circuit I1 to be described later the signal h is produced by causing the 60 cycle impulses f to block a mixer tube periodically whereby the impulses e do not pass through the mixer tube during 5b the blocking period.

chronizing signal which is to be transmitted to the receiver,

Second, the video blanking signals which are to be transmitted to the receiver alongwith the picture signals and the synchronizing signals,

Third, the horizontal synchronizing or driving impulses for the transmitter iconoscope,

Fourth, the vertical synchronizing or driving impulses for the transmitter iconoscope. and Fifth, the iconoscope blanking impulses. The present invention relates primarily to' the production of the first group of video im" impulses. The

The impulses 1, which are for the purpose of `doubling the width of impulses d in the region where alternate impulses d have been removed, are obtained by taking 13,230 cycle impulses '55 froma multivibrator 22 which is driven by the frequency divider 2 through a delay circuit D, the delay circuit determining the time the front edges of the impulses start and the adjustment of multivibrator 22 determining the width of the 13,230, cycle impulses from multivibrator 22 are `fed into a limiter-mixer circuit 23 together with the 60 cycle impulses f. The desired signal j appears in the output 'of a limiter 24 following the mixer 23.

Finally, the impulses m which, when added to impulses d, produce the slotted vertical synchronizing impulse, are obtained from a mixture of 60 cycle impulses derived from a multivibrator 26 and 26,460 cycle impulses taken from the limiter 1.

A comparison of curve m with curve f in Fig. 2 will show that the slotted impulse m should start at a considerably later time than the impulse f. This rather large delay is conveniently pulses d are the impulses upon which the final obtained by adjusting multivibrator 28 to pmduce impulses a which have such width that the lected 26,460 cycle impulse is caused to trigger d oif a 60 cyclenear the back edge of each impulse U. In the output-circuit of multivibrator 28 there appear the delayed impulses l which are fed into a limiter-mixer 28.

There are also fed into the limiter-mixer 29 the Y26,460 cycle impulses k shown in Fig. 2, these impulses having their width determined by the multivibrator 3l which is driven through delay circuits D and D from the limiter 1.

The iinal signal m appears in the output of a limiter 32 following the limiter-mixer 29.

'I'he signals d, h, i and madd in the mixing circuit I3 to produce the signal n which, when clipped at the levels indicated by the dotted lines, produces the iinal signal shown by the curve 0.

A comparison of the curves d, :i and m will show that the front edges of impulses d are also the front edges of the horizontal synchronizing impulses as well as the front edges of the individual impulses comprising the slotted vertical synchronizing impulse. The impulses d themselves are the double frequency preparatory impulses.

Reference will now be made to the production of the above-mentioned second, third, fourth and fifth signals. O

The second signal (the video blanking signal) is shown at a in Fig. 2. This signal is a mixture of 60 cycle impulses produced by a, multivibrator 35 and 13,230 cycle impulses produced by a multivibrator 31. The two groups of impulses are sup-l plied to a limiter mixer -circuit 38, the 60 cycle impulses first passing through a limiter 39. The final signal a appears in the output circuit of a line amplier di.

The third and fourth signals, the horizontal and vertical synchronizing or driving impulses, are shown at p and c, respectively, in Fig. 2..:

The horizontal driving impulses p are obtained from a multivibrator 42 through a limiter or clipper tube 43, the final signal p 4appearing in the output circuit of a line amplifier 44.

The vertical driving impulses c are obtainedy Main oscillator and frequency dividers My improved generator will now be more fully described in connection with the circuit diagram vshown in Figs. 3a to 3d.- Thefour sheets of fdrawings form a complete circuit diagram when they are placed next to each other with Fig. 3a in the upper left hand corner, Fig. 3b in the upper right'hand corner, Fig. 3c in the lower left hand corner and Fig. 3d in the lower right hand corner. It may be noted that the sheet containing Fig. 3a should be placed on its side while the other three sheets should be placed in an upright position. In the block and circuit diagrams like parts are indicated by the 'same reference characters. On the circuit diagram the lower the signals have the wave shapes shown bythe curves having corresponding letters in Fig. 2.

.Referring to Fig. 3a, the main oscillator I may be a sine wave oscillator of the negative transconductance type having a tank circuit comprising an inductance coil 51 and a condenser 58. particular oscillator is of the general type described in Patent 2,109,752 issued to Pooh et al. and assigned to the Radio Corporation of America, one of the 'resistors in the Poch et al. circuit being replaced by a tank circuit. l

The 'oscillator tube indicated at 56 is of the 6L? type, theisecond grid acting as the\plate and resistor 59 is not by-passed with the result that stronger and more stable oscillations are produced as described and claimed in RCV docket 5851.

The sine wave output of the oscillator I is fed into the limiter circuit .1 by means of electron coupling, the plate of the oscillator tube I being used for this purpose. i

The oscillator I is preceded by an automatic -frequency control (A. F. C.) tube 6I which forms part of the lock-in circuit 8 for holding the oscillator .i in a fixed frequency relation to the power line frequency, the-power line being indi-'- cated at 86. The lock-in circuit 8 will be described hereinafter.

The limiter 1 is for the purpose of converting the sine waves of oscillator I into rectangular waves or impulses. It comprises two limiter or clipping tubes 51 and 88, each of which is adjusted to pass only the more positive portions of an impressed wave. This is accomplished by grid-leak biasing the two tubes to make them clip at the desired level as described in the abovev identified Smith patent.

that the impulses drive the control grids of tubes 31 and 68 positive periodically whereby the grid condensers 89 and 1I are charged periodically to provide the biasing currents which flow through the grid resistors 12 and 13. 'I'he time constant of the grid condenser-grid resistor circuit of each tube is such that the grid condenser discharges only a very small amount between successive waves or impulses.

The means shown in Fig. 3b for deriving 60 cycle rectangular impulses from the 26,460 cycle rectangular impulses will now be described. The 26,460 cycle impulses are supplied from the limiter 1 over. a conductor 14 to the frequency divider 3 which divides the frequency by 1 to produce 3,780 cycle impulses.

Frequency divider 3 consists of an amplifier tube 16, a counter circuit comprising tubes 11 and .18 and a multivibrator comprising tubes 19l and 8|. The tubes 19 and 8| are of the 6F6 type in the example illustrated.

The amplifier tube 18 is operated at high effllciency,.and is made to limit or clip both positive and negative impulses by driving it alternately l to plate current saturation and to cut-olf.

The positive rectangular impulses appearing across the plate resistor 82 charge a condenser 83 and a condenser 84 which are in series with I the left-hand section of the diodelfl. The other case letters indicate the points in the circuit where It will be understood denser 84 being a fixed value between successive positive impulses and rising sharply from this value at the start of each succeeding positive impulse. This voltage is impressed upon the tube 18 which is biased beyond cut-oil? and, therefore,

will not pass a voltage impulse until the voltage across condenser 84 reaches a certain level.

The tube 18 may conveniently be a 6N? type with the plates and grids connected in parallel as shown. It will be seen that tube 18 is biased beyondcut-off by connecting its cathodes to a positive point on the voltage divider 88.

From the foregoing description it will be apparent that after a predetermined number of positive impulsesfrom the conductor 14 the condenser 84 is charged step by step to such a voltage level that the next positive impulse from line 14 drives the grids of tube 18 above the cut-off point whereby a negative impulse is applied to the screen grid 81 of tube 19. The screen grid 81 and the screen grid 88 of the tube 8| function as plate electrodes for the multivibrator.

The plate 88 of the tube 19 is connected through a conductor 9| to one side of the condenser 84 whereby the tube 19 may periodically discharge the condenser 84 to ground potential. Thus, each time the multivibrator 19-8| is triggered off by sufllcient rise in the voltage across condenser 84there is produced an impulse on the plate 92 of tube 8| and the condenser 84 is immediately discharged through the tube 18 since the control grip of tube 19 is driven positive at thisv instant. The counter circuit has now been returned to its original condition, and after another group of 26,460 cycle impulses has occurred the multi-vibrator will again be ltriggered off to produce another impulse on the plate 92 of the tube 8|.

The multivibrator 19-8| is adjusted to have a free oscillation period which is very loW compared with 26,460 cycles whereby it functions more nearly as a non-oscillatory driven circuit then as an oscillator which is merely pulled into synchronism. Also, it will be noted that the multivibrator is unsymmetrical, the two grid condensers and the two grid resistors diering greatly in value, whereby a very narrow impulse (of positive polarity) appears on the plate 92 of the tube 8|. 'Ihe plate 92 is used for electron coupling the multivibrator 19-8I to the next frequency divider in a well-known manner.

The adjustment of the frequency divider 3 is such that'it divides by 7 to produce 3780 cycle impulses which are impressed upon the frequency divider 4. Divider 4 produces 420 cycle impulses which are impressed upon the frequency divider 8 to obtain narrow 60 cycle impulses. These 60 cycle impulses are fed through an amplifier 98 to a conductor 91 which supplies 60 cycle impulses to the several circuits shown in Fig. 3d.

The frequency dividers 4 and 8 are the same as the unit 3 except for the circuit constants. Parts in units 4 and 8 corresponding to like parts in the unit 4 are indicated by the same reference numerals with the reference letters a and b, respectively, affixed thereto.

The frequency divider 8 also supplies 60.cycle impulses over a conductor 98 through an ampliiler tube 99 to the lock-in circuit 8 (Fig. 3a).

The lock-in circuit 8 is of the type covered broadly in my copending application Serial No. 237.052, filed October 26, 1938, entitled Frequency control circuits and assigned to the Radio Corporation of America.` The specific circuit shown is described and claimed in application Serial No. 237,051, filed October 26, 1938, in the name of Karl R. Wendt, entitled Frequency control circuits and assigned to the Radio Corporation of America.

The circuit 8 comprises four diodes, two diodes in each of the tubes |0| and |02, which are connected in the form of a bridge. Across one diagonal of the bridge there is connected an RC network |03 in series with the secondary of a transformer |04. The primary of -this transformer is connected to the output circuit of the amplifier 99.

Voltage from the 60 cycle power line is impressed across the other bridge diagonal through the phase shifter 8 which is of conventional design and through a condenser |08 across which the frequency control voltage appears.

The voltage across condenser |08, which is a measure of the phasedinerence between the 60 cycle wave and the 60 cycle impulses, is obtained as follows: The impulses supplied through transformer |04 drive the plates of the diodes positive periodically, an opposing voltage 'building up across the RC network |03. Each time the diode plates are driven positive, the 60 cycle line voltage is connected through the diodes across the condenser |08 and it receives an additional charge if the phase shift has been in one direction or is permitted to discharge slightly if the phase shift has been in the opposite direction.

The A. F. C. circuit comprising tube 8| is of the type which operates to vary the reactance of the tank circuit 81--88 of the main oscillator A circuit oi this type is described and claimed in application Serial No. 19,563, filed May 3, 1935, in the name of Charles Travis, and assigned to the Radio Corporation of America.

The A. F. C. circuit will be described with reference to specific circuit values and a particular type of tube but it should be understood that these are given merely by way of example. The plate oi' tube 8| is connected to the high potential end of the tank circuit 81--88 while the cathode is connected to ground, and thus to the other end ci' the tank circuit, through an 1800 ohm cathode resistor. The screen grid of tube 8| has a suitable potential applied thereto from a potentiometer or voltage divider connec- 56,000 ohm resistor rather than directly to ground, as this has been found to give improved results.

Current from the tank circuit 51-58 feeds through a condenser |01, a resistor |09 and the condenser |08 to ground. Because of the comparatively large capacity of the condenser |08 the input electrodes of tube 8| are, in effect, connected directly across the resistor |09 through which there flows a current nearly degrees out oi' phase with the current through the condenser |01. Thus. the tube 8| is caused to act as a reactance across the tank circuit, the amount of reactance depending upon the bias applied to the control grid of tube 8| by the condenser |08. Thus the frequency of oscillator is controlled to hold it locked in with the power line frequency."

A switch is provided to short circuit the condenser |08 during initial adjustments of the apparatus.

In order to obtain the 13,230 cycle impulses, i. e., the lineJfrequency impulses, the double fre quency impulses from the unit 1 are fed over a conductor ||2 tothe frequency-divider 2. 'I'his divider is the same as the frequency divider 3 except for the circuit constants. Similar parts in frequency dividersZ and 3 are indicated by the same reference numerals with the letter c aiiixed to the numerals in the unit 2.

The 13,230 cycle output of the multivibrator 19e-81e is supplied through an amplifier H3 and a conductor IN to a delay circuit IIB.

Production of blanking impulses and iconoscope driving impulses A Before describing the portion of the circuit which combines 26,460 cycle, 13,230 cycle and 60 cycle impulses to produce the video synchronizing signal, there will be described the comparatively simple part of the circuit for producing the iconoscope driving and blanking signals p, c and b. and the video blanking signal a.

Referring to Fig. 3d, there is shown the multivibrator et for producing the 60 cycle vertical driving or synchronizingimpulses c for the iconoscopeat the transmitter. This multivibrator is employed for controlling the width of the impulses c as follows: The 60 cycle impulses from conductor 91 have been made very narrow, considerably narrower than the desired width for the impulses c. The multivibrator 46 is given the proper circuit constantsk to produce impulses of the desired width when the positive bias on the grid ||1 has been adjusted to the proper value. Also, these circuit 'constants are such that the natural or free period of the multivibrator is very low compared with 60 cycles, whereby it functions more as a positively driven circuit than as one merely pulled into synchronism. Thus, the narrow 60 cycle impulses from line 91 drive the unit 4B to produce -the comparatively wide 60 cycle impulses c.

'Ihe impulses from unit 46 are clipped by the limiter tube 41 which is grid leak biased .before they are supplied to the line amplifier 48. It may be noted that the narrow impulses from the line 91- are negative whereby the narrow impulses applied to the tube 41 are positive, the polarities 4pulses are taken from a suitable point on the delay circuit H6 so that they start at the correct time and are supplied to the multivibrator 42 which, like the multivibrator 46, is utilized to determine the width of the synchronizing impulses. The unit 62 also is utilized for the reason that the .13,230 cycle impulses from the delay circuit ||6 are distorted and must be reshaped in' some way.

The narrow impulses in the output circuit of unit 42 are positive and are clipped by the llmlter 43, which is grid leak biased, to remove any irregularities at the baseof the signal. The nal signal p is amplified by a suitable line .amplitler 44.

The horizontal and vertical blankingA impulses for the iconoscope are obtained by -mixing 60 cycle and 13,230 cycle impulses. As shown in Figs. 3a and 3c, 13.230 cycle impulses are taken from a point on delay network H8 which gives the vproper timing for the beginning of each impulse. They are supplied to the multivibrator El which reshapes them into good rectangu`.'

lar impulses and which also determines their width. They are then ted into. the limiter-mixer tube 52, the left-hand part of this tube being utilized for adding the 13,230 cycle impulses to the 60 cycle impulses which .are supplied over a conductor H8 from the multivibrator ,49 (Fig. 3d).

Multivibrator 49 is similar to the unit 46 and functions to determine the width of the vertical iconoscope blanking impulses. The positive narrow impulses appearing in the output circuit of 49 are clipped by the grid leak biased tube d3 to supply negative impulses free from irregularities to the conductor H8. The actual mixing o f the 13,230 cycle impulses and 60 cycle impulses occurs in the plate resistor H9 of limiter tube 53, this resistor being common to -tube 53 and the mixer half of tube 52.

The mixed blanking impulses are impressed through a coupling condenser |21 upon the other half of tube 52 which clips off the tops of the narrow impulses since they are negative at this point and drive thev clipping section of the tube beyond cutoff. The resulting-iconoscope blanking signal b is supplied to a suitable line amplifier 5d. The signal b is shown in Fig. 2 with a break in it because of the fact that the signal is not drawn to scale, and it is desired to indicate both the width of a horizontal blanking impulse and the starting time oi a vertical blanking impulse.

The video blanking signal. is generated in substantially the same way as the iconoscope blanking signal by mixing 13,230 cycle impulses from the multivibrator 31 with60 cycle impulses in the left hand portion of the mixer-limiter tube 38. The 13,230 cycle impulses are taken from the proper point on the delay network H6' to give them the desired starting time and supplied to the multivibrator 31 which is adjusted to give them the desired width. The resulting impulses are added to the 60 cycle impulses taken from the conductor |22, clipped in the other half of the tube 38 and supplied to the line amplifier M as the video blanking impulses a. The signal a is shown in Fig. 2 witha'break for the reason given in connection with signal b. l

The 60 cycle impulses which are fed over conductor |22 are obtained from the multivibrator 38 (Fig. 3d) and the limiter tube 38 which function the same as units 49 and 53. respectively, the multivibrator 36 being adjustable to give the 60 cycle impulses, the desired width.

-The line amplier 4|, like the other line ampliers in the system may .be of the cathode follower type. In such ampliers the output signalV is taken olf a resistor between the cathode and ground, the polarity of the output signal being the same as that of the input signal. The

amplier tube illustrated for amplier 4| is of the so-calied beam type.

Production of video synchronizingsignals In accordance with my invention, the front edge of each impulse in the `iinal video synchronizing signal o (Fig.` 2) is derived from the front edges of the double frequency impulses d. 'I'he manner in which this isaccomplished will now be described.

The half width double .frequency impulses d.

pulses d whereby the multivibrator Il may be4 utilized to determine the width of the impulses d. The point on the delay networkv |23 to which conductor |24 is connected, of course, determines the starting point of each impulse d.

As described in connection with the multivibrator 46, the width of the impulses d may be adjusted to exactly the desired value by adjusting a variable tap |26 to change the positive bias on a multivibrator control grid. It will be noted that the bias is varied on that grid which is connected to a multivibrator plate through the smaller of the two multivibrator plate-to-grid coupling condensers.

Since the narrow impulses supplied over conductor |24 are negative, the narrow impulses which are supplied to the grid of the first half of the limiter tube I2 are positive, the input and output being from opposite multivibrator plates. The impulses are clipped in the first half of the 'tube |2 by utilizing grid leak biasing, and they frequency impulses are desired. The signal h.

is obtained by combining 13,230 cycle impulses e with a 60 cycle impulse l as follows.

Referring to Fig. 3c, 13,230 cycle impulses are taken from a. point on the delay network IIS (Fig. 3a.) where there is little or no delay and supplied to the multivibrator I6 which is adjusted to supply narrow negative impulses e to a grid of the limiter mixer tube l1. It will be noted that tube l1 reverses the polarity of impulses e as they appear in the signal h.

The 60 cycle impulses f are obtained from a multi-vibrator I8 (Fig. 3d) which is driven by the 60 cycle impulses fed over the conductor 91. i'

The multi-vibrator I8 is the same as the multivibrator 46 except for a difference in certain circuit constants and is adjusted to produce an impulse f of the desired width. The narrow 60v cycle impulses f appearing in the output of unit I8 are clipped by means of the limiter tubell, which is grid leak biased. Thus. the narrow impulses supplied over the conductor |28 and to the first grid of the tube I1 are of negative polarity. They are of sufilcient amplitude to block the tube I1 whereby the impulses e will not appear in the plate circuit of the tube for the duration of the impulse f.

Between narrow impulses f the negative impulses e will periodically drive the tube I1 beyond cut-off whereby they appear in the plate circuit of tube I1 as narrow positive impulses with squared tops. ,They are next further squared up by clipping twice in the limiter tube 2|, the first half of the tube being grid leak biased to provide the desired clipping and the second half of the tube being driven beyond by the.`

negative narrow impulses impressed on the second grid to aifect the second clipping. The final narrow impulse h of positive polarity (or wide impulse of negative polarity) is supplied over a conductor |29 to the Junction point' |25.

By comparing signals d and h, it will be seen that each negative impulse h (the wider impulse) occurs just before an impulse d and lasts longer than the impulse d whereby it may be utilized to remove this double frequency impulse.

Impulses i, which occur at the rate of 13,230 per second, are produced for the purpose of adding them with those half width impulses d which have not been removed by the impulses h to produce the full width horizontal synchronizing impulses. The impulses j which would normally appear in the region of the vertical synchronizing impulse are removed by the 60 cycle impulse f just as certain as the impulses h were removed. The circuit for accomplishing this is as follows: Impulses occurring at the rate of 13,230 per second are obtained from a suitable point on the delay network IIB and supplied over a conductor |3| to the multi-vibrator 22, which has the proper circuit constants and grid bias ad- Justment to produce 13,230 cycle impulses i ot the desired width.l The impulses i are supplied with positive polarity to the second control grid of the mixer limiter tube 23 while the negative 60 cycle impulse f is supplied to the first control grid of the tube 2l. As in the case of the mixer tube I1, the tube 23 is blocked for the duration of the negative impulse J' whereby the impulses i do not appear in the plate circuit of the tube 2l.

Between successive negative impulses j, the impulses i appear in the plate circuit of tube 23 as negative impulses, having been clipped a cert-ain amount in the tube 2l by the use of grid leak biasing on the second control grid. lThe output of tube 23 is supplied over a conductor |22 to the grid leak biased limiter tube 24 which further clips the signal and reverses the polarity to produce the final signal d, the narrow impulses being of positive polarity. Signal d is fed over the conductor |33 to the Junction point |25.

It will be seen from a comparison of the signal 9' and d thatieach impulse j has been made to start at a. slightly later time than an impulse d, but substantially earlier than the back edge of an impulse d. Thus, when impulses d and j are added, they always overlap a suilicient amount to prevent any possibility of a gap in the signal due to a change or shift in the starting timeof an impulse j or due to any other variation in the circuit. It will be apparent that in the combined signal the front edge ci' a horizontal synchronizing impulse is the front edge of an impulse d, while the back edge of this synchronizing impulse is the back edge of the impulse i.

The signals d, h and j, when combined, will produce a Signal consisting of horizontal synchronizing impulses and the half-width double-frequency preparatory signals. The video synchronizing signal is completed by the generation and addition of the signal m. which provides the slotted vertical synchronizing impulse. The means for generating the signal m will now be described- The slotted impulse m is obtained by combining the comparatively wide double frequency impulses Ic and the delayed 60 cycle impulses l. It will be noted that the wide impulses 1c occur at a slightly later time than the impulses d, whereby in the ilnal signal the front edges of the impulses d will be the front edges of the impulses making up the slotted vertical synchronizing impulse.

To produce the impulses k, 26,460 cycle impulses are taken from a suitable point in the delay network |22 (Fig. 3a) and supplied over a conductor |34 to the multivibrator Il (Fig. 3d). The impulses k appear in the output circuit of `the nmnuvibrator'a|l with the wide impulses have ing a positive polarity and 'the desired width. The multi-vibrator Il, like the multi-vibrator is'adjusted `to function as a driven oscillator, its

free oscillation frequency being much lower than 26,460 cycles. The positive wide impulses Ic are supplied over a conductor |88 to the second control grid oi the limiter mixer tube 29'.

The delayed positive 60`cycle impulse l is fed through a conductor |81 to the first control grid of the tube 28. This signal is produced as follows: The multi-vibrator 28 is driven by the narrow 60 cycle impulses supplied .over conductor 81 to produce the 80 cycle impulses a. The multivibrator 28. is adjusted to make the width of a narrow impulse `g such that its back edge occurs slightly before the time that the slotted vertical synchronizingr impulse is to start. Roughly speaking, it may be said that the back edge of lthe narrow impulse c triggers oil the multi-vibrator 28 to produce the delayed impulse I, but, as

. casacca time relation as to makethe rst impulse of the signal m of less than full width. Obviously this cannot happen when the impulse l is produced, in

' effect. by the back edge of an impulse k.

-Theabove-described circuit and method -for driving the u iultivibrator 28 to produce impulses at the rate of 60 per second while making such will appear from the following descriptiomthis is not stricuy true. Actually the multlvirator 2s, in eifect, is triggered oi! by the back `edge of a wide impulse 1c for reasons whichwill appear hereinafter.

The narrow impulse c is taken from the proper plate of the multivibrator` tube to make it of negative polarity whereby the wide impulse portion of the signal a is positiver The signal g is passed through a diilerentiating circuit comprising the small capacity condenser |88 whereby there is impressed upon the ilrst grid of the tube 21 a ,signal having a comparatively narrow positive portion indicated at z in Fig. 2. .It may be. noted that the curve z shows only the useful positive portionof the differentiated signal. To the second control grid of the tube 21 there is supplied the signal y having positive narrow impulses,

- signal y being the same a's signal k, but of opposite polarity. The positive narrow impulses u are taken from one plate of the multivibrator 3| and supplied over a conductor i 89 to the limiter mixer tube |21.

The impulses e' andy are added in the tube.

supplied to grids controlling a common *electron stream. The clipping action is obtained by providing the tube 21 with a' suiiicient self bias to bias the tube close to. cut-off whereby only the `portions of the signal appear in the more positive plate circuit. It may be noted that there is no reason why the impulse z could not be made considerably narrower whereby only one of the impulses y would appear in the output circuit of tube 21 except that,

asa practical matter, an impulse this narrow cannot readily be obtained by the differentiating circuit.

A comparison ofthe impulses l and a: will show that the multi-vibrator 284s triggered oi' by the leading edge of the rst impulse a: to produce in its output circuit the impulsel. I v

The reason for employing the above-described method of triggering of? ordriving the multivibrator 28 is that the impulse g may shift slightly in-its timing with respect to the impulses lc. Thus if the impulse l were produced by using the back edge of impulse g directly to drive themultivibrator 28, the impulses l and k, might add in such impulses occur in a fixed time relation to the 26,460 cycle impulses are described and claimed in application Serial No. 76,108, filed April 24, 1936, in the name of Alan D. Blumlein'and assigned to the Radio Corporation of America.

The impulses l and lc are added and clipped in the; limiter mixer tube 28 to produce a signal which, after further `clipping in the limiter 82 It may be noted that the addition of `the signals.

h, 1, m and d actually occurs in the plate resistor of the right hand section of tube 2| (Fig. 3c) this\plate resistor being common to the vacuum tube plates to which the conductors |28, |28, |2 1,;and |4| are connected. i

'I'he combined signal which appears at the4 Junction point |251is shown at n in Fig. 2. Itfwill be seen that the impulses d have been added to the front edges of theimpulss ofthe `signal m with a certain amount of` overlap, the overlap being provided to avoid 1the necessity of a'critical adjustment ofthe circuit. As previously pointed out, thegimpulses d have been added in a similar manner to the front edges of the impulses j. In the .region just preceding and just following the `slotted vertical synchronizing impulse, thev impulses d themselves act as the halfwidth doublefreuenc'y impulses. l

I'he nal video synchronizing signal which is to be mixed with the picture signal and transmitted to the receiver is shown at o, It will be seen that the ilnal signal o is obtained by clipping the signal n at the levels indicated by the dotted lines, the `signal o being the portion of the signal n which appears between these dotted lines.

` ,On the drawings, merely by"way of example, the types of various tubes have been indicated as well as the values of various resistors and condensers, these values being in ohms, megohms, microfarads.- and micro-microfarads.

It may be noted that the circuits of multi-l vibrator units 22, 31 and)5| are duplicates except as to slight diilerences in some circuit constants, and that the unit 42 is also a duplicate of unit 22 except as to certain circuit constants Aand except for the fact that the .10 mf. bypass condenser connected to the cathode in unit 22 is omitted.

Likewise the multivibrators'd, I8, 36 and 49 are duplicates except as to some of the circuit constants.

With reference to the curves in Fig. 2, they are not drawn to scalealthough the relative timing of the various signals is shown exactly. Specifically, the ratio of the duration of an impulse to the time between successive impulses is much less in practice than indicated in Fig. 2, the horizontal video blanking impulses, for example, occupying about 15 percent of the time between the beginnings of` two successive blanking impulses.

It should be understood that the various signals need not be produced and mixed in the specific manner described in the foregoing detailed description in order to practice my invention. For example, instead of adding waves d, n.1 and m to produce the wave n" before clipping, the adding the clipping may be done inseveral steps. For instance, the waves d and h may be added and then those alternate impulses from wave dwhich are depressed by the negative impulses of wave h can be immediately removed by clipping. Waves i and m may then be added to the wave so clipped. A final clipping operation will then produce the signal o.

It should also be understood that the invention may be practiced in various other ways. For example, the invention may be practiced in ac- ,wide negative impulses of signal E to depress the cordance with Fig. 4 which illustrates the use' I of full width "base impulses, some of these being narrowed to half width during the process of producing the final signal. No circuit diagram is illustrated for producing thewaves shown in Fig. 4 other than that previously described as it is apparent that the circuit shown in Figs. 8a to 3d may be employed for this purpose by making slight adjustments or modifications.

Referring to Fig. 4. double frequency base" impulses d are generated which have a Width equal to the desired width of the horizontal synchronizing impulses. These are then combined with the signal h.' (thus producing the signal r) for the purpose of removing alternate double frequency impulses d except in the region where the double frequency preparatory impulses are desired. y

Clipping or limiting the amplitude of signal r produces the signal s having double frequency, full width impulses. These are narrowed to half width by adding the signals s and j', the negativeimpulses of the signal j being delayed sumciently to depress only the last half of double frequency, full width impulses as shown by the curve t. It will be noted that the negative impulses of the signal j start during and last longer than the positive impulses of the signal d'.

After clipping the signal t, the signal u is produced which, when combined with the slotted vertical signal m', gives the signal v. Clipping off the top of the signal v as indicated by the dotted line gives the final synchronizing signal. Just as in the example shown in Fig. 2, the front edges of the base signal d form the front edges of all'impulses in the final signal.

In Fig. 5 there is illustrated one way of pro-4 ducing a synchronizing signal by utilizing a base signalhaving wide impulses, a few of which are utilized to form the slotted framing impulses. In order to simplify thecurves and explanation, the synchronizing signal assumed in Fig. 5 (curve G) has been simplified but it still has double frequency preparatory impulses of half width and a slotted vertical synchronizing impulse.

Referring to Fig. 5, double frequency wide impulses of positive polarity are produced, the front edges of the wide impulses being used to determine the starting time of impulses in the final signal G.

A signal B is produced by delaying signal A, reversing its polarity and combining with a 60 cycle impulse as taught in the foregoing description. 'I 'he addition of signals A and Bl produces signal C in which the wide negative impulses of signal B have depressed the back portions of certain wide positiveimulses of the signal A to produce the half width, double frequency preparatory signals.

Clipping the signal C to pass only the top part produces the signal D which contains the desired half width, double frequency preparatory impulses. K f

The signal E is made up of line frequency impulses which have been combined with a 60 cycle impulse to remove. line frequency impulses in the region of the framing impulse. This signal may be considered to consist of negative wide im pulses.

The addition of signals D and E causes the back portions of the wide impulses of signal D and also to depress alternate `wide impulses of signal yD as shown by the resulting signal F. Clipping signal F to pass only the top portion gives the final desired signal G.

It willbe noted that the front edges of the wide positive impulses of signal A determine the timing of the front edges of all impulses in the final signal G. It'will also be noted that each of the wide negative impulses of signal B and of signal E occurs during and last longer than each of the wide positive impulses of the signal A.

From the foregoing it will be apparent that in a rectangular wave the impulse may be either the upward part or the downward part, not necessarily the part having the shorter duration. In the claims the wording "adding" is used in an algebraic sense.

I claim as my invention:

l. The method of producing a synchronizing signal comprising comparatively high frequency horizontal-synchronizing impulses and comparatively low frequency vertical synchronizing impulses which comprises producing impulses occurring at said high frequency, producing irnpulses occurring at said low frequency, producing additional impulses occurring at a frequency at least as h igh as said high frequency and in harmonic relation thereto, and so combining all of said impulses that said additional impulses "determine the timing of the front edges of said horizontal and vertical synchronizing impulses.

2. The method of producing a synchronizing signal comprising comparatively high frequency horizontal synchronizing impulses and comparatively low frequency vertical synchronizing impulses which comprises producing impulses occurring at said high frequency. producing im pulses occurring at said low frequency, producing additional impulses occurring at a frequency at least as high as said high frequency and adding certain of said additional impulses to the front edges of said high frequency impulses and adding others of said additional impulses to the front edges of said low frequency impulses.

3.1'I'he method of producing a synchronizing signal which comprises producing high frequency impulses each beginning at a certain time for line synchronizing, producing low frequency signals each beginning at a certain time for framing, producing additional impulses occurring at a frequency at least as high as said high frequency impulses and each beginning at a time slightly before the time at which each of said line synchronizing impulses and each of said framing signals begin, and adding all of said signais and impulses whereby the front or first occurring edges of said additional impulses form the front edges of both said line synchronizing impulses and said framing signals.

4. The method of producing synchronizing Acurring at a high frequency for line synchronizaasaaia 9 ing, producing signals occurring at a comparatively low frequency for framing, producingadditional impulses occurring at a frequencywhich is a multiple of said high frequency with each of said additional impulses occurring Just before the start of each line synchronizing impulse and Just before the start of each framing signal and occurring in overlapping relation thereto, removing a group of said high 4frequency yimpulses which would normally occur in the region of the framing impulse, removing all of said additional impulses except those which occur in the region where said line synchronizing impulses have been removed, and adding said line synchronizing impulses, said framing signals and said additional impulses whereby the front edge of each impulse in the final synchronizing signal is thel front edge of one of saidadditional impulses.

5. The method of producing a synchronizing signal comprising impulses of different duration or width, the impulses of one width beginning at time intervals equal to Ic units andthe impulses of a different width beginning at time intervals equal to nk units where n is a small whole number, said method including the steps of producing a ilrst wave of uniform impulses which occur at intervals of k units, producing a second wave of impulses each of which begins during and which last longer than certain impulses of said rst Wave, adding said first and second waves to produce a third wave, and so limiting the amplitude of said third wave that a fourth wave is produced having certain impulses which start at the times corresponding to one of the edges of the impulses of the first wave and lasting for a time determined by the impulses of the second wave. y

fi. A synchronizing'signal generator for television or the like comprising means for produc- King impulses recurring at a certain frequency,

means for producing other impulses recurring in a fixed time relation to said certain frequency, means for producing additional impulses occurring in a fixed time relation to said certain frequency and means for so combining all of said impulses that said additional impulses determinev I'the timing of said first mentioned and second vcomprising horizontal synchronizing impulses,

frequency preparatory impulses occurring in the region of each framing impulse which comprises producing impulses occurring at said vmultiple frequency and each having a front edge, removing certain of said multiple frequency impulses outside said region to make the remaining impulses occur at the frequency of the horizontal l, synchronizing impulses, and causing the front occurring at a frequency which is a multiple of said Acertain frequency, means for producing additional impulses occurring at said multiple frequency, and means for so combining all of said impulses that said additional impulses determine the timing of the remaining impulses.

8. A synchronizing signal generator for television or the like comprising means for producing slotted framing impulses, means for producing impulses occurring at a frequency which is a multiple of the horizontal scanning frequency,

means for so removing certain of said multiple frequency impulses except-v in the region of a framing impulse that there are impulses occur'- ring at the horizontal scanning frequency outside said region, and means for so combining said remaining impulses that said multiple frequency impulses determine the timing of the slots inthe framing impulses.

9. A synchronizing signal generator for television or the like comprising electronic oscillator means for producing a synchronizing signal edges of the resulting signal to become the front edges of all oi said impulses.

l1. A synchronizing impulse generator comprising means for producing impulses occurring at intervals oi' kunits, means for producing other impulses occurring at intervals of nk units where n is a small whole number which impulses start during and last longer than said first impulses, means for adding all of said impulses and clipping the resulting signal to produce impulses which start at a time determined by said first mentioned impulses and which end at a time determined by said other impulses.

12. A synchronizing impulse generator comprising means for producing impulses occurring at intervals of k units, means for producing other impulses occurring at'intervals of nk units where n is a small Whole number which impulses start during and last longer than said i'lrst impulses, means for adding all of said impulses and clipping the resulting signal to produce impulses which start at a time determined bysaid first mentioned impulses and which end at a time determined by said other impulses, and means for periodically removing 1/11, of said rst impulses to make them recur at intervals of nk for said period.

13. A synchronizing impulse generator comprisingmeans for producing impulses occurring at intervals of k units, means for producing other impulses occurring at intervals of nk units where n is a small whole number, means for removing groups of'said other impulses periodically, means for so combining said first impulses and the remaining second-mentioned impulses in such time relation that each of said remaining impulses starts during and last longer than each of said rst impulses -whereby impulses are produced which start at a time determined by the front edges oi said first impulses and which Yend at a time determined by said other impulses.

a 14. The method of producing synchronizing signals for television or the like which comprises producing impulses -occurring at a frequency which is a multiple of the horizontal scanning frequency, producing impulses occurring at said horizontal scanning frequency, removing a group `of said last impulses periodically, so combining pulses and multiple frequency impulses, so adding other impulses to the back portion of said multiple frequency impulses as to remove said back portion'and produce narrow multiple frequency impulses, and adding slotted framing impulses to the resulting signal.

15. The method of producing synchronizing impulses for television or the like which comprises producing wide impulses occurring at double the horizontal scanning frequency, periodically removing the back portions of certain of signal comprising impulses of different width or.

duration, the narrower impulses beginning at time intervals equal to k umts and the wider impulses beginning at intervals equal to nk units where n is a small whole number, said method comprising producing a first wave of uniform impulses which occur at intervals of Ic units, producing a second wave of uniform impulses each of which occurs in overlapping relation to each of said first impulses, periodically removing a group of said second impulses, combining said two waves whereby said second wave changes the width of certain of said rst impulses. and means for passing only the signal on the same amplitude level as said impulses of changed width.

17.- The method of producing a synchronizing signal comprising pulses having leading edges recurring at precise intervals which comprises generating pulses recurring at a comparatively high frequency, generating pulses recurring at a comparatively low frequency, and adding said two groups of pulses in such time relation that certain of said high frequency pulses overlap the front edges of said low frequency pulses whereby the front edges of said high frequency pulses are the front edges of both high frequency pulses and low frequency pulses in said synchronizing signal.

18. The method of producing a synchronizing signal comprising pulses having leading edges recurring at precise intervals which comprises generating pulses recurring at the highest frequency at which pulses in said synchronizing signal are to occur, generating other pulses recurring at a lower frequency, and so combining said pulses that the leading edges of all pulses in the synchronizing signal are the original leading" edges of said highest frequency pulses.

19. A synchronizing signal generator for producing pulses having leading edges recurring at precise intervals which comprises means for producing a group of pulses recurring at a frequency at least as high as the line frequency, means for producing a second group of pulses recurring at the comparatively low vertical deflection frequency, and means for so combining said groups of pulses that there is produced a synchronizing signal including pulses of different widths having front edges which are the original front edges of said rst group of pulses.

ALDA V. BEDFORD.

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