US2408078A - Constant width synchronized pulse generator - Google Patents

Description

E. LABIN ETAL Sept. 24, 194

CONSTANT W IDTH SYNCHRONIZED PULSE GENERATOR I 2 Sheets-Sheet 2 Filed Feb. 5, 1942 1 mV 6 Y m m m E E DIPPPPD m m 9 (444144 W M a n I]! as I M w A I- E p km mm 7 1;?

m u [W Moi/r 6. m1 g E T v m A W 4 Wm M PI? Patented Sept. 24, 1946 CONSTANT WIDTH SYNCHRONIZED PULSE GENERATOR Emile Labin and Donald D. Grieg, New York, N. Y,, assignors to Federal Telephone and Radio Corporation, a corporation of Delaware Application February 3, 1942, Serial No. 429,376v

2 Claims.

- 1 This invention relates to impulse generating systems and in particular to an improved type of synchronized impulse generator for timing, calibrating, and other control purposes. The invention is considered particularly adaptable where a highly accurate timing interval is desired, as for example in aircraft identifier apparatus wherein small time intervals indicative of distance are observed on the screen of a cathode ray tube. Such apparatus has been disclosed, for example, in the copending applications Ser. Nos. 382,391 filed March 8, 1941, and Ser. No. 383,108, filed March 13, 1941, of E. Labin.

It is an object of the invention to provide a method and n'fe'ans for generating accurately synchronized impulses over a relatively wide range of desired impulse recurrent frequencies. Another object is to provide an improved form of constant-width impulse generator wherein for generating impulses of a desired controllable duration. 7

Other objects and various further features of novelty and invention will hereinafter be pointed out or will become apparent from a reading of the following specification in connection withthe drawings included herewith. In said drawings, Fig. 1 is a block diagram illustrating very schematicallya preferred'form of the invention,

Figs. la, b 1 indicate wave form treat merit through the various elements of the circuit of Fig. 1;

Fig. 2 represents schematically and in more detail certain of. the elements of Fig. 1;

Fig. 3 represents schematically and in more detail further elements of Fig. 1; and

Figs. 4a, b, e illustrategraphically certain circuitconditions occurring during a normal operation of the apparatus of Fig. 3.

Broadly speaking, the invention contemplates the use of a master oscillator of relatively high stability and having a generally sinusoidal wave form as theprime source of control energy. The

periodicity of this Wave form is related by a'simple factor to the desired pulse width or duration in the output of the apparatus. This sinusoidal wave form may be employed in a known manner to generate a series of extremely equal or factoriall-y" related to the desired pulse width. The synchronizing impulses thus obtained are then supplied to a novel multi-vibrator circuit forming part of this invention, to generate impulses of the desired shape and duration, that is, impulses equal. or fac-torially related in duration to the periodicity of the synchronizing, this relationship being dependent upon circuit adjustments. Thereafter, the output may be suitably shaped for whatever the required purposes.

For a more specific consideration, reference will now be made to Fig. 1, which shows in block diagram form, features of a preferred embodiment. As the master oscillator, we employ in the form shown, a quartz oscillator III to produce the required sinusoidal wave form. This. wave is then suitably shaped in .an inverter unit II for application to a full-wave rectifier I2 to give a balanced rectified output. Since the most accurately defined recurrent portion of the ouput of rectifier I2 is the cusp-shaped part where the wave hits zero voltage, we accentuate these cusps by applying the output of rectifier I2 to a pair of successive differentiator circuits I3 and I4, whereby in accordance with known principles, a series of extremely sharp alternately positive and negative impulses is produced. Since it is desired to use only one of these sets of impulses for synchronizatiom'output of diiferentiator I4 is applied to a clipper or limiting device I5 to produce a series of uni-directional synchronizing impulses.

These synchronizing impulses, as above-indicated,'may then be applied to a multi-vibrator circuit I6, which forms an important part of this invention. Since it is preferable that the impulses'applied tot-he input of multi-vibrator it are positive and of a controllable magnitude, suitable networks I! and I8, including a phase reverser and cathode follower, respectively, may be included in the circuit between clipper I5 and multi-vibratcr l6. Afterthe desired kind of impulse energy has been formed in multi-vibrator I6, the output may be appropriately shaped, phased, and amplified for the required purposes in networks I9, 26, and 2!, respectively.

Turning now to a more detailed consideration of the various elements involved in the circuit of Fig. 1, reference is made to Fig. ,2 in which oscillator i0 is seen to include a quartz crystal 22 and a pent'ode Ti having certain resistance R2 in its output circuit Illa. Since the stability of the entire system is seen to depend .to a large 'extent on the inherent stability of the master oscillator stage IB, it is considered preferable that certain precautions be taken to ensure the necessary stability. For this reason, the resistance R2 may be included in the output of tube T1 so that, should there be any impedance changes within tube T1 under operating conditions, these changes will be of a negligible nature, as compared with the total impedance, including that added by resistor R2.

Due to the method of pulse generation in accordance with the preferred form shown, the synchronizing pulse output forthcoming from clipper I5 is twice the frequency of the master oscillator. As will later appear, this relation means that for the minimum required pulse width in the output of multi-vibrator I6, the period of the master oscillator must be equal to twice the time width of these minimum-sized impulses. Expressing this relation between the master oscillator period To and the minimum time width of desired pulses tw, To=2tw, and since the relationship between a period t and the frequency f to which it corresponds is where F is the tfrequency of the master oscillator. Thus, by way of example, if a pulse width of microseconds were required for a certain purpose in the output of multi-vibrator I6, the fundamental oscillator frequency would necessarily be:-

F -10=100 kilocycles As above-indicated in the discussion of Fig. 1, an inverter circuit I I is employed to produce two balanced sine waves for application to the fullwave rectifier I2. In the form shown, the inverter I I includes an amplifier T2 having an output Ila including a load resistor R1. It will be noted that the output is taken directly across the cathode and plate circuits of tube T2, and that therefore balance with respect to ground may be regulated by a variable resistor R5 included in the cathode circuit to ground. By adjusting cathode resistor R5 to equal in magnitude the load resistor R1, zero amplification results in tube T2 and maximum balance may be obtained. In the form shown, load resistor R1 directly supplies input energy to the full-wave rectifier. This rectifier may include a double diode T3 symmetrically fed across a resistor R8, and the oath-- ode circuit may be connected through a resistor R9 to substantially the midpoint of input resistor R8.

As above-indicated in general language, we consider it preferable for increased timing accuracy that the timing of the pulses appearing in the output of differentiator I4 be determined solely by the time at which the sinusoidal wave from oscillator Ill crosses the zero axis, that is, by the cusp portions 23 of the rectified wave; see Fig. 10. Since the cusp timing is independent of voltage variations (the cusp representing zero voltage), a high order of pulse timing or frequency stability is possible by utilizing this portion of the rectified wave. In order to achieve maximum pulse stability, however, the sharpness of the cusp wave form must be maintained. This latter requirement necessitates that high-frequency discrimination and distortion at the wave cusps be kept at a minimum, that is, that the circuit be as evenly responsive as feasible to a relatively wide band of frequencies. To this end,

potentiometer R8 is connected as shown, and the.

resistor R9 is made small in order to minimize the shunting efiect of the input coupling to the following stage (differentiator l3) The two differentiator circuits I 3 and I4 are of essentially similar and known form, and include amplifier tubes T4 and T5 having coupling circuits which constitute the difierentiating networks. These coupling circuits may be of the simple resistance-capacitance type, and in the form shown, include condenser CII and resistor RH for the output of the tube T4 of differentiator l3, and condenser CI5 and resistor RIB for the output of the tube T5 of differentiator HI. The wave-form treatment, as energy from the rectifier I2 passes through differentiators I3 and I4 successively, is indicated graphically in Figs. 1d and 1e. It willbe seen therefrom that the output of differentiator I4 as appearing across resistor RI8 comprises a series of extremely short impulses of successively positive and negative sense.

Since the form of the multi -vibrator I6 shown requires positive synchronization impulses for operation, the output of differentiator I4 is next limited through a clipping device I5 so as to produce a series of uni-directional synchronizing impulses. In the form shown, clipper I5 includes a class C amplifier employing tube T6. As is well-known, in this form of amplifier negative excursions of the input voltage past cutoff cannot be reproduced in the plate circuit, and a limiting action thus results. Inherent in the operation of tube T6 is the fact that a phase reversal occurs. Accordingly, the result of cutting out the negative pulses in the output of differentiator I4 is to produce a series of negative pulses in the output I5a oi clipper I5. Passage of this energy through another vacuum tube device is therefore necessary in order to reverse the pulse phase and to produce the positive impulses required for the multi-vibrator I6. In the form shown, this latter stage is a simple class A amplifier TI. Now, since the input to this stage will be relatively high, tube T'I may be additionally employed for shaping purposes, that is, to limit the magnitude of output pulses due to saturation in tube TI. The resulting pulses in the output of this stage are thus at proper polarity for synchronization, but present the undesirable feature that they are delivered at a relatively high impedance, as presented by the plate circuit of tube T1.

In order for these synchronized impulses to be delivered to the multi-vibrator circuit at low impedance, we choose to employ a known type of cathode follower device I8, which in the. form shown, includes tube T8 from which the low impedance impulses are derived across resistor R28 in the cathode circuit. The cathode follower circuit may also serveadditional functions should the magnitude of impulse energy app-lied to the input thereof be too great for proper synchronization of the multi-vibrator. To these ends and due to the step-down impedance transformation from the input circuit to the output, voltage may be reduced with a minimum of distortion. Tube T8 may serve a further function should the input be of unduly large magnitude, in that, due to plate saturation and grid-current flow, amplitude limiting and further shaping may result. It will be clear from the above-described circuit that the output of this stage, as applied to a load through a co-axial line P1, is a series of regular synchronizing pulses of short duration and occurring at a frequency equal to twice that of the master oscillator I9.

The multi-vibrator used may be considered to be ,of a dissymmetrica'l type, that is, the time-censtant decay circuits of the input section are dissimilar 'to those used in the output or alternate section. One of these time-constant circuits is employed to control output pulse width, and the other to determine the recurrent frequency of the pulses whose width is :being controlled by the first of said circuits, as will later be, clear.

Referring to Fig. 3, the 'multi-vibrator i6 is shown'to include a double triode T9 comprising a triode section indicated generally by I and another indicated by II. A resistance 30, capacitance 3|, andga further resistance 32, between the output circuit of tube section II and ground are, included in the time-constant circuit which will be seen to be determinative of the width of the desired pulse; and a resistanc 33, capacitances 34, 35, and a further resistance 36, between the output circuit of tube section I and ground are included in the time-constant circuit which will hereinafter be seen to be determinative of the frequency of recurrence of pulses derived from the multi-vibrator.

A better understanding of the operation of the multi-vibrator may be had by reference to the various curves shown in Fig. 4. In this fig ure, curve a represents the series of synchronizing impulses supplied from the cathode follower 58 over the co-axial line P1, Figs. 2 and 3; curve 19 represents the instantaneous voltage appearing on the grid of tube section I; curve represents plate current for tube section I; curve 01 represents instantaneous voltage appearing on the grid of tube section II, and curve e represents output current for tube section II. All five of these i curves have been drawn against time, and for ductive, whereby this impulse is amplified andv at the same time its phase is reversed to make it in effect an amplified negative im'pulse. Instantaneously this large negative voltage is applied to the grid of tube section II to bias the latter below cutoff, whereby tube section II is rendered non-conductive. On the curves of Fig.

4, this reaction is illustrated on curve d by a large swing 38 of grid voltage on tube section II below cutoff, and the resultant subsidence of output current in this tube section to zero is indicated by the wall 39 dropping to zero current in curve e.

As tube section I continues to conduct a large quantity of current, a relatively high voltage drop persists across resistance 36; and, as a result of the circuit values of condensers 34 and '35 and resistance 33, a voltage begins to build up across resistor 33 so that the grid voltage of tube section II builds up in a sense approaching cutoff. In Fig. 4, this increase in grid voltage toward cutoff is shown by the portion 40 of the curve of Fig. 4d. "Now, as the grid voltage in tube section II is thus building up towards cutoff, the synchronizing impulses applied to the multi-vibrator circuit continue and are necessarily impressed upon the voltage appearing across resistor 33. As the synchronization impulses are thus applied across resistor 33, they will be of reduced magnitude, due to the fact that they have had to traverse certain circuit impedance represented by condensers 3|, 34, and

various leakage resistance paths. Thus, on curve d theyhave been represented as of reduced magnitude. The synchronizing impulses reaching the gridof tube section II-will be of a positive sense, however, due to the fact that they have reached this point directly, rather than by passing through a -vac'uum tube device. They are accordingly shown positively superimposed upon curve portion 40.

' Now, the magnitude of the synchronizing impulses when superimposed upon the voltage that fisbuilding up across resistance 33 (as represented by curve portion 40) is at first insuificient to carry the grid of tube section II to a point greater than cutoff; but, as this grid voltage builds up, there will become a time when the superposition of a synchronizing impulse upon a voltage that has built up across resistor '33 will be great enough to apply a potential greater than cutofi potential to the grid of tube section II. In the assumed illustration, this time occurs with the third synchronizing impulse after the grid of tube section II was placed below cutoff, as will "be clear from Fig. 411.

Once tube section II is thus rendered conducthe assumed case willbe-that indicated as 4 l may be greatly amplified by tube section II. This large output may then be instantaneously applied to th grid of tube section I as a large negative impulse. The magnitude of this negative voltage applied across the grid of tubesection I may thus be great enough to cut offconductivity of tube section I, as indicated by the sharp downward swing of grid voltage in tube section I (see the port-ion 42 of curve I) of Fig. 4). Once tube section II has thus been rendered conductive, it will remain so until the large negative voltage across the grid of tube section I builds up in a positive sens to cutoff. The rate of this buildeup, it will be clear, is governed by the particular time constant of the circuit defined by resistor 30, capacitance'31, and resisto 32, as will be clear. Now, due to the fact that synchronizing impulses are being continuously applied to the grid of tube section I with their full magnitude A, tube sec-. tion '1 maybe rendered prematurely conductive, owing'to the superposition of impulses of magnitube A upon the positively increasing negative voltage :across resistor 33. This phenomenon is shown to occur in Fig. 4b with the synchronizing impulse which next succeeds the impulse M which caused the grid of tube section I to be biased well below cutoff. Oncetube section I again becomes conductive, the grid of tube section II is immediately biased beyond cutoff and the above-described cycle of operation repeats itself.

It will be noted that, in the form shown, output from th multi-vibrator is taken in line 44 from across resistor 36; in other words, output is 'taken from tube section I. It follows from the above discussion of multi-vibrator action that this output current will have the form shown in Fig. 40. that is, it will "be characterized by relatively long-duration impulses with small interus vals between them. If it were desired to obtain small impulses with relatively large intervals therebetween, output should be taken across the late circuit of tube section II, that is, by connecting line .44 acrossresistor 32 instead of across resistor 3.6 as shown. Multi-vibrator output would-then present the wave form shown in Fig.

Presu-ming that multi-vibrator output is derived acrossresistor 3:2 to yield a series of regu- .larl-y' spaced relatively short-duration impulses,

tive, the applied synchronizing impulse, which in it may readily be seen how in accordance with the invention the periodicity of impulse recurrence may be varied while maintaining impulse duration constant. This extension of impulse separation may be obtained, for example, by increasing th resistance 33 across which voltage applied to the grid of tube section II builds up. Such an increase in the resistance 33 will have the effect of changing the slope of the curve portion 40 of Fig. 4d so as to correspond, for example, with the line 45. Now, when the synchronizing impulses are superimposed upon this alternate curve portion 45, -it will be clear that the third synchronizing impulse after the grid of tub section I! has swung below cutofi will be of insufiicient magnitude when superimposed upon. curve section 45 to render tube section II conductive. In the form shown, however, the next succeeding, that is, the fourth impulse, will be of suificient magnitude to render tube section II conductive and thus immediately to cut off the conductivity of tube section I, as will b clear. Operation thereafter will be of an analogous nature to that above described in connection with the full-line showings of curves 41) through 4e. This alternate operation is shown, for example, in dot-dot-dash lines to be distinguishable from the other fullline showings.

It will be clear from the above discussion that appropriate change in magnitude of any of the parameters affecting the voltage build up across resistor 33 may have the effect of changing the recurrent frequency of output impulses. It is further to be noted in this connection that the width of pulses in the multi-vibrator output may if desired be maintained precisely the same regardless of how the periodicity of recurrence varies. This feature follows from an appreciation of the fact that the time-constant circuit controlling output pulse width may always be maintained substantially the same, so that pulse width may always be determined by two synchronizing impulses of the same accurate time spacing.

In an analogous manner, the width of output impulse may also be controlled to be any desired multiple of the synchronization impulse repetition frequency 2Fo. To this end, a variation in the capacitance 3| may have the effect of increasing the build-up time of bias voltage impressed on the grid of tube section I as tube section II is conductive. This build-up time may be increased. so much that when the synchronizing impulse which succeeds the one which rendered tube section I nonconductive comes along, the magnitude of this succeeding impuls will be insufiicient when superimposed upon the voltage that has by that time been built up across resistor 30 to render tube section I conductive. It will thus remain for the next succeeding, or perhaps a still later, impulse to render tube section I conductive. It is accordingly clear that impulse width may be controlled to be equal to any integer multiple of the synchronizing impulse repetition frequency.

An alternate method of controlling either pulse repetition frequency or the width of output pulses from the multi-vibrator may be to control the magnitude of synchronization impulses applied to the grid of tube section I. Such control may be included within the circuit of cathode follower l8, as will b clear, and may for example b in the nature of a variable tap on the input resistor R21 of tube Ta. Should this control be effective to reduce the magnitude of applied synchronization impulses to a great enough extent, tube section I may fail to go conductive after an interval equal to the period between synchronization impulses and may thus go conductive after one or more synchronizing impulses have been impressed on this grid.

It will be clear that, in order to facilitate an understanding of the operation of the multi-vibrator in accordance with features of the invention, the showings in Fig. 4 have been greatly exaggerated, that is, the impulses present in the output of the multi-vibrator have been shown to be excessively large with respect to the intervals separating them. In actual practice, it is contemplated that greater separation intervals may be employed merely by appropriate selection of the circuit constants and current magnitudes present in the multi-vibrator circuit. For example, in an actual embodiment of the invention, we have been able to obtain output impulse recurrent frequencies of from 500 to 6000 cycles while maintaining the pulse width constant over this entire range. This result, it may be noted, was obtained when a quartz crystal oscillating at 200 kilocycles was employed.

Although the current output wave form from the multi-vibrator has been shown in Fig. 4 to be very regular, that is, zero current for a while followed by a constant maximum, conceivably such regularity may not be a fact. Accordingly, in order to assure that a better square-wave output will be obtained, we propose to us appropriate wave-shaping elements.

In the form shown the multi-vibrator output is applied to shaper stage It by way of a capacity coupling 46. Referring to Fig. 3, shaper it is seen to comprise an ordinary amplifier tube Tm. The input circuit of tube T10 is provided with adjustable biasing means 5'! whereby the tube may be preferably biased, beyond cut-off, thus performing a clipping action to eliminate any circuit noise or transient phenomena occurring near the base of square-waves generated by the multi-vibrator. Tube T10 also preferably has a high-p4 characteristic so that further shaping may be obtained due to saturation effects limiting the top of the square waves to a substantially uniform magnitude.

In the form shown the adjustable biasing means 47 includes a fixed resistor 58 adjustably tapped to a potentiometer 49, which is connected across the biasing source (not shown). t will be noted that in actuality then coupling condenser 46, resistor 48 and potentiometer 49 form part of the time-constant circuit which in the assumed illustrative case controls the longer of the two recurrent intervals defined by multi-vibrator action, If adjustment is contemplated in the magnitude of the bias voltage for tube T10, it is considered preferable that such adjustment be effected with a minimum of change in the overall impedance of elements 48, 48, and 49. Accord ingly, resistor 48 is preferably large compared with the impedance of potentiometer 49.

As shown output from the shaper stage i0 is taken from the anode circuit of tube T10. There is thus a reversal in phase (polarity) of resultant squared pulse energy, and in order to obtain positive wave-forms a phase reverser 2?) similar to phase reverser I! may be employed. As in the case of phase reverser I'l, phase reverser 20 may include an ordinary amplifier tube T11 capacitance-coupled to the output of tube T10. At this stage it may be observed that further shaping of the squared-waves may be effected by taking advantage of the fact that the input wave formis negative, y operating tube T11 at substantially zero bias and applying relatively large -values of input voltage, clipping of the negative maxim'a may take place at cutoff, whereby both the bases and" the crests of'the resultant positive squared-- waves are defined by clipping (cut-on) action;

; Next and in order that the squared-waves may be supplied for any desired purpose at relatively low impedance, a cathode followeri'l', similar to cathode follower 18; may be employed. The circuit for cathode follower 21 may thus comprise a conventional amplifier tube T12 capacity-coupled to tube T11, and output for a desired load Pi may be derived without reversal of phase across resistor d common to 'the input and output circuits of tube T12, aswillbe clear. 7

' Many useful applications "of the above-described device will doubtless occur to those skilled in the art. These' applications may include receiver blocking, wave-blanking, difierential delay circuits, and the like. One significant application will be briefly described.

As indicated at the outset, the invention iscontemplated to have particular utility in the field of obstacle, particularly aircraft, locating apparatus. According to this type of device, as fully described in the above-mentioned copending patent applications of Messrs. Busignies and Labin, an impulse transmitter is employed periodically to radiate impulse energy. For each impulse transmitted, provided there is a reflecting object within range of the apparatus, a reflection of this impulse may be detected at an instant of time later than the instant of transmission by an amount proportional to the distance from the equipment to the reflecting object. The receiving equipment includes means for detecting the refiected impulses and an indicating device, preferably a cathode ray tube having at least two electron beam control systems. One of these control systems may be a conventionaldeflection system to which sweeping voltages, synchronized with the periodic recurrence of transmitted impulses, may be applied. The other of these control s sterns may be another deflection system to which energy from detected received signals may be applied.

The teachings of this invention may be applied to obstacle detection systems of the abovedescribed character in substantially the following manner. Energy characterizing the synchronizin impulses which render tube section I of multivibrator non-conductive and simultaneously make tube section II conduct may be employed also to synchronize or energize the impulse transmitted so that impulse energy is transmitted only at these particular instants of time. Such a synchronizing signal could be obtained, for example, by sending output energy from either tube section (I or II) through a differentiator circuit, whereby sharp alternately positive 51 0f Fig. 4b; asobtaine'd for example by a high impedance connection across the inputof tube section I, be amplified,- appropriately polarized;-

" represented by the interval of non-conductivity of tube section I. Accordingly; if received: if F flections of transmitted impulses be detected within the interval of time during which. tube section Iis non-conductive, there will be observed'on the screen a needle-like indication transverse to the distance or time interval sweep scale; and the lateral disposition oi this needle-like indication with repect' to ends of the distance scale may be indicative of distance to the-reflecting object as will be clear. r

If it should happen that the reflecting object is relatively far away, the interval between successive synchronizing impulses may not allow sufiicient time for transmitted impulses to reach the object, be reflected, and then be detected by the receiving equipment. In such an assumed case the transverse needle-like deflection representing the reflecting object will appear at one end of the distance scale, and adjustment will be necessary before the distance to the object may be correctly determined. Such adjustment may be made very simply by making any of the abovenoted adjustments to change the period of nonconductivity of tube section I. A simple expedient would be to increase the time constant of the circuitdefined by elements 30, 3|, and 32 so that instead of the period of non-conductivity of tube section I being merely the period between synchronizing impulses, it may be precisely the period of every two, three, four, etc. of these synchronizing impulses, as will bev clear. In this manner, it would be possible effectively to magnify or enlarge the range of the obstacle-detection apparatus as desired, and at the same time always to have a precisely calibrated distance scale on the cathode ray screen, due to the high accuracy of the stable timing source, quartz oscillator II).

It will be appreciated that we have disclosed means and methods for generating synchronizing impulses having a high order of stability and accuracy of recurrence. These pulses may be highly useful for accurate synchronization of sawtooth generators, multi-vibrators, timers, and other devices. In a specific embodiment these synchronizing impulses are employed to produce other pulses of highly precise constant width, adjustable as desired to an integer multiple of the synthen negative impulses would result, and then clipping so that whichever of these sets of impulses characterized the above-noted instants of time may remain for application to the transmitter unit.

Concurrently with the use of multi-vibrator output energy just noted, the periods of nonconductivity of tube section I (i. e. the shorter intervals) could be employed accurately to define a distance scale on the cathode ray indicator tube. To this end it is suggested that sweeping energy proportional to the change in voltage represented by the solid line voltage build-up curve chronizing impulse period. These other pulses have the further feature of recurring at an easily adjusted sub-multiple frequency of the frequency of the synchronizing impulse recurrence, and have been shown to have utility in specific application to obstacle-detection apparatus.

Although the above specification has dealt with specific preferred embodiments of the invention in considerable detail, it is to be understood that these embodiments are purely illustrative and that many additions, adaptions, and omissions may be made fully within the scope of the invention.

What we claim is:

1. A device for generating periodically recurrent impulse energy characterized by impulses of accurately defined duration comprising: means for generating a regular series of relatively short accurately timed synchronized pulses, a multivibrator having two discharge sections, each having an input circuit, means to apply said synchronized pulses to one of the input circuits, first, to render in response to a synchronized pulse one of the sections conductive and the other non-conductive, and second, to effect in response to a later synchronized pulse the reverse operation, means providing a time constant for the input circuit of said one section to terminate the conduction therein upon the occurrence of a synchronized pulse a predetermined interval after initiation of conduction thereby generating an impulse of given duration, means providing a time constant for the input circuit of said other section to terminate conduction therein upon the occurrence of a synchronized pulse a selected interval after initiation of conduction to determine the frequency of the generated impulses, means 12 to independently vary the value of said time constant means, and means to withdraw the resulting periodically recurrent accurately timed impulse energy from said multivibrator circuit.

2. An impulse generating device according to claim 1 in which said synchronized pulse generating means includes: a stabilized sine Wave occillator means, a full wave rectifier means coupled to said oscillator to produce a series of accurately and equally time spaced cusps, a first difierentiator circuit coupled to the output of said full Wave rectifier means, a second differentiator circuit coupled to said first difierentiator circuit said differentiator circuits sharpening the cusps of the rectified sine wave, and clipping means coupled to the output of said second differentiator circuit for producing a unidirectional train of accurately and equally time spaced instantaneous pulses.

1 EMILE LABIN.

DONALD D. GRIEG.

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