Oct.. 15, 1946°1 L. E. `MßcrsoN, JR 2,409,577 SYNCHRONIZED BLOCKING OSCILLATOR Filed Dec. 3. 1943 BY WV ATTORNEY Patented Oct. 15, 1946 2,409,577 UNITED sTATEs PATENT OFFICE 2,409,57 7 SYNCHRONIZED BLOCKING OSCILLATOR Leslie E. Matson, Jr., Merchantville, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application December 3, 1943, Serial No. 512,681 5 Claims. (Cl. 250-36) l 2 This invention relates to oscillation generators, nization of the first of a series of oscillation trains or pulses with a suitable external signal. There are many uses for apparatus of the type Referring to the drawing, I show therein a discharge tube I which is preferably of the pentode type having a cathode 2, an anode 3, a control grid 4, a second grid 5, and a suppressor grid 6. The cathode 2 is grounded and is Valso connected to the grid E through a resistor 1. The input circuit of the oscillator proper includes a grid leak resistor 8 connecting grid 4 to ground. to Which this invention relates. Feedback means are coupled to this circuit and and more particularly to an oscillator which blocks itself automatically, and is provided with means for control of the intervals during which it intermittently oscillates, and also for synchro One require ment in some of the applications involved is that there shall be made available apparatus for pro ducing a succession of periodically recurrent os include a transformer 9, the primary I6 of which is in the output circuit of the oscillator, while» the secondary'V II is coupled to the grid 4 across cillation trains; that is, trains of equal duration capacitor I2. Anode potential is supplied to the and equally spaced apart in time. Another re anode 3 across the transformer primary I0, be quirement is that the ñrst train in such a group 15 ing delivered by a direct current source I3. This shall be synchronized with the leading edge of source also supplies screen grid potential to the a square Wave impulse of relatively low fre grid 5 across resistor I4. The usual by-pass con quency. Blocking oscillators are, therefore, capa denser I5 is provided, one terminal of which is ble of improvement in accordance with the dis~ connected to the screen grid 5 while the other closure of this application so that each train of 20 terminal is grounded. Any suitable utilization oscillations shall consist of a uniform number device may be coupled to the oscillator at the of cycles (usually one cycle), and the initiation terminals labelled “output,” Where one of these of the first of a group of trains of oscillations is so terminals is coupled to the anode 3 across capaci controlled as to be precisely synchronized with a particular phase of the applied rectangular tor IE. wave. It is an object of my invention to provide a blocking oscillator of vnovel type wherein the periods of oscillation are controlled by an ex ternal source of rectangular Waves. The output may, however, be taken at , any of several other points. 30 It is a further object to provide a blocking oscillator wherein the leading edge of a square wave and the trailing edge thereof shall serve to initiate and to stop respectively the generation of oscillations. 35 Still another object of my invention is to pro vide a blocking oscillator having a pentode tube in which the cathode, first grid, and anode are included in the oscillatory circuit, the second grid being arranged to function as a screen and 40 the third grid being used to initiate and to stop the oscillations in dependence upon the keying of an externally derived control potential. Another object of my invention is similar to that set forth in the preceding paragraph but 45 with the added feature that an auxiliary tube is provided for varying the control potential ap plied to the third grid of the oscillator tube. The forego-ing and other objects and advan tages of my invention will be made clear from the description to follow. This description is ac companied by a drawing, the sole figure of which shows a preferred circuit diagram of apparatus units which are combined for carrying out the invention. 55 If the suppressor grid 5 is maintained at cath ode or ground potential, tube I generates inter~ mittently blocked oscillations by virtue of a feed back circuit through transformer S, the oscillatory electrodes being the cathode, the anode, and the control grid, as is conventional. If, however, a negative potential is applied to the suppressor grid with respect to the cathode 2, then the oscillations are stopped. In order to supply this negative potential, an auxiliary control tube I'I is provided. This tube may, if desired, be of the triode type having a cathode I8,- an anode I9, and a control grid 20. A cathode resistor 2l is here shown, this element being preferably used to avoid tube saturation. An independent direct current source applies a negative potential to the cathode I8 through resistor 2|, the positive terminal of this source being grounded. The input circuit for tube il includes a grid leak resistor 23 connected between the grid 2l] and the negative terminal of the source 22. Grid 20 is also arranged to be fed with control potentials across capacitor 24. These control potentials develop a suitable volt age drop across the resistor 23. Input terminals 25, one of which is grounded, may be used for applying suitable control potentials. These po tentials are preferably of the rectangular or square wave type in order that the leading and 2,409,577 3 4 trailing edges of the wave may be sharply de fined. In the operation of my invention, it will be tions, and a keying circuit for at times blocking said oscillations, said keying circuit comprising a second discharge tube having at least a cathode, seen that the square wave input constitutes a an anode and a control grid, the anode whereof gate voltage which controls the space path im is directly connected to a grid of the oscillator tube adjacent its anode, an input circuit con pedance in the tube I'I. When this tube is blocked by a negative potential on the grid 20, then the anode I9 stands at ground potential since there is no voltage drop across the resistor 'I under nected between the cathode and control grid of said second discharge tube, and an output circuit for the second discharge tube including a direct When, however, tube I1 is 10 current source the positive terminal of which is these conditions. rendered conductive, it draws current by virtue of the negative potential applied to its cathode I8 maintained at the cathode potential of the iirst said tube, a ñxed resistor being interposed be tween said positive terminal and the anode of from the source 22. The current traversing re the second discharge tube. sistor 'i developsl a voltage drop which thereupon 2. In combination two electron discharge tubes, renders the suppressor grid 6 strongly negative. 15 each having a cathode, an anode, and one or Hence, the tube I is biased to cut-oil and the more grids, input circuits and output circuits oscillations instantly cease. individual to each of said tubes, the input and In this description of operation it should be output circuit of one of said tubes being so inter emphasized that in usual practice the oscilla tory state exists in ,a blocking oscillator during 20 coupled as to cause that tube to generate pe riodic and discrete oscillatory trains, two sources periodic intervals which are very brief compared of direct current, each individually constituting with the intervals during which the oscillator a means for supplying power to a respective one is blocked. The ratio between oscillating times of said tubes, direct ground connections for the and blocking times depends, of course, upon the negative terminal of the source which supplies circuit constants. A “train” of oscillations, as power to the oscillator tube and for the posi herein referred to, consists of the single impulse tive terminal of the source which supplies power or the plurality of impulses produced prior to to the other tube, a load impedance connected each blocking period. Commonly, the blocking between ground and the anode of said other state is reached so suddenly that only a single tube, a direct connection between that anode and cycle exists in each train. Under some circum a grid in the oscillator tube other than its oscil stances, however, each train may comprise a plu lator grid, and means for so controlling the rality of cycles. The function of the externally space path impedance in said other tube that, derived rectangular wave is to periodically ter when conductive, it interrupts the periodicity of minate the blocking periods. Thus it is possible production of said oscillatory trains. to control the starting time for the first of a 3. Apparatus for alternately initiating and in group of oscillatory trains in accordance with terrupting trains of oscillations generated in a the steep wave front of a rectangular wave and discharge tube which possesses oscillatory and to permit the oscillator to deliver a succession suppressor electrodes, said suppressor electrode of “trains” comprised in that group during the persistence of a half cycle of said rectangular 40 being iixedly connected through an ohmic resist ance to the cathode of said tube, comprising a wave. second discharge tube in which the space path At the instant when a group of oscillation impedance is varied by a rectangular wave input, trains is again to be initiated in tube I, the trail this second tube having its anode resistively con ing edge of the rectangular wave input to tube I'I blocks this tube so as to restore the ground 1 nected to the cathode of the ñrst said tube, means potential to its anode IQ. Thereupon the sup pressor grid S in tube I is brought back to ground potential and the generation of oscillations is re pressor electrode at all times with the anode sumed. It will be noted that the degree of accuracy for equalizing the bias potential of said sup potential in said second discharge tube, and means for shifting said anode potential from that of the cathode in the first said tube to a with which the oscillatory trains are synchro more negative potential whenever the oscillatory nized with respect to an external source of rec trains are to be blocked. 4. A control circuit comprising a vacuum tube to be controlled, said vacuum tube having an anode, a cathode, a control grid and at least one other grid, an input circuit connected be tangular waves depends upon the abruptness of transition between conductive and non-conduc tive states in the tube I'I. Hence by a carefully selected choice of circuit components, the control and synchronizing of oscillatory trains can be made as precise as is desired. tween the control grid and cathode, said cathode being connected to ground, an output circuit connected between said anode and cathode, a re My invention is capable of modiñcation in numerous ways without departing from the spirit 60 sistor connected between said "other” grid and the grounded cathode, a controlling vacuum tube and scope thereof. For example, it is not at having a plate, a control grid and a cathode, a all essential that the control potentials applied cathode return circuit including a source of oper to the tube Il' shall be periodic. In certain ap ating potential connected between the cathode plications, it is required that they shall be aperiodic, but that they, nevertheless, shall be f“ of the controllingtube and ground, the plate of said controlling tube being connected to said enabled to initiate and to block the oscillatory other grid in the first mentioned tube and the trains generated by tube I regardless of their plate circuit including said resistor, and means duration and of the duration of the blocking periods. for rendering said controlling tube alternately I claim: 1. In a device of the class described, an oscilla tion generator comprising a discharge tube hav ing a cathode, an anode, and at least two grids, conductive and non-conductive thereby to neg ativeiy bias said “other” grid of the tube to be controlled during conductive periods of the con resonant circuit means connected to the Vcath ode, anode, and ñrst grid for producing oscilla trolling tube. 5. In combination, a blocking oscillator com 75 prising a multi-grid discharge tube and means 2,409,577 coupling its output to one of its grids for apply ing feedback potentials thereto, a keying control device directly connected between the cathode of said tube and a grid adjacent its anode, said connections for the cathode of the oscillator tube, the negative terminal of the source in the oscil lator output circuit, and the positive terminal of the source in the output circuit of the tube in device comprising a fixed impedance in the out Ul said keying control device, the negative termi put circuit of a discharge tube the conductive and nal of the last mentioned source and the cathode non-conductive states of which are controlled by of the tube in said keying device being intercon an external source of rectangular Waves, inde nected through a cathode resistor. pendent sources of direct current in the respec tive output circuits of said tubes, and ground l0 LESLIE E. MATSON, JR.