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Nov, 26, 1946. 2,411,565 T. L. WILSON LOW IMPEDANCE OSCILLATOR Filed July 20, 1942 INVENTOR v; Fla/‘Ms [Ana/v7 Mum ; Mm - ATI‘ORNEY _ 2,411,565‘ Patented Nov. 26, 1946 UNITED STATES PATENT" OFFICE J., as Thomas Lamont Wilson, Scotch Plains, N.Newark, signor to Federal Telegraph Company, ’ N. J. , a corporation of California Application July 20, 1942, Serial No. 451,596 3 Claims. (01. 250-36) 1 two electron tubes, Ill and II, coupled to one This invention, relatesto an electronic oscilla another so as to constitute an electronic oscil-j tor, the output‘ impedance of which‘is relatively low. ' lator. While these tubes have for the purpose of simplicity in illustration been shown as tri odes, it is to be understood that my invention I In many industrial ?elds, it is desirable to couple the output of an electronic oscillator to ' is applicable to tubes having a larger number a utilization circuit or load having a very low of elements, such as tetrodes or pentodes and the modi?cations of my invention necessary, to adapt it for use with such last mentioned types of impedance relative to the output impedance of the conventional oscillator and to have the volt age across this load impedance remain approxi mately constant when the magnitude of the im pedance changes over a wide range. 10 tubes, will be apparent to those skilled in the The con ventional electronic oscillator, having a relative; ‘ly high internal impedance will not provide a art. ‘ The‘cathodes l2 and 13 of tubes [0 and II, respectively, may be heated from any conven ient source, as conventionally shown in the draw ing by the symbols LT applied to the v leads 15 whose magnitude varies widely. ‘ . proceeding from such cathodes. Likewise the One object of my invention is to provide an cathode of tube It is preferably grounded with electronic oscillator‘ capable of feeding a load respect to oscillatory currents by means of by circuit having an impedance whose magnitude constant voltage source for a load impedance pass condensers Hl connected in series across is-relatively low and varying, and of ‘keeping a substantially constant voltage across that im 20 the’ extremities of the cathode and having a‘ pedance. direct ground lead extending ‘from the conductor between the two condensers, as indicated at l5. At 56 is shown the control grid, and at I’! the anode of tube It. The exciting energy sup plied to grid I6 is derived in a manner which 25 cuit of an electronic tube, the excitation of the will be herein later described, but for the pur tube being accomplished by feeding energy, in poses of the present explanation, it is to be the proper phase relationship, to an input cir assumed that oscillatory electrical energy reaches cuit constituted by the control grid and cathode grid [6. Anode I1 is supplied with suitable high of such tube. With electronic tubes of types 30 tension energy derived through conductor 18, as’ which are available in the art, the output im indicated by the legend H'I‘+. This energy pedance of a tube connected in the manner just reaches the anode through a suitable impedance described is relatively high and therefore the such as inductance l9, connected in series there external impedance which feeds the load, must with. The ampli?ed oscillations appearing in for the sake of efficiency and voltage regulation In electronic oscillators as used‘ in the prior art, the output has customarily been taken from an impedance located directly in the anode cir circuit of anode I‘! are transferred through be made. quite high relative to the anode-cathode 35 the the combined action of impedance [9 and cou internal impedance of the tube, which latter value ' pling condenser 20, to the grid 2| of tube ll. is high, relative to values prevailing in gener This last mentioned grid is, with respect to ators of the non-electronic type. oscillatory energy, isolated from the ground by In carrying out my“ invention, I make use means of a suitable impedance such as induc of electronic tubes of conventional-types‘, hav 40' ' tance 22 and resistance 23, connected in series ing a comparatively great anode-cathode im in the ground circuit of the grid. Likewise the pedance, but I so connect the input and output static potential of grid l6‘is determined by its circuits, respectively, of such tubes that the im connection to the ground through‘ a suitable pedance of the external output circuit, to which 45. impedance such as inductance 24 and resistance the load is connected, shall be e?i‘ectively only 25, while the source of high tension supplying a fractional part of the impedance existing when energy to the conductor I8 has its negative ter conventional methods of connection are em minal connected to the ground, so that condenser ' ployed. 26 serves to by-pass oscillatory energy around Another purpose of this invention is to pro 50 this source. » vide a generator of ‘electronic oscillations hav ' The anode 21 of tube II is connected directly. ing an external output circuit of such low imped ance as to possess an inherent quality of good regulation, when connected to a load of rela to a suitable source of high tension energy as indicated at 28, which generally, but not neces sarily is the same source as for anode ll of tube tively low impedance. ill. This source likewise has itsnegative ter-, Referring now to the drawing,’ there are shown, 55 3 2,411,665 4 minal grounded as indicated at 29, while con denser 30 serves to by-pass oscillatory energy around this last mentioned source. The oscil latory energy reaches cathode l3 of tube II through condensers 31. Between the mid-con nection point of condensers 3| and the ground, is interposed a tank circuit comprising a con ance l9 to increase, thus depressing the poten tial reaching grid 2|. The total voltage between grid 2| and cathode I3 will be the grid-ground voltage less the cath ode-ground voltage. By choice of suitable values of the various impedances and capacities, as well known in the art, phase shifts e?ects may be denser 32, preferably variable, and aninductance 33 connected in shunt therewith. The constants kept at a minimum. .; A reduction of voltage on grid 2| will lower the 10 voltage drop across the tank circuit and thus will increase the net or effective anode-cathode volt of this tank circuit serve to determine the fre quency of the oscillations produced by my gen erator; and such oscillations may lie either in the audio frequency or in the radio frequency spectrum, according to the choice of such con stants. The exact point of grounding this tank 15 age. This brings about the result that the voltage appearing from cathode to ground is in phase with the grid-ground voltage. The voltage ap pearing at point 36 will then be 180° out of phase circuit may conveniently be determined by ad with the grid voltage and thus, when fed through justment of the point upon inductance 33 to coupling condenser 31, will appear upon grid l6 of which ground lead 35 is connected. The upper ‘ tube H1 in proper phase to sustain oscillation of the system. end 35 of the tank circuit-is connected tocathode l3 via condensers 3i, while the lower end 36 of 20 Since the e?ective grid-cathode voltage of tube this circuit is coupled back through condenser l l depends on the relative grid-cathode and cath 31 to grid l6 of tube Ill. The tank circuit 32, 33 ode-ground impedances, if a load be coupled into‘ constitutes the output circuit of my generator inductance 33, the cathode-ground impedance and it may ‘conveniently be coupled to the load will be lowered and the net grid-cathode voltage by means of an inductance, 38 placed in juxta 25 will therefore be raised, assuming that the driver position to inductance 33 although other methods voltage supplied ‘to tube l I remains constant. While this elfect of lowering the cathode-ground of coupling to the load, as well known in the art, may be employed. impedance will usually be less at low frequencies than at high frequencies, yet the effect is present The way in which oscillatory energy reaches under all conditions of oscillation. The cathode the tube H is such as to cause the e?ective input ground voltage supplied by tube II depends upon circuit thereof to lie between the grid and the anode, rather than between the grid and the 4 the oscillatory current in the anode circuit and upon the cathode-ground impedance of this tube. ‘ cathode, since the input voltage appears across If this output impedance be lowered, an increase points 39 and 4B, the latter being at ground po tential, while anode 21 is also at ground poten 35 in oscillatory current in the anode circuit, result ing therefrom, will tend to keep the cathode tial with respect to oscillatory energy, due to the ground voltage constant. Thus it will be seen action of by-pass condenser 30. The load circuit that there results _a regulatory action similar to thus becomes one of the type known as cathode that obtained in the case of a generator having follower, in that the load circuit is connected so 3 that not only the output energy in reaching the 40 low internal impedance. Various modi?cations of this invention may be cathode passes through such load circuit, but made in order to adapt it to special uses. For also the return between the grid and cathode example tube 10 may be excited from an inde takes place through this same load circuit. In the operation of my invention, tube I0 func 45 pendent source, rather than receiving its excita tion energy through feed-back condenser 31. tions chie?y to amplify the oscillatory energy im Optionally, it would be possible to substitute for pressed upon the grid IS, the ampli?ed oscilla~ tube II a pair of tubes connected in push-pull tions being passed on to grid 2| of tube II by fashion. Other modi?cations of my invention means of the impedance coupling circuit includ ing impedances l9 and 22 and coupling capacity 50 will be apparent to those skilled‘in the art. ' WhatI claim is: 20. The action of this tube and its coupling cir 1. A low impedance oscillator including two cuit will be apparent to those skilled in the art. electronic tubes, having cathodes, control grids, Tube H has the input energy impressed between and anodes, means for supplying suitable energy’ grid 2i and anode 21, while the output thereof is obtained between cathode l3 and a point of 55 to the respective cathodes and anodes, means for keeping the respective control grids at a suitable inductance 33 which is at ground potential. mean potential, means for coupling the output When a tube is connected in this fashion, its in ternal output resistance, as ordinarily measured ' anode-cathode circuit of the ?rst tube to the in put grid-anode circuit of the second tube, circuit between anode and cathode, will be multiplied by a fraction, the value of which depends upon the 60 means connecting the oscillatory energy of the anode of the second tube to ground, output circuit ampli?cation constant of the tube. Thus even a means connected in the common‘ grid-cathode tube having a very high IL may be employed as and anode-cathode return circuit of the second tube | I, notwithstanding the fact that such tubes, tube, means for withdrawing oscillatory energy as usually connected, have an extremely high out from said output circuit means, and means for put impedance. ' 65 feeding back to the control grid of the ?rst tube, Tracing the path of one cycle of oscillation in regenerative phase relationship, a portion of' through the circuits of my invention, let it be the energy present in said output circuit means. assumed that grid I6 is driven positive above its 2. A low impedance oscillator including a ?rst static potential. This will increase the anode electron discharge tube having a grid-cathode current of tube In and since the internal voltage 70 input and an anode-cathode output, a second drop of the tube plus that of the voltage drop electron discharge tube having a grid-anode in! across impedance l9 will always add'together to put and a cathode-ground output, means cou equal the voltage supplied by the high tension pling the output of the ?rst tube, to the input of» source through conductor l8, this increase 'of an second tube, means coupling the‘ oscillatory ode current will'cause the voltage across‘ imped 75 the energy of the anode of the second’ tube ‘to ground, 2,411,565 cathode-follower output meansof the second tube including a parallel tuned circuit connected be tween the cathode of the second tube and ground, and regenerative means coupling the output of said second tube to the input of said ?rst tube. source of;anode energy, capacitative means by- _ passing said source directly to ground, a resonant tank circuit connected between cathode and ground including a series inductance and means for grounding a predetermined point of said in ductance, means for withdrawing energy from 3. A low impedance electronic oscillator in cluding a ?rst tube having cathode, grid and anode, a choke coil and resistance in series be tween grid and ground to bias said grid, cathode 10 heating and grounding by-pass ‘means, a source of anode energy, capacitive means by-passing said source, a coupling impedance‘ in the anode said tank circuit, means for feeding back a por tion of said tank circuit energy to the grid of said ?rst tube, and a capacity coupling the anode of said ?rst tube and the grid of said second tube, ' cathode circuit, a second tube having cathode, oscillatory system. grid and anode, a choke coil and resistance in series between the grid andground to bias said 15 grid, cathode-heating and by-passing means, a whereby said fed-‘back energy is in regenerative phase relationship and whereby said ?rst tube excites said second tube so as to produce a self THOMAS LAMONT WILSON.