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April 5, 1938. 2,113,340 J. EVANS ULTRAHIGH FREQUENCY OSCILLATOR - Filed Sept. 21, 1935 III» hi IN vB/v'roR John, Evans Witness. 00 '7‘ Bo) HT'I'OHNEY Patented Apr. 5, 1938 2,113,340 UNITED STATES PATENT OFFICE 2,113,340 ULTRAHIGH FREQUENCY OSCILLATOR John Evans, Collingswood, N. J., assignor to Radio Corporation of America, a corporation of Del aware Application September 21, 1935, Serial No. 41,540 8 Claims. (01. 250-36)‘ My invention relates to ultrahigh frequency thermionic devices. More particularly, my in vention is an ultrahigh frequencyr oscillator em ploying thermionic tubes in which the anodes are a virtually at ground potential. I am aware of numerous circuits for generating high frequency oscillations. Some of the pro posed circuits will generate ultrahigh frequencies but the frequency is far from constant. Other circuits have been devised which generate oscil lations of high and constant frequency but it is impossible to extend the range to frequencies ex ceeding ?fty megacycles. Beyond these high frequencies the thermionic tube elements and the 15- leads within the tubes assume electrical lengths of proportions which interfere with the higher frequency ranges. One of the objects of my invention is the gen eration of oscillatory currents of ultrahigh fre 20 quencies. Another object of my invention is to reduce the effect of the anode load on the input circuits of a thermionic tube. A further object is to place the anodes of a 25 pair of push-pull oscillator tubes at virtually ground potential. Additional objects will appear in the following speci?cation and claims. Figure 1 is a schematic diagram of an ultra 30 high frequency oscillator in which the anodes are at ground potential, and ' Figure 2 is a diagram of an oscillator embody ing one form of my invention. It is well known to those skilled in the art that 35 the characteristics of the input circuit of a 'triode are dependent on the load in its output circuit. Although this e?ect may not be of great im portance at low frequencies, it is of extreme im portance at high frequencies. By way of ex-~ 40 ample, with one type of tube which has an input capacity of about 28 micromicrofarads with a zero plate circuit load, the effective input ca pacity will be approximately three times as great with an external load of 100,000 ohms. The out 45 put load may be inductive, capacitive or re sistive and in each case the effective capacity or reactance of the input circuit will be effected. The input reactance may be e?ected in either a positive or negative sense. 7 50 Although these effects are not always deleteri ous, I have found that at ultrahigh frequences the plate circuit load will limit the range of os cillation and ultimately limit the highest oscil latory frequency which can be reached. At fre 55 quencies of the order of. 50 megacycles and lower, depending mainly on the tube construction, the circuit of Figure 1 may be used.’ In Figure 1 a pair of triode tubes l-3 are con nected in push-pull relation. The grids 5-—‘l are connected to the conductors 9—ll of a trans 5 mission line l3. A bridging member I5 is ad justed on the 'lines 9-H until a ‘quarter wave length characteristic is obtained. The center I‘! of the bridge is grounded through a grid leak resistor Hi. The cathodes 2l-23 may be ener 10 gized by any suitable source; for example bat teries 25-21 or alternating current. In prac tice the capacity of the batteries or other source of cathode heating energy must be considered. Either ?lter networks or concentric lines should 15 be employed between the batteries and the cath odes as will be described below. The batteries 25-21 in Fig. 1 are shown as directly connected to the cathodes 2|, 23 merely for convenience of illustration. ' Conductors 29—3l of a second transmission line 33 are connected to the cathodes 2 l-23. An adjustable bridging member 35 is connected to the transmission line at about a quarter wave length position at which the tuned grid, tuned cathode will cause oscillations. The center 3‘! of the cathode bridging member is grounded. The anodes 39—4l are connected together with the shortest.l possible leads. The center 43 of the leads between anodes is connected to ground through a suitable capacitor 45. The center is also con 30 nected to a radio frequency choke coil 41. The choke in turn is connected to the positive ter minal of the anode current source 49. The nega tive terminal of the anode current supply 49 is grounded. . In the arrangement shown in Figure 1, if the length of the leads between the anodes is very short, the anodeswill be maintained at ground potential for radio frequency currents because of the low reactance of the capacitor 45 which vir tually grounds the anodes. Under favorable cir cumstances the anode output circuit will have substantially zero impedance and the effective input capacity will be relatively low and permit the generation of oscillatory currents of a fre quency of the order of 50 megacycles. However, as the frequency is gradually increased, the leads between the anodes, and particularly the leads within the tube envelopes, will assume sub- 0 stantial eifective reactances; i. e., substantial elec trical length. The higher the frequency the greater will be the reactive component of the leads, or the more effective their length. This reactive component will act as a load on the out-: 2,113,340 put circuit and effect the characteristics of the input circuit as explained above. I propose to overcome this di?iculty by ar ranging an output circuit which will have sub stantially no effect on the oscillation frequency and which will place the anodes at virtually 1. In an ultrahigh frequency oscillator of the thermionic tube type in which the inductance of the anode electrode lead has sufficient re actance at said ultrahigh frequency to prevent grounding the anode electrode within the tube, a pair of thermionic tubes, each of said tubes in ground potential at the highest frequencies. In cluding grid. cathode and anode electrodes, 2. Figure 2 a diagram of‘ a circuit employing anodes ground connection, a grid circuit connected be at virtual ground potential is shown._ A pairrof tween said grid- electrodes and said ground, a cathode circuit connected between'said cathode 10 triode thermionic tubes 5 1-52 are connected‘ as a ' electrodes and said ground, means for tuning said push-pull oscillator. The grids 53-55 are con nected respectively to the conductors 5'l--59 of a 1’ grid and cathode circuits with reference to the transmission line 6|. The line is adjustedto a frequency of; the oscillations to be produced, an anode circuit connected to said anode electrodes, quarter wave length by moving a bridging mem ber 63 to the required position. The center 65 of means for grounding said anode circuit, and the bridging member is connected to ground ‘ means for tuning said anode circuit to effectively a half wave length of said ultrahigh frequency through the grid leak resistor 61. The cathodes 69--'H are each energized by oscillation wherebysaid grid and cathode cir batteries 'l3—l5 or other suitable source. Radio cuits determine the oscillatory frequency of said -'oscillator and said anode circuit establishes an 20 frequency choke coils ‘Ill, 12 are connected "in" ultrahigh frequency groundhpotential on said each of the leadsbetween the batteries 13, 15 and anode. electrodeswithin said envelope. the cathodes 69-511. .. The batteries are each 2..In an, ultrahigh frequency oscillator of the grounded.‘ v“Ag-pairof ‘capacitors 14 and 16 are connected in series across. each of the cathode thermionic ,tube type in which the anode lead offers a reactance at the frequency of operation 25 ' __leads. The junction of. one pair of capacitors 14, which prevents directly groundingthe anode elec ‘i4 is connected to one of the conductors ‘ll of a transmission ,-line 8|; The junction of the other . trode within said tube, a pairof thermionic tubes, pair of capacitors ‘I6, 16 is connected to the other conductor“ of the transmission line. Although I have shown the ?lter network between the bat teries and the cathodes, .it is equally effective to make the transmission line 8| a pair of hollow conductors. One wire is connected within each conductor from the battery to the cathode and including, within. an evacuated envelope grid, cathode and anode electrodes, arranged to oper ate on opposite phases of ~ oscillatory currents; 30 a ground connection, a grid circuit connected be tween said grid electrodes and'ground, a cathode circuit connected between saidcathode electrodes and ground, means for tuning said grid and cath .», _,_the hollow conductors are used for the return . OdQ'CiI‘CUItS to said frequency of operation, means 35 wires from each cathode to the battery. The for impressing a positive direct current potential with respect to said cathodes on said anodes, and cathode leads are by-passed by» a suitableca pacitor. In either type of connection, it is pref- . means for establishing, an ultrahigh frequency erable to make the transmission» lines straight, ground potential on said anodes within said en parallel and of equal length. ' ~ The proper length of the transmission line to sustain oscillations is found by moving the bridg ing member 83 whose center point 85 is grounded. The anodes 8'l-—-89 are connected to the conduc . tors 9l—93 of a transmission line 95. Across the ' end of the transmission line opposite the anodes velope. ' 3. In an_ultrahigh frequency oscillator of the type, in which the anode lead of a thermionic tube offers sufficient reactance to the frequency 40 ' of operation to prevent directly grounding, the anode within said tube, a pair of thermionic tubes 45 including within an evacuated envelope grid, is placed the bridging member 91. The center‘ 99 = ' cathode and anode, electrodes and arranged. to of the bridging member 91 is grounded through a capacitor l?l whose reactance is low to the operate on opposite phases of their generated currents, a ground connection, a grid circuit con currents generatedgb-y the push-pull oscillator. nected between said-grid electrodesand ground, 50 nected through'a radio frequency choke I03 to If the bridging member 91 is carefully adjusted so that the transmission line is effectively a half wave length long, the anodes will be virtually at electrodes and ground, means for tuning said grid and cathode circuits to said-frequency of opera-, tion,;means, for impressing -a positive direct cur rent potential between said anode and cathode 65. electrodes, and means: for establishing an ultra high frequency ground potential within said en velope on said anodes with respect to said ground ground potential for the high‘frequency currents. connections. 50. The center. 99 of the bridging member is also con- , a cathode circuit connected between said cathode the positive terminal of the anode current sup ply. N15. The negative terminal of this supply is grounded. -. , The effect of the virtually grounded anodes is to ' 4.1m a push-pull ultrahigh frequency thermi 60., make the output load of the anode circuit sub- . onic oscillator of the type in which the anode stantially zero and to remove the effects of this lead offers a reactance at the frequency of op circuit on the input circuit. Using RCA type .852 eration which prevents directly grounding the tubes in push-pull relation with tuned input and anode within said tube, a pair of thermionic tubes . tuned cathode-circuits, I have been .able to gener having inputfanode and cathode electrodes; a 65 ate oscillations of the order of 500 megacycles, ground connection, a transmission line of sub or. 60 centimeters wave length. stantially one quarter wave length connected be Various obvious modi?cations within the scope tween said input electrodes and ground, a sec of my invention will occur to those skilled in the ond transmission line of substantially a quarter art; by way of example, the grid and cathode 70 wave length connected between said cathode elec-. circuits may be tuned with lumped inductance trodes and ground, and means .for maintaining and capacity. I do not intend to limit myinven tion except as required by the prior art and said anodes at points within said thermionic tubes at ground potential with respect to said the appended claims. ground connection for ultrahigh» frequency cur 75., I claim: » 2,113,340 rents and at positive direct current potential with respect to said cathode electrodes. 5. In a push-pull ultrahigh frequency thermi onic oscillator of the type in which the anode lead oii’ers a reactance at the frequency of operation which prevents directly grounding the anode Within said tube, a pair of thermionic tubes hav ing grid, anode and cathode electrodes, a ground connection, a transmission line of substantially 10 one quarter wave length connected between said grid electrodes and said ground, a second trans mission line of substantially a quarter wave length connected between said cathode electrodes and said ground, and a third transmission line of sub 15 stantially a half wave length connected to said anode electrodes at one end and to ground at the other end and tune whereby the ?rst men tioned end of said third transmission line is sub stantially at the potential of said ground connec 20 tion with respect to high frequency currents, and a source of anode current supply, having a grounded negative terminal and a positive ter minal connected to the second mentioned end of said third line. 6. In an ultrahigh frequency thermionic os 25 cillator of the type in which the anode lead offers 3 a reactance at the frequency of operation which prevents directly grounding the anode within said tube, a thermionic tube having an evacuated en velope including grid, cathode and anode elec trodes; a ground connection, a grid circuit con nected between said grid electrodes and ground, a cathode circuit connected between said cathode electrodes and ground and an anode circuit con nected between said anode electrodes and ground, means for tuning said grid and cathode circuits to 10 generate oscillations at said operating frequency, means for adjusting the effective electrical length of said anode circuit to a half wave length at said operating frequency whereby said anode elec trode within said envelope will be at ground po 15 tential for said high frequency oscillations, a di rect current supply and connections therefrom for positively biasing said anode electrode with re spect to- said cathode. 7. In a device of the character described in 20 claim 4, means for adjusting the effective length of said transmission lines. 8. In a device of the character described in claim 5, means for adjusting the effective length of said transmission lines. 25 JOHN EVANS.