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Jan._l1, 1938. J. EVANS 2,104,916 7 CONSTANT RADIO FREQUENCY GENERATOR Filed Oct. 51, 1955 2 Sheets-Sheet l \53 4, I //5 2342?. I25 223 2/9 Jan. 11, 1938. J, EVANS 2 l 0 4. 9, l 6 CONSTANT RADIO FREQUENCY GENERATOR Filed Oct. 51, 1935 ‘ \ arldvéV/’IOMTH COOL/1V6 FL U/D 2/7 22/ $2.5. 7m. 77 79 55 2 Sheets-Sheet 2 Patented Jan. 11, 1938 UNETED STATES 2,104,916 CONSTANT RADIO FREQUENCY GENERATOR John. Evans, @ollingswcod, N. J., assigncr to Ita dre Corporation of America, a corporation of Delaware Application October 31, 1935, C‘serial No. 47,563 20 Claims. My invention relates broadly to radio trans mitters. More particularly my invention deals with a generator of constant radio frequency. An increasing number of radio transm ters 5 has brought the requirement that each trans" mitter maintain, within very close limits, its as~ signed frequency. Deviation from assigned fre quencies causes interference and lessens the effi ciency of communication. Transmitters oper~ 31' ating on frequencies of the present day broad cast range employ piezo~eleotric crystals for stabilizing their frequency. Such piece-electric control is not entirely satisfactory at frequencies of the order of 25 megacycles and upward. 5* I am aware of the use of resonant lines for con~ trolling the frequency of oscillators. Resonant lines of the order of one quarter wave length have been used with and without temperature control for stabilizing the frequency of vacuum tube oscillators. The arrangement generally em“ ployed is to connect a resonant line to the input of a thermionic tube. The output of the tube is loaded with an inductive reactance. In a circuit of this type the effective input impedance de ,\ pends upon the ampli?cation .factor of the tube, ’ the output load, and other factors which may vary and affect the constancy of the oscillatory frequency. My invention embodies means for minimizing these e?ects. 1].) One of the objects of my invention is to gen erate constant frequency oscillations. Another object of my invention is to embody in circuit means for generating oscillations whose frequency will be constant throughout a wide range of operating temperatures. A further object is to improve the efficiency of a constant high frequency transmitter. A still further object is in the embodiment of my invention in circuits which employ novel L) temperature compensating means. ‘ Additional objects will be apparent from the accompanying specification, drawings and claims. My invention may be best understood by refer ;, ence to the accompanying drawings, in which Figure I is a schematic diagram of a trans_ mitter circuit embodying my invention, Fig. II is a view, partly in section, of a trans mi embodying my invention, III is a schematic diagram of the cathode .1; heater circuit used in Fig. II, and IV H) a more detailed illustration. of the thermionic tube shown in Fig. II. In Fig. I, a thermionic tube 5 having cathode 3. grid 5, and anode l electrodes is connected as 5.; follows: The cathode is heated by any suitable (Cl. Zoe-36) source which is shown as a battery 9 but may be a source of alternating current. The cathode is by-passed by a capacitor ii. The grid electrode connected to a suitable point on the inner electrode it of a concentric quarter wave line it. This quarter wavelength is measured from the open end. of electrode is to the cross piece it. The inner electrode is connected to the outer electrode i 'i of the concentric line by a conductive member iii. The cathode 3 is connected to the outer member by a grid leak resistor 2i which preferably bypassed by a capacity 23. The anode circuit consists of a battery 25, or other suitable source of power, whose negative terminal is connected to the cathode. The posi tive terminal of the power source is connected through a radio frequency choke coil 21 to the anode electrode l. The anode battery may be bypassed by a capacitor 29. An extension 3! of the outer member of the concentric line houses 20 the anode load circuit. The extension end of the outer member of the concentric line is closed by a conductor 33. In this extension a pair of con ductor elements til-32 are ?xed to the centers of the conducting members Ill-33, which close . the line. A pair of condenser armatures 38-41 are ?xed to the free ends of the pair conductor elements. The outer member ll‘ and the pair of inner conductor elements 35-31 form, in effect, a toroidal inductor. This toroidal inductor and condenser form the anode load circuit. The tuned anode load circuit is connected to the anode by a capacitor 53 between the anode elec trode ‘I and one of the armatures 39. The outer member is connected to the anode battery by a capacitor 45. While the theory of operation is substantially that of a triode oscillator in which the frequency is primarily determined by the constants of the circuits, I shall describe certain differences which 40 contribute to the results I have obtained. In an ordinary tuned grids-tuned plate oscillator, the coupling between the grid circuit and the plate circuit is the capacity between grid and plate. The feedback effects, through the grid to plate capacity, required to sustain oscillations, are only obtained in the proper phase when the plate cir cuit load. inductive. In this arrangement, the effective input capacity is dependent upon. the ampli?cation factor of the tube and the plate ciru cuit load. Any change in either of these elements affects the frequency of oscillation. Oscillators of this type have notoriously poor frequency regulation for the reasons set forth. Feedback in the circuit of Fig. I is not entirely 2 2,104,916 dependent on the grid-anode capacity. The con ductive member 29 is common to the grid and anode circuits. This common conductive con nection acts as a feedback coupling. With this common coupling, the grid circuit may be tuned to a. quarter wave length by a suitably propon tioned line 55. The anode circuit is made res onant to the fundamental frequency although connected to a circuit equivalent to a half wave length, and will feed back energy in the proper phase to sustain oscillations. The grid and anode circuits are therefore in the proper phasal rela tion to insure maximum coupling. Since the system will not generate oscillations when the 16 tuned anode load circuit offers a capacitive re actance, I prefer to adjust the anode load cir cuit slightly on the inductive side of resonance. I prefer to avoid the use of mica insulation in capacitors carrying the oscillatory energy as mica has a deleterious effect on frequency sta bility and power factor. In the oscillatory cir metallic bellows ‘H which permits the copper tube 75 to expand with respect to the invar rod T3. The variations in configuration of the bel lows, and corona discharge from the end of the inner electrode are neutralized by a corona shield 79, which surrounds the bellows. Since the outer electrode 5? and its invar rods ‘H and the inner electrode 75 and its invar rod '13 both expand the relative spacing between the end plate of the con centric quarter wave line 15 and the corona shield will remain substantially constant thereby mini mizing capacity changes. The upper section 65 of the concentric line 5‘! has within it a variable capacitor 8i which may be arranged as follows: An invar rod 83 is se i5 curely fastened to the dividing conductor H. A copper armature plate 85 is fastened to the free end of the invar rod. A copper tube 8'! surrounds the invar rod 83. The copper tube is fastened to the dividing conductor and is connected to the "o armature by a metallic bellows 89. A similar cuits of Fig. I extremely high efficiency is ob invar rod 9!, copper tube 93, bellows 95, and ar tained by the use of substantial copper conduc tors and the avoidance of dielectric losses. The mature 9‘.’ are arranged on the metal head mem grid lead is connected to the optimum feedback position in the grid circuit. I have further in creased the efficiency of the oscillator by an effec tive arrangement of short leads. The preferred embodiment of my invention will be described the head so as to provide adjustable means for ‘ more in detail in connection with Fig. II. as the inner invar rods expand. The expansion of the outer invar rods increases the spacing of In Fig. II, a metallic end plate 5! is suitably insulated from a grounded metallic base 53. The end plate and the base form the armatures of a bypass capacitor 55. An outer electrode 51 of a concentric line is fastened to the end plate by bolting, brazing, or the like. The opposite end of the outer electrode is closed by a metal head member 59. This head member may be secured to the outer electrode 5‘! by bolting or any means insuring a good mechanical and low resistance electrical connection. Intermediate the ends of the outer electrode is fastened a conductor 6| which divides the outer electrode into two sec tions 68, Each of these sections preferably includes an expansion joint El, 69. These ex pansion joints may be formed by spinning one or more concentric corrugations in each section of the outer electrode. All of the parts thus far described are preferably made of copper, al though other metals may be used. By way of example, for a transmitter operat ing at a frequency of the order of 40 to 50 mega cycles, the outer electrode consists of a copper cylinder having a length of 75 inches, an inside diameter of 12 inches, and a thickness of 14 inch. A copper cylinder of this size will expand and contract with temperature changes. Such changes will alter the electric length of the cir cuits and cause serious variations in frequency. lib The effects of temperature changes may be min imized by connecting the head and lower end plates by several rods ‘ii of invar steel. Invar steel has a very low coefficient of expansion. The invar rods will limit the expansion of the copper to the expansion joints and thereby sub stantially maintain the electric length. At high frequencies it is desirable to compensate for vari ations in the length of the invar rods as will be described below. In the lower section 63 of the concentric line, an invar steel rod '33 is fastened to the center of the dividing conductor 6|. The invar rod is sur rounded by a copper conductor tube 15 which is also fastened to the dividing conductor 6|. The free terminal of tie copper tube terminates in a ber 59 but the rod and tube are threaded into raising and lowering the upper armature with respect to the lower armature for tuning the cir cuit. In this section 65, as in the lower section 53, the outer electrode and its invar rods expand the armature plates, but expansion of the inner rods decreases the spacing. Thus the armature spacing and resulting capacitance tends to re main substantially constant. The upper section 65 of the concentric line forms, in effect, a toroidal inductor, the arma ture plates 85-81 forms a capacitor 8| , the com bination is a timed anode load circuit. It is adjusted to be substantially equivalent elec- * trically to a half wave length, or slightly less than twice the wave length of the grid circuit, as I prefer to keep slightly on the inductive side of resonance. The tuned anode load circuit may be coupled to an external circuit, such as a push pull ampli?er. The coupling is preferably ar ranged through two small capacitors 99--l0l. Each armature of the tunable anode circuit may also form an armature of the coupling capaci tors. The other armatures l03—l05 of each of these coupling capacitors 89—I0l. are circular copper plates supported by suitable insulators £81, 109 fastened to the dividing conductor El and the head plate 59. The edges of the several armature plates are rounded to avoid the effects of corona discharge. The circuit connections have been briefly de scribed in connection with Fig. I. I shall here point out certain features. The thermionic tube H! is supported by brackets not shown. These 60 brackets may be fastened to the outer electrode of the concentric line. The tube may be ofv the water cooled type. The water jacket is supplied by cooling water fed through an insulated hose H5. The anode electrode III, which is also the water jacket, is connected to the anode supply through a radio frequency choke I IS. A by-pass condenser IN is connected between the choke and the outer electrode. The exposed anode I I1 is coupled to the tuned anode load circuit by a coupling capacitor [23. This coupling capacitor is comprised of the anode itself and a copper band I25 which surrounds the anode H7, but is insulated therefrom. The copper band I25 is connected directly to the circumference of the 2,104,916 lower armature plate by a conductor IZ'I. This connection is made through a suitable ori?ce I29 in the outer electrode. The grid electrode of the thermionic tube is connected by a conductor I3I directly to an ap propriate point on the inner electrode of the con centric quarter wave line. The ?lament or cathode of. the tube is energized by a special means I33 which will be described in connection 10 with Fig. III. The grid leak resistor I35 is con nected from the lower end plate 5I to the grounded base 53. The grid leak path may in clude an ammeter I31 for adjusting purposes. The grid resistor I35 is by-passed by the capaci tor 55 formed by the end plate and‘ the grounded base. In certain cases I have found that the electric length of the grid-cathode path may be such as . to include reactances which prevent the genera tion of high frequency oscillations. This effect may be eliminated by virtually grounding the cathode. The method and means for virtually grounding an electrode is disclosed in copending application Serial No. 41,540, ?led by John Evans on September 21, 1935 entitled Ultra high fre quency oscillator and assigned to the same as signee as the present application. In Fig. III, a transformer primary 20I is connected to a source of alternating current 203. The secondary 205 of the transformer is connected to an adjustable inductor 201 which is hollow. Within the in ductor is an insulated wire 209. The heating currents for the ?lament 2“ are carried by the hollow inductor 201 and inner connecting wire 239 which are connected to the ?lament 2“. The ?lament is by-passed by a capacitor 2l3. The outer inductor is connected to ground by a capacitor 2I5. The inductor is adjusted so that its effective length or inductance will resonate with the grid cathode capacitance and form a circuit of very low impedance at the lower or parasitic frequencies. At frequencies other than the resonant frequency the shunt impedance of the grid cathode circuit will be relatively low. This arrangement virtually grounds the cathode. Similar results may be obtained by tuning the inductor with a capacitor. The thermionic tube proper is shown in Fig. IV. This tube may be an RCA Type 846, or the like. Tubes of this type are water cooled. The connections 2I1 to the water source are through electrically insulated hose connections II5 to avoid grounding the exposed anode. The grid ' tion of different materials, copper or silver plat ing and the like, .and physical arrangements, within the scope of my invention will occur to those skilled in the art. I do not limit my in vention to the precise devices shown and de scribed, but intend to only limit same as required by the prior art and appended claims. I claim as my invention:— 1. An oscillation generator comprising an ain pli?er having input and output terminals, 2. con centric line whose effective length is substan tially equal to one-quarter of the fundamental wave connected to said input terminals, a tunable circuit connected to said output terminals includ ing a concentric line whose electrical length is substantially half the length of the fundamental wave, means for compensating for the effects of temperature changes in said quarter wave line. and means for compensating for the effects of temperature changes in said tunable circuit, whereby there is obtained in said tunable circuit oscillations of a constant frequency correspond ing to the frequency of the fundamental wave. 2. A generator of high frequency oscillations comprising a thermionic tube having input and “ output terminals, a concentric line whose effec tive length is substantially one~quarter of the fundamental wave connected to said input ter minals, a tuned circuit whose electrical length is substantially hall the length of the funda 30 mental wave connected to said output terminals and including a hollow inductor and a capacitor located within said inductor, means for compen sating temperature changes in said quarter wave line, and means for compensating temperature changes in said tuned circuit, whereby there is obtained in said tunable circuit oscillations of a constant frequency corresponding to the fre~ quency of the fundamental wave. 3. An oscillation generator comprising a therm ionic tube having an input and an output cir cuit; a concentric line having two sections, one of said sections including a line whose length is substantially one-quarter of the fundamental wave connected to said input circuit, the other of said sections including a circuit whose elec trical length. is substantially one-half of the length of the fundamental wave and connected to said output circuit; and means for compen sating for the e?ects of temperature changes in i the two sections of said line, whereby there is obtained in said tunable circuit oscillations of a constant frequency corresponding to the fre quency of the fundamental. wave. 4. An oscillation generator comprising a therm- ' terminal 2!!! is shown as projecting toward the right. The ?lament connections 22I extend be low the tube. The lower section 223 of. the tube is class. The glass is welded to the copper anode which also acts as the water jacket. The anode ionic tube having grid, cathode, and anode elec coupling capacitor I23 is formed by the anode length is substantially one-quarter of the funda II‘.’ and the spaced copper band I25. The band supported by a suitable insulator which is not shown. I have described a high frequency generator. The tuned circuits of this generator are arranged mental wave connected to said grid. and cathode electrodes, the other of said sections including a tunable circuit whose electrical length is sub~ ‘ within concentric lines. Temperature compen sation means are included whereby the electrical length remains substantially constant. The fre— quency of oscillation is very constant. In actual experiments. I have found a constancy of fre quency exceeding a piezo-electric element and the required frequency multipliers. In the em bodiment shown the leads are very short. Several kilowatts of power may be handled in a single generator embodying my invention. Various modi?cations, such as, the substitu ‘ trodes: a hollow member having two sections, one of said sections including a concentric line whose stantially half the fundamental wave and cou pled to said cathode and anode electrodes; and means for compensating for changes in the elec trical length of said sections, whereby there is obtained in said tunable circuit oscillations of a constant frequency corresponding to the fre quency of the fundamental wave. 5. In a device of the character of claim 4, means To for making the grid-cathode circuit a path of low impedance for parasitic frequencies. 6. In a device of the character described a pair of circuits included within a concentric line, one of said circuits comprising a quarter wave line ,.... Ir) 4 2,104,916 having means for compensating for the e?ects caused by variations in temperature, and the other of said circuits comprising a tunable cir cuit whose electrical length corresponds to sub stantially one-half the fundamental wavelength and having means for compensating for the ef fects caused by variations in temperature, where by there is obtained in said tunable circuit oscil lations of a constant frequency corresponding to the frequency of the fundamental wave. '7. In a device of the character described, a pair of circuits included within a. concentric line. one of said circuits comprising a line whose effec tive length is substantially one-ouarter of the fundamental wave having means for compensat ing for the e?ects caused by variations in tem perature. the other of said circuits having an electrical length corresponding to substantially half the fundamental wave length. and having means for compensating for the effects caused by variations in temperature, a thermionic tube, and means coupling said thermionic tube to said circuits so that oscillations of high and constant frequency corresponding to the frequency of the k. Cl fundamental wave are generated. 8. A high frequency generator comprising a Water cooled thermionic tube havin‘T a grid, cath ode, and exposed anode. a concentric quarter wave line connected to said grid and. cathode. a tunable circuit whose electrical length is sub— stantially half the fundamental wave length cou~ pled to said anode by a capacitance formed by said anode and an armature insulated therefrom, and means for transferring high frequency en~ ergy from said tunable circuit to an external cir cult. 9. In a device of the character of claim 8, means for compensating for the effects of tem perature changes which tend to vary the elec 40 trical lengths of said circuits. 15. A concentric line resonator comprising an outer hollow conductor and an inner hollow c0n~ ductor, means for mechanically connecting to gether said conductors at one of their adjacent ends, a rod having a low temperature coe?icient of expansion within and extending substantially the entire length of said inner conductor and mechanically connected to said means at said one end of said conductors, a metallic shield sur rounding a portion of and extending beyond the 10 other end of said inner conductor and connected to said rod, and an expansible metal bellows located within said shield and connected at one end to said shield and at its other end to said inner conductor. 16. A tuned resonator comprising a pair of inner and outer conductors coupled together more closely at one of th lr adjacent ends than at their other ends, an expansible metallic bel lows attached to and extending beyond said other ‘ end of said inner conductor, and a metallic shield surrounding said bellows and a portion of said inner conductor, said shield being also connected to said bellows. 17. A concentric line resonator having an inner and an outer conductor, said outer conductor having an expansion joint intermediate its ends, and a plurality of rods of low temperatin‘e coe?i cient of expansion extending parallel to the length of said outer conductor securely fastened to both ends of said outer conductor for maintain ing the length of said outer conductor substan tially constant. 18. A concentric line resonator having an inner and an outer conductor, said outer conductor ' having an expansion joint in the length thereof, electrodes, a hollow tube closed at both ends and formed into two sections by a transverse and two rods of low temperature coe?icient of expansion extending parallel to the length of said outer conductor, located on substantially op posite sides of said outer conductor and securely fastened to both ends of said outer conductor for maintaining the length of said outer conduc tor substantially constant. 19. An ultra high frequency oscillatory circuit conductor intermediate sai _ ends, an expansion comprising a substantially enc joint in each of said sections, rods having a low coefficient of expansion linking Sold ends to limit the expansion of said tube, a rod having the same coef?cient of expansion as the aforemen tioned rods secured within one of said sections and forming therein a quarter wave length line, face of revolution, capacitor comprising two separated plates wihin said enclosed surface of revolution, a metallic supporting rod devoid of 10. A high frequency transmitter comprising a thermionic tube having grid, cathode an ' anode a pair of rods of the same coefficient of expan sion as the aforementioned rods for supporting armatures within the other of said sections and forming with said armatures a circuit electri cally equivalent to a half wave length line, means coupling said quarter Wave length line to said grid and cathode, and means coupling said elec trically equivalent half wave length line to said anode and cathode. 11. A device or" the character of claim 10 fur ther characterized by a conductive coupling e?ec tively located between said lines. 12. In a device of the ‘character of claim 10, 65 means located at the end of said quarter wave line for minimizing corona discharge from said quarter wave line. 13. In a device of the character of claim 10, copper rods surrounding the tubes positioned within said line and connected expansion bel~ lows to free ends of said rods. 14. In a device of the character of claim 10, means for virtually grounding said cathode elec trode. Lil) ed metallic sur concentrated reaotanoe directly connect i vf said plates to said surface, said rods forming , an inductance which, taken toeether with said capacitor, comprise the oscillatory circuit, the adjacent ends of said rods being separated sub stantially by the distance between said plates, and leads capacitively coupled to said plates and extending externally of said surface of revolu tion. 20. An ultra high frequency oscillatory circuit comprising a substantially e losed metallic sur~ face of revolution, a capacitor omprlsing two (50 separated plates within sai'i enclosed surface of revolution, a hollow metallic supporting rod de~ void of concentrated reactance connecting each of said plates to said surface, expansible metal bellows between each plate and its supporting iii rod, and a rod of low temperature coeflicient of expansion located within each sup_ ting~ rod and mechanically said surface of linked revolution, to its associated ....d supporting rods forming an inductance which, taken to gether with said capacitor, comprise the oscilla tory circuit. JOHN EVANS.