US2408410A - Frequency converter - Google Patents

Description

Oct. 1, 1946. J. w. CLARK FREQUENCY CONVERTER Filed Julie 19, 1941 2 Sheets-Sheet 1 NV N J W CLARK d- 1, 1946- J. w, CLARK 2,408,410

' I FREQUENCY CONVERTER v Filed June 19, 1941 2 Sheets-Sheet- 2 Patented Oct. 1, 1946 FREQUENCY oo vvitarr'za JohnW. Clark,'Chatham, N: J., assiaom Beu- .Telephone Laboratories, Incorporated, New ,York, vY a corporation Qf INCWJYOIK This invention relatesto modulating system for ultra-high frequency electromagnetic waves and currents and is particularly applicable towaves a few centimeters or less inwave-length. The invention relates more especially to afrequency converter, mixer, or first detector in a superhetero dyne'radio receiving system.

An object of the invention is construction and operation of 'a superheterodyne radio receiver adapted for usein the ultra-lush frequency a l I A feature of the-inventionis .a compact means for introducing a received sign'al wave into the interior of a hollow resonator in an ultra-high frequency electron velocity variation type of oscillator to effect frequency conversion with no substantial disturban-ce tov the normal operation of the oscillator and with high efliciency of conversion.

Another feature. of the invention resides in impressing the received signal-modulated wave between the drift tube and the adjacent elec-: trodes in a'single cavity type of oscillator, ef-

fectively across. the. input .andoutput gaps, in

parallel. I

1 lnaccordance with the invention, the beating oscillator is of a type-employing electron velocity variations, operated substantially in the normal manner, and provision is made for impressing the incoming signal modulated wave substantially simultaneously across the input and output gaps efiectively in parallel. A velocity variation in accordance'with the'incorning wave is superposed uponthe velocity variation due to The velocity varied electhe local oscillations. tron streamisthen subjected to a conversion process to develop density variations. Anynon linearity in the conversion process will result in thejappearance of modulation components, for

example, sum and difference frequencies, in the density variations. To 'secure'airelatively low intermediate frequency, the difference frequency component maybe utilized. vThe modulation componentsmay be developed; at the collector electrode in various ways, as, forexample, by

operating the collector at a-retarding' potential adjustedto turn backthe slower moving electrons; Alternately, the collector electrode may be operated at an electron'accelerating 'potential'or a substantially field-freedrift space may be proto simplify the partiallycut away;

Application June 19, 1941, Serial No; 398,757

1 Claims. (01.31545) 7 modified inaccordance' with the' invention, shown Figs.- 1A} and 1B show-alternativedetails which may be substituted in the'arrangement of Fig. 1 'Fig.'2' is an end viewof the structure of Fig. 1, shown partially cut away; I

' of a superhetero- Fig. 3 is a schematic-diagram dyne-radio receiver embodying the invention; "and vided .inwhich bunching' ofithe :electrons may 7 take place in any suitable manner. :Inthe drawings: l 1

Fig. 1 is aperspective .viewiof" an oscillator- Fig. 3A shows analternative coupling arrangement which maybe substituted for a portion of the circuit showninFigJi. I

Referring to the drawings, there is shown in Figs. 1 and 2 a resonant cavity oscillator of the electron velocity variation type such as is disclosed in application Serial No. 386,794 filed April 4,1941, by A. E. Anderson andA. L. Samuel and assigned to the assignee ofthe present application. My oscillator structure herein disclosed includes certain modifications to accommodate the introduction of waves intercepted by a doublet antenna l, or other-ineans'of intercepting ultrahigh frequency po'wen The respective branches of the antenna'or other interceptorare connected with the outer conductor 2 and inner con ductor 3 of a suitable coaxial transmission line, The line 2, '3 preferably has two branches, one'of which; compris'ingan outer conductor 4 and an innerconductor 5, is an adjustable tuning stub.

The other branch, comprising "an outer conductor 6 and 'an inner conductor "lfis fitted through an in the semicylindrical casing section 2| aperture of the Anderson-Samuel oscillator. Throughout the drawings-the elements which are the same as corresponding elements in the Anderson-Samuel oscillator have been given'the same reference numeralas in the drawings of the Anderson-Samuela'pplicationfl The cylindrical insulating envelope lll'oftheoscillator, for example, a glass tube, encloses 'an electron gun shown generally at llg'togethe'r with an electron collecting electrode or collector 'IZ. Betweenthe electrongun II and the collector lz'there are sealed into and through the walls ofthe envelope In a pair of disc members'fj3 and M formed respectively into protruding, approximately conical" electrodes l5 and I6, coaxial with'the electron gunand provided with alignedapertures at their respective apices for'the passage-therethrough of an electron stream 'or beam from the electron gun. A

tube l1, referred to herein'as the drift tube, is axially mounted between the electrodes l5 and I6 and has aligned apertures at its ends for themtrance and exit of the electron beam. The'electrodes l5 and I6, in cooperation with the respec-- tive adjacent ends of the disc 'tube l'l, form a pair it of gaps l8 and I9 spectively as the input gap and the output gap. The discs l3 and I4 and the drift tube I! are preferably of highly conductive material, for example, copper. The discs l3 and M are hermetically sealed into and through the walls of the tube by any suitable process or form of seal, for example, a copper-glass seal. The drift tube H has attached to it a conductive rod 20, by which it is supported in position and by means of which electrical contact may be made from the exterior of the envelope Ill. The conductor 20 is sealed into and through the Wall of the envelope l0 through a glass bead or other. suitable hermetic seal. Alternatively, three supporting rods H, 12 and 13 may be employed as shown i'n' Fig.

1A, or the drift tube may be supported by-a disc 1 electrode 14 as shown in Fig. 1B. The inner conductor is conductively connected to the drift tube I! in any suitable manner as, for example, by means of the rod 20,0rby one of the rods 1|, 12 and 73 shown in Fig. 1A, or by=connectionto the-disc electrode 14 of Fig. 1B. The outer conductor 6 is conductively connected to-the casing 2| as by means of a snug frictional engagement or in other suitable manner. 4 The tuning stub comprising the outer conductor 4'and inner conductor 5 may beadjusted by-means of an annular piston 8 of conductive material connected by rods or other suitable means with a knob 9. 7

Inthe oscillator, the ,discs |3- and |4 form a portion ofthe walls of the resonant chamber or cavity resonator together with thecasing" sections ZI and 22, which sections'fit closely together and are provided with milled semiannular surfaces 23'and 24,respectively, which fits snugly inside the edges of the disc members |-3 and M. A pairof cylindrical collars 25 and '26 of magnetic material, provided with flanges Z'Iand 28, respectively, are placed over the tube 10- and against the outer surfaces of the respective disc members |3and M. 0m one-side of the casin'ga ring 6| and-screws are provided so that when the screws are tightenedithe disc -3-and flange 21 are clamped securely between thering BI and surfaces 23 and 24 on the casing. A

similar ring, 62 and screws 29 areprovided on theotherside of the casing.

v, A plurality of plungers, in the formof-screws 3 4, 35, 36 and 31, are threaded into the walls of thecasin'g sections 2| and 22 for altering the size and shape of the resonant cavityfor tuning purposes.

A permanent magnet 45 has pole-pieces' extending perpendicular to the main body the pole-pieces being milled out with cylindrical-depressions at 46 and '41 to form a cradle to support the cylindrical collars and 26, respectively. The tube assemblyincl-uding the collars is held to the permanent magnet by the magneticforce and, in addition, the lower half section 22 of the casing-may be securedto the middle portion of-the permanent magnet by means of a screw;48. If desired, the magnet may be attached to a base plate or other mounting in any suitable manner. .A U-shaped magnet or one of other, suitable shape may be used in placeof-the one illustrated, or an electromagn'et may be substituted for the permanent'magnet.

The electron gun may be of thetype dis closed in Figs. 3 and 4 of the Anderson-Samuel application, comprising adished cathode 49erranged to be heated'by a heating element, 50-,as shown schematically in Fig. 3 herein. A shape which will be referred to re-- mg electrode 5| for forming the electrons emitted from the cathode 49 into a conical beam in cooperation with the shape of the cathode may be provided in the vicinity of the cathode as shown schematically in the figure. The electrode 5| is preferably electrically connected with the cathode. An accelerating electrode 52 serves to regulate the beam current and in conjunction with the shaping electrode 5| to focus the beam at approximately the center of the input gap l8. One side of the heating element 50 may be connected to the cathode Within the tube ID and brought out of the tube by means of the common lead 53. In that case, the lead 53, together Withithe remaining'heater lead 54 and a lead 55 from the accelerating electrode 52 constitute the external connections from the electron gun. The'remaining electrical connections to the oscillator comprise a lead 56 connected with the walls of the resonant chamber, which lead 55 may conveniently be grounded or connected with the mounting .plate, and a leadfilconnected to the collector l2. The leads 53, 54, 55' and .51 are brought out through the walls of the tube Ill-in suitable presses or scale.

The interconnections of the tube with suitable sources of biasing potential andheating-current are shown schematically inFig. 3. 58 is apower transformer or other source of suitable current for operating the heating element 50. The lead 53 is connected to the negative terminal of a biasing battery or other source of biasing potential '59. The lead 55 from the accelerating electrode 52 is connecte di't'o the variable contactor of a potentiometer 50,, one ofthe two potentiom'eters '60 and 'Iil connected in shunt across the battery 59. The lead '55 from the resonator is connected to the variable contaotor of the potentiometer l0 and maybe grounded. Ifdesired, the potentiometers 60 and 10 may be replaced by asing'le potentiometer "with two contacts, either or both'c'f which contacts may in some cases befixed.

The head" 51 from-the collector 12" is connected to the common terminal of'a resistor and a condenser 8|, the remaining terminal of'the condenser being connected 'to "one of the input terminals of an intermediatefrequency amplifier 82'. The remaining input terminal of the ampli fier 8-2 is preferably grounded. The remaining terminal of the resistor is connected-"to a point in the power "supply circuit, forexainp le;

eitlier'to the negative or to-th-e pos-itive terminal of the battery 59. A switch 851s shown inFig. 3 whereby either of 'the latter-two "connections may be selected as desired. The I output tennin'als of the intermediate freqlie'ncy amplifier 82 are connected to the'input terminals of a detector "84:, whi'chis :connecte'dwto a suitable-translating device such as a 'telephone receiver =85.

alternative coupling --arrangement for use between the collector I2 :and the intermediate frequency. amplifier :821 is shown 1 Fig. 3 3A and may be substituted for "thezportioniof the circuit in Fig. 3: shown between: the broken .li'n'e's .X' and Y. In Fi'g.i3A,:86 is a transforr'ner suitablefor' 'pedance ratio 'tomatch the impedance or the V collector-circuit,.which maybeof'the order of fillflfliohms'rx.11; I Q f 3'.-In the operation of the system as shown in the figures; Ethe oscillator functions to sustain electrdmagnetic waves of ultra-high frequency. with-. in the resonant cavity .in substantially. the same v intensity inthecavity, and, therefore,:do not ma-y terially alter the configuration of the field.*The main differenceis asmall changein theeffective shape'and-volume of the cavity and a resultant difference-g innthe resonating;frequency, ,1 which maybe allowed for inithe tdesignxof .the. resonator. The :function of .the =.oscillator;in the present arrangementi's-to establish a'strong electric field of the. :resonant frequency across both, the input gapE'. l.8t-and.,the outputgapilll. The antenna l is.-idesigr'ied for the reception ofa desired high frequency and; theresonant frequency of the oscillator is preferably chosen to differ from the frequency to be'received upon the antenna by an amount, fjust equal to -a desired intermediate frequency.:.-,'Ih'e piston 8 is adjusted to resonate therline;tothe incoming frequency in known mannento impress,a;maxi1num alternating voltage upon .thedrift: tube IL The voltage, thus ape plied is effectively in parallel between the drift tubeand the electrodes: I3 and I4, respectively.

Referring more specifically to the operation .01

the syste'm .as' afmodulator, frequency converter or first detector, it will be evident that the incoming signal waves and the locally generated waves are superimposed upon the input gap [8 and the output gap IS in such manner as to simultaneously impressvelocity variations upon the electrons passing through the gaps. known that velocity variations in an electron stream may be converted by various means into successions of density variations of the same effectediby a sorting out of the electrons on the basis of theirxvelocity, the f aster electrons enter-' ing the; collector. .The process is analogous to rectification and in aisimilar manner, as in the useof a'rectifier' as a modulator or converter; sumland difference frequencies are produced in the resultant current. The difference frequency with re'spectto the incomingwaves. andthe local oscillations'is usually chosen as the intermediate frequency in order to take advantage of a relatively 1 low frequency in the intermediate frequency. amplifier. The modulation products in the collector circuitcarry theoriginal signal modulationi-asfrec'eivedat the'antenna and the intermediate freq'uency compone'ntlmay be selected, and, amplified-,4 and-ksubjecteduto .a second detection toreproducesthe original signals as in any superheterodyne radio receiving system. The intermediate frequency amplifier82, detector 84 anditranslating'device 85 are not shown in detail, asthey-maybe of any suitable type... f When theswitch 83 is placed in the upper position,;the.collector isconnected to a positive portionxof source 59, or other suitable potential to provide an.-.electron accelerating effect .in the spacebetween'the output gap [9 and the collector 1 2.. ..Allthe. electrons, in this case, are drawn to the collector :but due to their unequal velocities they. become, somewhat grouped into. bunches while .traversingithe distance between the output gap1l9 and thecollectorJZ. Itis. known that this process of .bunching is generally a non-linear one... Consequently, modulation components appear. in the density variationsof the; electron stream: asfiit .-'strikes .the .collectorelectrode; l2, and, an; intermediatev frequency component, is im-v pressed upon the coupling circuit with results similar to those describedin the preceding case.

. What-is claimed is:

stream at some point later traversed by the stream. It is also known that the process of conversion from velocity variations to density variations may be a non-linear one, so that modulation products such as sum and difference frequencies appear in the density variations so produced. In the present system, the conversion may be accomplished in at least two ways, either one of which may be selected by means of the switch 83. In accordance with one method, the switch 83 is placed in the lower position, as shown, so as to connect the collector I2 to the negative terminal of the battery 59, thereby placing the collector at substantially the same direct current potential as the cathode 49. The electrons, after passing the output gap I9, are in this case subjected to a strong retarding field. Having different velocities, the individual electrons possess different amounts of kinetic energy and are able to penetrate respectively different distances against the retarding field before being stopped and their motion reversed by the field. By proper adjustment of the initial velocity of the electron stream, it is possible to arrange matters so that the faster electrons strike the collector l2 while the slower electrons are turned back. The density variations above referred to are in this case 1. In a frequency converter, an oscillator comprising a resonating chamber for ultra-high frequency waves, a drift tube enclosed within said chamber, and said chamber walls and. said drift tube having aligned apertures, means for directing a stream of electrons through said apertures whereby said electron stream is velocity varied by electromagnetic waves within said chamber, and means for adjusting the transit time of the electrons traversing said drift tube to initiate and sustain said oscillations; means for impressing between said drift tube and said chamber walls a Wave having a frequency comparable to but different from the frequency of said oscillations whereby a second velocity variation is superposed upon said electron stream, and means non-linearly responsive to velocity variations of said electron stream, operative upon a doubly velocity-varied portion of the stream.

2. A system in accordance with claim 1 in which the non-linearly responsive means comprises means for sorting electrons on a basis of different electron velocities.

3. A system in accordance with claim 1 in which the non-linearly responsive means comprises mean for converting velocity variations of the electron stream into electron density variations in the stream.

4. A system in accordance with claim 1 in which the non-linearly responsive means comprises means for grouping electrons into bunches in accordance with their differing velocities.

5. In a frequency converter, an oscillator comprising a resonating chamber for ultra-high frequency waves, a drift tube enclosed within said chamber, and said chamber walls and said drift tube. having aligned. apertures, means for direct-, inga .streamof electrons through'said "apertures whereby said electron stream is velocity varied by.electromagnetic oscillations Within said chamber, and means for adjusting the transittimeof the electrons traversing said drift tube to initiate and sustain said oscillationsya coaxial line for ultra-high frequency waves, said line extending radially through the Wall of said chamber, the outer conductor of said line being conductively connected to the walls of said'chamber and the inner-conductor of said line being conductively connected "to said drift tube, means for impressing upon said coaxial line waves having a vfrequency comparable to butdifferent .from the frequency of said oscillations'and non-linearly operative means responsive'to velocity. variations of said electron stream.

6. In a frequencyconverter, :aresonating chamber for ultra-highfrequency waves, the wall of said chamber being apertured to admit .an electronstream into the interior'thereof, means to inject an electron stream through saidaperture, a drift tube supportedwithin said resonating chamber, said drift tubecbeing arranged to surround said electron stream and to define together with the chamber Wall a pair of gapstraversed by saidielectron stream, means cooperating .with said drift tube, said chamber wall, and'said electron stream for producing sustained electromagnetic oscillations within said resonating chamber at. a resonant frequency thereof, r a transmission line having concentric inner and outer .conduc tors extending in a direction perpendicularto the linesof force of the electric field within said .res-. onating chamber, said-transmission line-passing through the wall of said resonating chamber-and extending through a substantial portion of the interior space of said resonating chamber, means electrically connecting the outer conductor. of said line to thewall of :saidv resonating chamber, means electrically connecting the innersconduc'tor of 1 said line .to said= drift tube "and an external wave sourcewconnected to said'transmission line.

'7. In a frequency converter, .a resonating chamber forultra high frequencywaves,.the';wal1 of said chamber being apertured to admit anelectron stream into the-'rinteriorythereof, means'to injectan electron streamuthrough saidaperture, a drift tube supported within:said1 resonating chamber, said drift tube being arranged 1 to sunround said electron stream and to define together with the chamber wall a. pair of gaps traversed by. said e1ectron-stream,x means cooperating with said drift tube; said chamber walLandzsaid electron stream to produc .sustainedelectromagnetic oscillations within saidresonating chamber at aresonant 'frequencythereof, aitransmissionzlin'e having 'concentricinner-andi outer. conductorsv ex. tending in av direction substantially perpendicular to the lines of'forceof' the electric fieldwithin said resonating chamber, said transmission line passing through "the wallof said resonating chamber and extending through a substantial portion of the interior space of said resonating chamber, means electrically.connecting the outer conductor of saidlinetozthe wall of .said'resonating chamber, means electrically connecting the innerwconductor of said lineto said drift tube, an externalwave source connected-to saiditransmission line and means for tuning said transmission line to the frequency :of. saidexternal wave source to impress substantial .poten'tialsatthe frequency of said.externaliwave'source across. at leastone of said gaps insuperposition.withpotentials developed by said sustained electromagneti oscillations.

:JOHN W. CLARK.

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