# Патент USA US2110664

код для вставкиMarch 8i, 1938..v D_ E_ HARNETT _ 2,110,664 MODULATION CIRCUIT _ Filed Aug. 12, 1935 ‘3 Sheets-Sheet 1 @l ~ . l ¿el y „ ¿l E ¿e fé ’6" 2 _l ' f5v ~ î 5005er y ¿à ' . ' ". ' /7 y Q @di f2@ ATTQRNEYS 2/ March 8, 1938. _ D. E. HARNETT 2,110,664 MoDULATIoN CIRCUIT Filed Aug. 12.l 1933 5 sheets-'sheet 2 à: , L ill'l || . ATTORNEYS A2,110,664 Patented Mar. 8, 193_8_ uurrsoI STATES "PATENT , ori-‘lcs 2.11am f MonULs'rroN omom'r Daniel s. nar-'neta Tucuman. N. y.. misant» to s Hazeltine‘ Corporation. a corporation of Dela WIN Application August iz. 193s. sensi 1ra-escasa, ze claim». ici. 25o-_sol The present invention relatesto a selective circuit, and more particularly to an adiustably selective system designed to respond simultane ously to two or more widely separated fre ß queneies. The system includes appropriately selective. in ` ductively reactive and capacitively reactive ele ments. so arranged and connected in- the system that adjustment oi’ a sinsle variable element 10 produces two points ci maximum impedance widely separated and bearing a fixed law of vari ation with respect to each other as the variable element is adjusted over a substantial range. In its fundamental aspect, the circuit vmay be oon sidered as a tuned circuit having two oscillatory periods widely separated and moving simultane» the two circuits will have. relatively no ei'lect upon the voltages developed in the other oi'ithe two circuits. In other words, a high-frequency diil'erence is selected so that the tuning induct- '_ ance of the signal-frequency circuit will act as. acholre at the oscillation frequency. Similarly, " with a high diilerence, the auxiliary alignment condenser and the oscillation-frequency induct ancc will constitute a high impedance in this path at the signal frequency. 10 Having thus briefly described the invention. ` attention is invited to the accompanying draw ings in which: , ' " -llîi‘ig. l is.an elementary circuit diagram of thev fundamental circuit comprising the present in 16y vention: ' . ‘ ~ » Fig. 2 is a circuitdiasram kof a superhetero ously as the adjustable element is varied. It is the object of this invention to produce dyne radio receiver,v including -a frequency a circuit which may be tuned to two different changing circuit,l constructed in accordance with 20' this invention; . ' ' frequencies, by means of a singlevvariable ele Fis. 3 is a diagram of a circuit similar to that ment. It is a further object of this -invention to'pro-` of Fig. 2. but'includins an additional radio-fre quency amplil‘ler before the irequency-deter duce a system in which a single variable ele . , _ mment may be utilized to tune said system to mining circuit; and, ’Fig á isa diagram ci’ a similar selective cir 25 simultaneously vary two resonance~ frequencies for supplying voltage corresponding to each of cuit. in which a Esingle tube is utilized tc act asY the oscillatory periods, to a plurality of vacuum both oscillator and modulator. ‘ »Referring now more 'particularly to Fig. .1 of tubes, thus providing a selective input system i’or each of said tubes, which Ísystem requires the drawings. an input circuit connected to a 'so a single adjustable clement. _ source of high frequency. includes a primary inr v It is another object of this invention to pro vide a modulation of frequency-changing cir cuit for the input of a superheterodyno. which requires a single variable condenser to simultane ously tune to lthe desired signal and oscillation frequency. ,» ` - . These. and further objects of this invention. will become 'apparent _from the following speci fication and claims taken in connection with the v40 accompanying drawings. v In accomplishing: the object of this invention. with particular yreference to a superheterodyne radio receiver for the purpose of illustration.'the signal frequency tuned input circuit oi.’ the first 45 `detector or modulator ci’ the superheterodyne ~ i receiver, is tuned by c. variable condenser in the ‘ usual manner to receive audio-modulated carrier waves. The oscillation-frequency-determining v " circuit. or oscillation circuit. as it will be referred n" to hereinafter. Vis so connected in shunt across thc signal-frequency tuned circuit. or signal cir cuit. as it will be referred to hereinafter, that the .same variable condenser may be utilized to tune - _ the oscillation circuit. A high intermediate tre'-- 55 qucncy is chosen so that the tuning of each oi ductance Li which is inductively coupled to a secondary inductance La, included in the tunable oscillatory circuit il. The circuit i6 may include an additional inductancc La' and variable ccn-. denser Cz, by means of which the resonance frequency ci’ the circuit il may be adiusted. In shunt with the variable condenser Ca is con nected the tunable circuit is. which `includes condenser C_a, inductance La and condenser C4, which, together with Ga, constitutes a second tunable oscillatory circuit. The input oi' tubs i! includes the tunable circuit it. and the input of the tube i1 includes the inductance La of the tunable circuit it. ' In'operation, the characteristics of the various elemental of tunable circuits it and il are .so chosen that a wide 'frequency difference will exist between the resonance periods of each .of these circuits. the frequency oi.' the tunable circuit ' Il being higher than that oi' the tunable circuit i4.` 50 At the high resonant-frequency of the circuit il, the total inductance o! circuit I4 will act ,as a high-frequency choke. and at the lower resonant frequency o! the circuit il, the'capacities C: and C. will actas a high impedance. Furthermore. 2 2,110,664 I the series capacity Caand C4 of circuit I8, act to limit the tuning rangeof the condenserl Cz with - respect to the tunable circuit I 8, by means of which the variation of the condenser Cz serves to simultaneously tune the two circuits I4 an'd I8 in the same sense to low and relatively high radio frequencies, respectively, and over substan tially equal frequency ranges. It is obvious that voltages of both frequencies will egrist across the .150' feed-back and oscillation circuits and, therefore, may provide additional coupling between> these i two circuits. « ~ _ That portion of the oscillation voltage which is impressed across the condenser C2 will be im pressed upon the input of the modulator or first condenser C2 and therefore voltages of both fre _detector tube I5 and thus be combined in the input of said tube with received radio-frequency 10 quencies may be supplied to the input of tube I 5. However, the/inputv of tube I1 is connected across the inductance La and therefore is substantially signal voltages which are also built up across the .condenser C2. The bias of the tube I5 is so ar ranged that it will act asa modulator,- and an . isolated from the circuit I4, and consequently, . s the tube I1 Iresponds merely to the frequency of " the tunable circuit I8. Furthermore, since circuit I4 is parallel-resonant with respect to condenser C2 and circuit I8 is parallel-resonant with respect to inductance La, an impedance maxima will ap pear across condenser C2 at`the resonant Yfre quency of circuit I4 and across inductance La' at .2.10 cuit of. the oscillator tube I 'I yand the oscillation circuit. The condenser C4 is common both to the the resonant frequency of circuit I8. - « . A particular application of this circuit to ’a . ._ superheterodyne radio receiver is illustrated in 2'5 Fig. 2, in which corresponding elements are desig nated by the same reference characters. In Fig. 2, the antenna circuit includes the antenna Il, ground I2, and input primary induc ' tance L1.. The inductance L1 is inductively cou 30 pled to the inductance La of the signal circuit I4, which circuit is tuned to resonance with the de v sired signal frequency by the variable condenser l C2. The' signal frequency voltage developed 1 across the condenser ‘C2 is impressed between the 35 control grid and cathode of the modulator tube I5, which may be of the pentode type as, for instance, the type 58. A gridebiasing resistor R5 audio-modulated intermediate frequency will be produced in the output circuit of the modulator 15 tube. f ‘ The output circuit ‘of the modulator tube I5 includes the radio-frequency choke L5 and the high-voltage source I6. The screen grid of the modulator tube I5-may be supplied with the ap 20 propriate voltage by means of a tap in the bat tery I6. The high-voltage source I6 is by-pessed for highV frequencies by means of condener C7. That portion of battery I6 which supplies the screen grid potential may be similarly provided 25 with a. by-pass condenser Ca. The intermediate-frequency voltage developed across the choke L5 is coupled through condenser Cn 'to the input of the intermediate-frequency re sponsive radio receiver 20 by which it is further 30 amplified, detected and reproduced in the usual manner by «the loudspeaker 2| _. The details of the remainder of the receiver and reproducer are common to those found in the art and, therefore, need no further description. 'I'he oscillation-frequency voltages impressed across the inductance L2 may be transferred ca is included in the cathode lead of the tube I5 for pacitively, or inductively to the antenna primary the purpose of providing the proper grid bias, . inductance L1. Therefore, to prevent radiation of the oscillation-frequency voltages, a neutrali 40 40 and a radio-frequency by-pass condenser C5“ is zation arrangement may be provided as shown. provided in shunt with the biasing resistor.y . The oscillatorv tube I1, which may be of the This system comprises the connection between triode type, as for instance type 56, has the oscil- ‘ the lower end of the feed-back coil L4 through lation circuit I8 connected between its grid and the neutralizing condenser C1 to the upper end of X Y, s , the antenna primary inductance L1. The neutral cathode. The oscillation circuit <I8 comprises in series . izing capacity C1 is ,so adjusted that the feed the inductance La, the alignment condenser Ca, back of the oscillation-frequency voltage to the the variable condenser C2, whichds common to upper end of the coil »L1 is just sufficient to 'neu- _ tralize that transferred thereto by the tuning in „ 50 The oscillation frequency is controlled by the ductance Ia. Appropriate cathode heating circuits may be variable condenser C2, the capacity range of which is limited relative to its effect upon the provided and these, together with' the voltage oscillation frequency by the alignment condenser `- source represented by the battery I6, may be the ‘Cs ~and to some extent by by-pass condenser C4. vsaine as those provided for supplying the various 55 A paddingycondenser Cp, for assistingthe align voltages required in the receiver 20. As above stated, the oscillation frequency ment, is connected between the junction of in the tuned input circuit I4, and condenser C4. 50 ductance Le with condenser C: and ground, and is, therefore, substantially in shunt with _the in ductance La. The resistor R4 is for th'e purpose 60 of providing the proper bias on the grid vof the oscillator tube I'I. lThe bias is produced by the grid current and limits the oscillation amplitude. The plate electrode of the tube I1 is connected chosen should be considerably higher than the frequency of the signals which it is desired to re ceive. For instance, an intermediate or differ ence frequency of 4800 kilocycles may be selected, 60 in` which event, in order to cover the broadcast band of from 550 kilocycles to 1500 kilocycles, the oscillation-frequency circuit I8 mustl tune through the coupling resistor Rz’to a. source'of through a band of from 5350 kilocycles to 6300 high potential indicated as the battery I6. A radio-frequency by-pass condenser Cv is` provided kilocycles. Therefore, the percentage variation across the battery I6. ' of> capacity required to tune the oscillation in ductance L3 through this range of frequencies be- ' The radio-frequency voltage ñuctuations, which ing rather small, the condenser C3 maybe of such lare developed across R2, are impressed upon the 70 oscillation circuit bythe feed-back circuit which low capacity- that it will present a very high im pedance to voltages‘of the signal frequency. In other words, there will be but slight loss of sig ' includes vthe connection through the condenser Cs to thelow'er end'of the inductance L4 and the blocking condenser C4. The inductances La and L4 are inductively coupled, thus providing an elec 75 tromßgnetic' coupling between the feed-back cir nal-frequency voltage _through thev condenserV C; and inductance La, which are in shunt with the inductance La. The impedance of the inductance ` Le, which is in shunt with the condenser C2 across 'is 3 2,110,064 which voltages ofthe oscillation frequency are developed, is so lhigh relative to oscillation-fre quency voltages that vit will have a _negligible effect> on these voltages.v , ì ' Thus, ~an arrangement has been produced in which the single condenser C2 may be utilized to tune4 two inductances to considerably different frequencies, and the voltages of the two frequen V cies which are» developed across the single variable 10 condenser may be impressed -upon the input of the modulator tube I5 and there combined to produce the modulated intermediate frequency in the usual manner. ‘ y ‘ . The condenserCs acts, as has been stated above, 15 to limit the range of the condenser C2 and thus acts as an alignment condenser by means of » which the diiïerence between the frequency of the signal currents and the frequency of the oscilla tion currents may be maintained substantially 20 uniform as the condenser Ca is varied to tune the input circuit throughout theA tuning range. The 25 input’ of the radio-frequency amplifier tube 8. The output of the amplifier tubeA 8 includes pri mary inductance Li, which corresponds _to the antenna inductance Li of Fig. 1.~ This primaryV ’inductance vis inductively’coupled to the second ary inductance Lz of the signal-frequency circuitl Il. With this arrangement, the necessity for the neutralizing condenser Ci of Fig. 2 is` obviated, as . ' the oscillator-frequency voltagesimpressed across the inductance’Lz will be effectively yblocked by the unilateral transmission characteristics of the screen grid tube 8. The tube 8' may for instance be a pentode, as shown, although any other suit able tube'may be used. It-is obvious, of course, that the input of the tube 8 might be untuned, in 15 'which event the tube would constitute a coupling` tube. The condenser of the tuned circuit 1 may be connected as shown, to be operated in a uni control manner with the condenser Cz of the radio-frequency tuned- circuit I4.'> ~ - 20 The output of the modulator is impressed upon the input4 of the intermediate frequency amplifier padding condenser Cp permits aÍ three point ad vof the receiverv20 by means of the tunedl inter- ~ ‘ justment of alignment to be obtained. The pad ding condenser, Cp, isadjusted to correct the mediate frequency transformer I9, the primary alignment when tuned to the upper end of the L5’ _of which: isincludedin the plate circuit of broadcast band. The’inductance La is adjusted togive correct alignment in the middle of the band, and the condenser C3 is adjusted to correct the alignment at the low-frequency end of the band. These three adjustments are mutually de pendent, but when properly made the circuits will maintain their alignment 4as the condenser C2 is tuned over its range. Although condenser C4 is a blocking condenser and has such large capacity 35 as to affect but slightly the tuning of the oscil lation circuit, its capacity may be so chosen as the tube I5. ~. ’ . » Appropriate voltage sources may be provided" for the operation of the amplifier tube 8,/i and these sources may be combined with those pro viding the voltages for the remainderI of» the 30 circuit shown. f l _ , ' _Attention is now invited to Fig. 4, which shows a similar frequency-changing circuit in -which ' a -single tube performs the function of oscillator and modulator, corresponding parts being des 35 ignated by the same reference characters.- In> to assist in maintaining the alignment, as well _, the circuit shown, the tube I5' is ,of the virtual as to assist in maintaining uniforml oscillation cathode> electron coupled type. Any other- type `_ of oscillator-modulator may be used if desired,- voltages. 40 \ » Although the various elements of the circuitv ` As shown,lthe tuned input circuit Il is connected to number four grid, and this grid, the plate, îsl-.own may have a wide variety of characteris tics, the following approximate values have been and a virtual cathode, positioned just inside the found to be satisfactory in producing anv oscillator andv modulator system which' will operate to re-` ceive` signals in the broadcast band lextending 45 from 550 kilocycles to 1500 kilocycles using an in termediate frequency of 4800 kilocycles: 50 circuit comprises the condenser Ce, inductance L4, and condensers C4 and C5. This circuit >is coupled to the oscillation circuit I8 bymeans of the inductive coupling between inductance L4 50 and inductance La and by the capacitive coupling inductance L1=1 mh. inductance La=.2 mh. inductance L3=.015 mh. Inductance L4=.015 mh. - Condenser Ca=20 mmf .-500 mmf. Condenser C3=30 mmf. l ‘Condenser C4-_-.1 mf.Y number three grid, act as an electron-coupled modulator. Number two grid acts as the oscil lator anode, and is connected through resistor 45 Rz to the voltage source "I6. The second` grid ' Condenser Ce=.001 mf. Condenser Cp=10 mmf. . of the condenser C4 which is common to these -circuits. ' The oscillationl voltage is impressed i upon the flrstf- grid, to 'which it is directly con nected. In operation,.the first grid voltage -con~trois the cathode Vemission, and the lsignal volt , age impressed on vthe fourth grid controls the Resistor R`a=50,000 ohms. portion of this emission which reaches the plate. Resistor R4=20,000 ohms. Although any appropriatel tubes may be used in voltage of the first grid. The operation is other-- 60 „wise similar to that of the >circuits -shown in the circuit described above, >a type 58 has been found appropriate for use as the modulator I5, This voltage, however, is powerless to affect the Figs. 2 and 3. ' -~ Whereas the invention has beenfdescribed‘as - . and a type 56 has been found-to be appropriate ' a frequency changer for a superheterodyne radio 65. for use as-the oscillator tube I1. receiver, it may be utilized as the frequency Figure 3, to which attention is now invited, changer for any heterodyne reception system, shows a similar frequency-changing circuit‘for and it is equally applicable to frequency changers use in a superheterodyne receiver. In this figure, for use in connection with the production of parts corresponding to Ythose shown in Fig. 2 are 4'radiant energy'for any- purpose, or to any system designated by the same reference characters. In in which it is desired to tune two resonant'cir 70 70 this circuit, however, ' an additional radio-fre-A cuits over a range in frequency.. maintaining a quency amplifier is provided between the antenna ‘ constantgfrequency interval between _- them and and the modulator tube I5. This circuit com prises’the usual radio-frequency ytuned circuit 1 „ using only one variablereactance element. which is inductively coupled to the inductance 1. A frequency-chanoine circuit which includes 75 75 L1 kof the antenna circuit and connected in the 4 2,110,664 a modulator tube and an oscillator tube, each of said tubes having input and output terminals, a first t'uned circuit connected to the input ter 'minals of one of said tubes and tunable to a desired frequency, said circuit comprising an - inductance and a variable condenser, a second tuned circuit connected across the input termi ductance and a variable condenser, a second tuned'circuit connected across the input termi nals of the other of said tubes and tunable to a different frequency, said second circuit includ ing a second inductance,y a. ñxed condenser, and said first-mentioned variable condenser and hav ing reactive constants so proportioned with re nals of the other of said tubes and tunable to spect to those of said first circuit that each of - a different frequency, said last-mentioned circuit said circuits has a high impedance to currents of the frequency to which the other is resonant, 10 and a combined electromagnetic and electro static coupling between the output of said oscil lator tube and the tuned circuit connected to the 410 including a second inductance, a iixed'condenser -and. said first-mentioned variable condenser and having reactive constants so proportioned with respect to those of said first circuit that each of said circuits has a high impedance to currents input thereof, whereby the resonant frequency' of the frequency to which the other is resonant, ' of each of said tuned circuits is controlled by 15 and a coupling between the output of said 0s said variable condenser to tune said circuitsl cillator tube and the tuned circuit connected to the input thereof, whereby the resonant fre-‘ quency of each of the tuned circuits is controlled . 20 by a single variable condenser to tune said cir cuits through a band in frequency. i 2. A frequency-changing circuit which includes a modulator tube and an oscillator tube, each of said tubes having input and output terminals, 25 an input circuit, a first tuned circuit, coupled to said input circuit, connected to the input ter minals of one of said tubes, and tunable to a desired frequency, said circuit comprising an in , ductance and a variable condenser, a second 30 tuned circuit connected across the input termi nais of the other of said tubes and tunable to a different frequency.,l said circuit including a second inductance, a fixed condenser and said first-mentioned variable condenser and having reactive constants so proportioned with respect to those of said first circuit that each 0f said through a band in frequencies. 5. A radio-frequency circuit comprising a first tuned circuit, tunable over a desired range of radio frequencies and comprising an inductance 20 and a variable condenser, and a second tuned cir cuit, tunable over a different range of radio fre quencies and including a second inductance, a fixed condenser, and s-aid first-mentioned vari able condenser and having reactive constants so 25 proportioned with respect to those of said iirst circuit that each of said circuits has a high im pedance to currents of the frequency to whichl the other is resonant, said second inductance and said fixed condenser being so proportioned that 30 a variation of the capacity of said variable con denser will tune both of said circuits throughout a range in frequency and maintain> a substan tially constant frequency diiference vbetween the frequencies of each of said circuits, whereby the 35 frequencies of both of said circuits may be simul taneously controlled by a variation of the capac -circuits has a high impedance to currents of the frequency to which the other is resonant, a coupling between the output of said oscillator tube and the tuned circuit connected to the input thereof for producing oscillations of a frequency determined by said circuit, and means for neu and a variable condenser, and a second tuned tralizing the oscillation-frequency voltage devel oped in said input circuit, whereby the resonant circuit, tunable over` a different but substantially equal range of radio frequencies and including frequency of said circuits is controlled by a single variable condenser to tune each of said circuits through a band -in frequency. 3. A frequency-changing circuit which includes a modulator tube and an .oscillator tube, each 50 of said tubes having input and output termi nals, a first tuned circuit co-nnected to the input terminals of one of said tubes and tunable to a desired frequency, said circuit comprising an inductance and a variable condenser, a second 55 tuned circuit connected across the input termi nais of the other of said tubes and tunable to a different frequency, said second circuit includ ing a second inductance, a fixed condenser, and said first-mentioned variable condenser and hav 60 ing reactive constants. so proportioned with re spect to those of said iirst circuit that each of said circuits has a high impedance tol currents of the frequency to which the other is resonant, ity of said variable condenser. 6. A radio-frequency circuit comprising a first tuned circuit, tunable over a desired range of 40 radio frequencies and comprising an inductance a second inductance. a iixed condenser, and said >first-'mentioned variable condenser, said second inductance and said fixed condenser being so pro portioned thateach of the circuits will have a high impedance to currents of the frequency to which the other is resonant, whereby both of said circuits may be simultaneously tuned by 50 variation of the capacity of said variable con denser. ' ,7. A radio-frequency circuit comprising a ñrst tuned circuit, tunable over a desired range of 65 radio frequencies and comprising an inductance and a variable condenser, and a second tuned cir cuit, tunable over a different range of radio fre quencies and including a second inductance, a fixed condenser, and said first-mentioned variable condenser, said second` inductance and said fixed condenser being so proportioned that each of the circuits will have a high impedance to currents and a dual coupling between the output of said - of the frequency to which the other is resonant, 65 oscillator tube and the tuned circuit connected and will resonate to a frequency having a definite 65 70 to the input thereof, whereby the resonant fre substantially ñxed rel-ation to the frequency to quency of each of said tuned circuits is con trolled by a single variable condenser to tune said circuits through a band in frequency. which the other circuit resonates as both of said circuits are simultaneously tuned through a band in frequency by a variation of the capacity of said variable condenser. 70 4. A frequency-changing circuit which in cludes a modulator tube and an oscillator tube, each of said tubes.`having input and output termi nals, a first tuned circuit connected to the input terminals of one of said tubes and-tunable to a 75 desired frequency, said circuit comprising an in 8. A radio-frequency circuit comprising a'iirst tuned circuit, tunable over a desired range of radio frequencies and comprising an inductance and a variable condenser, and a second tuned cir cuit, tunable over a different range of radio fre 75 2,110,006 s lator tube, whereby. voltages of said signal fre - quencies and including a second inductance, a quency and said oscillation frequency are im condenser. said second inductance and said fixed pressed upon the inputterminals ofsaid modula condenser being so proportioned that each of the tor tube by said variable condenser, which vcon circuits will have a high impedance to'currents denser serves to simultaneously control the reso of the frequency to which the other is resonant nance frequency of each of said circuits. s 13. 'A frequency-changing circuit comprising a andI will resonate to a frequency having a sub stantially constant frequency difference relative nrst tuned circuit, tunable to the frequency oi'` a to the frequency to which the other circuit reso v desired current itis desired to modulate and com nates as both _of said circuits are simultaneously prising an inductance and a variable condenser. a second tuned circuit, tunable -to an oscillation tuned through a band in frequency by a varia tion of the rcapacity of- said variable condenser. . frequency and ,including‘a second inductance. a 9. A radio-frequency circuit lcomprising a first fixed condenser. and said first-mentioned variable tuned circuit, tunable over a desired range of condenser, said second inductance and said fixed radio-frequencies and comprising an inductance condenser being so proportioned that a variation 16 of the capacity of said variable condenser will and a variable condenser. and a second tuned cir fixed condenser and said first-mentioned variable ` -10 is ' cuit, tunable over a different but substantially tune both of said circuits through a range in fren equal range of radio frequencies and including a quency and maintain a substantially constant second inductance, a fixed condenser and said first-mentioned variable condenser. said ~fixed difference between the frequencies of said cir cuits, and a modulator tube having its input ter 20V minalscoupled to both of said circuits. whereby high impedance to currents of the frequency of. voltages of the frequencyI of both of said cir 'so- ‘condenser being so chosen that it will act as a the first tuned circuit. and the elementsv of said cuits are impressed upon the input of said modu . second circuit being so»chosen as to cause said lator tube. ~ 14. A_frequency-changing circuit which com 25 prises a first tuned circuit. tunable to a desired radio frequency and comprising an inductance and a variable condenser, a second tuned circuit, tunable to an oscillation frequency and including 80 a second inductance. a fixed condenser. and said circuit tol be resonant to a frequency to which ` at the first-mentioned inductance has a high im pedanQQ. whereby each of said circuits will E resonate at a distinct frequency without >affect ing the voltages in the other circuit. 10. A frequency-changing circuit which com-l prises a first tuned circuit, tunable to the fre _‘ „quency of a current which it is desired to‘modu first-mentioned variable condenser, said second - inductance and said fixed condenser being so '- late~ and comprising an inductance and a variable Y. condenser, a sccondftuned circuit tunable to the proportioned that a variation of thc capacity oi' ‘ said variable condenser will tune both of said - frequency of a modulating current, and includ circuits throughout a range in frequency and maintain a substantially constant frequency dif» . ing a second inductance. a fixed condenser, and said first-mentioned variable condenser, and a ference between the frequencies of the current modulator tube including input terminals, said ' in each of said circuits. means for producing an input terminals being connected across said vari oscillation-frequency voltage in the second tuned able condenser, said variablecondenser serving circuit, and a modulator tube having its input 40 to impress voltages representative of both of said terminals connected across said variable con currents upon the input of said modulator tube and' simultaneously controlling the resonance fre quency of said circuits. p 11. A frequency-changing circuit comprising a first tuned circuit, tunable to the frequency .of a current it'is desired to modulate, and comprising an inductance and a variable condenser, a second tuned circuit tunable to the frequency of a modu- » 50 lating current,l and including a second inductn ance, a fixed condcnser,_ and said first-mentioned variable condenser, a modulator tube including input terminals connected across said variable s condenser, means for supplying current of one of 55 said frequencies to said first tuned circuit. and means for supplying an oscillation-frequency voltage vto said- second tuned circuit, whereby voltages of both of said frequencies'ma‘y be irn-l pressed upon the input of said modulator tube 60 by said variable condenser, said condenser serv ' ing 'simultaneously to control the resonance fre - denser, whereby voltages of two frequencies, as controlled by variation of the capacity of said variable condenser, are impressed upon the input 45 of said modulator tubel 15. A frequency-changing circuit which corn prises a first tuned circuit tunable to a desired signal frequency and comprising an inductance and a variable condenser, a second tuned circuit, tunable to an oscillation frequency and including 60 4a second inductance, a fixed condenser and said first-mentioned variable condenser. said second inductance and said fixed condenser being so proportioned that a variation of the capacity of 55 said variable condenser will tune both of said cir cuits throughout a range in frequency and main, tain a substantially ~constant frequency difference between the currents in each voi' said circuits, a modulator tube having its input connected across 60 said variable condenser. an oscillator tube having its input terminals connected across said second inductancepand a feed-back circuit connected be-. 12. A frequency-changing circuit comprising a t tween the output terminals of said oscillator tube first tunedcircuit, tunable to a desired signal fre 'and coupled to said second tuned circuit for prc 05 65 quency and comprising an inductance and a vari ducing oscillation frequency currents in said sec-_ ` v quency of both of said circuits. able condenser, Va second tuned circuit, tunable >to an oscillation frequency and including a sec Aond inductance, a fixed condenser. and said first mentioned variable condensc'r, a modulator' tum 70 having its input terminals connected, across said variablefcondenser, an oscillator tube including input and output terminals, .said input terminals being connected across the inductance- of said second_tuned circuit. and a feed-back circuit 75 connected >to the output terminals of said oscil ond tuned circuitfwhereby there is produced in the output of said modulator tube a signal-modu lated intermediate frequency having a substan tially constant frequency as said variable con 70 denser is tuned to receive- signals covering a band in frequency. _ 16. A frequency-changing circuit which includes a first vacuum tube having input and output terminals, a first tuned circuit connected across 75 6 g -. >andes-1. L . the input terminals of said nrst vacuum tube and> one of said tuned circuits into the other o_f said tunable to a radio frequency, said circuit in circuits,_and the inductance of one of said tuned cluding an inductance and a variable condenser,' circuits being so proportioned as to act as a a. second tuned circuit connected in shunt with radio-frequency choke with respect to the fre said variable condenser and including in series quency produced in the other of said tuned a ñrst fixed condenser, a second inductance, and circuits. 19. A radio-frequency circuit comprising a first a second ñxed condenser.' said fixed condensers and said second inductance being so proportioned Vtuned circuit tunable to a desired radio fre quency and comprising an inductance and a that said second tuned circuit will resonate at a 10 constant frequency difference from the frequency . variable condenser, a second tuned circuit tunable to a different radio frequency, and including a of the first tuned circuit as said variable con denser is varied to tune both o/f'said circuits second inductance, a fixed condenser, and said `first-mentioned variablelconden'ser, two ther through a range in frequency, a‘second tube in 15 from one end of said second inductance and thejunction of said » variable condenser and said mionic vacuum ~tubes each having a pair of input terminals, a connection- from one of said tuned circuits to the input terminals of one of said second fixed condenser to the input terminals of vacuum tubes, and a connection from the second cludingfinput and output terminals, connections said second tube, and a feed-back circuit con nected to the output terminals of said second 20 tubef'or providing a dual feed-back coupling to said second tuned circuit, said feed-back circuit including in series, a feed-back condenser, athird inductance, inductively coupled to said second in~ ' ductance, and said second fixed condenser, where 25 by voltages of the frequency of both of said tuned circuits, as controlled by said variable condenser, I 'are impressed upon the input of said first-men tioned tube. ‘~ 17. A frequency-changing circuit which in 30 cludes a modulator tube having input and output terminals, a signal-frequency circuit connected across said input terminals 'and including an xin-` ductance tunable by a variable condenser to the frequency of the current to be modulated, an r35 oscillation circuit connected in shunt with said variable condenser and including in series a first fixed condenser, a second inductance, and a sec ond fixed condenser, said fixed condensers and said second inductance being so proportioned that 40 said oscillation circuit will resonate at a con stant frequency difference from the frequency of the signal-frequency circuit as said variable con denser is variedto tune said signal-frequency circuit' throughout a range in frequency, an oscil-- lator tube including input and output terminals, connections from one end of said second induc tance and the junction of said variable condenser and said second fixed -condenser to said input > ‘ terminals, and a»feed-back circuit connected to 50 the output terminals of said oscillator tube for providing a dual coupling to said oscillation cir cuit, said circuit including in series a feed-back condenser, a third inductance,v inductively cou . pled to said second inductance, and said second- ñxed condenser, whereby voltages of the fre quency of a signal current and an. oscillation current, the frequencies of both of which are de termined by >said variable condenser, are im pressed across said variable condenser and upon 60 the input of said modulator tube, and whereby a signal-modulated difference frequency voltage 15 i tuned circuit to the input terminals of the other of said vacuum tubes, whereby the frequencies of the currents impressed upon the input of each 20 of said vacuum tubes may be simultaneously varied in the same sense through diilîerent` fre quency bands by a variation of the capacity of said variable condenser. ». ‘ 20. A ¿frequency-changing circuit which in cludes a first tuned circuit comprising an in-` ductance anda variable condenser, a lsecond tuned circuit including a second inductance, a fixed condenser and said first-mentioned variable condenser and having reactive constants so pro- ‘ portioned with respect to those of said first cir _cuit that each of said circùits has a high im pedance to currents of the frequency to- which the otherj is resonant, two vacuum tubes each comprising input and output terminals, a con- 1 nection between the first of said circuits and the input terminals of one of said vacuum tubes, a connection between the other of said circuits and the input terminals of the other of said vacuum tubes, and a coupling between the output terminals of one of said vacuum tubes and the input thereof, whereby said tube and its asso ciated circuits operate as an oscillator and modu late currents impressed upon the input terminals of the other of said tubes. A ' 21. A radio-frequency circuit comprising a first circuit tunable over a desired range of radio fre quencies, a second circuit tunable over a sub stantially equal range of substantially different radio frequencies and having reactive constants so proportioned with respect to those of said first circuit that each of said circuits has a high im pedance to currents of the frequency to which the other is resonant, and an adjustable re actanceelement common to said tunable circuits 55 and effective to tune them in the same sense over their respective ranges. 22. A radio-frequency circuit comprising a flrst circuit tunable over a desired range of radio frequencies, a second circuit tunable over a sub 60 stantially equal range displaced with respect to said ñrst-named range in the frequency scale and having reactive constants so proportioned with respect to those of said first circuit that - 18. In a frequency-changing circuit, tuned cir 65 (cuits tunable to the frequency of a signal-fre' each o said circuits has a high impedance to 65 curren l of the frequency to which the other is quency to b_e modulated and an oscillation-fre resonant, and an adjustable condenser common quency, respectively, each of said circuits inclúd to said tunable circuits and effective to tune them ing the same variable condenser, and a fixed con denser included in one of said `tuned circuits in the same sense over their respective ranges. 23. A radio-frequency coupling network includ 70 for aligning the tuning of both of said circuits, is produced 'in the output circuit of said moduf> lator tube. whereby the frequency to which eachof said circuits Yis _tuned by variation of said 'variable , condenser has a substantially constant difference, ing _a plurality" of reactance elements, said net work comprising- component resonant portions having points of impedance maxima substan»v l said fixed condenser being so proportioned as to , tially displaced on -the frequency scale, means 75 restrict passage of currents of the frequency of for substantially eliminating reactionpf said ' 7 / t' 2,110,664 component portions upon ‘each other. and means for .tuningl said network over a desired range and for adjusting said >points in thesame sense and ~ to equal extents comprising lan adjustable re actance element common yto said portions. 24. A radio-frequency coupling network includ-4 ing a plurality of> reactance elements, said net work “comprisingr component resonant portions across which appear voltage maxima displaced on s means for simultaneously >tuning said circuitsover a -range of frequencies and adjusting said points of maximum voltage in the same direction on the frequency scale comprising an adjustablev reactance element common’to‘ said circuits', and output circuits coupled to said impedance -ele ments. x . v' f , L 4 - À ’ 27. A radio-frequency circuit comprising a first circuit tunable over a desired range of radio fre quencies, a second circuit tunable over la range the frequency scale, means for substantiallyl of substantially different radio frequencies "'and eliminating reaction of said component portions 'having reactive constants so proportioned with for tuning said net-- upon each other and means respect to those of said ilrst’circuit ~that each of said circuits has a high impedance to currents of the frequency towhich the other is resonant, 15 an adjustable reactance- element common to said ing an adjustable reactance element common to` tunable circuits ‘and effective to tune them over. said portions. _ their respective ranges, electron-discharge means 25. A radio-frequency network comprising a having two input circuits and an output circuit, ` first component resonant circuit. a second com tunable circuits being individually connected having a‘point of maxi-y said 20 ponent resonant .circuit to said input circuits, and a coupling between mum impedance displaced on the frequency scale said output circuitland one. of said input fcircuits, with respect to that of said first circuit.l means . whereby said electron-discharge means' and- its for substantially eliminatingl reaction of said com associated circuits operate as an oscillator and ponent circuits upon each other, and means for modulate currents impressed upon the other of work over a range‘ of frequencies and maintain ing a substantially constant frequency difference 15 between said points of voltage maxima compris 25 simultaneously tuning said circuits over a range ¿said input circuits. . ' of frequencies and adjusting'their points of maxi ` 28. A radio‘frequency circuit comprising a first 1 mum impedance in the same direction and to circuit tunable over a desired range of radio` .equal extents on the frequency scale-comprising frequencies, a second circuit tunable over a range an adjustable reactance element’common to said « _of substantially different radio frequencies and 30 circuits. ` 26. A radio-frequency coupling system compris having reactive constantssol proportioned with respect to those of said first circuit that each ' ing a first resonant circuit, a second resonant « of said circuits has a high impedance to currents, 4 circuit having reactive constants so proportioned ofthe frequency to which thelgother is resonant, with respectto those of said first circuit that each of said circuits has a high impedance to currents of the frequency to which the other is resonant, a circuit for supplying radio-frequency energy to said circuits,"said circuits including impedance 40 elements individual thereto across which appear voltage maxima displaced on the frequency scale, and an adjustable reactance- element directly as, connected in circuit with, and common to, both of said tunable circuits and effective to tune them inthe same sense over their respective ranges. ' DANI’EL E. HAnNE'r'r. 40

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