US2383345A - Reflex converter circuit - Google Patents

Description

g" 1945; I K. SEILER 313 2,383,345

REFLEX CONVERTER CIRCUIT Filed 'Sep'fi. 15, 1942 Snuenloi f l nard Patented Aug. 21, 1945 oFFlcE REFLEXCONVERTER CIRCUIT i Delaware i Karl Seiler, 3rd, Jenkintown, Pa., assignorto Radio Corporation of ;America, a;corporation a Application September 15, 1942, Serial No. 458,432

r a 1 Ill-Claims. (oi. 250) This invention is concerned with an improve- ,ment; in radio receivers of the superheterodyne tyamsQarid more particularly with a reflex converter cuit which combines the function of afirst del tor, oscillator, and first intermediate frequency Inthepresent state ,of theflart it is known to use in superheterodyne circuits'a multifelectrode type of tube designed to performsimultaneously the functions of a first detector and an oscillator.

lhesecorhbined; tunctions are frequently referre tofas frequency conversion. According to my invention the saline or equivalent multie etrode tube is made to periorm in addition the function of intermediate frequency amplification.

Asia result necessity for the use of a separate tube 2-15 circuit f or performing the combined functions of detector-oscillator and intermediate fret quency amplifier, utilizing an electron discharge having'tvi'thina common envelope electrodes triode and other electrodes 0011-;

heated; to the; signal grid electrode of the heptodefthe triode electrodes having circuit elements connected thereto to constitute'a generator of i ea oscillations which are injected into the search stream'of the heptodeptheoutput of the heptoiieincluding' an intermediate frequ'encyfcin f cui t hetweedwhich cincuit and the signal grid 1 e ctrode of theheptode afeed back circuit is confn ted for thepurposeor reliexing and amplify- ;i said intermediate frequency energy.

Other objects of the invention are to provide a co Qe'rt circuit which Wdflld The attractive in o I rice receiving sets wherethe cost must wri to a to provide a receiver of educed sizeandweight; andin battery-opera its a; prevm e e nonne r perauon by reprovide in a superheterodyne receiver, a

atteryconsumption. In' single frequency.

the following description takenin connection with the accompanying drawing in which the single figure illustrates a preferred converter circuitembodying the present invention of combined first detector, oscillator and intermediate frequency stages.

In the circuit of the accompanying drawing the tube designated V is a multi-electro-de' vacuum tube and may *be of the typeknown as 6J8-G, or oneequivalent thereto. This tube,also'known as a triode-heptode converter,yc0ntains a triode section anda heptode section within the same evacuated envelope, an indirectly heated cathode K ibeing common to tooth. The heptode section comprises the cathode K, "an output or plate electrode P and a plurality of grid G1 to G5 interposed inthe space between K and P in the order named. The triode section comprises the oathode K, grid Go and plate P0." In the normal'use or this tulbeas a converter, the cathode K, first grid Goan'd plate P0 constituting the triode section have external circuit elements connected thereto to perIorm the function or a local oscillator for generating the local oscillations, the grid G0 serving as the output electrodeof theoscillator. The signal oscillations are impressed on the grid G1 of the heptode section and'the locally produced oscillations are injected into theelectron stream ibetween cathode K and {plate P by way of the grid G3 which has a direct connection to the oscillator "grid Go Within the tube. Du to the mixing action withinthetube, oscillations of intermediate frequency appear in the output circuit connected to the plate P. The second and I'Ourth'-gridsGz, G4 re connected together inside the tube envelope, have a positive potential impressed thereon, and serve to accelenate the electron stream and to shield electrostaticallythe signal control grid G1 from voltage fluctuations on theinjector grid G and on the plate P. Grid Gals the usual suppressor grid having an internal connection to the cathode K.

The use ofjthe above or equivalent tube and the circuit connections therefore in accordance with the present invention will now be pointed out more particularly. The grid Gi serves as the signal control grid and has connected between it and the cathode K the input circuit L1C1 which is tuned to the received incoming signal oscillations. If desiredanRE amplifier stage may precede the detector-oscillator-I.F, amplifier tube V,the same being interposed lbetw-een the antenna A and aidre'sonaht circuit Iii- 0; through the radio frequency transformer T1.-

The gr id G3 being directly connected to at triode grid Go derives therefrom the oscillations generated by the triode section, the electrodes of which have connected thereto external circuit 1 elements to constitute the local oscillator of the R1 and C7 are respectively the usual grid-leak and grid-condenser employed in oscillators of this type. Voltage for plate P is applied from a suitable power supply source indicated by +B+. Voltage for the plate P is applied from said source through a voltage dropping resistor R2 andtha't for screen grids G2-'Gi is applied through'a dropping resistor R3. C8 is a screen grid bypass condenser. j i

In order to provide suitable operating bias for thesignal control grid Grand oscillator grid Go, the cathodeK has connected between it and ground the conventional self-biasing resistancecapacit'y network, R4' C4. In the event that it is desired to provide the receiver with automatic volume control, the AVG control bias may be obtained in the usual manner from the second detector and fed either to .the signal grid G1 or to the injector 'grid G3, or both.

The variable tuning condensers C1 and C2, and theyariable' condenser 03 of the R. F. amplifier, if oneis used, are mechanically interconnected as sho'wnby'the, dotted line U for the purpose ofpr'oviding uni-control. j As is wellknown, by reason of the interaction between the receivedsignals impressed on grid G1 and the locally generated oscillations injected on grid G3 there Willbe developed'in the fixed tuned circuit I1 connected to the plate P oscillations of the intermediate frequency (I. F.)'. Coupled to the circuit I1 is a second fixed tuned circuit I2 alsoresonant to the intermediate frequency oscillations, the coils of said circuits constituting the transformer T2. The oscillations occurring in the circuit I2 may then be further amplified in a second intermediate frequency stageor else fed directly to a second detector, the resulting audio currents being fed to an audio frequency amplifier and reproduced by a loudspeaker in the usual manner, the'latter elements not being shown.

In order that the frequency converter above described may assume the additional function of an amplifier of the resulting intermediate frequency, the latter frequency (sum or difference) developed in the plate circuit of the combined converter oscillator tube V is fed for maximum gain back onto the signal control grid G1 by way of the feedback loop FB which includes the filter network in the "form of I. F. transformer T2 and series-connected condenser C9 and resistor R9 so that only the difference (or sum) frequency is' fed back, the original'and the unwanted sum (or difference) of the original frequencies being suppressed by the I. F. transformer tuned circuit acting as a-band'pass filter for only the difference (or sum) frequency in the heptode plate" circuit. This arrangement is most advantageous in applications-where the intermediate frequency is considerably removed from the tuning range frequencies and oscillator frequency because locki in of the intermediate and signal frequencies in I the I. F. transformer would occur were the difphase reversal through the tube itself and an additional 180 phase reversal through the condenser C9 inthe feedback loop since when one plate of this condenser is positive the other is simultaneously negative and therefore adequate amplification of the signal can under these conditions take place. H The gain that can be realized from thearrangement is limited because if a considerable amount of intermediate frequency is fed back, the circuit will oscillate, hence the reason for the se'rie sresistor R9 in the feed back loop. With a converter tube of the type having a high conversion conductance maximum gain will be obtained."

'While'I'haVe shown and described only'one preferred embodiment of the invention; it will be understood that "modifications and changes may be made without departing from the spirit and scope of the invention, as will be understood by those skilled in the art.

WhatIclaimisz v j 1. In a superheterodyne receiver, a circuit for performing the combined functions of firstdetector-oscilla'tor and intermediatefrequency amplifier, comprising an'electron discharge tube having within a common'envelope a cathode, a pluralityofgridelectrodes and a pair of anode electrodes; a tuned input circuit having im- *pressed thereon the received signal oscillations connected between cathode and one of "the grid electrodes, external circuit'elements' connected betweena second grid electrodasaid cathode and one of the anode electrodes to serve as a generator of local oscillations, an intermediate frequency circuit connected to *the'second anode electrode andhaving an output terminalgand-a circuit forfeeding back some of the intermediate frequency energy for amplification bysaid tube, saidcircuit being connected between the output terminal of theintermediate frequency circuit and the grid electrode towhich the tunedinput circuit is connected; 2. In a superheterodyne receiver, a circuit for performing the combined functions of first detector-oscillatorand intermediate frequency amplifier, comprising 'an' electron discharge tube having within a common envelope a cathode, a plurality of grid electrodes'andapair-of anode electrodes, a tuned input circuit'having impressed thereon the received signal oscillations connected between cathode and one of the grid-electrodes,

external circuit elements connected between a cuit conncted to the second anodeelectrodeand having an output terminaL-and' a circuit for feed me back some of the interme'diatefrequency energy for amplification bysaid tube, said circuit including a series resistor-capacitor network connected between the output terminal of the intermediate frequency circuit and the gridelectrode to which the tunedinput circuit is connected.

3. A combined first detector-oscillator anamtermediate frequency amplifier circuit, comprising an electron discharge tube having with-in: a common envelope a cathode, a pluralityor grid.

I electrodes and an output anode electrode, a tuned 'input circuit having impressed thereon the re- I ceived signal oscillations connected between cathode and one of the grid electrodes, external tween the received and local oscillations con- I nected to the output anode electrode, a second circuit tuned to the intermediate frequency oscillations coupled to thefirst intermediate frequency circuit, and means for feeding back to the signal grid; in phase with the received signal oscillations the intermediate frequency oscillations derived from said second circuit for further amplification by said discharge tube.

4. A circuit asdefined in claim 3 wherein the feedback means comprises a circuit including series connected resistance and capacity con- 3 nected between the second intermediate frequency I circuit and the signal input grid.

5. In a superheterodyne receiver, a circuit for performing the combined functions of first detector-oscillatorand intermediate frequency ampllfier, comprising an electron discharge tube having within acommon envelope electrodes constituting a triode and other electrodes constituting a heptode, the triode and heptode having a common cathode a tuned input circuit having impressed thereon the received signaloscillations connected to the signal grid electrode of the heptode, circuit elements connected to the triode 'electrodes constituting a generator of local oscillations, means for injecting said local oscillations into the electron streamlof the heptode, an intermediate frequency circuit connected to the output of the heptode, and a feedback circuit connected betweensaid intermediate frequency circuit and 1 the signal grid electrode of the heptode whereby it said intermediate frequency energy is amplified by the heptode portion of the tube.

16. A circuit as defined in claim 5 wherein the feedback circuit includes a resistor and a condenser connected in series.

I 7. In a superheterodyne receiver, a circuit for performing the combined functions of first detector-oscillator and intermediate frequency amplifier, comprising an electron discharge tube having within a common envelope electrodes constituting a triode and other electrodes constituting a heptode, the triode and heptode having a common cathode, a tuned input circuit having impressed thereon the received signal oscillations connected to the signal grid electrode of the heptode, circuit elements connected tothe triode electrodes constituting a generator of local oscillations, means for injecting said local oscillations into the electron stream of the heptode, a bandpass filter network which transmits only the intermediate frequency resulting from the frequency conversion connected to the output of the heptode, and a feedback circuit connected between said filter network and the signal grid electrode of the heptode whereby said intermediate frequency energy is amplified by the heptode portion of the tube. l

8. A combined frequency converter-intermediate frequency amplifier stage utilizing a tube having a plurality of electrodes, comprising a i tuned input circuit on which the received signal output to the input of said stage for feeding back some of the intermediate frequency energy to be amplified by said stage.

9. A combined frequency converter-intermediate frequency amplifier stage as defined in claim 8 wherein the feed back circuit includes a resistor and a condenser connected in series.

10. In a superheterodyne receiver, a circuit for performing the combined functions of first detector-oscillator and intermediate frequency amplifier, comprising an electron discharge tube having within a common envelope, cathode, grid and anode electrodes which constitute a triode, and a cathode, an anode and a plurality of interposed grids which constitute a heptode, said grids including a signal grid and a mixer grid, said cathode being common to said triode and heptode, a tuned input circuit having impressed thereon received signal oscillations connected to the signal grid electrode of the heptode, circuit elements connected to the triode electrodes constituting a generator of local oscillations, a connection between the grid of the triode oscillator and the mixer grid of the heptode for injecting the local oscillations into the electron stream of,

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