US2554107A - Push-pull mixing circuit - Google Patents

Description

May 22, 1951 D. KLEIS ET AL 1 PUSH-PULL MIXING CIRCUIT Filed Feb. 12, 1947 D.KLE|S A. VAN WEEL I VENTORS BY fi%% AGENT Patented May 22, 1951 PUSH-PULL MIXING CIRCUIT Derk Kleis and Adelbert van Weel, Eindhoven, Netherlands, assignors to Hartford National Bank and Trust Company, Hartford, Conn., as

trustee Application February 12, 1947, Serial No. 728,134 In the Netherlands July 26, 1944 Section 1, Public Law 690, August 8, 1946 Patent expires July 26, 1964 Claims. (Cl. 25020) This invention relates to a mixing circuit, more particularly for ultra-short waves, in which the incoming oscillations and the local oscillations are supplied respectively in push-pull and in phase coincidence to the input electrodes of two discharge systems.

In a superheterodyne receiver for ultra-short waves, in which the local oscillations and the incoming oscillations are supplied respectively in phase coincidence and, through an adjustable Lecher system, in push-pull to the mixing tubes, it was previously proposed to connect the aerial to the push-pull circuit at a point where a voltage node occurs with respect to the local oscillations. This was accomplished by lengthening the Lecher wires on the side remote from the mixing tubes by a suitable amount and by interconnecting the ends by means of a short-circuiting bridge which is coupled to a point of constant potential.

This arrangement prevented radiation of the local oscillations by the aerial, while the influence of variations in the impedance of the aerial on the tuning of the circuit was eliminated.

The invention is directed to the attainment of the same object by simpler means and in a more eflicacious manner. The invention provides a circuit-arrangement in which the aerial does not radiate the local oscillations, even if the frequency of these oscillations is varied over a broad range.

According to the invention, in the aforesaid mixing circuit the local oscillations are supplied to the discharge systems in a particular manner and the impedances between the discharge systems and a point of constant potential (earth) are so chosen that substantially no voltage having the frequency of the local oscillations is produced between the input electrodes of the discharge systems and the point of constant potential.

The local oscillations are preferably supplied in such a manner and the said impedances are given such values that, with any adjustment over a broad frequency range, substantially no voltage having the frequency of the local oscillations is produced between the input electrodes and the point of constant potential.

In order to attain the object aimed at, the input electrodes of the discharge systems may, for example, be connected, via a path of comparatively low impedance for the local oscillations, to a point of constant potential (earth), and one or more other. pairs of electrodes of the discharge systems may be connected to the point of constant potential via a path of comparatively high impedance.

The local oscillations can eifectively be supplied to the discharge systems in such manner that the push-pull circuit through which the incoming oscillations are supplied to the discharge systems and the co-phase circuit or circuits through which the local oscillations are supplied to the discharge systems, have only the discharge systems in common.

With each of the discharge systems the source of local oscillations can advantageously be coupled between a pair of electrodes. If each of the discharge systems is coupled separately with the source of local oscillations, for example by inductive means, each of the two circuits having the same phase, of which at each instance one of the discharge systems forms part, is preferably tuned to the frequency of the local oscillations. If the discharge systems are fed in parallel connection by the source of local oscillations, the circuit having the same phase as this source, the parallelconnected input impedances of the discharge systems and the parallel-connected coupling impedances, is tuned to the frequency of the local oscillations.

Furthermore, a material improvement of the circuit according to the invention may be obtained by connecting one or more points, which in the part of the co-phase circuit have the same potential as the input electrodes of the discharge systems, to a point of constant potential (earth) either directly or through a path of low impedance with respect to the local oscillations.

The latter step has the effect of reducing the radiation of local oscillations by the aerial almost to nothing. Besides, in this circuit arrangement the direct current supply of the discharge tubes may take place in a very simple manner.

In order that the invention may be clearly understood and readily carried into efiect, it will now be set out more fully with reference to the accompanying drawing in which:

Figure 1 is a schematic diagram of a mixing circuit according to the invention,

Figure 2 is a schematic diagram of another mixing circuit according to the invention,

Figure 3 is a schematic diagram of a third mixing circuit according to the invention,

Figure 4 shows one cavity resonator arrangement for use in the circuit of the invention, and

Figure 5 shows another cavity resonator arrangement for use in the circuit of the invention.

Fig. 1 shows a mixing circuit pertaining to a superheterodyne receiver for short waves, in which the invention is applied. The oscillations as received bya dipole aerial l, l" are supplied in push-pull to the input electrodes of two mixing diodes 3, 3" by means of two conductors 2, 2". The latter form part of a Lecher system which is tuned to the frequency-"f the incoming oscillations by means of an'earthe'd *short-circuiting bridge 4. The aerial I, l is connected to a point of the Lecher system 2, 2", so as to obtain a correct adaptation of the aerial to themixing-tu-bes.

A local oscillator is coupled by inductive means with a coil 5, one end ofrwhi'ch isconnected-to the anodes of the discharge systems through condensers 6', 6", the other -end-being connected to the junction of the cathodes of the two mixing diodes. The local oscillations1=arevconsequently supplied in phase coincidence to "stheztmixing diodes.

In this connection it may be' observedtthat. the co-phase circuit through which the local oscillations are supplied to the mixing diodes,:and:the push-pull circuit through which the incoming ostcillations aresupplied .to .the mixin diodesrhave solelythemixingdiodes in common. .\In circuitarrangements :previously proposed, the whole of sthepush-pull-circuit was included in the co-phase circuit.

.The said'junction of the cathodes of the mixing diodes is earthed through a path of: comparatively high impedance relatively to the local-oscillations. -In the present .case the .path is throughaa choke or a. system ofchokes =1. The

.. cathode. .direct currentrrand '-the current for .-the Jfilaments; arefsuppliedeto the twoi mixing diodes through thesaid choke. or. chokes.

;The intermediate-frequency output voltage is -.obtained in push pull-iromthe mixing diodes.

.In order-thata maximum voltage of -the-ire- ,guency .of the .localoscillations. may be r-sup- ,i-pliedetorthe inputelectrodes of- .the mixing. diodes, ..-.the coephase :circuit, formed .by the inductance coil '5, the; paralleleconnected; coupling capacities -.-6',\.6". a and the paralleltecon-nected input imped- .ancesof.the two mixing diodes 3';.-3",-is tuned: to the frequency of .the'local oscillations.

By using the afore-described method-bywwhich -the -local .oscillations: are supplied to the input electrodes-of the mixing. diodespand by the :choice .-rof-:the impedance between :the cathodes of the mixing. diodes "and :earth, in the present-case z-a -.-choke which 'iconstitutesa high impedance 'rela- :tively; to -the frequency. of thetlocal oscillations, it lisensured that between the inputelectrodes and earth .substantially. no- :voltage having 1 the ire- -,guency of the-local:oscillations occurs. :The'local :oscillation :voltage which: occurs: between theingput electrodes .onxthe one. handaand between the interconnected cathodesaof the-mixing. diodes on the other; hand.- brings; aboutzia' high: local; oscillation :voltage; across;.=the.rchoke F! and only. a very low: voltage. across the; impedance: between themputs-electrodes and earth. This voltagerdivision occurs because :ofwthe Ehigh impedance .of the '1choke '1.iand:;the 'low impedance of the: Lechersystem 6 with respecttothe local;.oscillations. 'sConsequently, :between athe dipole aerial l I and earth there issubstantiallyno voltageiof the frequencymf the 'local oscillations: and therefore the aerial .does .not radiates oscillations of this :.frequency. .;This applies not: only .to one :definite afrequency of the local'oscillationszbut also; applies -when .this frequency is. varied. through a broad .zrange. ...This is of:importanceior.receivers:tuna'bleiin'ia' 'broad range of. frequencies.

' Under certain conditions:itzmaysoccunthat. the :zcoephasezimpedanceibetweentheinputelectrodes ."z bitthelmixingidiodeszanllearthz (riiazthe pnshepull circuit) accidentally assumes a high value. In this case the object aimed at can nevertheless be attained in a simple manner, since in the cophase 'part'of the circuit, one -'.or more points 5 (points of symmetry) which have the same potential for the frequency of the local oscillations :as the input electrodes may be connected to rearth. .Inthe present circuit-arrangements this may be effected by connecting to earth point A lo of-the coil"5. This point is chosen so that in the 'circuit constituted by the coil 5, the capacity 6 andthe'mixing'dio'des 3' and 3" and the capacity 6" respectively, the point A has the same potenztial asxthe anode of .the mixing diode 3. This is io thecasewhen the inductance of the coil 5 to the left andto the right of point A is approximately iinverselyzproportional to the input capacity of one of the diodes 3, 3" and the capacity of one of the condensers 6, 6".

If two co-phase circuits (double coil 5) are used 1 and if each of these circuits:includeszxa-coupling 'condenser (616), it is possible to=indicate-a point A on each of the coils, which'can-serve as'a point of symmetry for one of the anodes.

By connecting point A to earth the input electrodes of the two mixing diodes and consequently, the aerial I, I", are effectively-at'earth potential .with respect to the local oscillations. The aerial is thus prevented under any condition from-radiating local oscillations and this, practically speaking, independently ofthe frequency of the local oscillations.

The circuit-arrangement'ofiers the additional advantage that the'cathode direct current "and theheating currents can be supplied 'via;point Azsov that the choke'or the system of chokes :1 may .be dispensed with.

Fig. 2 shows a circuit-arrangement.in'which the push-pull circuit isiincluded between-:the

cathodes of two mixing:triodes'3,-"3". "The control grids of these triodes are jointly connected to earth througha high'resistance 8. Thelocal oscillations are generated by the"circuit itself.

.To this end, the co-phase circuit provide'd -between the anodes-and the control gridsof the I mixing'triodes is tuned to the"freq-uency of the local oscillations. This circuit is constitutedby the parallel connection of two'inductance coils 9', :'9", the parallel connection of'two capacities l0, l0", an impedance ll arranged-between the 'junction of the capacities l0, "lW' and -the'intel-connected control grids, and by the parallelconnected anode-control grid capacitiesof'the =m-ixing triodes l2, l2". The figure furthermore shows'the anode-cathode capacities I 3', l3" and the control grid-cathode capacities-M3 14. The

positive feedback required for the generation of the local oscillations is brought about hy means of the aforesaid internal capacities of the tubes. Thelocal oscillations 'generated'are supplied in phase to the input electrodes of the mixing triodes.

The intermediate-frequency output voltage is taken from the circuit through chokes I, 1". The direct current supply of the anodes of-the mixing triodes. also takes placethrough this path. The controlgrids may begiven-anappropriate -biassing potential via the resistance '8.

The co-phase impedance which occurs between "the anode and earth relativelytothe lo'cal'oscillations is determined substantially by the impedance of the chokes '1', 1", whereas ther'corre- :sponding. impedance between the :control :grids and earth is determined by the resistancesfl.

lid

These impedances are chosen so that their value, with respect to the local oscillations, is high as compared with the co-phase impedance which occurs between the cathodes of the triodes and earth, measured via the push-pull circuit. It is thus ensured in a manner similar to that in the circuit shown in Fig. 1 that substantially no voltage having the frequency of the local oscillations can occur between the input electrodes of the triodes 3', 3 and earth and, consequently, between the aerial I, I and earth. If, however, the co-phase impedance between the two cathodes and earth should accidentally assume a high value, one or more suitably chosen points of the co-phase circuit may be earthed in the same manner as used in the circuit shown in Fig. 1, so that under any conditions it is ensured that the aerial cannot radiate local oscillations.

It is frequently possible to indicate on the impedance II a point whose potential with respect to the local oscillations corresponds to that of the cathodes of the mixing triodes. By earthing this point it may be ensured that the cathodes and, consequently, the aerial are earthed with respect to the local oscillations. In those cases in which it is not possible to indicate a point of symmetry of the cathodes on the impedance II, or in which it is not desirable to earth a point of this impedance, a point of symmetry of the cathodes of the mixing triodes may be obtained in the co-phase circuit by providing some few impedances, for example, some few capacities, and this point may then be earthed.

Such a case is assumed in Fig. 3, in which only the corresponding parts of the circuit-arrangement shown in Fig. 2 are represented separately. The point of symmetry of the cathodes of the mixing diodes is now obtained by arranging two series-connected capacities l5, between the anodes of the mixing triodes 3', 3" and by connecting the junction B of these capacities, on the one hand via a condenser IE, to the control grids of the triodes and, on the other hand, directly to earth. The point B constitutes the desired point of symmetry provided that the ratio between the capacities I3 and I4 is equal to the ratio between the capacity l5 and half the capacity of the condenser Hi.

In order to stabilize the oscillator frequency, it is frequently advisable to realise the impedance H as a cavity resonator whose outside is earthed. In this case the mixing systems may be coupled with the cavity resonator by means of a coup-ling loop completely insulated from the cavity resonator. In an alternative arrangement, the two supply lines to the cavity resonator may be realised in the form of loops which are led-in so as to be insulated from the outside and which are secured to the inside of the cavity resonator at such a height that the input electrodes of the mixing systems are effectively at earth potential with respect to the frequency of the local oscillations.

Fig. 4 shows a cavity resonator IT, in which use is made of a coupling loop is which is completely insulated from the cavity resonator. Fig. 5 shows a cavity resonator in which two coupling loops l9 and are led-in in an insulated manner and are secured to the inner wall of the cavity resonator at the desired points. The ratio between the surfaces of the loops determines the point of symmetry with respect to the input electrodes.

What we claim is:

1. An electrical circuit arrangement for mixing a first wave and a second wave to produce an intermediate frequency wave, comprising a pair of mixing elements each having a pair of cooperating electrodes, a Lecher-system tuned to the frequency of said first wave and having an open end thereof coupled to a corresponding electrode of each of said mixing elements in push-pull re-' lationship and having a closed end, means to couple said closed end to a point at constant potential of said circuit arrangement, impedance means intercoupling said corresponding electrodes and the other electrodes of said mixing elements, means to apply said second wave to said impedance means thereby to apply said second wave to said mixing elements in phase coincidence, an impedance element having a high impedance value at the frequency of said second wave intercoupling said other electrodes and said point at constant potential substantially to isolate said other electrodes from said point of constant potential at the frequency of said second wave, an output circuit coupled to said mixing elements, and means to apply said first wave to said Lecher-system thereby to develop said in-- termediate frequency wave in said output circuit.

2. An electrical circuit arrangement for mixing a first wave and a second wave to produce an intermediate frequency wave, comprising a pair of mixin elements each having a pair of cooperating electrodes, a Lecher-system tuned to the frequency of said first wave and having an open end thereof coupled to a corresponding electrode of each of said mixing elements in push-pull relationship and having a closed end, means to couple said closed end to a point at ground potential of said circuit arrangement, impedance means intercoupling said corresponding electrodes and the other electrodes of said mixing elements, means to apply said second wave to said impedance means thereby to apply said second wave to said mixing elements in phase coincidence, an inductance element having a high reactance value at the frequency of said second wave intercoupling said other electrodes and said point at ground potential substantially to isolate said other electrodes from said point at ground potential at the frequency of said second wave, an output circuit coupled to said mixing elements, and means to apply said first wave to said Lecher-system thereby to develop said intermediate frequency wave in said output circuit.

3. An electrical circuit arrangement for mixing a first wave and a second wave to produce an intermediate frequency Wave, comprising a pair of mixing elements each having an anode and a cathode, a Lecher-system tuned to the frequency of said first wave and having an open end thereof coupled to the anodes of said mixing elements in push-pull relationship and having a closed end, means to couple said closed end to a point at ground potential of said circuit arrangement, a first inductive element intercoupling the anodes and cathodes of said mixing elements, means to apply said second wave to said first inductive element thereby to apply said second wave to said mixing elements in phase coincidence, a second inductive element having a high reactance value at the frequency of said second wave intercoupling said cathodes and said point at ground potential substantially to isolate said cathodes from said point at ground potential at the frequency of said second wave, an output circuit coupled to said mixing elements, and

18 means to apply said first wave to said Lecherat scamsystem:thereby;tcdevelop;said:intermediate.free quency wave in saidoutput circuit.

4.. iAneelectrical circuit arrangement for-mixing; azfirst waveaand .a,-secondiwave tov produce an intermediate frequencywave,- comprising a pair-of mixing elementseach having an anode and alcathode electrode, a Lecher-system tuned to the :frequencyof saidfirst wave and having-an open; end thereof coupled to acorresponding electrode of eachof said mixingelementsin pushpull' relationship and having-a closed end, means to couple said closediend to a-point at ground potential of said circuit arrangement, a tapped inductive element intercou-pling saidlcorresponding electrodes and the other electrodes. of said mixing elements; means to -couple thetapping of said tapped inductive :element-to said point at ground potential, means to; applysaidsecond wave-to said tapped inductiveelement thereby to=rapp1y said second wave to said mixing-elements inphase coincidence, an inductive. element having a. high reactance value at thefrequency of saidsecond Wave intercouplingsaid other electrodes and said point at ground potential substantially to isolate said other electrodes from said point at ground potential at the frequency: ofsaidz-second Wave, anoutput circuit coupled to said mixing-elements, and meansto apply said first wave'to said Lecher-system-therebyto develop saidintermediate frequency wave in said output circuit.

5. An electrical circuit arrangement for mixing .-a"first Wave and a second wave to produce an intermediate frequency wave, comprising a pair of mixing elements eachhaving an' anode 1 and a-cathodeelectrode, a Lecher system tuned to the frequency of said first wave and having an open end thereof coupled to acorresponding electrodeof each of said mixing elements in pushpull relationship and having-a closed end, means to couple said closed end to a point at ground potential of said circuit arrangement, a first inductive elementhaving-one endthereof coupled to-the otherelectrodesv of said ,mixing, elemen s;

first and second capacitive elements coupled-inseries between. said corresponding electrodes Y and. having at junction, means. to couple the other. end of saidinductive-element to said junction,

said mixing elements, said first inductive element andvsaid capacitive elements constituting a pair ofseries circuits each tuned to the frequency .of said'second wave, means to apply said second wave to said first inductive element thereby to apply said second Wave to said mixing elements in phase coincidence, a second inductive element having a high'reactance value at the frequency ofsaid second wave intercoupling saidother e1ectrodes, and said point at ground potential sub stantially to isolate said other electrodes from said .point at ground potential at the frequency of said second Wave, an ouput circuit coupledtosaid mixing elements, andmeans to applysaid first wave to said Lecher-system thereby to develop said intermediate frequency wave in, said output circuit.

DERK KLEIS. ADELBERT VAN WEEL..

REFERENCES CITED The-following references are of record in the file of this patent:

UNITED STATES .'PATEN"IS Number Name Date 1,968,610 Mathieu July 31, 1934 1,978,446 Aubert Oct; 30,- 1934 2,101,438 Lindenblad Dec. 7, 1937 2,211,003- Conklin' Aug. 13, 1940 2,434,474 Strutt- Jan. 13, 1948 2,441,452 Strutt et a1. May, 11, 1948 12,453,078 Posthumus Nov. 2, 1948 FOREIGN PATENTS Number Country Date 507,495 Great Britain June 15,1939 544,675 Great Britain July 14, .1943

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