US2038294A - Coupling system - Google Patents

Description

J. K. JOHNSON GOUPLING SYSTEM Filed Feb. 27, 1954 22,49 7 :1Q/sguardo!! April 2, 1936.

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BY www ATToRNEY Patentes Apr. 21, 1936 UNITED STATES PATENT oFFicE ooUPLING SYSTEM" JohnKelly Johnson, Rye, N. Y., assignol' to y Hazeltine Corporation, .a corporation of Dela- Application-February 2i, 1934, sensi No. 713,119

(ci. 25o-4o) 10 Claims.

This" invention relates to high frequency coupling systems and more4 particularly to coupling systems adapted to operate over Van unusually Wide frequency range or over a plurality of fre- 5 quency ranges.

An object of this invention is to improve the transmission eifciency and to reduce the effects of local disturbances in high frequency coupling systems operable over extreme ranges of fre- 0 quency.

Another object is to improve the operation of coupling systems tunable over the usual radio broadcast range and over'another range of frequencies-higher than the broadcast'range. 5 -It is the usual practice to construct high frequency coupling systems lby shunting van inductance coil with a variable condenser for tuning to the desired frequency. Such a coupling system is ordinarily tunable over a more or less lim- D ited range of frequencies the limits of which are determined by the magnitude of the inductance and by the maximum and minimum capacity values which can be connected across the coil. For example, it is customary to-.tune over the broadcast range inthe United States of approximately 550 to 1 500 kilocycles by means of a fixed coil of about 250 microhenries inductance shunted by a variable tuning condenser having a maximum capacity increment of about 350 micromicrofarads. 'I'he minimum -capacity (associated with the coil and condenser) is generallyin the neighborhood of 35 micromicrofarads.

It is often required that this tunable coupling system` shall tune over other frequency ranges in i addition to the usual broadcast range. It is frequently a particular requirement that the system, in addition to'tuning over the broadcast range, shall tune to an ultra-high frequency range, commonly known as the short-wave range. For this purpose, it is common practice to substitute a second coil of diierent inductance than that of the coil used for tuning in the broadcast range. This second coil is usually connected in series with the rst coil; and any other coils corresponding to additional frequency ranges are also connected in series. For tuning in an ultra-high frequency range, the coil used for the broadcast range (and coils corresponding to other ranges) is ordinarily removed from the circuit by some form of switching arrangement, thereby leaving in circuit the ultra-high frequency coil, which will be of smaller inductance than the broadcast range coil.

The above form of coupling system has been found to be att/ended by undesirable disturbances. Such disturbances are frequently introduced into from the following detailed description and the 30 y ranges. including an antenna I 0 f tercepting signals.

is coupled to the antenna-ground circuit through 45 the ultra-high frequency coil as a' result of local parasitic currents generated in the broadcast or other coil. These parasitic or circulating currents are often created in the coil or coils switched out of circuit by resonance eiects involving por- 5 tions of the coiland stray capacities associated with the coil. These resonance eilects. may take the form of standing waves so that substantial coupling to the coil which is in circuit may exist from points of the switched-out coil which have 10 a considerable potential, with reference to the standing waves. These undesired resonance effects are likely to exist within the ultra-high frequency range, thereby deleteriously affecting the transmission emciency in that range. l5

In 'accordance with this invention, means is provided for reducing the coupling between one or more windings corresponding to one or more frequency ranges so that the effects yof parasitic currents in an adjacent, unused coil are mini- 20 mized. More specically, this means takes the form of an electrical conducting ring, or closed winding, situated between any two coils between which the coupling effects `are to be reduced. Such a closed winding has the eil'ect oi' reducing 25 the magnetic :field interlinking the two coils so that currents iiowing in one are not introduced 1 into the other to an appreciable extent.

The invention will be more fully understood accompanying drawing.

Fig. 1 illustrates a radio receiver embodying multi-wave band tunable coupling systems according to the invention;

Fig. 2 shows the construction of a transformer 35 adapted tc be used in the receiver of Fig. 1j; and

Fig. 3 shows graphically how the coupling systems of the invention improve the transmission etliciency.

Fig.U 1 shows a superheterodyne type of radio 40 receiver adapted to tune over three frequency The receiver is provided with a circuit and ground II for in- A pentode amplifier tube I2 a coupling system I3 adapted to tune over the three frequency ranges. The input of a pentode modulator tube I4 is coupled to the output of the amplier I2 throughanother tunable couplingvsystem I 5 somewhat similar to coupling 50 system I3. For the purpose of supplying local oscillations to the modulator, there is'provided a local oscillator tube I6 of the triode typev having associatedl therewith a tunable frequency determining circuit I1. A coil I8 is connected in 55 2 the oscillator anode circuit and is coupled to the oscillating frequency determining circuit I1 to feed back the energy required to create the sustained oscillations. This coil I8 is also effectively connected in the grid-cathode circuit of the modulator I4 through the ground connections associated with tubes I4 and I6.

As a result of the combination of the signal and local oscillator voltages at the modulator tube, there is produced at the output of the mod ulator the well-known product of modulation which is the diierence between the signal frequency and the local oscillator frequency. This difference frequency is known as the intermediate frequency of a superheterodyne receiver, and the difference between the local oscillator frequency and the signal carrier frequency is known as the intermediate carrier frequency. For the transmission of signals corresponding to voice and music, the signal carrier frequency has associated with it at least one, and generally two, sidebands of modulation. These sidebands extend to about 5 kilocynes on either side of the carrier frequency, so that the signal frequency channel is ordinarily about 10` kilocycles in width. Hence, the intermediate frequency channel is also ordinarily about 10 kilocycles in Width, and the intermediate frequency selecting circuits are designed to pass such a band Width.

There is connected to the output of the modulator a xed tuned coupling system I9 designed to select the intermediate frequency channel. This coupling system is connected to the input terminals I and I of apparatus designated generally by the rectangle 20 as intermediate frequency amplifier, detector and audio frequency apparat This rectangle denotes all the apparatus which ordinarily follows a modulator, and since it constitutes no part of this invention, it is not shown or described in detail.

As explained above, the receiver is designed to receive signals in any of three frequency bands. The bands usually desired are the broadcast band which is about 550 to 1500 kilocycles in the United States, a band somewhat below the broadcast band, which may extend from about to 350 kilocycles, and a short Wave band of about 5500 to 15,000 kilocycles. For the purpose of this description, the three ranges will be considered to have these frequency limits, although other frequency limits could as well be used in so far as this invention is concerned. All these bands are known as high frequency bands, but for the purpose of this description the range above the broadcast range will be called the short wave or ultra-high .frequency range, and the range below the broadcast range will be called the sub-broadcast range.

As noted previously, the three frequency ranges are too widespread to permit tuning by means of a single coil and condenser. Hence, the tunable coupling systems are each provided with three coils having progressively varying electrical characteristics, one coil for use in each range. Referring to coupling system I3, there is provided a primary coil 2I electromagnetically coupled to secondary coils 22, 23 and 24, having progressively larger inductance values, each in' ductance being materially different from the other, and a coupling capacity, 66, common to both primary and tuned secondary circuits. The three secondaries are connected in series and have connected across them avariable tuning condenser 25. The magnetic coupling between primary 2I und secondary coils 23 and reduced by means of the closed turn t3 as will t explained more fully later. The coupling sys tem I3 thus provides a combined electro-magnetic and electro-static coupling. The electromagnetic coupling component is composed essentially of the mutual inductance between primary 2| and secondary 22, and the electro-static coupling comprises condenser 66. In the ultra high frequency range the coupling is essentially electro-magnetic due to the low impedance of the condenser B6 to high-frequency currents. In the broadcast range, and particularly in the sub-broadcast range, the condenser 6G has a much higher impedance, and, therefore, provides the principal coupling component. In the sub-broadcast range the electro-magnetic coupling effect between primary 2I and secondary 22 is negligible.

A switch 26 having two switch arms is connected to the lower end of coil 24 and is adapted to make contact with two oi the three contact points 21, 28 and 29. Contact points 28 and 29 are connected respectively to the upper ends of coils 24 and 23, so that these coils are shortcircuited by the switch connection to the corre sponding contact points.

The secondary coil 23 is wound to the proper inductance to conveniently tune over the broadcast range. The upper coil 22 is a coil of much smaller inductance adapted to tune with the condenser 25 over the ultra-high frequency range. Coil 24 is of greater inductance than the broadcast coil 23 and is adapted to tune with condenser 25 over the sub-broadcast range.

When it is desired to tune to a signal channel within the broadcast range, the switch 26 is adjusted so that the two switch arms make contact with points 2'I and 28, respectively, thereby short-circuiting and effectively removing from circuit the sub-broadcast coil 24 so that coils 22 and 23 are the only ones left effectively in shunt with the variable tuning condenser 25. Since coil 22 is of small inductance, its effect in the broadcast range is negligible as compared with coil 23.

When it is desired to tune in the ultra-high frequency range, the two switch arms are moved to contact points 28 and 29, respectively, thereby short-circuiting and effectively removing from circuit coil 23 as well as coil 24. This leaves only coil 22 connected across variable condenser 25, and tuning is thereby permitted over the ultrahigh frequency range.

Tuning over the sub-broadcast range is permitted when the contact points 28 and 2S are both open. Under this condition, coil 24 is of predominating eifect since it has a much larger inductance than either of the other two secondary coils. The inductance is large enough so that the tuning condenser is enabled to tune over the desired sub-broadcast range.

Fig. 2 shows the physical construction of a transmorrner comprising the four coils 2I to 24, adapted for use in the coupling system I3 of Fig. 1. The transformer comprises a cylindrical form 30 of a suitable insulating material. The primary coil 2| is wound around the central portion of the cylindrical form, and the two secondary coils 22 and 23 are wound on either side of the primary. The sub-broadcast. secondary coil 24 is a self -supporting compact coil of the universe` type wound at random or in layers on a cylindrical form 3l fastened within one end of the large] cylindrical form 30. Coils 2|, 22 and 23 are eacl Acoil winding data have wound evenly in a single helical layer winding. All the coils of the transformer are co-axial so that some magnetic coupling exists between the primary coil and each of the secondaries. There also results from this construction a. certain amount of incidental magnetic coupling between the secondary coils, particularly adjacent secondary coils. For the purpose of reducing the magnetic coupling between certain of the secondary coils of the transformer assembly there is provided a closed ring 33, the operationI of which will appear more fully hereinafter.

For the purpose of preventing extraneous couplings between the transformer and'other portions of the radio receiver, the transformer is enclosed in a shielding can 32 of a good electrical conducting material.

The following constructional dimensions and been found satisfactory for the above-described transformer:

u Inches Length of form 30 31A Diameter of form 30 1% Diameter of form 31' r T 1/2 Axial length of compact winding on form 31-- Inside diameter of shielding can 21% Coil Turns Wire (B & S gauge) Winding 2l 4 #38 single silk enamel Close. v 22 l111/6 #16 enamel 12 turns per inch. 23 106 #32 enamel 104 turns per inch. 24 430 #38 single silk enamel 49-50 gear universal winding. 33 u l #16 enamel (short-circuited).

It is understod that these specifications refer only to a specific transformer construction embodying the invention and found suitable for actual use. Agreat variety of types of coil constructions, circuit combinations and Ashort-circuited turn or turns could be devised all emboding the principle of the invention.

It is found that a transformer assembly constructed as described above (in the absence of the closed ring 33) is often characterizedk by transmission ineiliciencies, generally occurring in the ultra-high frequency range. These inemciencies are found to be due to resonance effects in the form of standing waves in a. coil, or coils, which areshort-circuited or effectively removed from circuit. The short-circuited coil which produces these deleterious effects is usually the coil in closest proximity to the ultra-high frequency coil, in this case the broadcast coil. The cause of these standing waves is the presence of capacities distributed across portions of the short-circuited, coil winding. These capacities winding and adjacent grounded objects, notablyv the shield. In consequence of the distributed capacity of the short-circuited coil, the stray capacities noted, and the inductance of the coil, this short-circuited coil has a natural resonant frequency Within the frequency band over which the active or ultra high-frequency coil is tunable by the tuningcondense As a result, parasitic resonant currents due to created in the short-,circuited coil. There are usually present standing waves of a length corresponding to one or more frequencies within the ultra-high frequency range. These local resonance effects are induced into the ultra-high frequency coil through the magnetic coupling which exists between the coils. At whatever frequency such a parasitic-resonance occurs, a reduction of exist between the standing waves are in which the transmission level is plotted against frequencies of the ultra-high frequency range. Curve A shows two dips within this range, this being a typical effect experienced in transformers of the construction described.

To avoid the above harmful effects, there is provided the short-circuited winding, or closed ring, 33, around the cylindrical form 30, between vthe ultra-high frequency coil and the remaining secondary coils, as shown. This turn is of high 'electrical conductivity, is in the path of the incidental coupling between'the coils 23 and 24 and the coil 22, and thus tends to prevent the magnetic fields of coils 23 and 24 from interlnking withcoil 22. This reduction of magnetic coupling between the secondaries reduces the effect of local resonances which could be induced into the ultra-high -frequency coil from one or more of the other secondaries when short-circuited. If desired, or necessary, the closed ring 33 could be employed between other secondary coils for the same purpose.

As a result of thus minimizing coupling effects between the secondary coils, the sion characteristic tem changes from form of curve B, in Fig. 3.

Coupling system I includes a transformer and switching arrangement very similar to that of coupling system I3. The principal distinctions are that the transformer comprises two primary coils 34 and 35 instead of the single primary coil 2l of coupling system I3; and also, that capacity coupling between the primary circuit and secondary coil 36 is introduced by means of a few dead-end turns 44 associated with the primary coil 34. The use of the additional primary coil and the dead-end turns improves the transmission gain characteristic of the coupling system. Primary coil 35 is of larger inductance than Yprimary coil 34 and serves to transfer most of the energy at the broadcast and sub-broadcast frequencies; whereas coil 34 serves to transfer the energy at ultra-high frequencies. The secondary coils36, 3'I and 38 of coupling system I5 are respectively the ultra-high frequency. the broadcast and the' sub-broadcast` coils.- The short-circuiting switch 39 is adapted to make contact with switch points 40, 4I and42 as in the case of switch 26,points 4I and 42 being for the purpose of of the tunable coupling systhe form of curve A to the uiting coils 38 and 31, respectively. I'he i ated between the transmis- ,v

broadcast ranges.

The oscillator frequency determining circuit l1 is composed of a transformer constructed somewhat similarly to that of Fig. 2. The transformer comprises the coil IB and three series-connected coils 41, 48 and 49 corresponding respectively to the ultra-high frequency, broadcast and sub- The closed ring, or shortcircuited winding`50, is located between coils 41 and 4B. The short-circuiting switch 5l likewise has two arms arranged to make contact with any adjacent two of points 52, 53 andv 54. Contact with points 53 and 54 short-circuits respectively coils 49 and 48. Variable condenser 65 is the adjustable frequency determining element of the oscillator circuit. This condenser is so related to variable condensers 25 and 46 as to maintain the fixed frequency difference at the output of the modulator, that is, a constant intermediate carrier frequency.

In addition to the above-described switching arrangements, the lreceiver includes two additional switches 55 and 56. Switch 55 is arranged to short-circuit the lower frequency primary coil when the receiver is adjusted for tuning in the ultra-high frequency range by means of `the switch point 51. The same switch also serves to shunt a condenser 58 across the 'primary 35 by means of switch point 59, when the receiver is adjusted for tuning in thesub-broadcast range. Switch 56 serves to connect an additional alignment condenser 60 across the permanent alignment condenser 6l by contact with switch point 62, when adjusted for the ultra-high frequency range.

To facilitate switching from one frequency range to another, there is provided a mechanical control device represented by the connecting lines S for simultaneously operating each of the switches 26, 39, 5l, 55 and 5E. The device S will usually be in the form of a knob so arranged that all of the secondaries are switched for the ultra'- high frequency range, the broadcast range or the sub-broadcast range, as desired.

A second mechanical control device U is provided to simultaneously tune all the variable condensers 25, 46 and $5.

Other elements such as resistors and by-passing condensers are employed where they serve to improve the general operation of the receiver. The sources of operating voltage for the vacuum tube electrodes and for heating the cathodes are not shown because their application is well understood -in the art, and constitutes no part of this invention.

1. A high-frequency coupling system adapted to operate over a plurality of different frequency bands comprising; a primary circuit; a secondary circuit coupled thereto and including a plurality of seconday coils, a variable condenser, and means `for connecting said secondary coils in circuit with said condenser and selectively effectively removing at least a first one of said secondary coils therefrom, sai-d secondary coils being f of progressively varying electrical characteristics proportioned so that said first coil is naturally resonant at a frequency to which a second of said coils isl tunable by said condenser, whereby the efficiency of said second coil is impaired when said first coil is effectively removed from circuit; and means for Substantially eliminating interaction between Said first and second coils resulting from the effects of said natural resonance comprising a short-circuited winding interposed between said first and second coils.

2. A high-frequency coupling system adapted to operate over at least two different frequency bands comprising; a primary circuit; a secondary circuit coupled thereto and including at least two secondary coils of materially different inductance, a variable condenser, and means for connecting said secondary coils in circuit with said variable condenser and for selectively effectively removing therefrom at least the secondary coil of larger inductance, said secondary coils being 4so positioned as normally to have inci dental coupling therebetween and said secondary coil of larger inductance having a. natural resonant frequency within the frequency band over which the other of said coils is tunable by said condenser, whereby the operating characteristics of said other coil are impaired when said coil of larger inductance ispeffectively removed; and means for minimizing said impairment due to resonance effects in said effectively removed coil, comprising a closed winding disposed between said two secondary coils substantially to reduce said incidental coupling.

3. In a high-frequency coupling system; a. primary circuit; a secondary circuit coupled thereto comprising a plurality of secondary coils, a shield within which all sai-d secondary coils are disposed, a variable condenser, and means for selec tively connecting said secondary coils effectively in circuit with said variable condenser foroperation of the system over any one of a plurality of different frequency bands, at leasta first and a second of said secondary coils being so pro portioned that the natural resonant frequency of said first coil is within a frequency band over which said secondary circuit, with said second coil effectively connected therein, is tunable, said first and second coils being proximate to each other but having a coupling therebetween the effect of which is negligible except at and near said natural resonant frequency of said first coil; and means for substantially eliminating the interaction between said coils incident to the natural resonance of said first coil, comprising a short-circuited winding between said first and second coils` 4. A high-frequency coupling system adapted to operate over at least two different frequency bands comprising; a primary circuit; a secondary circuit coupled thereto and including at least two secondary coils of materially different inductance, a shield within which said secondary coils are disposed, a variable condenser, and means for connecting said secondary coils in circuit with said variable condenser and for selectively short-circuiting the secondary coil of larger inductance, said secondary coils being so positioned as normally to have incidental coupling there between and said secondary coil of larger inductance having a natural resonant frequency within the frequency band over which the other of said coils is tunable by said condenser, whereby the operating characteristics of said other coil are impaired when the coil of larger inductance is short-circuited and means for minimizing said impairment due to resonance effects in said short-circuited coil, comprising a closed winding disposed between said two secondary coils substantially to reduce said incidental coupling.

5. A high-frequency coupling system for op eration over two different frequency bands, com prising; a primary circuit; a secondary circuit coupled thereto including two secondary coils of materially different inductance, a variable tuning condenser, and means for connecting said secondary coils in circuit with said variable condenser and for selectively short-circuiting the secondary coil of larger inductance, said secondary coils having a normally negligible incidental inductive coupling therebetween and said secondary coil of larger inductance having a natural resonant frequency, when shorted, within the frequency band over which said coupling system is tunable by said tuning condenser when said secondary coil of larger inductance is shorted; and means for minimizing the energy transfer between said secondary coils by way of Y to comprising a plurality of series-connected secondary coils, a variable :condenser connected.v

across all of said secondary coils, and means Ifor selectively short-circuiting one or more of said secondary coils for operation of the sysf tem over any one of a plurality of different frequency bands, at least a rst of said secondary coils being so proportioned that its natural resonant frequency is within a frequency band over which said secondary circuit is tunable when it is short-circuited and being proximate to at least one active secondary coil for such band, but having a coupling with all such proximate active secondary coils the effect of which is negligible except at and near said natural resonant frequency of said rst coil; and means for substanti-ally eliminating the interaction between" said first coil and said active secondary coils incident to the natural resonance of said rst coil, comprising a short-circuited winding between said rst coil and all such active secondary coils. f 7. A high-frequency coupling system comprising; a primary circuit including a primary winding; a secondary circuit coupled thereto and including two secondary `windings of different inductance; a load circuit; means for connecting said secondary windings to said load circuit and for selectively eiectively removing one of said secondary windings from said load circuit; and means for substantially eliminating the eiect upon said coupling system of local resonances in said last-named secondary winding when effectively removed from said load circuit,- comprising a closed windingl between said last-named winding and said other windings for reducing the coupling therebetween. 8. A tunable high-frequency coupling system for operation over two diierent frequency bands, comprising; a single primary coil; Vtwo secondary coils ci? diiferent inductance; a variable tuning condenser; means for selectively interconnecting said tuning condenser with only the secondary coil of smaller inductance for operation in the higher frequency band or with at least the secondary coil of larger inductance for operation in the lower frequency band; and means for minimizing the eifect of local resonances in the coil of larger inductance, when removed from circuit, upon the remainder of the coupling sys- 5 tem, comprising a closed low-resistance winding interposed between said secondary coil of larger inductance and the other two coils.

9. A high-frequency coupling system for op- I eration over two. different frequency bands, comprising; a primary circuit including a primary winding; a secondary circuit including two se-' rally-connected secondary windings of differ-v' ent inductance, a capacitance element coupling said circuits', a. variable tuning condenser, and means for eifectively removing from circuit the secondary winding of larger inductance; vand means for reducing interaction between said sec-- ondary winding of larger inductance and said other two windings when said winding is removed from circuit, comprising a closed low-resistance winding positioned between said secondary winding of larger inductance and said other two windings..

10.1 A high-frequency coupling system adapted to operate over at least -two dierent frequency primary winding; at least two secondary windings of diierent inductance vpositioned so that each is inductively coupled to said primary winding; va variable tuning condenser; means for connecting said secondary windings in circuit with said variable condenser and for selectively shortv circuiting the secondary coil of larger inductance to form a secondary circuit tunable by said variable condenser over at least two different frequencybands, said two secondary windings being so positioned as normally to have incidental coupling therebetween and said secondary Winding of larger inductance having a natural resonant frequency within the frequency band over which the other of said windings is tunable by said condenser,- whereby theoperating charactteristics of said other winding are impaired when the secondary winding of larger inductance is short-circuited; means coupling said primary circuit with said secondary circuit independently of said primary winding andsubstantially effective 1 only when said system is adjusted to operate nl.' the lower frequency band; and means for minimizing saidimpairment duetoresonance eiects in said short-circuited winding, comprising a closed winding positioned so that said primary winding and said secondary winding of smaller inductance are at one side thereof and so that said secondaryv winding of larger inductance is at the other side thereof, substantially to reduce said incidental inductive coupling'between said secondary windings and to reduce the inductive couplingbetween said primary winding and said winding of larger' inductance without substantially -reducing the inductive coupling between said primary winding and said secondary winding of smaller inductance. .y

JOHN KELLY JOHNSON.

bands comprising; a' primary circuit including a-

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