US2452560A - Band-pass transformer - Google Patents

Band-pass transformer Download PDF

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US2452560A
US2452560A US610373A US61037345A US2452560A US 2452560 A US2452560 A US 2452560A US 610373 A US610373 A US 610373A US 61037345 A US61037345 A US 61037345A US 2452560 A US2452560 A US 2452560A
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transformer
winding
windings
primary
band
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Joseph B Gainer
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Joseph B Gainer
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    • HELECTRICITY
    • H03BASIC ELECTRONIC CIRCUITRY
    • H03HIMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H7/00Multiple-port networks comprising only passive electrical elements as network components
    • H03H7/01Frequency selective two-port networks
    • H03H7/0153Electrical filters; Controlling thereof
    • H03H7/0161Bandpass filters

Description

Nov. 2, 1948. GAINER BAND-PASS TRANSFORMER 2 Sheets-Sheet 1 Filed Aug. 11, 1945 FIG. 3
Nov. 2, 1948. J. B. GASNER BAND-PASS TRANSFORMER 2 Sheets-Sheet. 2
Filed Aug. 11, 1945 FIG.4
FIG.5
ammo/whom JOSEPH B. GAINER Patented Nov. 2, 1943 UNITED STATES PATENT OFFICE (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) 10 Claims.
My invention relates to transformers and particularly to transformers utilized in radio-frequency amplifier or oscillator circuits.
In accordance with my invention, the primary and secondary windings of a transformer are mounted in a fixed relative position affording greater than optimum or critical coupling and a tertiary windin inductively related to both the primary and secondary windings is adjustable to reduce their effective mutual inductance to an extent affording the desired frequency-response characteristic, of an interstage transformer for example, or to afford the desired amount of a feedback in an oscillator, detector or amplifier system.
My invention further resides in features of construction and arrangement hereinafter described and claimed.
For an understanding of my invention and illustration of embodiments thereof, reference is made to the accompanying drawings, in which:
Fig. l, in perspective, shows an interstage transformer.
Fig. 2 is an explanatory figure mentioned in discussion of Figs. 1 and 3.
Fig, 3 schematically shows a portion of an amplifier system using the transformer of Fig. 1.
Fig. 4, in perspective, shows another type transformer.
Fig. schematically shows an oscillator system using the transformer of Fig. 4.
Referring to Fig. l, the primary winding P and secondary winding S of an interstage transformer T are wound respectively on the tubular forms l and 2 suitably fastened to the base member 3. The coil and base assembly is enclosed by a conductive shield 4 provided with lugs, not shown, which pass through notches 5 in the base 3 and through the receiver chassis, or equivalent. not shown. The terminals 6 to 9 fastened to and extending through base 3 provide for external'connection of the transformer windings to other circuit elements, for example, Fig. 3, to the output and input electrodes respectively of amplifiers tubes V1, V2 for implicity only shown as triodes. The inductances of the windings P and S may be and usually are more or less exactly equal.
It is usually desired that the frequency-response curve of such an interstage transformer as tuned by condensers C1, C2 and/or by the cores !2, 13 shall have the general shape of curve ill, Fig. 2, characterized by a relatively flat top and steep sides to provide for substantially uniform amplification of all frequencies throughout a band of frequencies ii to f2 and with great attenuation for all frequencies lower and higher than if and f2 respectively.
Because of the interdependent variables involved, it is difiicult to design and manufacture radio-frequency transformers which have the desired bandpass characteristics both as to width of band and limiting frequencies: moreover when the desired band-width is but a small fraction of the mean frequency in, the required coupling is so small the corresponding relatively great physical separation of the windings enforces, when the usual practice is followed, large overall dimensions of the transformer.
In accordance with my invention however, the windings P and S are purposely positioned close to one another affording a percent coupling which is substantially in excess of optimum or critical and resulting in a band-pass characteristic generally as exemplified by curve ll, 2. To reduce the mutual inductance of transformer '1, there is provided a tertiary winding W comprising one or more turns coupled to and slidable along the primary and secondary windings P and S.
By adjustment of winding W along the coils P and S, the frequency-response characteristic may be varied from one having generally the shape of curve H to one having generally the shape of the curve l6. Winding VJ may be secured in a properly adjusted position by a suitable coil cement, tape or the like. It is understood that the physical position of winding W may be altered to produce either an additive or substractive effect on the coupling between coils P and S as, by reason of the closeness of coupling between the primary cell P and one part of the winding W and between the secondary coil S and the other part of the winding W, the winding W can be adjusted to have considerable effect on the coupling between coils P and S so that it may be adjusted to the point Where it not only reduces the normally over-coupled condition between coils P and S to zero but actually produces a reversal of phase in the output of coil S. The two parts of winding W may be cross-connected, as shown, so that the part on form 2 opposes the secondary coil S or the part of winding N on form 2 may be wound in a direction to aid the secondary coil S when it is desired to increase the mutual coupling between coils P and S. The adjustment of W also can be used to compensate for stray coupling of coil leads or components such as condensers or resistors within the shield 4.
Variation of the mutual inductance of two circuits individually tuned to same frequency, substantially equally and simultaneously shifts the upper and lower resonant frequencies is and f4 toward or away from the median frequency. Consequently although the aforesaid adjustment of winding W may afford the desired band-pass requirements and shape of curve ill, the position of the frequency band passed may not exactly coincide in the frequency spectrum with the desired band because of manufacturing Variations or tolerances in self inductance of windings P and S.
Preferably therefore, the self-inductance of 3 each of windings P and S may be individually adjusted by cores l2 and I3 which may be of magnetic material, such as powdered iron, or of nonmagnetic material such as copper or brass, or in the who-1e or part of dielectric, the choice of Ina-.- terial depending at least in part on the position in the frequency spectrum at which the trans--' former is to operate. and 13, the upper and lower frequencies is and f4 may be individually shifted so that in combination with winding W, the desired band width and the desired upper and lower frequencies of the band may be accurately determined without need for precise manufacturing tolerances and construction,
As shown in Fig. 1, the cores may be mounted within-and rather closely fit the tubes l and 2 for adjustment by the rods l4, l5 which are engaged by threaded inserts, I5, l'l, Fig. 1 secured to the upper ends of forms I and 2. This transformer has the desirable feature that all freely variable tuning adjustments are from the same side of the transformer-and usually outside of the chassis, the winding W being fixedly secured in position by cement, tape, or the like when finally adjusted before the shield 4 is placed in position.
Preferably the rods l4, l5 of Fig. 1 and metallic parts electrically connected thereto are grounded through spring material 58 and the shield can 4 to avoid effects of external coupling and capacity during alignment.
In amplifiers used in television receivers for example where the band-width is large, for example 4 to 6 megacycles as contrasted with a maximum of 10 or kilocycles for broadcast recep-- tion, damping resistors, such as resistances l9 and 26, may be used.
By way of example, the dimensions of the transformer T for use at frequencies between 50-56 megacycles are as follows:
Overall height inches 1 /8- Overall diameter "inches" 1 Coil forms diameter inch Coil forms length inches 1 Coil form turns (#26 enameled -wire) 11 Center to center of coils PS inch Tertiary winding turns 2' Condenser C1, C2 mmf 7-10 Resistor pri ohms 1800 Resistor sec "ohms" 2700 From the foregoing dimensions, it is apparent that the coil forms I and 2 are spaced from each other about one-eighth of an inch. Thus, as can be seen from Fig. l, the two partsof winding W have very little .mutual inductance therebetween because the turns onform I arepractically in the same plane as those on form 2 and the crossed connections between them are very shortand cross each other substantially at right angles. The latter feature is of considerable importance in eliminating mutual inductance between the parts of coil as therecan be little inductance between very short leads and there is no inductance. between leads whichcross at right angles in that there can be no interaction between the magnetic fields surrounding such leads.
In absence of an oscilloscope and a sweepfrequency generator suited for wide-band alignment, a signal generator and output meter constitute the only test equipment needed for attainment of proper adjustment of the tertiary winding and cores.
The transformer exemplified in Fig. 4 is for use in an-oscillator circuit such for example as shfiwn By adjustmentof coresl2..
in Fig. 5. The construction of transformer T-1, is generally similar to transformer T of Fig. 1 and accordingly need only briefly be described.
The primary and secondary =coils P1 and S1 are Woundrespectively on forms l9 and 20 disposed side by side and extending from base 2|. Ordinarily the primary turns are fewer in number thanthe secondary but in any event the mutual coupling of these windings is purposely greater than" that required to sustain oscillations.
The mutual coupling may effectively be reduced in control of the feed-back voltage introduced by coil P1 into the tuned grid circuit Cs. S1, Fig. 5, by adjustment of the tertiary coil W1 which for ease of control is wound on tubular forms 26, 2'! slidable respectively along forms I9, 20 and connected by the insulating bridging member 28. The knob 29 and rod 30 connected to member 28 permit adjustment externally of the transformer shield can 3| of the position of the feed-back control link W1. Again the phase of the tertiary winding may be to aid or oppose the mutual coupling.
A similar transformer may be used in a regenerative or degenerative amplifier or detector stage in which the feed-back voltage may be determined or adjusted by a tertiary winding W1. Such transformer may for example be used to advantage in a regenerative detector circuit utilizing a screen grid tube, Fig. 5. Ordinarily in such circuit, feed-back is controlled by varyingthe screen grid voltage to maintain the operating point (i. e. below the threshold of oscillation). The chief difiiculty or objection is that the voltage supplied to the screen may not correspond with the operating point of the tubes characteristic curve affording the desired or maximum sensitivity. With the present arrangement the screen voltage may be set independently at a point for maximum. sensitivity and the feed-back independently controlled by adjustment of link Wi. In addition, this construction in common with that of the interstage transformer allows for a reduction on the physical size. of the unit andv elimination of need for close tolerances in manufacture.
Typical values for an oscillator or a regenerative detector embodied in Fig. 5 operating between 30-50 megacycles with tetrode V1 follow:
P1 6 turns (#22 wire) S1 15 turns (#22 wire) Forms diameter..
Spacing between coil centers l' 2 turns (#22 Wire on "forms) 250 micro-micro-farads (fixed) CZ 50 micro-microfarads (variable) R1 33,000 ohms (grid resistor) C3; .1"micro-farad (fixed) L1 High impedance choke 50.
henriesi compactness the primary and secondary windings are themselves overcoupled.
The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
What I claim is:
1. A structure comprising a radio frequency transformer including primary and secondary windings inductively coupled and disposed in close side by side relation with their axes substantially parallel, a two-loop closed circuit tertiary winding slidably mounted on said structure having at least one turn in each of its loops and one of its loops substantially coaxial with said primary winding and the other of its loops substantially coaxial with said secondary winding, said tertiary winding bein adjustable as a unit towards and away from adjacent ends of said primary and secondary windings to effect thereby a variation in the mutual coupling between the primar and secondary windings.
2. The radio frequency transformer of claim 1 in which the tertiary winding is arranged to produce a flux in opposition to the flux linkage between said primary and secondary windings.
3. The radio frequency transformer of claim 1 in which the tertiary winding is arranged to produce a flux aiding the flux linkage between said primary and secondary windings.
4. The radio frequency transformer of claim 1 includin means for determining the location in the frequency spectrum of the band of frequencies passed by said transformer comprising cores adjustable to vary the self-inductance of said primary and secondary windings.
5. A structure comprising a radio frqeuency transformer including primary and secondary windings inductively coupled and disposed in close side b side relation with their axes substantially parallel, means for determining the location of the frequency band passed by said transformer comprising means to adjust the self inductance of at least one of said windings, a twoloop closed circuit tertiary winding slidably mounted on said structure having at least one turn in each of its loops and one of its loops substantially coaxial with said primary winding and the other of its loops substantially coaxial with said secondary winding, said tertiary winding being adjustable as a unit towards and away from adjacent ends of said primary and secondary windings to effect thereby a variation in the mutual coupling between the primary and secondary windings.
6. The radio frequency transformer of claim 5 in which the tertiary windin is arranged to produce a flux in opposition to the flux linkage between said primary and secondar windings.
7. A. radio frequency transformer comprising first and second winding forms disposed in close side by side relation with their axes substantially parallel, a primary winding disposed on said first form, a secondary winding disposed on said second form substantially in juxtaposition to said first winding and inductively coupled thereto, a two-loop closed circuit tertiary winding having at least one turn in each of its loops and one of its loops disposed on said first form substantially coaxial with said primary winding and the other of its loops disposed on said second form substantially coaxial with said secondary winding, said tertiary winding being adjustable as a unit along said forms towards and away from adjacent ends of said primary and secondary windings to effect thereby a variation in the mutual coupling between the primar and secondary windings.
8. The radio frequency transformer of claim 7 in which the tertiary winding is arranged to produce a flux in opposition to the flux linkage between said primary and secondary windings.
9. The radio frequency transformer of claim 7 including means for determining the location in the frequency spectrum of the band of frequencies passed by said transformer comprising cores adjustable within said winding forms to vary the self-inductance of said primary and secondary windings.
10. The radio frequency transformer of claim 9 in which the tertiary winding is arranged to produce a flux in opposition to the flux linkage between said primary and secondary windings.
JOS. B. GAINER.
REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS Number Name Date 2,051,012 Schaper Aug. 11, 1936 2,106,226 Schaper Jan. 25, 1938 2,144,214 Below Jan. 1'7, 1939 2,206,041 Moore et a1. July 2, 1940 2,216,874 Case Oct. 8, 1940 2,258,147 Roberts Oct. 7, 1941 2,383,475 Dodington Aug. 28, 1945
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Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2802068A (en) * 1953-05-11 1957-08-06 Robert H Harwood System of impedance matching utilizing grounded-grid amplifier termination
US2889522A (en) * 1953-08-05 1959-06-02 Gen Instrument Corp Tuned transformer assembly
DE1062766B (en) * 1954-12-21 1959-08-06 Philips Nv Constantly changeable coupling device for two coils, preferably components of a two-circuit intermediate frequency band filter
US2953756A (en) * 1959-01-06 1960-09-20 Daven Company Inductive coupling of toroidal coils
US3283239A (en) * 1966-11-01 Precision solid state ratio bridge
US4315102A (en) * 1979-03-21 1982-02-09 Eberbach Steven J Speaker cross-over networks

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2051012A (en) * 1935-06-26 1936-08-11 Johnson Lab Inc Permeability tuning means
US2106226A (en) * 1935-06-26 1938-01-25 Johnson Lab Inc Coupling means for permeabilitytuned circuits
US2144214A (en) * 1935-07-26 1939-01-17 Philips Nv Band pass filter with variable band width
US2206041A (en) * 1937-08-12 1940-07-02 Rca Corp Variable tuned transformer
US2216874A (en) * 1937-10-29 1940-10-08 Hazeltine Corp Band-pass selector
US2258147A (en) * 1939-01-28 1941-10-07 Rca Corp Coupling circuit
US2383475A (en) * 1942-07-18 1945-08-28 Standard Telephones Cables Ltd Transformer

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2051012A (en) * 1935-06-26 1936-08-11 Johnson Lab Inc Permeability tuning means
US2106226A (en) * 1935-06-26 1938-01-25 Johnson Lab Inc Coupling means for permeabilitytuned circuits
US2144214A (en) * 1935-07-26 1939-01-17 Philips Nv Band pass filter with variable band width
US2206041A (en) * 1937-08-12 1940-07-02 Rca Corp Variable tuned transformer
US2216874A (en) * 1937-10-29 1940-10-08 Hazeltine Corp Band-pass selector
US2258147A (en) * 1939-01-28 1941-10-07 Rca Corp Coupling circuit
US2383475A (en) * 1942-07-18 1945-08-28 Standard Telephones Cables Ltd Transformer

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3283239A (en) * 1966-11-01 Precision solid state ratio bridge
US2802068A (en) * 1953-05-11 1957-08-06 Robert H Harwood System of impedance matching utilizing grounded-grid amplifier termination
US2889522A (en) * 1953-08-05 1959-06-02 Gen Instrument Corp Tuned transformer assembly
DE1062766B (en) * 1954-12-21 1959-08-06 Philips Nv Constantly changeable coupling device for two coils, preferably components of a two-circuit intermediate frequency band filter
US2953756A (en) * 1959-01-06 1960-09-20 Daven Company Inductive coupling of toroidal coils
US4315102A (en) * 1979-03-21 1982-02-09 Eberbach Steven J Speaker cross-over networks

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