US1855055A - High frequency transformer - Google Patents

Description

April 19, 1932. J. K. JOHNSON 1,855,055

HIGH FREQUENCY TRANSFORMER Original Filed Feb. .15, 1931 2 Sheets-Sheet A l ATTORNEYS Apri 19, 1932. J. K JOHNSON 1,855,955

HIGH FREQUENCY TRANSFORMER Original Filed Feb. 13, 1951 2 Sheets-Sheet 2 [55 /r/egacuy /f//Oycles /aer Serena? ATTnpN :vc

1. 515,560,1i1ed Feb. 13,1931.

v 50 fective coupling between the coils is reduced latented Apr. 19, 1 932 UNITED STATES Parrsur OFFICE JonN 'KELLY JoHNsoN, or nAarsDALE, NEW Yoan, assrGNoa ro HAzELrnm conf rona'rroN, A coarom'rrou or DELAWARE HIGH FREQUENCY TRANSFOBMEB Original application iiled February 1d, 1931, Serial No. 515,560. Divided and this application led y'February 28, 1931.

for use inl amplifiers of medium-high fre lo-quencies, such as .the intermediate-fre uency1 amplifier of a superheterodyne typeo radio receiver.

This application is a division of my conding original application, Serial .No.

The princi al object of this invention is to adjust the egree of coupling between two circmts of a carrier-frequency coupling sys'- tem to the pro r value to rovide a high degreeof ampli cation, uni orm transmission and good selectivity.

Another object is to provide a coupling system which shall be compact, inexpensive and easily adjustable? z5 l The, coupling systems contemplated in this invention comprise an input circuit which is connected to a pair of input terminals Vand an out ut .circuit which 1s connected to a pair o output terminals. The input and output circuits each include an inductance tuned by` a capacity; these inductance elementsare coils ,which are spaced in close relat-ion to4 each other so that there exists a vsubstantial degree 'of magnetic coupling therebetween. The coupling system will generally be connected between the output of one tube of a high-frequency amplifier and the input of a succeeding tube. There may be two or more-of these coupling systems coupled in tandem. f y

-An important feature of the invention is the provision of an electrical conducting shielding arrangement surrounding, or partially surrounding, both coils. This shielding arrangement has the eect of reducing the degree of coupling between the inductances of the input and output circuits to a lower value than would exist in the absence of the shield. The amount by .whicli the ef- Serial No. 518,986.

by virtue of the shield, depends upon the form and separation of the coils and upon the spacing of the shield from the coils.

ln high-frequency transformers heretofore employed which comprise primaryand secondary windings each of which is tuned to the same frequency by fixed or adjustable capacities, it has been found necessary, where Y relatively loose coupling between circuits is required, to physically space the coils a considerabledistance apart, or in the alternative, to provide an auxiliary element between the windings to reduce the electromagnetic coupling. If this relatively great spacing between the coils is not provided, or if there is present no' auxiliary means for reducing thecoupling, there results the well-known effect of double resonance which makes it impossi- 'ble to tune the system to a single frequency.

Thereactionofonecirc ituponthe other produces the two resonant peaks of which differs from the frequencyto which each coil is individually tuned. When the electromagnetic coupling between the two circuits is decreased, the frequency difference between theseresonant peaks decreases, so as opti'- mum coupling is approached, the double resonant peaks merge into the single resonance.

It has been found possible to vary the effective coeicient o electromagnetic coupling and hence the mutual inductance between the coils within wide limits by vary-- ing the relative sizes of the shielding ring and of the coils and the spacing between coils. By arranging the shielding ring close tothe coils it is possible to locate the coils in close proximity to each other while at the same time maintaining absolute control over the leffective coefficient of coupling and the mutual inductance betweenv coils, and hence the 9o reaction of one circuit upon the other. Practically, it is possible to sb arrange the elements of the coil structure that it is small, compact and inexpensive to manufacture.

Of the drawings: l

Fig. 1 illustrates a radio receiver of the superheterodyne type in which the intermediate-frequency amplifier employs coupling systems of the type of this invention; Y

Fig. 2 illustrates the construction ofthe in- 10 eol ductances and the arrangement ofthe shielding`of the coupling systems;

ig. 3 shows graphically how the ratio of the coil separation to the coil dia-meter affects the effective coefiicient of coupling between the coils;

y Fig. \4 shows graphically the change in effective electromagnetic coupling as a function ofthe ratio of the coil diameter to the diameter of the shielding ring;

5 shows transmission characteristics of the coupling system with and Without thel shield.

Fig. 1 illustrates a conventional type of superheterodyne radio receiver. embodying the invention. The receiver comprises an ani tenna circuit 10 connected to a radio-frequency amplifier shown in generalized form as the rectangular 11. The output of the radio-frequency amplifier is associated with a local oscillator indicated in generalized form by the rectangle 12. The local oscillator and the radio-frequency amplifier are connected in the input of a vacuum tube modulator 13, theA purpose of the modulator being .to modulate the amplified signals from the amplifier with the oscillationsfrom the local oscillator. The construction of a local oscillator and of an amplifier for this purpose and the manner of their connection in the input circuit of the modulator are well understood in the art, and require no further `discussion here.

The modulator tube 13 is of the four-electrode type comprising an anode 14, a cath.- ode 15, a control grid 16 and avscreen grid 17. The modulator 13 operates in the well understood manner upon the signal voltage and the local oscillatorvoltage to' produce a signal in its output having a carrier frequency which is the difference between the frequency of the radio signal and the frequency of the local oscillator. Since this difference in frequency is lower than the frequencies of the radio signaling range, itis called an intermediate frequency.

Thegoutput of the modulator is coupled to the input of'an intermediate-frequency amplifier 18 through a coupling system 19. The' amplifier 18 is also of the four-'electrode type and includes an anode 20,- a cathode 21, a control grid 22 and ascreen grid 23.. The output of the intermediate-frequency amplifier is coupled to a detector tube 24v through loudspeaker 31.

a coupling system 25. The detector tube, which is also of the four-dt\\'o `le type, includes'an anode 26, a cathode 27,`a control grid 28 and a screen grid 29. The output of the detector feeds into an audio-frequency amplifier represented by the rectangle 30. The output of the audio amplifier operates a There are illustrated no seni-ces of operating potentials for the various electrodes of the vacuum tubes of the receiver. The manner of applying these energizing potentials is well understoodin the art and since it constitutes no part of the present invention, these sources are not illustrated.

The feature of this invention resides in the coupling systems 19 and 25 associated with the intermediate-frequency amplifier. The coupling system 19 comprises two circuits, the first of which is connected in the output of modulator 13 and the second of which is connected in the input of amplifier 18. The first circuit includes an inductance 32 shunted by a fixed capacity 33, connected in the anode circuit of modulator 13. The second circuit includes an inductance-34 shunted by a .greater detail.

The coupling system 25 'in the output of the intermediate-frequency amplifier 18 is similar in its circuit arrangement to coupling system 19; it includes inductively related inductances 37 and 38 situated respectively in the output circuit of the amplifier '.18 and inthe input circuit of the detector 24. The inductance 37 is shunted by a fixed condenser 39, and inductance 3S is shunted by fixed condenser 40. Y f I Fig. 2 illustrates in cross-section the construction and assembly of the inductively related inductances and the associated shielding ring, of coupling systems 19 and 25. The arrangement comprises coils 41 and 42 random wound, or layer Wound, respectively on bobbins 43 and 44. The bobbins are fastened over a core 45 which is adapted to be fastened to a base, or chassis, by brackets 46 and 47. Coil 41 is the `anode circuit coil and coil 42 is the grid circuit coil. The coil terminals marked A, B, C and D, represent respectively the connections to the anode, the B- battery, the cathode and the grid of the associated tubes. Surrounding the bobbins containing the coils is a cylindrically-shaped shielding ring 48 closed at .the upper end and adapted to be fastened to the base at the other end. The shield-ing ring is preferably heavy copper or aluminum or other metal having low specific electrical resistance; Any joints used in completing the ring should be of very low resistance, so that the total electrical resistance of the entire ring is very low. The

Yshielding ring is located in close proirimity s to the coils so that there exists a substantial coupling between the ring and the coils. Signal current flowing through one of the coils produces a magnetic eld which interlinks. with the turns of the second coil and with the shield. Currents are thereby induced in the second coil and in the shield. The current induced in the shield, in turn, produces a magnetic field which is approximately oppositein phase to the field of the first coil. As a result, the Idegree of coupling between the two coils is reduced to a lower value than would exist in the absence of the shield.'

Due to the close.l spacing between the shielding device andthe coils and because of the low resistance of the shielding device, the coefficient of coupling between the coils and the shield will usually be greater than that 4between the two coils. It has been found possible, in fact, to reduce the effective .magnetic coupling between coils practically to zero. v

The dimensions of the` coils will, of course, be'idependent upon the intermediate frequency'which the amplifier is required to transmit. The following table gives a suitable design for a coupling system for transmitting a carrier frequency of 175 kilocycles per second, and the associated sidebands, this frequency having been found highly satisfactory for the intermediate frequency of a superheterodyne receiver:

Diameter of core-1/2.

Each winding-900 turns, #38 B. & S. gauge. double silk covered fcopper wire.

Vidth" of each coil-l.

Distance between coils-fig.

Outside diameter of each coil- Q.

, Inside diameter of shieldingring--1%.

Length of shielding ring-1%.

The above dimensions will provide a coil structure having an inductance of about 8.8 millihenries in each` coil; the effective coefficient of coupling between each coil will be about four percent. In order to cause .each o the coils to be resonant at a frequency of 175 ilocycles, the fixed capacity shuntmlcro-farads. Fig. 3 illustrates a family of curves which indicate-the relationship of the effective coefficient'of coupling between coils to the ratio g of the separation between coils tothe outside diameter of the coils.. In this figure curve' a illustrates the variation of the effective coefiicientof coupling between coils in the absence of any shieldi-ng ring. Curve b illustrates the variation in the coefficient of coupling when the coils are placed 'within a shielding ring which is so proportioned that the inside diameterl of t e ring is one and 4one-third times the'outside coil diameter. Curve c indicates the variation in 6 vthe 'effective coefficient of coupling when the .having the design ing -each coil should be about 100 micro` yamplification characteristic when the shieldmij inside diameter of the shielding ring is two times the outside coil diameter. A casual inspection of the curves of Fig. 3 shows that the effective coupling between the coils bef comes smaller when the distance between coils becomes greater relative to the outside coil diameter.

Fig. 4 illustrates another family of curves which may be derived from the curves of Fig. 3 and which show the effect" of the diameter 75 of the shielding ring upon the effective electromagnetic coupling between the coils. ln this figure the effective coefficient of coupling is plotted against the ratio of the inside diameter of the shielding ring to thefoutside 8o coil diameter. Curve a shows the variation of the effective coefficient of coupling between the coils when the distance between the coil centers is one-half the outside coil diameter. Curve b illustrates the varia- S5 tion inthe effective coefficient of coupling when the distance between the coil centers is three quarters of the outside coil diameter. Curve c indicates the variation when the distance between coil centers is equal to the outside coil diameter. f The curves of Figs. 3 and 4; are experimental curves obtained from the coil structures constants given `in the above table; 95

Experiments with coil and shielding ring structures of various sizes and shapes have indicated that the most important variables are the ratio of the-inside diameter of the shielding ring to the outside coil diameter, and the ratio of the coil separation to the outside coil diameter.

` The most .favorable ratios of theQ inside shielding ring diameter rto the outside coil diameter lie between one and two. The spacing required between coils is spbject'to 'variation', dependent upon the desired coefficient of coupling and hence the mutual inductance `required, the power'factor of the coils. the form factor of the coils, and the diameter of the shielding ring. When the coil structure is proportioned in accordance with the above table, favorable results are obtained when the spacing between the centers of the coils does not exceed the meanY diameter of either coil. Where the radius of the core itself is equal to orgreater than the depth of winding of the coil'` the spacing between centers of the respective coils may be reduced.

to a distance which' is ofthe same order off-'31225 magnitude, as one-half of the mean diameter of the coil. lt should be understood that the above mentioned preferred proportions should not be construed to be limitations upon the invention, but are given to indicate how favorable resultstmav be obtained.

Fig. 5 illus-trates amplification vcharacteristics of la coupling system such-as 19 and 25 of Fig. 1.-- Curve fa of Fig. 5 illustrates the- -ing ring is removed; the coupling coeilcient `in'this case is about 15%. This is the condi- By the term optimum coupling is meant that degree of coupling between the input and output circuits of a vcoupling system which will provide the maximum amplification. It is well known that when the coupling between a pair of syntonously tuned circuits of a coupling system is optimum, or less than optimum, the system is characterized by" a'single resonance. When the coupling becomes greater than optimum, the resonances s read, giving rise to the doubleresonance e ect. The distance in the 'frequency scale between the two resonances is greater, the greater the degree of coupling;

so it is possible to obtain any desired spac-l ing byv adjusting the coupling by means of the shield.

of frequenciesyother design conditions require that there be a single resonance. It is within the contemplation of this invention to'provide either type of resonance characteristic. It is clear that whether a double resonance effect or'a single resonance e'ect is to be obtained, the required coeicient of coupling is quite critical. This critical value can be readily obtained in accordance -with this invention, by suitably proportioning the dimensions of the shielding ring in relation to the coil dimensions.

Although there is illustrated in Fig. 1 only oneA double tuned coupling system between each successive tube, there are instances where it is desirable vtoprovide more than one such double tuned system between stages. A plurality of double tuned systems may be coupled either inductively or capacitively in tandem between successive Vacuum tubes.

Although the coupling' systems have been described as being particularly well lsuited for use in the intermediate frequency amplifiers of superheterodyne receivers, the in- -vention should not be construed to be limited to such receivers. The coupling systems of thisr invention are equally applicable to radiofrequency amplifiers and to .any other highfrequency s stem.

Y What is c aimed is: l"

VY1. "Ah'gh-frequency coupling syzem comprising two coils and a shielding device, said coils being electroma etically coupled to i each other and having t cir centers separated by a distance which is between one-half and two times their outside diameters, said .shield- -ing device surrounding said coils, the diameter of said shielding device being of the same order of magnitude as the separation between the coils whereby lthe coupling between said coils and said device is substantially greater than the coupling between said coils.

2. A high-frequency transformer comprising a primary coil, a secondary coil and a shielding ring, said coils being multi-layer wound, the distance between the centers of said coils being no greater than the outside diameter of .said coils, and said shielding ring surrounding said coils, the ratio of the inside diameter of said shielding ring to the outside diameter of said coils being no greater than r 3. A high-frequency transformer compris# ing a primary-coil, a secondary coil yand a shielding device surrounding said coils, said'- shielding device having an lelectrically conducting surface situated no further from said coils than half the coil diameter, said coils Y being spaced apart by a distance no less than the approximate radial depth of said windings,whereby the coeiiicient of coupling between said coils and said ring is greater than the coeicient of coupling between said coils.

4. A high-frequency transformer comprising a primary coil, a ,secondary coil and a 'shielding ring, the coefficient of coupling between said coils being about 15 per cent in theI absence of said shielding ring, and said shielding ring closely surrounding said coils by a distance suicient'to reduce the effective coecient 'of coupling between said coils to about 4'per cent. l

5. -A high-frequency transformer compris- -ing a pair of coils, each of said' coils being wound in layers, said coils being co-axially situated and separated from each other by av diameter of said coils, said' shield being placed closely around' said coils so that the coeicient of coupling Abetween one of said coils and said shield is greater than the coeilicient of coupling between said coils would be in the absence 'of said shield.

7. A shielded' high-frequency transformer according'to claim 6 in which said coils are wound with approximately the same number ofturns.

8. A carrier frequency transformer adapted to transmit a carrier wave and side bands corresponding to voice waves comprising a pair of coils placed in such close inductive relation to each other that when said coils are acting alone, transmission of signals through them is characterized by `a pair of resonance peaks, a low resistance shielding means surroundinv said coils and having a diameter less than twice that of said coils whereby said resonant peaks become more closel spaced and are separated by a frequency iference no greater than the frequency range of said side bands.

In testimony whereof I ax my signature.

J. KELLY JOHNSON.,

DIS'OLAlMr-:R

1,855,055.-Jm Kelly John son, Hartsdale, N. Y. HIGHFREQUENCY TRANSFORMER. Patent dated A prll 19, 1932. Disclaimer tiled March- 26, 1937, by the asslgnee, Hazeltzne Corporation.

Hereby enters this disclaimer to claims 1 and 8 of said patent.

[Qic'ial Gazette April 20, 1.937.]

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