US2631192A - Permeability-tuned coupling unit - Google Patents

Description

March 1953 G. w. WALLIN PERMEABILITY-TUNED COUPLING UNIT Filed March 6, 1948 INVENTOR Gus W. Wallin Patented Mar. 10, 1953 UNITED STATES PATENT OFFICE PER-MEABI LITY- TUNED OUPLING UNIT Gus .-Wailin, Chicago, 111., assignor to Motorola, .Inc., Chicago, Ill.,-a corporation oflllinois Application March 6, 1948,"Serial No. 13,469

2 Claims. 1

"This invention relates to permeability-tuned coupling units employed in radio sets and the like. Aspecific example of such a couplingunit is-an intermediate-frequency transformer having -movable, low-loss'iron cores, and the description of the invention contained herein is, forillustrative purposes, particularly directedltoa transformer of that'type.

A permeability-tuned 'inteimediate-frequency transformer, in commonwith other intermediatefrequency transformers, includes a .coil-and-capacitor assembly mounted in a shield can to prevent stray electromagnetic fields from being picked up by the transformer. As constructed heretofore, such a transforrner has included 'a tubular-coil form f molded plastic with a specially built, fiat capacitor carried by the base of the iorm. lron'cores or slugs are mounted in the -coil formin such mannerthat'they may be moved axially thereof to vary the .inductances of the coils when'tuning the transformer .to the desired intermediate frequency. The screw r adjustments "for the slugs customarily have-been mounted on the ends-of the coil form.

Oneo'f the problems attending'the' use of such "transformers has been the I difiiculty 1 of obtaining the needed coil inductances within rather close :space" limitations. Thus, there have'been practicallimits asto the maximum size ofshield cans "and the-minimum size of coil forms and coils in prior constructions. Because of these :factors, the shield can of the transformer unavoidably was-included iill the magnetic field of the coils to an extent where it appreciably.affectedzthe'coil characteristics. in such instances,.the shield can would actin a: short-circuited transformer winding, reducing :the effective ainductances of th coils. To overcome this undesirable.efiect,:it.has lbeen proposed to provide .the: shield can with .an inner sleeve or lining of powdered iron .toincrease the coil inductances and divert most of themag- -netic fiui: from the :shieldcan, thus preventing the can .from acting as a. shortecircuited turn. Such provisions, of course, add substantially "to the cost-of manufacturingthese coupling units.

Itis an object of the present invention toprovide an improved permeability-tuned intermediate frequency unitwhich isof inexpensive con- :struction.

"furthercbject is' to provi'de an' intermediate- "frequency 'unit' which is 0f simple construction andwhich includes. a'minimurn' number of "parts.

A'still' further object is'to provide anirn'prove'd capacitor onthe 'base of the coil' form.

. Ai'ieature of the invention consists of replacing the ..usual mol'ded..plastic coil i form and Ltuning :accordancawith land embodying the principles-10f .construction shown islugs respectively with -a plastic "impregnated, wound paper tube and with tunin slu s which 'have direct screw threaded engagementwiththe tube. The tuberhas ,an-extremelythin Wall-n50 that close coupling is afiorded between thelslugs and the-windings or coils of the transformer. -Alsogithe tube is not requiredto support the clips which formerly held the-adjusting screws. Therefore, both the coils and the slugs may-be made quite small in diameter, :greatly -increasi1 1g-athe space between the coils and the .sidesof theshield Another feature of the invention :is the novel capacitor assembly comprising, .for -example,.-a that micapiece silvered on both sidestoprovide -,capacitor plates and mounted directly one-aloeiramic base to which it is securedby .the .base

terminals. This condenser is very:low-.in costby comparison with the type of capacitor aformerly employed.

It has been found that the new unit constructed in accordancewith my invention. costs considerably-less than therexisting-units. available forthis purpose,-=and has equal or better performance.

The foregoing and other objects features and advantages of-the. invention will beapparentfrom a studygof the, specification taken in connection with the accompanying drawings,in which:

tFig. 1 is a vertical sectional view of am-intermediate-frequency transformer constructed in the invention;

.Fign2 'is-a crossesection'on :the lineE-2-.,2 in

Fig. 3 is a longitudinal section through a paper tube coil form which may be employed in the in Fig. .1;

Fig. .4 is a cross-section on s- 3 Fig. isa perspective view ofithe flatcapacitor assembly employed in the transformerpfTEigJl;

Fig-6 1s aplan view of aspringclipused n the transformer of'Fig..1

Fig. is a longitudinal. section throughia modified co1l form --Wh1Ch may be usedinlieuofflthat shown m Fig. 3;

'Fig. 8 isa plan view inFig. 7;

' Fig. 9 is .a verti al sectional view of an L. other embodiment of the invention;

,Fig. 10 1s a cross-section..onlhelline fl0.1l.0 in

the line i l-41in vof the coil form .shown ace 1,192

Fig. 11 is a bottom view of the transformer looking from below the chassis on which it is mounted. In practicing the invention, the stationary coils of an intermediate-frequency transformer are mounted on a thin-walled, small-diameter tubular coil form made of insulating material that is capable of being indented, such as plastic impregnated paper. Screw-threaded tuning slugs are disposed within the coil form, which is indented to cooperate with the threads on the slugs. Flat, fixed capacitors are mounted directly on an annular insulated base which i secured to one end of the coil form. The capacitors comprise a common sheet of dielectric material such as mica which is silvered on both sides to afford condenser plates. The terminals of the unit, which are connected directly to the silver coatings on the mica sheet, serve to secure the capacitors on *the base. The coil-and-capacitor assembly is mounted in a shield can and locked into place. '"Access to the tuning slugs can be had from either 'end of the coil form by inserting a screw driver therein.

Referring now to the drawings, the embodiment of the invention shown in Figs. 1 and 2 comprises a tubular coil form 52 on which are mounted stationary coils M and 15, one of which constitutes the primary winding and the other the secondary winding of the transformer. Tuning slugs or cores of powdered iron or other suitable low-loss magnetic material, indicated respectively by the reference numerals i8 and 20, are asso- '-'-ciated respectively with the coils it and it. The slugs l8 and 253 are disposed within the tube l2 and are provided with external screw threads. The tube 12, in accordance with the invention, is made of an insulating material which, while thin, can be indented without breaking. A suitable material for this purpose is spirally wound paper impregnated with a plastic composition. The tube i2 is indented to cooperate with the threads "of the slugs l8 and 28 so that the same can be positioned longitudinally of the tube 12 by tuming them.

One manner in which the tube 12 can be indented to provide a track for the screw threads of the slugs l8 and 26 is illustrated in Figs. 3 and 4. -As there shown, transverse notches or indenta- -"-ti'ons 22 are formed in the tube at regularly spaced intervals corresponding to the pitch of the screw threads. Opposite each indentation 22 there is a corresponding internal rib or projection 24 within the tube 82, and the screw threads of the slugs 3 l8 and 20 track in these ribs and the intervening valleys, In Figs. '7 and 8 there is shown a modified coil form 26 which has longitudinally extending indentations 28 to provide ribs or ridges 30 running lengthwise of the tube 25 interiorly thereof. These ridges 363 preferably are spaced apart about 120 degrees. Being readily deformed, they yield to thethreads of the tuning slugs as it and 2%,

"Fig. 1, so that the slugs cut their own tracks in the coilform 26,

A disc-like annular base 32, Figs. 1 and 2, is fitted on one end of the coil form I2 and is cemented or otherwise suitably secured thereto. *Mounted directly on the base 32 are the fixed capacitors 36 and 38 which are associated with the coils M and it of the transformer. A sheet or washer of mica or other suitable dielectric *material, Fig. 5, has conductive coatings on both sides thereof to afiord the plates or the capacitors.

"Preferably, these coatings are films of silver which are printed on the mica washer 34.

Thus, the capacitor 36 has a plate 38 which consists of an arcuate silver coating on the upper side of the washer 34, and a plate 40 consisting of an arcuate coating on the underside of the washer 34. The plates 38 and M? are arranged so that they are in partially offset relation. Another capacitor 38 comprises plates 42 and 44 on the upper and lower faces of the washer 34, respectively, each of these coatings consisting of an arcuate strip of silver. The plates 42 and 44 likewise are arranged in staggered or partially oifset relation.

The soldering terminals of the transformer are mounted on the base 32. These terminals consist of external lugs 46 projecting outwardly from the base 32, and inner lugs 48 to which the leads from the coils l4 and it are connected. Each terminal comprises an outer lug 46 and an inner lug 48 connected together by a hollow rivet or eyelet 59 which passes through an aperture in the base 32. This construction enable the capacitors and terminals to be assembled on the base in a single eyeletting operation. Certain of the rivets 50 are in electrical contact with the coatings 38 and 42, while other rivets 50 contact small coating segments 52 which are spaced from the plates 38 and 42 on the upper side of the Washer 3A opposite the offset ends of the coatings 40 and i l on the underside of the washer 34. The rivets 56 which are engaged with the coating segments 52 also have edge contact with the coatings 0r plates ii! and id. At the frequencies for which these units are used, there is established a good electrical connection between these terminals and the lates 4% and 44 by virtue of this arrangement. Coating segments 54 are provided on the underside of the washer 34 to correspond with the segments 52 so as to afford uniformity and enable the washer 34 to be used either in the position shown or in an inverted position.

The coil and capacitor assembly thus far described is adapted to be mounted in a shield can es, Fig. 1, which is open at its lower end and is closed at its upper end except for a small aperture through which the coil form or tube !2 projects. The illustrated shield can 60 is of the type which is adapted to be secured permanently on a chassis 62, and the coil-and-capacitor assembly is inserted therein through the opening in the chassis 62. Mounted on the tube I2 near the upper end thereof is a spring clip 66, shown in detail in Fig. 6, havin resilient arms 66 that are adapted to bear against the closed end of the shield can 66 when the coil-and-capacitor assembly is inserted therein. The base 32 may be of the twist-lock type shown, for example, in the copending application of Rudolph A. Becwar, Serial No. 651,399, filedMarch 1, 1946, now Patent No. 2,483,801, issued October a, 1949. The spring arm 6% resiliently press the base 32 against the retaining lugs 68 on the chassis 62 when the base 32 is turned to its locked position. The precise form of the transformer mounting, however, is merely incidental as far as the presen invention is concerned. 1 y In Figs. 9, 10 and 11 there is disclosed a portable transformer in which the shield can 10 is removable from the chassis 12. The coil form 14 is similar to the coil form E2 of Fig. 1 or the coil form 26 of Fig. 7, except that it is still smaller in I therein as in the previously-described embodiments. An annular base 84, preferably of ceramic insulating material, is secured on one end of the coil form 14. The can I has a circumferential bead 86 which bears against one side of the chassis 12, and the base 84 has lugs 88 and 90 which extend through recesses in the end portion of the shield can 70 and bear against the other side of the chassis 12. A retaining clip 92, Fig. 11, extends across the underside of the base 84 and is received in apertured lugs 94 on the end of the shield can I0 to lock the entire transformer assembly in position on the chassis 12.

The base 84 (as in the embodiment of Fig. 1) carries a pair of fiat, fixed capacitors which are electrically connected to the coils I6 and 80. Arcuate silver coatings such as 96 and 98, Fig. 10, on both sides of a mica washer I 00 are electrically connected to hollow rivets or eyelets I02, each of which connects together an outer lug or terminal I06 and an inner lug or terminal H0. The base 84 is recessed to receive the anchor portions of the lugs I06, as indicated at H2, Fig. 11. This prevents the lugs I06 from turning and increases the resistance of the leakage path between terminals. Since the base 84 is not of the twist-lock type, the coil form I4 need not be provided with a spring clip such as 64, Fig. 1, although one may be used if desired.

The tuning slugs I8 and 20 of Fig. 1, or 80 and 82 of Fig. 9 are conveniently adjusted by inserting a screwdriver into either end of the tubular coil form, which guides the tool into engagement with the slugs. The outer ends of the slugs are slotted to receive the blade of the screwdriver.

The invention substantially reduces the costs of the coil form, tuning slugs and shield can by virtue of the new coil assembly. The improved base and capacitor assembly likewise effects substantial savings in cost. Thus, a considerable overall economy results, without any sacrificing of utility and with improved performance in some respects.

While certain specific embodiments have been disclosed herein, these obviously are capable of modification without departing from the spirit of the invention, and it is intended to cover all such modifications in the appended claims.

I claim:

1. A permeability tuned coupling unit adapted to be disposed in a shield can, including in combination, a disc-like insulating base, an elongated coil form secured to said base and extending on one side thereof, at least one coil mounted on said form, capacitor means positioned on said one side of said disc-like base and comprising a dielectric sheet and first and second pairs oi. conducting coatings thereon, said coatings of each pair being on opposite sides of said sheet and including rela tively close spaced portions having capacity therebetween and terminal portions individually offset with respect to each other, said first and second pairs of coatings being ofiset with respect to each other so that said terminal portions are spaced about said base, and at least two pairs of terminal means securing said dielectric sheet to said base and having portions extending on either side of said'base, each of said terminal means extending adjacent said sheet and engaging a terminal portion of different ones of said conducting coatings to provide electrical connection therewith, said terminal portions extending on said one side of said base forming means for interconnecting said coil and said capacitor means, and said terminal portions extending on the other side of said base forming means for making electrical connections to said coupling unit.

2. A permeability tuned coupling unit adapted to be disposed in a shield can, including in combination, a disc-like insulating base, an elongated tubular coil form secured to said base and extending on one side thereof, first and second coils mounted on said form, first and second magnetic cores supported within said coil form and individually movable with respect to said coils, capacitor means positioned on said one side of said disc-like base and comprising a mica sheet and first and second pairs of conducting silver coatings thereon, said coatings of each pair being on opposite sides of said sheet and being partially offset with respect to each other so that each pair includes relatively close spaced portions having capacity therebetween and terminal portions individually oifset with respect to each other, said first and second pairs of coatings being offset with respect to each other so that said terminal portions are spaced about said base, at least two pairs of terminal means securing said sheet to said base and having portions extending on either side of said base, each pair of said terminal means extending through said sheet and individually engaging the terminal portions of one pair of said conducting coatings to provide electrical connection therewith, and mean connecting said portions extending on said one side of said base 01' each pair of said terminal means to one of said coils, said terminal portions extending on the other side of said base forming means for making electrical connections to said coupling unit.

GUS W. WALLIN.

REFERENCES CITED The following references are 01' record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,479,315 Pickard Jan. 1, 1924 2,035,439 Crossley Mar. 24, 1936 2,055,431 Garvey Sept. 22, 1936 2,111,490 Jacob Mar. 15, 1938 2,318,415 Patzschke May 4, 1943 2,417,182 Sands Mar. 11, 1947 2,435,630 Ketcham Feb. 10, 1948 2,447,002 Faust Aug. 17, 1948 2,462,822 Wood Feb. 22, 1949 FOREIGN PATENTS Number Country Date 675,421 Germany May 11, 1939 516,924 Great Britain Jan. 16, 1940 578,218 Great Britain June 19, 1946

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