US2477979A - Dual band permeability tuning unit - Google Patents

Description

Aug.

A. M. HADLEY DUAL BAND PERMEABILITY TUNING UNIT Filed Aug. 17, 1946 lllllllllllllllull INVENTOR ALLAN M. HADLEY BY KW ATTO RN EY Patented Aug. 2, 1949 UNITED STATES PATENT OFFICE DUAL BAND PERMEABILITY TUNING UNIT Allen, M. Hadley, Longmeadow, .Mass., assignor to The F. W. Sickles Company, .Chicop ee, Mass, a corporation of Massachusetts Application August 17, 1946, Senial No; 691,294

I 5. Claims. 1

This invention relates to a permeability; tuning unitzcapab'le of: simultaneously tunin two separate frequencyxbands.

The; employment of. magnetic cores movable witinrespect to? inductance coils in. order to vary the: inductanceof. the: latter and, thus. tune the circuit mwhich the coil-is included is well known. 'It'uning: devices embodying this principle have fbundi'considerabie:acceptance in the radiofield, comparatively:simpletunits of the type described nepla'cin'gathe more expensive conventional rotary variablecondenser tuningunits. The acceptance and impnrtancaof: the permeability tuned units has: been marked. in the. manufacture of small mdio.=.recciving sets. The present trend of the industryisto maketh'ese. sets still smaller and lightenso. thatthey may: be carried by the user ina': convenient manner wherever the user may get-- In-the manufacture of such sets, space and weightconsiderations are critical and it is in conjunction With==such a set' that the present invention offers exceeding fine commercial possibility. It may, however, be employed in any type of receivingorsending set, its employment bringing' with it improved: simplicity of construction, easier maintenance and a considerable decrease in cost when-compared with sets employing conventional tuning units.

The tuning structure of the present invention is so-const ructed as, with asingle mechanical drive, to'tune two separate inductance coils each of whi'oh may be employed for the reception of a -separatefrequency band, such as the commerclal and shortwave broadcasting bands or the commercial amplitude modulated and frequency modulated broadcasting bands. The choice betweenthe two frequency bandscan be made by suitable switches in a manner well known to the art;

It is a prime object ofthe present invention to provide a: tuning device which will function as abovedescribed; which is of simple and inexpensive construction, and the use of which involves.-a;.c'onsiderably saving in size, weight and expensera'szcompared. with tuning units as heretofore knownevenas compared with prior permeability, tuned units;

Another object of the-present invention is to provide in such a tuning unit a means for so adjustingthe unit" as toachieve accurate trackin'g'. between the: tuning of thetwocoils. This featuremay be of particular importance in cases where the'two coils areto besimultaneously emplayed: in: applications where a fixed difierence betwecmtheresonant frequencies is to'be maintinned, inz the detector and. oscillator. circuits ofisuperheterodynew receiving: sets.

Itzisa stills anotheraobject of the present inventiom-tmpmvide such a .devicewith which. ampli- 2. tudemodulated. and' frequency modulated broadcasting. bands can be simultaneously tuned.

To the accomplishment of the foregoingv ob-' jects and such other. objects as may hereinafter appear, the present invention relates to a dual band permeability tuning unit as defined in the following claims and as described in this speciiicaticn, taken together with the appended drawings, in which:

Fig. 1 is a perspective exploded View ofone embodiment of the tuning. unit of the present in vention';

Fig. 2,.is a cross-sectional view taken along the line 2-2 of Fig. 1 when the tunin unit is in its assembled and telcscoped position;

Fig. 3 is a perspective view of anotherembodrment of the magnetic shell particularly adapted for frequency modulation tuning; and

i is across-sectional View of the movable element of the. tuning unit taken in the direction of the line l4 of Fig. 2.

The tuning unit comprises a coil support, generally designated A, upon which two coils B and C are concentrically mounted. As used in this specification; the term concentric mounting refers to a. construction in' which the coils have the same axis but. have difierent radii of curvature and in which the coil having the greater radius of curvature at least partially surrounds the coil havingithe lesser radius of curvature. Ashere illustrated, coil C has a greater radius of curvat-urethan coilB; It will be understood that the coils neednot be circular, in which case the term internal dimension rather than radius of curvature will apply.

For simultaneously tuning the two coils B and C there is employed a pair of elements of magnetically permeable material comprising a core D' which is of such a size as to be movable within thecoilB in: the direction of its axis and a shell E movable between the two coils B and C at the same. time and. in the same direction as the core D. A means F, which may be attached to any suitable mechanical drive (not shown), is provided to which the two magnetic elements D and. E are fastened so as to be simultaneously movable withrespect to the coils B and C. It will be apparent,however, that the same result could be achieved were the magnetic elements D and E' stationary and the coils B and C appropriately moved.

In order to control the tuning of the device and particularly in order to achieve tracking between the tuning of the two coils B and C, a means G may optionally be employed to adjust theposition of the magnetic core D and the mag netic shell E with respect to one another. This may; Of'iC0l1IS8, be accomplished-by moving either one. or both. Ofi the magnetic elements D and E 3 independently with respect to the support F upon which they are mounted.

Another optional constructional feature is the employment of a sheath H of non-magnetic concluctive material around the magnetic shell E.

By the construction above described, it is possible by moving the means F to simultaneously move the magnetic elements D and E with respect to the coils B and C, thus simultaneously varying the inductances of both of the coils. Insofar as the inner coil B is concerned, its inductance is affected both by the core D and the shell E. The shell E apparently provides an increase of approximately 10% in the effective inductance of the coil B over a situation in which the core D alone is employed.

With respect to the coil C, the shell E is the primary tuning element, it having been noted that the inductance of the coil C is not appreciably affected by the presence or absence of the core D.

Thus it may be seen that while the position of the core D with respect to the coil C has relatively no effect upon the inductance thereof, its position with respect to the coil B is of primary importance in determining the inductance thereof and it will also be noted that the position of the shell E with respect to the coil B has only a minor effeet, while its position with respect to the coil is almost completely determinative of the inductance thereof. On the basis of these observations it will be apparent that by adjusting the relative positions of the core D and the shell E with respect to one another, any desired relationship, within limits, may be obtained between the inductances of the coils B and C. It is understood that the number of turns of those coils, their radii of curvature, the diameter of the wires, and the other factors well known in the art will affeet the relationship between the inductances of the two coils B and C, but these factors are ordinarily fixed in manufacture and are difficult, if not impossible, to vary upon installation.

The relative adjustability of the core D and shell E may be achieved in a number of ways. In Figs. 1 and 3 the shell E is fixedly attached to the dielectric plate 2 which connects the shell E and core D mechanically, but neither electrically nor magnetically, and also defines the means F for moving both the core D and the shell E, a suitable recess 4 being provided in the surface of the plate 2 to receive the shell E. The core D is provided with a threaded stem 6 which is engageable with an internally threaded aperture 8 in the plate 2. By a suitable rotation of the core D, its position with respect to the shell E may thus be adjusted.

In Fig. 4 an alternate mounting means is disclosed in which both the core D and the shell E are individually adjustable with respect to their support 2, the adjustability of the core D being achieved in the same manner as disclosed in Fig. 1 and the adjustability of the shell E being achieved by engagement of an internally threaded portion thereof In with an externally threaded portion l2 of the supporting plate 2.

During operation of the device, the shell E.

is interposed and slides between the two coils B and C without touching either. Because of this position, it performs certain functions other than those of tuning, among which may be mentioned the prevention of transformer coupling between the coils B and C and the prevention of the shorted-turn effect of one coil upon the other..

In order to make the tuning in each frequency .4 band independent of the other frequency band, it is desirable that these coupling and shortedturn effects be minimized as far as possible. To this end, it has been found desirable that the free end I4 of the shell'E project beyond the free end I 6 of the core D (see Fig. 4), thus increasing the shielding effect of the shell E.

Each of the coils B and C may be wound in normal fashion about hollow cylindrical forms 18 and 20, preferably formed of some insulating material, such as Bakelite, the forms in turn being fastened in any suitable manner, as by adhesive, to a support plate 22 which may in turn be suitably positioned within the apparatus with which this tuning unit is employed.

It is preferable both for mechanical and electrical reasons that the coil to be used in the higher frequency band be the external coil C. For resonance at the higher frequencies a coil of low inductance must be employed, and the increased radius of curvature of the outer coil C assists, in conjunction with a reduced number of turns, in attaining this low inductance. Furthermore, it is generally true that in order to tune over a commercial high frequency band such as the frequency modulation band, the total change in inductance needed is less than in the case of tuning over for example the standard broadcast band. The effect in inductance variation of the core D and shell E upon the inner coil B exceeds the inductance variation of the shell E upon the external coil C. Thus, if the core D and shell E move with respect to the coils B and C between positions in which the former are completely withdrawn from the latter and in which the former are completely telescoped into the latter, a greater change in inductance is effected in the coil B than in the coil C.

In one tuning unit made according to the present invention, the coil B was formed of 495 turns of 10/44 Litz wire wound on a form I8 .207 x .223 inch and the coil C used for tuning over the shortwave broadcast band was formed of 10 turns of No. 28 wire wound at a pitch of 5 turns to the inch on a form 28' having inch outer diameter. The core D was 2 inches long and .2 inch in diameter and the shell E was 2 inches long and inch in outer diameter. With this tuning unit, the coil B was employed to tune the complete broadcast band from 540 to 1610 kc. and the coil C was used to simultaneously tune a shortwave band of 14.8 to 18.55 me. These specifications are given by Way of example only and it is apparent that many variations may be made in the windings and in the dimensions of the various parts of the tuning device, all within the skill of the ordinary radio technician.

In order to tune over the frequency modulation band, which extends between 38 and 108 mc., it has been found necessary to employ for the material of the shell E an extremely high grade of iron or other magnetic material in order to reduce the losses and thus maintain the Q of the coil satisfactory at its low frequency end.

Since iron of such high quality is difficult to procure and even when procured is very expensive, an alternative construction has been developed which permits the employment of ordinary iron. By enveloping the exterior of the shell E with a sheath H of conductive non-magnetic material such as copper (see Fig. 3), it has been found that satisfactory tuning over the frequency modulation band is achieved. A unit in which this sheath H has been employed conforms to the following specifications: The broadcast coil B is Wound on a support 18 .187 x .207 inch using a core D inch long and .182 inch in diameter. The frequency modulation coil is wound on a form 20 having a /8 inch outer diameter and a wall thickness of about 3 2' inch. The shell E is inch long, has an inner diameter of .304 inch, an outer diameter of .484; inch and an enveloping copper sheath 3; inch thick.

With this device, the interaction of the various elements appears in some respects to be different from that of the previous device. As the shell E and sheath H are inserted within the coil C, the inductance of the coil C decreases, thus indicating that even if insertion of the shell E exerts any inductance-increasing effect upon the coil C, that effect is counterbalanced by the in ductance-decreasing effect of the conductive sheath H. However, the shell E still acts as a magnetic shield between the coil C and sheath H on the one hand, and the coil B on the other. As in the previously described device, the core I) and shell E both affect the inductance of the broadcast coil B, that inductance increasing as the elements D and E respectively pass within and envelop the coil B.

While the various elements of the device are here illustrated as being of circular cross-section (see Fig. 2), it is apparent that this is not an essential feature of the tuning unit, it being necessary only that the cross-sectional shapes of the various elements be so related that the ma netic tuning elements D and E may be movable with respect to the concentric coils B and C in the direction of their axis, that the core D be slidable within the frame l8 and that the shell E be slidable between the coil B and the frame 20.

By the construction here described, a tuning unit is produced which by a single mechanical action will achieve the simultaneous tuning of a pair of concentrically mounted coils. The inductances of the coils and the range of inductance change imparted by the tuning elements may be set in the same manner as these factors are controlled in similar single band units. Tracking between the two coils may be achieved in a simple manner by means of adjustment of the relative position of the two tuning elements. The entire tuning unit is easy to construct, the moving parts thereof may be moved in a frictionless manner, the resulting structure is ex ceedingly small and compact and of very light weight, the cost of the unit is minimized to a large degree, and in case of damage the entire unit may be withdrawn and a fresh unit put in its place.

It will be apparent that many changes may be made in the detailed construction of this tuning unit without departing from the spirit of the invention as set forth in the following claims.

I claim:

1. A dual band permeability tuning device comprising a coil support, a pair of concentrically mounted coils, a core of magnetically permeable material movable within the inner of said two coils, a shell of magnetically permeable material movable between the inner and outer of said two coils, the end of said shell projecting beyond the end of said core, and means for simultaneously moving said core and said shell with respect to said coils.

2. A dual band permeability tuning device comprising a support, a first cylindrical frame mounted thereon, an inductance coil wound on said first frame, a second cylindrical frame of greater diameter than said first frame mounted on said support so as to be coaxial with and envelop said first frame, an iron core slidable within said first frame and attached to a moving member of insulating material so as to be adjustable in its axial direction with respect thereto, an iron shell slidable between said first coil and said second cylindrical frame and also attached to said moving member, the end of said shell projecting bethe end of said core, and an inductance coil wound upon said second cylindrical frame.

3. dual band permeability tuning device coming a coil support, a pair of coils mounted conrl cally thereon, a core of magnetically permeable material movable within the inner of said two coils, a shell of magnetically permeable material fixedly enveloped by a sheath of conductive non-magnetic material movable between the inner outer of said two coils, the end of said ll projecting beyond the end of said core, and es s for simultaneously moving said core and ell with respect to said coils.

l. A dual band permeability tuning device comprising a coil support, a pair of coils mounted concentrically thereon, a core of magnetically permeable material movable within the inner of two coils, a shell of magnetically permeable material movable between the inner and outer of two coils, a support on which said core and shell are mounted, said shell extending from support a greater distance than said core, ,1 h core and said shell being individually .rstable in the direction of their longitudinal axes with respect to said support, and means for simultaneously moving said core and said shell the same direction with respect to said coils.

5. A dual band permeability tuning device comprising a coil support, a pair of coils mounted concentrically thereon, a core of magnetically permeable material movable within the inner of s two coils, a shell of magnetically permeable ial movable between the inner and outer of two coils, said shell being longer than said core, a support for said core and said shell, said support comprising an externally threaded ,nrr'tion cooperable with an internally threaded ortion of said shell so that said shell is adjustable n the direction of its longitudinal axis with repect to said support, said support also having internally threaded aperture cooperable with n externally threaded stem attached to said core that said core is individually adjustable in the irection of its longitudinal axis with respect to aid support, said shell extending from said suport a greater distance than said core, and means for moving said support so as to simultaneously move said core and said shell in the same direction with respect to said coils.

ALLAN M. HADLEY.

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

UNITED STATES PATENTS Number Name Date 2,695,420 Polydoroff Oct. 12, 1937 2,145,742 Wechsung Jan. 31, 1939 2,392,701 sanders Jan. 8, 1946

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