US2538525A - Metal-case portable receiver - Google Patents

Description

Jan. 16, 1951 F D. M. KALTENBACHER 2,533,525

METAL-CASE PORTABLE RECEIVER Filed June 10, 1947 4 Shee'ts-Sheet 1 II M w H l T Ig z A TTTT EY 1951 D. M. KALTENBACHER 2,538,525

METAL-CASE PORTABLE RECEIVER Filed June 10, 1847 4 Sheets-Sheet 2 INVENTOR.

ATTORNEY Jan. 16, 1951 D. M. KALTENBACHER 2,533,525

METAL-CASE PORTABLE RECEIVER Snventor Gttorueg Patented Jan. 16, 1951 so STATES smear ore-ice 2,538,525 METAL-CASE PORTABLE RECEIVER Dominic Kartcnbacher, Cincinnati, "Ohio, as- "signor to Radio Gorporati'on of America, a corpulsation oi Delaware Applicat-ionfllune 10, 194i, SeriaLNo. 7533710 2 Claims.

My present invention relates generally to portable radio receivers oi the metal case "type, and more particularly to a metal-cased portable :reoeiver provided "withv a "satisfactory radio signal collector.

, Animportant object of this inventionis to provide'a satisfactoryradio signalpickup device,'suoh as a "loop, for a metal-cased portable receiver. 'In accordance with this object of 'my invention, the 'short-circu'iting effect of the metal case on 'the :receiver loop removed .by providing a 'gap or discontinuity "in "the "metal casing. Since the 'metal :case must be in place when the loop circuit "is aligned, means is provided. for aligning the loop, circuit through an insulated gap in the metal case.

Amara-specific object 'oftmy'inventionis to provide a broadcast 'rece'iverin which a loop antenna is protectively mounted .in a recess of an insulation end wallrof ametal cabinetfthe latter'being :frrom one endwa'llto the opposite end-wall to prevent :"it ffromfhaving a single-turn short circuiting effect on the loop. In accordance with this object the split the metal cabinet may be provided at the 'hottom thereof so as to be least noticeable thereby to permit attractive styling.

The split is, "furthermore, provided with a nonmetallic closure to provide the effect of a continuous cabinet surface.

Stillfurther objects of 'the invention are to -improve generally the :utility and appearance of metal-cased portable receivers employing loop type antennas, .and more especially "to provide a construction which is not only economicallymanuiacturedbut is readily assembled.

Still other features and objects of my invention will best be understood 'by reference "to "the .fol-

lowing "description, taken in connection with the l 5 Fig. 4 is a sectional'v'iew taken on "line '44 of Fig.3 looking in the direction or the arrows; Fig. 5 is a section taken on line 5- .3 -of"Fig-. lookingin the direction of the-arrows;

Fig. 6 is a front View showing the operating panel of a different "type of metal-cased'portable receiver of the personal type;

'Fig."7 shows an end view'of the receiver of Fig. 6., a portion of the wall being brokenawayto show the'interior'thereof: N

Fig. 8 shows the outer face of the removable rear wall'oi the receiver,

Fig. 9 shows an end-view of "therear'wall; Fig. 10 shows a planviewof the rear'waill;

Fig. 1'1isaseotiontaken-on line Il H offi'ig. '8 looking inthe direction of the arrows V Y M Fig. 12is a-section takenon line 12-12 of Fig. 8 looking in the direction of the arrows; and Fig". I3is a'view or the -bottomof the 'p'ort'aiile receiver to showthesplit in-thernetal'case. Referring now *to the accompanying drawings, wherein like reference numerals in the several figures denote "similar elements, Figs. 1 and '2 Show the appearance of a metal-cased portable receiver constructed in "accordance with my inven tion.. In general, 'andviewed externally, the em bodiment "shown comprises a metal casing i and a pair of end walls '2 and 3. The upper andlower edges of the end walls are "contiguous withthe top and'bottom surfaces of easing "I 'to provide smooth 'overall'surfaces. The 'end'walls 2 and 3 are hole low or recessed, andt'hey are made of anysuit able insulation material. For example, (the ,p'he; nol condensation composition lknown under.,.the trade-mark Bakelite 'mayibe used, or polysterene'may be employed. 'flhe' casing i is composed preferably of thin sheet aluminum, although magnesium metal cou'ld'he used "if desired. l'Ihetes" .sen'tial thing is to employ a light metal of attractive appearance. A handle 4 of'anysu'italile construction may be secured to the top surface ata median point thereof.

Further, .in this particular embodimentro'taft able cylinders 5 and '5 .provide .tuningand volume adjusting devices, whereas .numeral Tdenotes the usual tuning dial. The elements 5, 6 and 1 are located behind an opening 'B'proVided adjacent the top of the front .wall of Caring I. With'inthe casing "I there will be located ara'dio receiver chassis, a battery .pack and a loop antenna. In

general, the chassis is located in the upper half of the casing while the battery pack is located in the lower half, while the loop antenna is pro tectively located within the hollow or recess of the insulation end wall 3.

Looking at the bottom of the casing shown in Fig. 2, it will be seen that there is provided a split or gap 9 which extends from end wall 2 to end wall 3. A non-metallic closure strip I is secured to the casing in overlapping relation to the split 9 so as to close the gap, and thereby to provide the effect of a continuous space. The opening I l is provided in the metallic and non-metallic material so as to permit access to the interior of the casing. If desired, an external loop strap may be passed through the opening II. The same opening is used for adjustment of an aligning condenser thereby to provide loop adjustment,

The opening 12 is provided in the insulation strip ID to permit the passage of a power line cord therethrough. In addition, the bottom of the casing is provided with a pair of fiat supports l3 and I4, which may, also, function as slideable latches to permit the hinged rear section of the casing to be opened for access to the interior of the casing. Attention is directed to Figs. 3 and 4 for a showing of certain of the mechanical details of construction of the interior of the easing, it being understood that these details are shown for the sake of completeness. My present invention relates to the loop antenna circuit and its electrical and mechanical association with the metallic casing.

In any receiver using a loop antenna for radio signal pickup, the signal voltage delivered to the first control grid of the first receiver tube is proportional to the area, the Q and the number of turns of the loop. In receivers of the portable type the area is limited by the size of the case, while the number of turns is limited by the inductance requirements. The Q, however, is determined by the type of wire employed, the proximity of metals, and the quality of the material on which the loop is fastened. When the receiver is housed in a metal cabinet, the ordinary problems of designing a satisfactory loop are multiplied. Since for satisfactory operation in medium and low priced radio receivers a loop cannot be completely covered by metal, some insulating material must be used in the cabinet construction. A solution is provided herein by having a metallic sheet wrap-around with plastic end-pieces. Since the metal case is a shorted turn in the loop field,'this effect must first be removed. This is accomplished by providing a gap, such as split 9, in the casing, preferably at the bottom where it is unnoticeable. The gap may be closed by any desired insulation material.

The next problem is to obtain a satisfactory figure of merit for the loop. Since the figure of merit varies directly as the effective area of the loop, a box type loop is preferable to a flat wound loop. The box type loop has a larger effective area, and by mounting it at several points less Q is lost than with a flat loop mounted to a flat surface. In general, with limitation in space and the extra losses involved, it is desirable to have the product of loop area, Q and the number of turns a maximum.

' In Figs. 3, 4 and 5 I have shown the hollow or recessed insulation end wall 3, and the manner of protectively mounting the box type loop antenna I6 within the recessed end wall 3 so as to provide maximum signal pickup and yet have the loop antenna as far from the metal case and 4 chassis as is possible. It is emphasized that the short-circuiting effect of the metal case i on the loop antenna [6 is removed by virtue of the split or gap 9 in the case.

The end wall 3 is shown provided with spaced insulation support pins 20. These pins project from the wall, and may be an integral part of the insulation wall. As shown in Figs, 3 and 4, a set of three spaced pins is provided adjacent the upper and lower edges respectively of the end wall, while a pair of spaced pins is provided in horizontal alignment at the middle of the end wall. The pins 20 are arranged in a substantially oval pattern so that the box loop antenna [6, which is of generally oval shape, may readily be slipped on to the support pins. As shown in Fig. 5, each pin 2|] has a length substantially equal to the depth of the hollow wall 3 and the depth of the wound loop antenna 16. In this way the loop I6 is protectively located entirely within the end wall, and its axis is in the axial line of the metal case. Further, the effective area of the loop is of the order of the area of the end Wall 3, the pins 20 being located close to the ledge 2| of the end wall.

The edge of the end wall 3 may be secured to the open end of case I in any desired and suitable manner. The structural details of the interior of the case are no part of my present invention, and such details are only generally referred to. As shown in Fig. 4, the open end of case i fits snugly in alignment with the periph-,- eral flanges of end wall 3. The opposite insula tion end wall 2 is constructed in the identical manner as wall 3. With such an arrangement only one part is stocked, and only one mold is necessary for limited production. Both end walls may have a shelf 22 projecting therefrom to sup} port the receiver chassis. The space below the shelves receives the energizing dry batteries. Any suitable looking or clamping devices may be provided to keep the chassis firmly positioned on the shelves. v The insulation boss 24 projects from wall 3 below shelf 22, and carries the L-shaped bracket 25. A trimmer condenser 26 of any suitable con-.- struction is secured to the bracket 25. The ad: justing head 21 of the trimmer condenser is located above the opening H (Fig. 2) so that the blade of an aligning tool may be inserted (see Fig. 3) to adjust the capacitance of the trimmer without disturbing the case. The loop It has its terminal leads 28 and 29 connected to the respe c tive electrode terminals 28 and 29' of trimmer condenser 26. The usual tuning condenser (not shown) is shunted across the loop I6, the trim.-

mer 25 being connected in parallel to both the tuning condenser and loop. The loop and tuning condenser provide the usual parallel resonant input circuit connected between the control grid and cathode of the first receiver tube. v

The metal case affects the inductance and dis.- tributed capacity of the loop, and it is necessary that the complete receiver be in its operating condition when the loop circuit is aligned.

The loop is designed for a definite value of inductance with the receiver in operating condition and the metal case closed. The trimmer condenser adjusts the capacity of the antenna circuit at the high frequency end. When the case is opened the inductance and capacity of the loop are a different value than when closed. If the trimmer is adjusted when the case is open and then the case is closed, alignment no longer exists and. the loop is tuned to a different ire attests wherea satisfactory Q is not obtainable, for

the loop a'lowimpedance loop may be used.'and a high Q loading coil is then connected in series with the loop to bring the total inductance of the tuned loop circuit to the correctvalue. In the modification shown in Figs. 6 to 13 there is employed a low impedanceloop3fl (Fig. '7) In this particular set the inductance of the loop, for example, comprises about 20% of the total inductance of the tuned circuit. There is an optimum relation between loop and loading coil which depends on the Qs of the two.

As shown in Figs. 6 and '7, the portable receiver is of the so-called personal type. It comprises a metal case 31, made of zinc for example, which is rectangular in shape and houses the receiver chassis and batteries. The operating panel, or

' front wall, consists of an insulation panel 32 made of any suitable insulation material, and a grille section 33 made of metal. The grille section 33 is a part of the case casting. The tuning dial and volume control dial 35 are fastened to respective shafts on the chassis. The rear wall or closure 35 is made of an insulation material, for example polysterene. The loop 30, of the box type, is mounted within the back wall 35. In Fig. 7 the back wall 35 and casing 35 are broken away to show two anchor points of the loop 30. In Fig. '7 the circular object B is the end view of the dry cell A battery mounted in battery holder H. The two terminals T are fastened to the insulator I which is held by, and is part of, the battery holder. The two terminals T are anchor points for the loop, and are not connected to anything shown in the drawing. It will be sufficient to show only these components of the receiver. One side of the loop is connected to the high potential side of the tuning condenser through a high Q loading coil, and the opposite side of the loop is connected to the low po tential side of the tuning condenser.

In Figs. 8 to 12 there is shown the construction of the rear wall 35 and the manner of protectively mountinng loop 30 therein. In Fig. 13 I have shown the gap provided in the metal case 3! .to remove the short-circuiting effect of the case on the receiver loop 30. The non-metallic, or insulation, strip 5| is located on the inner face of the case, and overlaps the gap 5%]. The brackets 32', shown dashed, in Fig. 6 are part of the case casting. The case is cast with all sides continuous, and the gap or split 50 is milled in between the two brackets 32. A molded stri 5| is then fastened to the brackets to fill up the gap. The specific manner of providing the gap and its insulation closure is not material to my invention. There is provided a continuous casing surface. It will be recognized that gap 50 in metal casing 3| functions in a manner analogous to gap 9 in the aluminum case I of Fig. 2, while insulation strip in of the latter functions in the manner of strip 5| of Fig. 14. In both instances the axis of the metal case is common with the horizontal axis of the loop, and the plane of the loop is across one end of the case. The latter is split to prevent it'fromactingasa short-circuiting turn on' the loop. In addition, both metal cases have the op posite open ends thereof closed by insulation end walls.

The rear wall 35 consists of a rectangular frame 52 provided with opposed vertical flanges 5 3 r and? upper and lower horizontal flanges '54. These flanges fit inside (not shown) the casing 31 to provide the smooth continuous surface shown in Fig. 7. The rear rectangular opening of insulation frame 52 (see Figs. 11 and 12) is closedby slidable insulation plate 55. Plate-55,

which is the back cover, slides off to provide access to the batteries, tubes etc., without disturbing the loop. The loop frame 52 is fastened to the case 3! by screws at the four corners (see Fig. 8) The plate 55 may have any suitable construction, and an illustrative joint between the plate 55 and the inner edge of frame 52 is shown in Figs. 11 and 12.

The frame 52 is constructed as a double wall so as protectively to receive the loop 30. The frame is a plastic molding with a slot molded in to receive the loop. As shown in detail in Fig. 12,the frame 52 is molded to have an inner wall (it all around the four sides thereof. The space between inner wall 65 and outer wall (Fig. 12) is suflicientl wide to receive the loop 30, and to house the latter snugly. In this personal type of set the loop is hidden in the slot in, the molded back. The main goal is to get the loop as far from the metal case and chassis as practicable with the required styling. In Fig. 7 the outer wall 50' of frame 52 is broken away to show the wires of loop 38. It will be recognized that the mounting of loop it in end wall 3 of Figs. 3 and 4 is analogous to the mounting of loop 30 in insulation rear wall 35 of metal case 3 l.

The small gang capacitor (not shown) used on this particular receiver requires a large tuning inductance. It was impossible to get this large inductance in a reasonably small space, and the Q would have been unsatisfactory. That is why the low impedance loop and load coil were provided to secure a reasonable Q. As previously stated, it is desirable to have the product of loop area, Q, and number of turns a maximum. I

While I have indicated and described two constructions for carrying my invention into eifect, it will be apparent to one skilled in the art that my invention is by no means limited to the par- I plane to prevent the case acting as a short cirmetal case adapted to house a receiver chassis and batteries therefor, said case being split on a line parallel to the transverse axis of said case to prevent the case from acting as a shortcircuiting turn in the loop field, said case having an insulation rear wall, and a loop antenna protectively located in said rear wall, said rear wall 7 8' having a peripheiai'slot in which to house the Number Name Date loop, the plane of the loop being perpendicular to 1,821,236 Pratt Sept. 1, 1931 the transverse axis of said case. 2,137,035 Swallow Nov. 15, 1938 DOMINIC M. KALTENBACHER. 2,322,126 Grimditch June 15, 1943 REFERENCES CITED 1 7 L y Apr- 29, .7

' FOREIGN PATENTS The following references are of record in the file of this patent: Number Cmntry Date 604,353 Germany Jan. 15, 1933 UNITED STATES PATENTS m OTHER REFERENCES Number Name Date 1 73 249 Kolster June 2 1923 TM War Department Technical 71,763,459 Deason June 10, 1930 fi r e

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