US2398406A - Radio receiver - Google Patents

Description

April 6- 7 w. J. BRQWN ET 2,398 406 RADIO RECEIVER Filed Oct. 17, 1942 3 Sheets-Sheet 1 INVENTORQ MIALTER J. BkOWN JOSEPH J. NEFF TTORNEY.

Ap 16,19 6. w. J. BROWN Em 2,398,406

v RADIO RECEIVER Filed Oct. 17, 1942 s Sheet-Sheet 2 INVENTORS WALTER J- BROWN JOSEPH J. NEFF RADIO RECEIVER Filed Oct. 17. 1942 5 Shets-Sheet 5 INVENTORS mum .1. anew uoszPn .1. NEFF BY Patented Apr. 16, 1946 Walter J. Brown,

Cleveland Heights, and Joseph .1.

Neil, South Euclid, Ohio, assignors to The Brush Development poration of Ohio Application October 17, 1942, Serial No. 462,332

1 Claim.

This invention relates to radio receivers and, more particularly, to miniature portable receivers of the pocket type adapted to be carried on the person.

For purposes of convenience in describing an embodiment of the invention, radio receivers of the general type to which it pertains will be referred to hereinafter as wearable. The use of such term, however, is not to be construed as limiting the invention to portable radio receivers, inasmuch as many of the features thereof are applicable to receivers of other and different types.

Previous to this invention, it was considered necessary to provide a miniature. wearable radio receiver with an external antenna and a counterpoise or with clips, binding posts or the like enabling the connection thereto of extraneous conductors to constitute a collecting circuit for energy at radio frequency. The necessity for employing a separate signal receiving element, or elements, militated against the popular acceptance of wearable radio receivers and against their usefulness for military purposes and, accordingly, the primary object of the present invention is to provide a miniature radio receiver that shall be entirely self-contained and shall require no outside connections whatsoever for satisfactory operation.

Another object of the invention is to provide a compact and sensitive fwearable radio receiver and one that also shall be capable of withstanding rough handling while in service.

Another object is to so dispose the component parts of a wearable radio receiver relative to each other that undesirable feedback therebetween shall be minimized.

Another object is to provide an improved tuning system for a radio receiver of the wearable type.

Another object is to provide an improved chassis for a radio receiver.

Another object is to provide a labor saving method of wiring a radio receiver.

Another obj ect is to provide an improved methd of affixing and anchoring bare connecting wires to the chassis of a radio receiver or the like.

A still further object of the invention is to provide a radio receiver chassis that shall require the minimum number of metallic parts in its construction.

The primary object of the invention, in one embodiment thereof, is achieved by utilizing the telephone cord of the receiver as an antenna, a self-contained counterpoise being provided by a Company, Cleveland, Ohio, a corthin sheet of metal foil that surrounds the chassis of the receiver and also serves as a shield to which the cathode of the thermionic tubes are connected. Preferably, a single telephone receiver of the ear-insert type is employed, the actuating means for the diaphragm thereof being a piezoelectric crystalelement that offers low impedance to currents at radio frequencies. For the purpose of impressing radio frequency potentials, corresponding to desiredsignals, upon the input circuit of the radio frequency amplifier tube in the receiver, connections are provided whereby both conductors of the telephone cord function in parallel with-respect to the input circuit insofar as radio signals are concerned and function noninductively thereto with respect to signals at audio frequencies being simultaneously conveyed to the earphone. This result may be accomplished, for example, by providing an input transformer, for the radio frequency amplifier tube, whereof the primary winding is constituted by both conductors of the telephone cord.

Alternatively, the input transformer may be omitted and an inductor constituted by a bifilar winding, the conductors of which are in series, respectively, with the telephone cord conductors, may be substituted therefor. In such case, the free end of only one of the conductors of the input inductor is connected to the grid. of the radio frequency amplifying tube, the other conductor being connected to the plate of the audio frequency amplifying tube by way of a blocking capacitor.

As will be'hereinafter pointed out, still further alternative embodiments of the invention are commercially feasible.

Tuning may be accomplished conventionally, if desired, although it has been found convenient, from the standpoint of economy of space, to utilize permeability tuning by providing a slidable' magnetic core for the antenna transformer.

Further objects of the invention are accomplished by providing a chassis fabricated from non-conductive material, preferably a plastic of the thermoplastic, non-inflammable type such as Vinylite or the like, to which bare connecting wires may be anchored through the use of heat and pressure. p

In addition,.the chassis is so shaped that it is substantially impossible to incorrectly insert the A and B batteries into the receiver and the radio and audio frequency components of the device are'so disposed withrespect to the batteries, when in place; that the metallic portions 2 of the said batteries function as a shield to minimize feedback.

Similar tuning means are provided for the intertube transformer between the radio frequency amplifier and the demodulator and the cores are simultaneously adjustable by a yoke-member that reciprocates' in slide-ways in the chassis. The tuning dial, which projects slightly from one end of the carrying case, rotates in a plane parallel to the long axis to the sliding yoke-member by suitable means for converting rotary motion into reciprocating motion of the yoke.

A pre-determined fixed amount of positive feed-back is provided, but osc'llation is prevented by the use of screen-grid tubes.

The novel features considered characteristic of the case and it is connected of the invention are set forth with particularity in the appended claim. The invention itself, however, together with additional objects and advantages thereof, as well as methods of construction and operation, will be understood best from the following description of a specific embodiment when read in connection with the accompanying drawings, in which:

Figure 1 is an exploded view of the bare chassis;

Figure 2 is a plan view of the bare chassis;

Figure 3 is a view in perspective of the chassis and certain of the electrical components mounted thereon, all wiring being purposely omitted;

Figure 4 is a view in perspective of the complete receiver, portions ofthe carrying case, of the shield and of the chassis being broken away;

Figure 5 is a view, partly in cross-section, greatly enlarged, exemplifying the method of ailixing and anchoring bare conductors to a thermoplastic chassis or the like. through the application of heatand pressure;

Figure 6 is the wiring diagram of the receiver;

Figure '7 is-an end view, partly in section, illustrating the mounting of the tuning-control yoke in slideways on the chassis; and

Figure 8 is a simplified circuit diagram illustrating the dual function of the earphone cord,

In all figures of the drawings, identical elements are similarly designated.

For purposes of convenience in describing the invention, the end of the receiver from which the controls project will be termed the top, the opposite end will be referred to as the bottom, the side adjacent to the tuning dial will be called the back and the opposite rounded side will be called the front. Such nomenclature is consistent with the orientation of the receiver when carried in a vest pocket or attached to a belt.

7 It is also to be understood thatFigure 5 is very greatly enlarged with respect to the views disclosing structural details of the device; had they been drawn to the same scale, the section of a conductor shown in Figure 5 would have had a diameter comparable to the thickness of the shade-marks on the dial in Figures 1 and 2. The actual commercial embodiment of the invention is approximately six inches long from top to bottom, two and one-half inches wide and one inch thick from front to back.

Referring now to Figures 1, 2, 3 and 4 of the drawings, a chassis fora "wearable radio receiver constructed according to the invention is constituted by a trough, or channel-shaped element, indicated generally by the numeral I, fabricated from a thermoplastic material such as Vinylite, or the like. The chassis is provided with a plurality of spaced apart tr n v r D r tions 3, 5, 1 and 9 which divide it into two large correctly and is a safety factor.

compartments ll, l3 and a small compartment IS. The partitions may be held in position by rivets (not shown) or they may be cemented in place if desired. As will be clear from Figures 1, 2 and 4 of the drawings, the width of one of the large compartments is slightly greater than that of the other. Thewider coinpartment accommodates a multi-c'ell B battery l1 having apotentiai of the order of volts, and a 1 volt A battery 19 just fits into the smaller of the two.

Difference in width of cludes the possibility of inserting the batteries in- The central partition is provided'with a pair of oppositely disposed resilient contact elements 2| and the end partitions 3 and I, which define the battery receiving compartments, are each provided with a single resilient contact element 23. The contact elements may be affixed to the partitions by rivets (not shown) or the like.

The edges '25 of the trough are bent over and extend laterally parallel to the bottom thereof to provide supports for certain of the circuit components such, for example, as a radio frequency amplifier tube 21 atone side, a detector 29, two audio frequency amplifier, tubes 3| and 33, and an output choke at the other side, as well ascoupling resistors and capacitors, etc. (not L shown) tends through the coup A volume controldevice 31, the shaft 39 of which extends outwardly from the top ofthe receiver, is disposed between the partitions 1 and S,

The back face of the compartment in the chassis that acccommodates the A battery is pro vided with an opening 4| through which a rivet 43 extends to constitute-the bearing for a tuning control dial 45' preferably fabricated from plastic. Although not so illustrated, the tuning dial may be provided with appropriate indicia. The edge 41 thereof may be knurled to facilitate adjustment.

Referring to Figures 3, 4 and 6, the inductors 49 and 5| constituting the inputcircuit or antenna transformer of the receiver are superim-.

posed upon a cylindrical coil-form 53 that is mounted adjacent to the radio frequency amplifier tube 21 beneath one laterally extending flange 25 of the chassis. the same direction. The inductors55, 51 and 59, respectively constituting the output circuit of the radio frequency'amplifier tube 21, the input circuit of the demodulator tube 29 and a tickler coil are wound upon a similar form 6| that is mounted beneath the flange at the opposite side of the chassis. For the purpose of holding the coil forms and tubes in place upon the chassis, each may be provided with an encircling band 63 of insulating material such as cellulose acetate or the like, the ends of which are overlapped and held to the chassis by rivets (not shown) or by other suitable means.

For tuning the antenna transformer 49-5], it is provided with a centrally disposed axially movable magnetic core 65 and a similar core 61 exng transformer -55-5l between the radio frequency amplifier and the demodulator. Each core is provided with an axially extending threaded rod 89, the saidrods, respectively, having threaded engagement with an extension II of a yoke element 13 thatis slidably mounted upon the bottom of the chassis exteriorly thereof. Slideways for the yoke are provided by two L -shape strips 15 of thermoe plastic materialthat are riveted along the outer corners of the bottom of the large chassis comthe compartments pre- These twocoils are wound in pertinent and are spaced apart therefrom a'distancesufiicientto accommodate the'bent-over extensions H :ofth yoke into which'the rods 69 extending from the magnetic cores are threaded. The free 'end' of each rod is provided with a slot ,1! in order that the relative position of each core with respect to the yoke may be factory-adjusted for unic'ontrol tuning.

Rotary motion of the tuning dial 45- is trans lated into sliding motion of-theyoke 13 by a fiat connecting rod 19 of plastic or the like, one end of which is pivotally connected to the dial adjacent to its periphery and the other end ofv which is pivotally connected to the yoke.

The actuating element 8| of an on-oif switch 83 for theA and B batteries projects from the top of the receiver. As shown in Figure 4 a shield 85 of metal foilpartially encircles the back of the chassis and it is held firmly to thelater+ ally extending flanges thereof by a plurality of screws 81 or the like, only two of which are illustrated. A sheet (notshown) of thin non-conductive and non-hygroscopic material such as cellulose acetate or the like is interposed between the metal foil'shield and the chassis proper for insulating purposes.

The shield is conductively connected to the cathode of the thermionic tubes and serves as a counterpoise. Shielding between the radio frequency stage and the demodulator stage is contributed by the metallic shells of the dry batteries.

The outer carrying case of the receiver is constituted by a shell 89 of Bakelite, cellulose acetate or the like, having a closed bottom 9|, the back of the shell being flat and the front thereof being rounded. The chassis complete with tubes, shield, etc., telescopes into the outer shell and is held snugly therein by friction.

Shoud the receiver be intended for military use, it may be strengthened and rendered substantially immune to rough handling by filling the space between the chassis and the casing with a non-conducting material such as Cerowax, Superla wax, carnauba wax, or the like which is solid and rigid at temperatures encountered during use of the apparatus. The filling serves as stiffening means and prevents the chassis from weaving should force be applied to the enclos ing case.

In th event that the receiver is intended primarily for military. use, it may be protected still further against rough handling by making the shield 85 of stiff metal and by interposing cushioning means (not shown) of sponge rubber or the like between the shield and the carrying case. Also, the case itself could be made of metal instead of plastic if extreme durability and resistance to shock is necessary.

All circuit connections, coupling resistors, etc., have been omitted purposely from Figures 1 to 4 and 7; their inclusion would serve no particularly useful purpose.

Though utilization of thermoplastic non-conductive material for the chassis and other parts, substantially all danger of short circuiting is obviated and bare wire may be utilized for most of the connections between the circuit components, provided such wire is anchored against subsesequent movement while the receiver is in use. According to the invention, therefore, the conductors are anchored to the chassis by means of heat and pressure in a manner analogous to the operation of spot-welding. The process is exemplified by Figure 5 of the drawings and it comprises heating asmall section of the bare wire and simultaneously pressing the heated wire a slight distance into the thermoplastic material of the chassis." 6 For the purpose of heating a small section of the wire, it has been found advantageous to utilize a tool constituted by two resilient conductive contact elements 93, aflixed, respectively, to the opposite sides of an insulating element 95 having a free knife edge 91. An extension (not shown) of the insulating element 95 serves as a handle for the tool. The free ends of the contact elements are curled up and back as shown in the drawings and, before the tool is applied to a wire embedded in the section of thermoplastic material I, these ends lie somewhat below the plane of the knife edge and are spaced slightly away from it.

If, therefore, the tool is supplied with potential from a battery or the like and is placed upon a 20 bare wire overlying the chassis, a small part of the wire beneath the knife edge may be heated sufliciently to soften the chassis material and the heated portion may be forced slightly below the surface of the plastic by the application of pressure. The plastic curls up over the heated portion of the wire and, after the plastic cools and hardens, a firm anchorage is provided.

The circuit for the receiver exemplified by Figure 6 of the drawings is, in general, substantially conventional. The thermionic tubes are of the type manufactured by Micro-tube Laboratories, 2414 Lawrence Avenue, Chicago, Illinois.

Referring to Figures 6 and 8, the earphone, indicated in its entirety by the numeral 99, is of the piezoelectric type illustrated conventionally in Figure 8, including a multiplate flexing piezoelectric crystal ml to whicha diaphragm I 03 is mechanically connected. The anode I05 of the output tube 33 is connected through a blocking capacitor III! to one of the electrodes of the crystal by way of one of the conductors I09, of a phone cord Ill and the other conductor of the cord, leading from the other electrode of the crystal, is connected to the cathode of the tube by way of a portion of the secondary winding 5| of the input transformer. The primary winding for the transformer is constituted by an inductor that is serially included in the first mentioned connection between the crystal and the plate of the output tube. Alternatively, both conductors of the phone cord may merge into a bifilar winding which constitutes the primary of the input transformer.

The phone cord, obviously, is non-inductively coupled to the input circuit of the radio frequency amplifying tube insofar as circulating currents at audio frequencies are concerned, but it is inductively coupled thereto for currents at radio frequencies which flow simultaneously therein in the same direction. The phone cord, therefore, serves the dual purpose of conveying the audio output to the earphone and of receiving radio frequency energy and impressing it upon the first amplifying stage of the apparatus.

Inasmuch as the cathodes of the tubes are connected to the shield 85 that partially surrounds the chassis, the said shield functions as a counterpoise and the receiver needs no extraneous antenna and ground connections for operation. Accordingly, it is always in condition to operate, irrespective of the environment of the wearer. From the military standpoint, that constitutes an important advantage.

It also will be apparent from a consideration of the foregoing description of an embodiment of the invention that, the substitution .of thermo plastic material for metal, forthe chassis and for other parts, isan important improvementinthe construction of "wearable radio receivers, 'Ihe occurrence of short circuits is rendered less likely and, at the same time, the process of wiring the chassis is simplified,

Other advantages will be apparent to those mary winding inductively. coupled to the tuning 2 coil, 2. regenerative detector having an input circuit coupled to the output of the radio frequency stage and tuned by means of a movableiron core mechanically linked to the core of the radio frequency stage, an audio frequency amplifier having its input connected to the detector output and having an ironcore coil in its output plate circuit, a blocking condenser connected between tector,- a shielding enclosure for said amplifiers and detector and batteries connected to the filament circuit, a piezoelectric earphone, a pair of closely spaced conductors each connected at one end to said earphone and connected at its other end to the input circuit of the radio frequency stage, one conductor connecting to the tap on the tuning coil and the other conductor connecting to the second of the ends of the primary winding whereby said pairIof-conductors in parallel together with the shielding enclosure act as a radio frequency signal collecting means for the receiver and the pair of conductors in series conduct the demodulated signal output of the receiver to the earphone without applying to the earphone the plate potential of the audio amplifier.

WALTER J. BROWN. JOSEPH J. NEFF.

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