US1960479A - Dual wave band radioreceiver - Google Patents

Description

May 29, 1934. L. F. CURTIS ET AL DUAL WAVE BAND RADIORECEIVER Filed Oct. 28, 1931 2 Sheets-Sheet l OQOOOOOOOOOOOOOQCOO INVENTORS leslie I-T Cari/5.

William E Cotter. leopard .a5iman Q2 z nsmlva May 29, 11934. L. F. CURTIS ET AL DUAL WAVE BAND RADIORECEIVER lFiled Oct. 28, 1951 2 Sheets-Sheet f2 INVENTORS 19511: F. (a/as.

P/z'lh'am E Cotter: leonard Eastman- QQEfl Patented May 29, 1934 UNITED STATES PATENT FFHIE DUAL WAVE BAND RADIORECEIVER Leslie F. Curtis, William F. Cotter, and Leonard E. Eastman, Springfield, Mass, assignors to United American Bosch Corporation,

Springfield,

4 Claims.

Our invention relates to improvements in receivers; and especially to receivers for use in broadcasting and other forms of radio communication.

An object of the invention is to provide a radio receiver of such design that it will operate on at least two distinct and predetermined bands of wave lengths or frequencies, so that the receiver can readily be utilized in different localities where separate bands are necessary for transmission; or in one locality to operate on either band, as the user may wish.

A further object of our invention is to provide a radio receiver which has means for enabling it to receive on one band or another; and which is built to contain for this purpose suitable electrical devices which can be manipulated to adjust the receiver according to the band on which reception is to be accomplished.

Another object of the invention is to provide a radio receiver which is equipped with one or more coils in separate sections, all of which may be connected in circuit for the band of longer wave lengths; or only part of which may be actively employed when reception on shorter wave lengths is required.

A still further object of the invention is to provide a convenient arrangement of the coils by which long or short wave reception can be effected; together with suitable members in the form of switches or similar parts by which the coils can easily be controlled in unison; so that the change in adjustment necessary to shift from one band to the other can be quickly brought about.

In practice, the receiver is designed to work upon a band of wavelengths having a range of say 200 to 600 meters; and it has an additional set of windings to afford a greater inductance and adapt the receiver to be set for the other band, which lies between 1000 and 2000 meters; together with regulating switches to include or out out the additional windings at will; these switches being arranged and joined in tandem, so that all of them can be actuated at one time.

An additional object of the invention is to provide a radio receiver having novel resistance-repeating cascade-connected amplifier circuits designed to aiford excellent control of the gain or amplification in each stage, and ease of obtaining wave length range.

The objects and advantages of the invention are fully set forth in the ensuing description, taken with the accompanying drawings which show the preferred form of the invention. The

disclosure, however, is explanatory only and variations in the connections and other relations of the various elements and appliances included in our improved receiver, may be adopted without departing from the principle of the invention or exceeding the scope of the appended claims.

On the drawings:

Figure 1 shows a circuit for a receiver according to our invention;

Figure 2 is an end view of the regulating or adjusting devices or switches to set the receiver for the separated bands of Wavelengths or frequcncies, and means for actuating the same; some of the covering and mounting parts being in section;

Figure 3 is a front view of said devices; and

Figures 4 and 5 present charts to explain the mode of operation of the repeating circuits.

The same numerals identify the same parts throughout.

As illustrated the receiver comprises electric circuits containing vacuum tubes for radio frequency amplification in cascade, together with a suitable detector and at least one stage of audio frequency amplification; all disposed to operate on the resistance-repeating principle, and to give suitable amplification on both bands; tuned circuits for selectivity; and a rectifier with asso ciated means to supply current from ordinary lighting or power mains; so that batteries can be dispensed with as sources of electrical energy for the cathodes and anodes of the tubes or thermionic valves. It is to be understood, however, that our invention is to be by no means limited to such a receiver but be embodied in receivers of various constructions.

Referring particularly to the drawings, we show a terminal 1 for an antenna at one end of a resistance 2, with which is associated an adjustable contact 3 connected to ground The terminal 1 is also connected to one terminal of an adjustable electrical condenser 5, the other pole of which is joined to the grid of the first vacuum tube member or amplifier 6. The terminal of the resistance 2 remote from the condenser 5 is united through a suitable resistance 7 to the cathode in the tube 6, this tube being or" the screen-grid type, the cathode being of the unipotential type and grounded as shown through a fixed condenser 8. The shield or screen in the tube 6 is grounded in the same way. Attached to the lead between the grid of the tube 6 and condenser 5 is a coil including a pair of sections 9 and 10, these sections being in series and grounded. They are also associated with an adjustable condenser 11 connected to the grid of the tube 6 at one end and grounded at the other. The sections 9 and 10 and condenser 11 constitute a tuning circuit and the tube 6 as shown is joined to the antenna by a resistance coupling because of the presence or the element 2. When the receiver is to be used for waves of the longer length, both sections 9 and 10 together with the condenser 11 are put into circuit. When, however, the band of shorter wave lengths is to be employed, section 10 can be cut out by bridging the terminals 12 connected to the two ends of the section 19 by suitable switch mechanism. Obviously more than two sections may be utilized if operation on more than two bands of wavelengths is desired.

The second radio-frequency amplier tube (in is of the same description as the first tube 6 and is connected to the first tube by a conductor extending between the plate of the first tube and the grid of the second, with a fixed condenser 5a in line thereof. Similar connections are pro vided for the filament of tube 6a extending from the terminal of the resistance 7 and including a condenser 8a joined to ground as before; with another condenser 8a to ground the screen between the anode and grid. Between the con denser 5a and the grid of the tube 6a is a tuned circuit consisting again of a coil in two sections 9a and 10a in series and grounded, together with an adjustable grounded condenser 11a connected to the grid of tube 6a; the section 10a having contacts 12a joined to its extremities, so that this coil can be switched out at the same time as the coil 10.

Between the condenser 50', and the plate of the first tube 6 is joined one end of the resistance 2a which is of high value and across which the plate circuit load is developed; this high resistance 2a having capacity-coupling through the condenser 5a with the tuned circuit comprising coils 9a and 10a and condenser 11a. Similar coupling exists between the first resistance 2 and the first tuning circuit of the tube 6.

The same connections exist between the plate of the tube 6a and the grid of the radio frequency detector tube 62); the corresponding repeating resistance being shown at 22), tuning coil section at 91) and 10b, tuning condenser at 11b, switching contacts at 121) and coupling condenser at 5?). Associated with the tuning circuits of the tubes (is and 6b are suitable adjustable trimming condensers lla and 111) which are grounded the same as the condensers 11a and 11b. Suitable condensers 8 and 3" ground one terminal or the resistances 2a and 2b. We also connect the filament of the detector tube 6b to one end of a resistance 7b and condenser 81) in parallel, the opposite terminals of these two elements being grounded on the framework of the receiver.

The condensers 8, 8a, 8 and 8 are by-pass condensers for high frequency oscillations; while the condensers 8b attached to the screen and the cathode of the tube 6b constitute by passes for both radio and audio frequency oscillations. The resistance 72) of the detector cathode is for grid bias purposes.

The last stage in the circuits of the receiver comprises an audio frequency amplifier 6c having a capacity coupling through a condenser 50 with the plate of the detector tube 612. To the lead between this condenser and the plate of the tube 62) is united one end of a resistance 20; and joined to the conductor of this plate between the resistance 20 and the tube 62) is a ground detector plate condenser 110 for rectification. The screens of the tubes 6, 6a and 6b are connected through leads 13, 13a and 13b to a common terminal 14; and a suitable resistance 7b may be inserted in the lead 131).

Joined to the grid of the tube 60 and between the tube and the condenser 50 are two coupling resistances 15 and 16 in series, between which is one pole of a condenser 1'7; the other pole 01 which is grounded and connected to a pair of coils 18 bridged across the filament of the audio amplifier tube 60. The resistance 15 and condenser 17 are in a circuit between grid and filament for audio frequency current, and are connected to the mid-point of the windings 18 to allow for alternating current fluctuations of the heating current. The plate of the tube 60 is connected to one terminal of the primary coil 19 of an iron core transformer, the secondary 20 of which is to have its terminals connected to the movable coil of the dynamic loud speaker.

To supply current to the plates of the tubes the resistances 2a and 2b and 2c are joined to a common conductor 21 which is grounded at one end and connected at the other to the heated cathode of a rectifier 22. This rectifier also contains two anodes each united to the outer terminal of a pair of secondary coils 23 and 24 in series. The cathode of the rectifier is heated by current from a secondary 25 and a secondary coil 25a supplies current to the heaters of the cathodes of the tubes 6, 6a and 6'0, and the cathode filament of the tube 60 respectively. All of these secondaries are mounted upon the same iron core to be energized from a primary 26 connected to a light or power circuit. From the junction point of the coils 23 and 24 is led a conductor 27 which is grounded through a resistance 28. The cathode of the rectifier 22 is connected through a similar conductor and a coil 29 to the lead 33 rimning to the conductor 21. The coil 29 may be the field coil of the loud speaker and may be in multiple with a condenser 30. Condensers 31 may be shunted across the terminals of the coil 29 and resistance 28. The midpoint of secondary coils 23 and 24 is also joined by a conductor 32 to the resistances 15 and 16 in series; and the lead 21 may be grounded through a pair of suitable resistances 35 and 36 in series. The common terminal 14 of the screens for the plates of the tubes 6, 6a and 6b is connected to a point between these resistances; and a branch conductor 34 connects the primary 19 to the coil 29.

This receiver operates in the well known man ner with its heater-type screen-grid tubes and resistance-repeating arrangement of circuits. When the band of longer wavelengths is to be employed, the coils of the tuned circuits are all used with both sections active; and when the signals are to be received on the band of shorter wavelengths, the sections 10, 10a and 10?) are shorted out by bridging the two terminals of these coil sections. This result may be accomplished by suitable switching means which will aiiect all three sections 10, 10a and 10b together, as will be described later.

The receiver thus consists of two stages of radio-frequency amplification followed by a detector; and this is succeeded by a single stage of audio-frequency amplification employing a vacuum valve. Three tuned circuits provide for selectivity.

The radio frequency section is designed specifioally around a suitable screen-grid valve. As the characteristics of this valve are such as to allow the plate circuit load to be developed across a high resistance unit, which, in turn, is capacitycoupled to the tuned circuit, the use of only low plate-current valves is permitted. This circuit arrangement has an advantage in that it allows the elements of the tuned circuits to be connected directly to the frame of the receiver, and simplifies considerably the radio-frequency filtering in the supply leads.

The performance of the receiver as regards sensitivity on both wave bands, selectivity on both wave bands, fidelity and power output, is quite satisfactory. The fidelity curve of the receiver illustrates an unusually good response over the audio range and is brought about by special circuit connections wherein the C bias resistor 15 of the power tube 60 is removed as an impedance common to the grid and plate circuits.

Reduction in loud speaker hum is brought about by the combination of by-pass condensers 31 above described in the filter circuit, using the field winding 29 of the loud speaker as the filter choke; tuning this field winding by means of a condenser 30 across its terminals, connecting the power tube grid circuits as shown, and a proper polarizing of the field winding and the primary 19 of the output transformer. A copper ring or slug may be placed adjacent to the field coil in the loud speaker assembly to contribute to the speaker hum reduction.

In practice we can obtain marked advantages with this receiver by adopting certain comparatively low values of the coupling resistances 2a, 2b and 2c and the coupling condensers 5a, 5b and 5c.

Heretofore in resistance coupling between amplifiers in cascade the coupling resistances have been of the order of 250,000 ohms or more and the coupling condensers have had a value of .001 of a microfarad and over. With such values there was always difiiculty in obtaining wave length range over the broadcast band with conventional variable condensers and -coils.- Also there could be no control of the stage gain or amplification. This state of affairs is shown by reference to Figure 4 which presents a chart having a curve showing the relation between the repeating resistance measured horizontally and the gain measured vertically for a large value of a coupling resistance, and a condenser of comparatively large capacity. It will be seen that with large resistance this curve flattens out and becomes horizontal and along the horizontal portion the gain is constant and invariable. Only along the bend or diagonal part of this curve can control be obtained.

The essential reason for the limitation in the wave length range, which can be obtained with a coupling capacity of large value, is that this capacity, which is in series with the plate-cathode capacity of the tube, is shunted across the tuned circuit, associated with the input circuit of each of the tubes. Thus the gang condenser, that is to say the assembly of tuning condensers, must be much larger than in our invention.

Further, large coupling resistances of 250,000 ohms, which are required with large coupling condensers, cannot be used with vacuum amplifying tubes of the type usually made in this country; and cannot be operated with anode supply voltages of reasonable amount, because the large resistance wastes too much of the electrical energy which the anode circuit receives. On the other hand, with a smaller coupling capacity, the practical value of the resistance may be very much reduced; as is done in the practice of this invention; because the small coupling capacity in series with the parallel tuned circuit constitutes an impedance of only a few thousand ohms. It is unnecessary to make the coupling resistance any greater than this effective impedance of the combined coupling condenser and tuned circuit. But

when a large coupling condenser is used, the effective value of the impedance of the tuned circuit may be 200,000 ohms or more depending upon the losses associated with the coil and condenser. Hence to obtain good amplification, one must use both high coupling resistance and high anode voltage; which with tubes of the kind available in this country is impractical. By means of relatively lower coupling resistance at smaller coupling capacities all of these difficulties are avoided.

We therefore give to these coupling resistances a value of the order of 25,000 ohms and to the coupling condensers a value as low as 10 micromicrofarads. Upon plotting a similar curve, as shown in Figure 5, one sees that for condensers of relatively low values the curve does not flatten out quite so abruptly, and that at low resistances the bend or slope of the curve can be utilized for working effect. Thus there is case of obtaining wave length range and the stage gain or amplification can readily be controlled.

Obviously instead of two bands of wave lengths we can provide for more than two by increasing the number of tuning coil sections; and several bands can be obtained within any limits from the very high frequency range of 25 meters to the far lower frequency range of 25,000 meters.

In Figures 2 and 3 there is presented an actual construction showing how the coils for the separate bands of wave lengths can be mounted and controlled in unison by actuating a single member which switches the coil sections 10, 10a and 101) into or out of circuit. At 37 is a panel or support to which is attached three coils comprising the sections 9 and 10, 9a and 10a, and 9b and 10b. The sections 9, 9a and 9b are wound on tubular forms 38; and other sections, which are indicated as to position at 10, 10a and 10?), are wound on cylindrical forms 10; fixed on rods or pins 39 in the outer ends of the forms 38 and having their axes at right angles thereto. By spacing the various pairs of coil sections so that the axes of each pair of sections are at right angles to each other, the coil sections have no inductive effect upon each other. This is important because otherwise when the section 10, for example, is short-circuited a large current would flow therein and a disturbance in function would result. The forms 39 are attached to the panel 37 by angleshaped clips 40 and suitable screws and other fastening devices. Suitably affixed to the panel are annular projections 41 concentric with the forms 38. These tubular projections have circumferential ribs 42 which act as stops and 43 are caps or covers for the various pairs of coil sections. The caps engage projections 41 by being slipped thereon until their ends abut the stops 42.

These caps or covers 43 for the coils also serve as electrostatic and electromagnetic shields for the coils and confine all electrical effects adjacent each coil to the space within the shield; thus preventing condenser reactions between the groups of coils in the receiver.

The forms 38 have at their outer ends terminal clips 44 and 45 to which conductors may be attached, so as to connect the ends of the coil sections into circuit. Each of these forms 38 also has a second pair of terminal clips 44' and 45. One circuit wire may be connected to the terminal 44 of the section 9, for example, and another terminal wire may unite the opposite terminal l5 of the section 9 with one terminal 44." of section 10. The other terminal 45' of section 10 may be connected to the ground. Hence, if terminal 45 is grounded, the section 10 will be out of circuit.

To the face of the panel is attached a shelf 46 having its middle portion 47 bent up or raised. Near its opposite ends the shelf has turned down side portions 48 and 49 with apertures to receive screws to secure the shelf against the face of the panel 37. Adjacent the portion 48 this shelf carries two casings 50, each of which contains a single pclsingle throw toggle switch; having projecting terminals 51 and a toggle lever 52; the outer end of each lever 52 being cleft as shown. At 53 is a switch red, one end of which is provided with fiat surfaces 54 for a knob; and on this rod are rigidly mounted arms 55 which engage the cleft end of each lever 52 to enable these switches to be operated when the rod 53 is turned. A U-shaped member affixed to the bent up portion 57 of the shelf 46 provides bearings for the rods 53.

In practice terminals 44 of each of the coils 10, 10a and 1% may each be connected to one of the terminals 51 of one switch 50 and the terminal 45' of each of these coils may be similarly connected to the remaining terminals 51 of one of the switches. Then when the rod or shaft 53 is turned, all of the switches 50 can be operated together to open circuit or short circhit the various coils 10, 10a and we as above described.

Of course, condensers 11, 11a, 111) will also be connected together in the usual way, so that they can all be tuned in unison by means of a single knob and shaft provided for this purpose.

The panel 37 may have ends or wings 58, one of which is perforated as indicated in Figure 3 to enable the rod 53 to project through it and carry the operating knob on the outer side thereof.

By the use of resistance repeater coupling and capacity between various stages, the simple switches shown at 50 are all that is needed to shift from one wave length range to another. On the other hand, if electromagnetic coupling involving primary and secondary cells were employed, both the primary and secondary coils would have to be adjusted by increasing or decreasing the number of turns in each to maintain the proper coupling between each primary and secondary and thus complicated switching devices would become necessary. But, with resistance repeater coupling such complicated switching devices can be dispensed with, because the resistance is just as effective at one wave len th as at another.

Many changes in the details of the circuits and the construction shown and described herein may of course be made, and the invention is not to be construed as limited to the precise form set forth, except as required by the express terms in which the appended claims are set forth.

Having described our invention, what we claim i. In a radio receiver having amplifying stages in cascade, tuning means for the input circuits of each stage including asectional inductance comprising two coils connected in series, one coil being mounted in non-inductive relation inside the other of said coils, a tuning condenser connected across sectional inductance, and means for simultaneously short-circuiting all of said non-inductively mounted. coils.

2. In multistage amplifier having a plurality of tuned input circuits, means for altering the tuning range of said circuits, each of said circuits including a sectional inductance comprising two coils connected in series, one coil being non-inductively mounted inside the remaining coil, said means comprising a switch for simultaneously short-circuiting all of said non-inductively mounted coils.

3. A radio receiver comprising amplifying circuits in cascade, each of said circuits having a tuning circuit connected thereto, said tuning circuits comprising coils in sections, and means for short-circuiting one section of all the coils simultaneously, each of said shert-circuited sections being in non-inductive relation to the remainder of the associated coil.

4. A receiver comprising radio frequency amplifying stages containing vacuum tubes in ciscade, each of said stages having a tuning circuit at its input side, said tuning circuit comprising a variable condenser and a coil in sections, and coupling means comprising a fixed resistance of the order of 25,600 ohms in the output circuit in each tube and a capacity of the order of 10 micromicrcfarads in the input circuit of each tube, and means for simultaneously short circuiting a section of all of said coils.

LESLIE F. CURTIS. WILLIAM F. COTTER. LEONARD E. EASTMAN.

Images