US2238475A - Tuning device for radio receivers - Google Patents

Description

April 15,1941- F. A. MITCHELL TUNING DEVICE FOR RADIO RECEIVERS Filed Sept. 1, 1938 4 Sheets-Sheet 1 SPEAKER TERMINALS ll l-L INVENTOR FRANK ALLENZ/TCHELL BY ATTORNEY April 15, 1941. F. A. MITCHELL 2,238,475

TUNING DEVICE FOR RADIO RECEIVERS Filed Sept. 1, 1958 4 Sheets-Sheet 2 :Qm o

OFF 1Q 0 i5 o l al 2 w.

INVENTOR FRANK LE MITCHELL #i wwl L/ Afro/um April 15, 1941.

F. A. MITCHELL TUNING DEVICE FOR RADIO RECEIVERS Filed Sept. 1, 1938 4 Sheets-Sheet 3 F1 19. INVENTOR FRAN/(Al NM/TC/IELL 7% from/5r April 1941- F. A. MITCHELL TUNING DEVICE FOR RADIO RECEIVERS 4 Sheets-Sheet 4 Filed Sept. 1, 1938 ITCHELL INVENTOR FRANK AL EN By W A TTORNEY Patented Apr. 15, 1941 7 2,238,475 TUNING DEVICE roa aanro aacnrvnas Frank Allen Mitchell, London, England, assignor to Electrical 8; Musical Industries Limited, Mlddlesex, England, a com any of Great Britaln Application September 1, 1938, Serial No. 227,881 In Great Britain September 1, 1937 Claims.

This invention relates to tuning devices for radio receivers of the kind in which the tuning device can be rotated to one or other of a pluralit'y of predetermined positions by the oper ator either at the receiving apparatus or from a remote point. I

Proposals have heretofore been made whereby a radio receiving apparatus may be tuned mechanically under the control of the operator as, for example, by depressing one'of a plurality of push buttons which causes rotation of a tuning condenser by energising an electric motor, the tuning condenser being rotated by a predetermined amount after which it is brought to rest in the desired station receiving position.

Other proposals have also been made but most of these are not satisfactory owing to the complication of the mechanism employed resulting in large manufacturing costs, service difliculties and uncertainty in operation.

It is the chief object of the present invention to provide an improved tuning control-for automatically rotating a tuning device, for example, a tuning condenser, into a plurality of stationreceiving positions under the control of the operator either at the receiver or from a remote point.

Accordin to the invention the tuning control comprises a selector member having conducting and insulating zones thereon and a plurality of electrical contact members in engagement with said selector member so as to be capable of contacting with the insulating or conducting zones thereon, some of said contact members serving to control directly or to operate relays to control an electric motor for rotating said selector member and a tuning device connected thereto to predetermined positions, the arrangement being such that when a selected contact member is in engagement with an insulating zone of the selector member the electric motor is rotated in one direction and when a selected contact member is in engagement with a conducting zone the electric motor is caused to rotate in the reverse direction.

In the preferred form of the invention the selector member comprises a disc directly coupled to the shaft of the tuning device which, in most cases will be a variable condenser, the disc generally being of conducting material but having an insulating zone thereon, said insulating zone being so formed that during rotation of said disc the contact members bear either on the conducting or the insulating zones of said disc. The disc is arranged to be angularly moved through with the tuning condenser and the Junction between the insulating and the conducting zones of said disc is preferably of serrated iorm and during angular movement of said disc an edge of each serration moves past a corresponding one of said contact members. The tuning control may be operated by a selector mechanism of the type disclosed in United States Jating zones associated with the particular contact member. If, on depressing one 01' said push buttons, the associated contact member is in engagement with the insulating zone of said disc,

then the tuning condenser would be rotated in one direction, but if the selected contact member is in engagement with the conducting zone of said disc, then the tuning condenser will be rotated in the opposite direction.

In order that the present invention may be clearly understood and readily carried into eflect it will now be described with reference to the accompanying drawings in which:

Figure l is a circuit diagram of a tuning ccntrol in accordance with the invention,

Figure 2 is an enlarged view of the selector member,

Figure 3 is a plan view of a selector box having a plurality of push buttons for use in the invention.

Figure 4 is a plan view of the underside of the box shown in Figure 3 with the bottom of the box removed,

Figure 5 is a cross-section view taken along the line 8-5 of Figure 4 with the bottom of the box in position,

Figure 6 and Figure 7 are respectively side elevation and plan views of a modification showing another selector member which may be employed in accordance with the invention,

Figures. 8 and 9 show different methods of supporting and adjusting the contacts on ihe selector member,

Figure 10 illustrates an alternative form of selector box having a slidable selector, and

Figure 11 is a circuit diagram of another modiflcation having a simplified form of selector member using circumferential adjustment for the contact members which may be employed in accordance with the invention.

Referring now to Figure l of the drawings, the mechanism in accordance with the invention comprises a selector member 5 which, as shown in detail in Figure 2, comprises a disc of metal I, the metal constituting the aforesaid conducting zone whilst the zone of insulating material 8 is recessed into the surface of the disc or arranged in an aperture stamped out from the disc. As aforesaid, the disc is rotated with the tuning condenser, not shown, and arranged for rotation through an angle of 180 by a reversible electric motor hereinafter referred to. Arranged diametrically of the disc 1 is a plurality of contact members A-O, as shown in Figure 1, the contact members being mounted ina block 9 of insulating material the ends of the contact members having contact elements which bear on the surface of the selector disc I. Since the disc rotates only through 180", eight of the contact members are arranged on the righthand side of the disc and the other seven contact members are arranged on the left-hand side, as shown in Figure 1, the disc '5 having insulatin zones arranged in the manner hereinafter referred to. The contacts A, B, C, D, E, F, G, and the contacts H, I, J, K, L, M, N on either side of the disc serve as station selector contacts, the function of the remaining contact 0 being hereinafter referred to. The junction between the conductor and insulating zones of the disc is, as shown in Figure 2, of serrated form providing edges ill. An edge is is provided for each contact and each edge is spaced radially from the centre of the disc a distance such that it is adapted to move in a path which will bring it into engagement with its associated contact 4 member. Referring to Figure 2, the selector member is shown in its extreme position of movement in ananti-clockwise direction and the edges H! at the upper half of the member 6 are adapted to move into engagement with their respective contact members A G when the selector member is moved in a clockwise direction. Similarly the edges to at the lower half of the member 6 are adapted to move into engagement with contacts H N when the selector member is rotated in a clockwise direction.

The edges ID of the insulating zone are spaced angularly round the selector member so that the The arrangement of the apparatus is such that the selector member and tuning element of the radio receiver are brought to rest when an edge Ill of the insulating zone of the selector member lies substantially in engagement with the selected contact member, and the radio receiver is "tuned in to receive a selected station when the tuning element is in that position, as will be described more fully hereinafter. Each of the contact members A-O is connected by the leads shown to a corresponding number of sockets mounted on a plug panel indicated by the dotted line it, the plug sockets being lettered with the same lettering as the contact members. To select a particular station, in the example shown in Figures 1 to 5, one of a plurality of five push buttons i2 is depressed, the push buttons being associated with selector and switch controls mounted in a selector box shown in detail in Figures 3, a and 5. For the sake of convenience in Figure 1 only one push button it? and associated selector switch contacts are shown and five sockets A, D, H, I and M are connected by a single lead to one of the switch contacts although it will be understood that each or" the said sockets will, in practice, be connected by a separate lead to the appropriate switch contact or" the respective one of the iive push buttons shown in Figure 3. If desired, the selector box 52 may contain fourteen push buttons for association with the fourteen contact members A@ and H-N, but in the arrangement illustrated in Figures 8, e and 5 where only five push buttons are employed, a removable multipin plug may be provided whereby the push outtons may be connected to any group of five contact members according to the requirements of the operator. The selector box or panel may be mounted on the cabinet of the radio receiver or in a position remote therefrom and connected to the plug panel by a flexible or other lead termh mating in the removable plug, or, if desired, several selector boxes or panels may be connected to the same radio receiver.

Each selector switch comprises a push button l2 projecting through an aperture in the selector box and a bank of switch contact fingers it, it, i5, i6 is located beneath the push button. The uppermost contact finger it is insulated fiomthe push button bye strip ll of insulating material and is adapted to engage with contact finger l5 to close a circuit when push button I? is de pressed. Coniact finger i5 is insulated from contact it by the strip it of insulating material and, when depressed by movement of the push but ton, contact finger l5 causes contact finger it to engage contact finger it to close a second circuit. The lowermost contact l3 lies adjacent the metal base plate of the selector box, which plate is connected to earth in any suitable manner. A plate of insulating material it is mounted on the metal base plate so that the contact ilnger i3 is insulated from the base plate along a portion of its length, but the arrangement is such that the endof contact finger it under the push button i2 is adapted to come into contact with the base plate when the push button is depressed to close a third circuit. When a push button is depressed all of the contact fingers i3, i4, i5 and I6 are depressed and when the push button is released it is held in an intermediate position by a latch 20, which is common to all of the push buttons, as shown in Figures 4 and 5, the latch being operated by a relay 2i and released as hereinafter referred to. The latch 28 comprises a bar pivoted on trunnions 2?; and the end of each push button is provided with a shoulder 23 with which the latch engages when the relay is energised to draw the latch towards the push. button.

Direct current for the operation of the relay 2i, and further relays hereinafter described, is derived from a contact rectifier 24 connected to a secondary winding 25 of a. mains transformer indicated generally at 25. The selector member 6 and the tuning condenser are rotated by a reversible electric motor which, as shown, may be an induction disc motor and is supplied with current by tapping the primary winding 2! of the transformer, as shown. The electric motor has a main current winding 28 and two voltage windings 29 and Elli which control the direction of rotation of the motor, only one of said voltage windings being in circuit at a time. Current is supplied to the motor on depressing one or other of the push buttons l2 through the medium of a relay 3|. The relay 3| is associated with contact iingers 33, I4, 35, 33, 31, 38, and 33, which are normally maintained apart, as shown in Figure 1, but which, when the relay 3| is energised, as hereinafter described, are closed, the contact finger 33 engaging contact finger 34, contact fingers 35, 36 and 31 engaging one another, and contacts 38 and 33 likewise engaging one another. A further relay 32, is provided, associated with contact fingers 40, 4|, 42, 43, 44, 45 46, 41 and 48, which are normally maintained in the positions shown in Figure 1, but which, when the relay is energised, as hereinafter referred to, are closed in the following manner. The contact 4|! is moved out of engagement with contact 4| and the contact 42 moved into engagement with 4|. Contact 43 is moved out of engagement with contact 44 and contact 45 moved into engagement with contact 44. Contacts 48 and 46 are engaged and thereafter contact 43 moved out of engagement with contact 41. Relay 3| controls the supply of current to the current coil 28 of the motor and also to the changeover switch represented by contact fingers 40, 4|, 42 which permits current to how through one or other of the potential coils 29, 30 of the motor.

Relay 32 controls the direction of rotation of ie motor and when energised opens the circuit of potential coil 3|! which energises the motor to rotate the selector disc in a clockwise direction and closes the circuit of potential coil 29 to reverse the direction of rotation of the motor and cause movement of the selector disc in an anti-clockwise direction. The various switch contacts associated with the relays 3| and 32 are connected to the motor, to the contacts associated with the selector member and to the contacts of the selector box, as shown, the contacts 31 and 45 being connected to' earth. The mains transformer 23 may be the same transformer that supplies current for the operation of the radio receiving apparatus and, as shown, further secondary windings are provided for heating the valves and Supplying operating potentials, the secondary winding 49 supplying current to the cathodes of the valves through normally closed contacts and a further secondary winding 5| supplying current for the rectifier valve of the receiving apparatus through normally closed contacts 52, whilst' a pilot lamp 53 normally derives current fromthe primary 21 of the transformer through normally closed contacts 54. The function of the contacts 5!, 52 and 54 will be hereinafter referred to.

The operation of the mechanism is as follows. Assuming that it is desired to select a station represented by the contact M, and that the selector disc is, as shown in Figure l, in its extreme position of anti-clockwise rotation so that contact M bears against the insulating zone of the disc, then the appropriate push button i2 is depressed which, closes the contacts l3 and i4 and causes contact i3 to bear against the earthed plate of the selector box. Earthing of contact i3 closes a circuit which includes the transformer secondary 25, rectifier 24, relay 3|, conducting lead R, switch contact I3, earth plate of the selector box and so to earth and back to the transformer winding 25. Relay 3| is thus energised and closes switch contacts 3334. Closure of switch contacts 3334 completes the driving motor circuit and current flows from transformer primary 21, switch contacts 33, 34,

ear'thed plate.

current coil of motor, and back to the transformer primary 21.- Current also flows from switch contacts 33, 34 to the closed switch contacts 40, 4| controlled by relay 32, potential coil 30, and back to transformer primary. The driving motor is thus energised, and since potential coil 30 is energised the selector disc and the tuning element of the radio receiver will commence to rotate in clockwise direction, and the edge in of the insulating zone of the selector disc will move towards contact M.

Referring again to the selector switch, pressue upon push button |2 has also brought switch contact |4 into engagement with contact member I3. A further circuit is thus closed which includes transformer secondary 25, rectifier 24, lead U, relay 2| in the selector box, contact members I4 and I3, earthed plate of the selector box and transformer secondary 25. Relay 2| is then energised, and the latch 20 is drawn into position to latch push button |2.

It will be understood that the energisation of relays 3| and 2|, the closure of the various contacts controlled by relay 3| and movement of latch 20 of relay 2| is effected instantaneously, and after a momentary pressure has been applied to press button l2, pressure upon the press button may be removed so that the bias of the switch contact blades will return it to an intermediate position in which it is latched by the latch 20. When the push button i2 returns to its intermediate position selector switch'contacts |3, |4 remain in engagement, but contact is broken between switch contact I3 and the The motor controlling relay 3| and the selector box latching relay 2| continue to be energised, however, through the following circuits: terminal R of relay 3|, resistance l3, closed switch contacts 46, 41 of relay 32, switch contacts 35, 36 and earthed contact 31 of relay 3|, which are closed since relay 3| is energised. Current also flows from contact S on relay 2| through selector switch contacts l4, l3 and resistance l3.

Referring again to the act of pressing the selector switch push button l2, this action also causes contacts |5, IE to close, and the said contacts are connected in a circuit which includes thefearthed selector disc, contact member M,- socket member M on plug panel selector box switch contacts l5, i6, lead Q, switch contacts 46, 48 of relay 32 which are at present open, since relay 32 is not energised.

As stated hereinbefore, the selector disc is rotating in a clockwise direction and the edge ill of the insulating zone is moving towards contact element M. As soon as rotation of the selector disc is sufficient to cause the contact element M to pass from engagement with the insulating zone to engagement with the conducting zone of the disc, relay 32 is energised through transformer secondary 25, rectifier 24, relay 32, lead Q, closed contacts 38 and 39, selector switch contacts |6, |5, socket M on plug panel H, contact member M, selector disc, earth and so back to transformer secondary 25.

Energisation of relay 32 causes changeover switch contacts 40, 4|, 42 to be reversed thus deenergising voltage coil 30 of the electric motor and energislng voltage coil 29 of the motor. The direction of rotation of the motor and thus of the selector disc 6 and the tuning element is reversed and the selector disc is rotated in an anticlockwise direction to bring the insulating zone of the selector disc intoengagement with the contact element M.

Energisation of relay 32 also causes contact member 48 to engage with contact member 48 to provide alternative path for current flowing through relays 3|, 2| and resistance l3 and immediately after contacts 48 and 48 engage contact 46 is disengaged from contact 41. The effect of this is to transfer control of relays 3| and 2| from switch contacts 35, 38, 31 of relay 3| to the selector disc and current now flows from relays 3| and 2|, through resistance 13*, switch contacts 46 and 48 of relay 32, lead Q, switch contacts l8, ii, of selector switch, contact socket M of plug panel ll, contact member M, the conducting zone of the selector disc and so to earth.

The motor continues'to rotate the selector mernber in an anti-clockwise direction, after relay 32 has been energised, until the contact M bears against the insulating zone of the selector member and when this position is reached the circuit for the motor is disconnected through the opening of the contacts 33 and 34 on relay 3!; The deenergisation of relay 2| which occurs at the same time as de-energisation of relay 3| owing to the circuit being broken by contact member M bear-. ing against an insulating zone, causes the push button of the selector switch to be unlatched and thus allows switch contacts l3, I4, I! and I8 to be opened, and the press button l2 to be returned to its off position due to the return movement of uppermost contact finger l8. Relay 32 is thus de-energised since the contacts l5, l8 have opened. In this position the .tuning cbndenser has/been rotated to a position to tune in a-station represented by contact M, the selector meniber 8 having been rotated until, as above mentioned, the contact M is in engagement with the insulating zone of the selector disc. ,"I'hreceiving apparatus is thus tuned to the/required station and the relays and the motor are de.-energised and the various contacts ,are returned to" the positions shown in the drawing;

When the desired station has been tuned in and the relays have thus been de-energised, it will be possible to operate the tuning mechanism from another selector box 82 located in another position but connected to the plug panel II by parallel circuits.

In some cases the position of the selector disc I may be such that the selected contact member is bearing upon a conducting zone of the selector disc. In such cases relays 2|, 3|, and 32 will all be energised substantially simultaneously when the press button is depressed and the various contacts operated by the press button, and relays 3| and 32 will be opened or closed in the manner hereinafter described, ,so that the motor rotates the selector disc in an anti-clockwise direction .until the selected contact member engages with the insulating zone of the disc to de-energise relay 2I and 3| and to cause the circuit of relay 32 to be de-energised.

It will be appreciated from the above that when the stationary contact of a selected station bears against an insulating zone of the selector member, relay 3| will be energised 'so that the motor rotates the selector member 8 in a clockwise direction. Conversely, when the contact member of a selected station bears against a conducting zone of the selector member 6, the selector member will be rotated in an anti-clockwise direction.

It will also be appreciated from the above that although the selector disc may move in either dijustments of the apparatus to be made with great accuracy.

A radio receiver to which the invention may be applied will, in most cases, be provided with the, usual manual control and it, for example, during such manual control, the selector member 6 is rotated in a clockwise direction from the position shown in Figure 1 through it will be seen that the right-hand contacts on the selector member are traversed first by the insulating-zone and then by the conducting zone and one or more contact members mayengage the insulating zone again in this extreme position. If one of the contact members bearing against the edge of the insulating zone were selected, the result would be that only the relay 3! would be energised and the selector member would be rotated in a clockwise direction, whereas. the apparatus requires that under these conditions the selector member should rotate in an anti-clockwise direction. To obtain this reversal of rotations to an anti-clockwise direction in the extreme position, it is necessary to arrange for the relay 32 to be energised when a push button is depressed. This is eii'ected by so'shaping the conducting zone of the selector member 8 as indicated at 58 so that when the selector member is in the position above-mentioned the contact G bears against the conduct.- ing zone 88. The contact G, as will be observed from Figure l, is connected to the contact 38 of relay 3| and when the relay 3| is energised the contact 39 is moved into engagement with contact 38 with the result that current then flows through relay 32, the contacts associated with the relay 32 are operated as above described and, the direction of rotation of the motor is reversed To enable the receiving apparatus to be switched out of operation-from the selector box, a further button HA is provided as shown in Figure 3, this button being connected to the contact Own the selector member 8 so that when the button HA is depressed the selector member 8 is rotated in an anti-clockwise direction until the extreme position is reached. It will be observed i'rom Figure i that the contact 0 is normally in engagement with the conducting zone I, but in the extreme position it comes into engagement with the insulating zone, which is specially shaped for this purpose, as indicated at 51. The selector member is therefore brought to rest in this position. The contacts 58, 52 and 54 are mounted adjacent the selector member 8 and a striker 58 is provided on the selector member so that in the extreme position of said member the striker engages the contacts to open the circuits controlled thereby so that the current to the receiving apparatus is switched off;

' The contacts 38 and 31 associated with relay 3| and contacts 44 and 45 associated with relay One such arrangement suitabl ior a moving.

coil loudspeaker with a permanent magnet is illustrated in Figures 1 and 4 of the drawings.

output transformer of the radio receiver, the primary winding of which is not shown, is earthed at one end and'the other end is connected to switch contact 44 of relay 32. A lead from contact 43 is connected to one oi two plug sockets 59 and the other plug socket is connected to the adjustable arm 40 of a potentiometer the resistance element 05 oi which is connected at one end as illustrated in Figure 1 to the lead from contact 43 and at the other end to contact O or plug panel II and so to earth.

The plug sockets I! are adapted to receive the speech coil leads of a loudspeaker, not shown, and the strength of the repmduced sounds may be controlled by adjustment of the arm of the potentiometer which is provided with a suitable control member projecting through the selector box and terminating in a control knob 0|.

It'will be appreciated that the distance between adjacent edges II of the selector member 0 corresponds to a range oi adjustment of the the vertical heights of the station selector contacts bearing against the selector member I, it is possible for the operator to select what sta ticns he may require to be selected on operation oi the push buttons. To enable the operator to adjust the station selector contacts, it is prei'erred to mount the station selector contacts in such manner in the insulating block 0 that their vertical positions can be adjusted. For this purpose the station selector contacts may be held in grooves or slots in the block I and screws may be provided in engagement with the contacts so that on rotating the screws the vertical positions of the station selector contacts can be adjusted.

It will be understood that if desired a number of selector discs and associated contact members may be employed and, furthermore, instead of employing selector discs, drums or cylinders may be used.

Reference is now made to Figures 6 to 9 of'the accompanying drawings which show a modified form of selector member and contacts that may be employed in accordance with the invention.

In Figures 6 and 7 the tuning device of the receiver is shown as a condenser IOI and the cabinet front of the receiver is shown by the chain line I02.

The station locating mechanism is preferably supported entirely on the condenser mounting plate I III to keep strict relation between the parts and to minimise vibration.

The station selector member in the form 01' a disc I03 is rigidly mounted on the condenser shaft I which also carries the usual station indicating pointer I00. The selecting member I03 is engaged by the friction drive I01 which is adapted to be rotated in known manner by means of the hand operated knobs I, or by an electric motor (not shown) such as the motor described in connection with Figures 1 to 4 of the accompanying drawings which is coupled to the control shaft 9.

. 10 The secondary winding 44 (Figure 1) of the The mounting plate I I 0 also carries a plurality of contact members III to III in spring engagement with the selector member 3, the contacts III to H9 being mounted in grooves cut in a block I20 of insulating material rigidly attached to the plate II. The plate III also rigidlygsupports the frame I2l, which carries adjusting means whereby the contacts III to III may be adjusted to predetermined positions.

The contact members III to II! are each preferably in the form of a fiat strip of spring-y metal having a contact point I22 at one end and bent to a.V shape at the opposite end, as shown in Figures 8 and 9, so that pressure on the short limb will keep the contact strip III located in its groove in the block I20. The extreme end of the short limb is bent at right angles and engages the recessed end I23 of an adjusting lever I24 pivoted at I25. The lever I24 has a toothed segment I20 formed thereon which is engaged by a screwedadjusting member I2'I mounted on the frame I2I carried-by the mounting plate IIO as tuning condenser and, consequently, by adjusting hereinbefore mentioned. Each lever I24 is spaced from adjacent levers by a spring pressed nonrotatable spacer I32 whereby they are adjustable independently. The screw I2! is mounted so that it has no end play, but can be rotated by the knurled head I28 or by the slotted head I29 to rotate the lever I24 and thereby move the contact strip III and contact I22 angularly relative to the station selector disc I03. Similar adjustment means may be provided for the contact strips III to III.

Each of station selecting contacts, III to II! is adapted to operate in conjunction with one of the stepped edges of an insulated zone I04 as described in connection with Figures 1 to 5.

The zone of insulation I04 formed on the selector disc I03 is formed witha plurality of radially spaced steps, as shown in Figure 7, so arranged that the adjustable contacts III to H0 may be supported in parallel relation and with their contact points lying approximately along a line radial to the disc I03. The adjusting levers I24 may thus be mounted on a common shaft I25 supported by the frame HI and the screwed adjusting members I21 may be arranged in one or more lines parallel to the shaft I25. The ends of the adjusting members I21 preferably pass through apertures in a panel I33 mounted on the frame I2I and the panel is 1 located in an aperture in a wall of the cabinet whereby adjustments may be made from the exterior of the cabinet. The panel may be provided with waveband or other markings to indicate the frequency range of each adjustable contact of the rotary switch.

Figure 8 shows a modified form of adjustment device I24 for the adjustable contacts III to III.

The lever I24 is formed with a projection I 2411 which is located in a recess in the contact III, and the edge I26 oi the lever is provided with teeth which mesh with a worm I2I. The worm shaft carries a knurled disc I 28 which projects through an aperture in a wall of the cabinet and is adapted to be rotated to adjust the contact III.

Figure 9 shows a further modification of the adjustment device I24 wherein the lever itself projects through an aperture in the cabinet and may be rotated to adjust the contact III.

Referring now to the modifications shown in Figures 10 and 11 of the accompanying drawings the station selector mechanism shown in Figure by a chosen station name is selected, and a single press-button 223 adapted to put the contact member 20i into operative circuit with the relays so that they function in the some manner as described with reference to Figure 1. In selector panel unit Figure 10, 222 may be connected to the plug panel ii in place of or in parallel with the press button box 52 in Figure l, and the remainder of the circuit beyond the panel i i may remain as in Figure 1.

When a desired station is to be selected, the sliding contact 205 is moved to the desired stud 204 (c for example) to connect the adjustable Contact member operating on the disc 6 (Figure 1) to the spring contact finger 205 (Figure 10). The actuating button 203 is then pressed to close contact fingers 205, iii and i4 and contact fingers i5 and i5. This permits current to flow from the rectifier 24 (Figure 1) through magnet 206, contact fingers i4, 205 to earth through connector P as described with reference to Figure 1, to cause magnet 206 to hold the contacts to and N as well as I3 and it closed so that current is then able to flow from the rectifier 24 through relay 3i (Figure 1) and the holding magnet 20B re turning to earth through connection R. and resistance I 3A as described with reference to Figure l. The press-button is returned as soon as the operators finger is removed, by the spring contact 205, the magnet 200 keeping the circuit active until the desired station is found. In the modification illustrated in Figure the electrical components of the complete mechanism operates exactly as described with reference to the circuit of Figure l. The magnet 208 becomes demagnetised when the desired station is found and the selector panel contact fingers i3, l4, l8 and I5 return to their neutral position to break the circuit through the slider 2% so that any other station may be selected on it or on another panel or press-button selector working in parallel therewith.

The above selector mechanism shown in Figure 10 or the press-button panel (Figures It, 55, 4 and 5) can be built into a portable loud-speaker case, the connections 59 (Figure 1) being permanently connected to the loud-speaker. The case or the panel may sometimes carry an additional switch or press-buttons to operate a wave-change device. such as a relay, on the wireless receiver, for on ample in the manner referred to in U. 8. Patent No. 2,100,609 previously referred to.

Another modification of the invention is shown diagrammatically in Figure 11 in which the disc 2% of insulating material has a metal segment 208 inserted therein so that the surface of 2b? and 208 are fiush. The disc is rigidly attached at 209 to the rotatable tuning element of a wireless receiver and the whole is adapted to be driven by the reversible electric motor 2 iii. A plate preferably of insulating material 2 is non-rotatably mounted in front of the rotatable disc 20? and carries a number of sliolable contact members 2l2 capable of adjustment into desired station selecting positions in the following manner. The tuning element (not shown) is first turned by hand until the desired station is in tune, then one of the contact members 2l2 is released by means of the-screw H3 and is slid around the slot 214 until the contact edge 2!? lies on the insulated portion close to the edge 26E of the metal segment 2055. The screw 253 is then tightened and the name or cypher for the station inserted in the control box or panel 2W against th press-buttom switch or stud by which the r or is reversed whereupon contact 22'! opens.

the use of relays the circuit may be arranged as I shown in Figure 11, in which the control panel 217 has a series of press-button 230, each open ating a. contact finger 2l8 connected by a separate lead 288 to its associated contact member 2l2. The A. C, supply indicated conventionally in Figure 11, from the mains or a. transformer (at 25 volts for example) is connected to the contact finger 220 which is preferably in the form of a comb so as to be common to all the independent contact fingers 2l8. The other side of the A. C. supply is connected to the current coil 22] and the potential coil 222 of the (induction) motor 2I0. The opposite side of the current coil 22! is connected to the metal segment 208 on the disc 201.

The contact fingers 223 are connected to the opposite side of the potential coil 222, and the above connections are suflicient to cause the motor to run in one direction for example, clockwise, if the selected contact 2l2 happens to be on the metal segment 208. To enable the motor to run in the opposite direction when the circuit is not complete through 208 and 2l2 a suitable condenser 224 is inserted between the current coil 22i and the A. C. supply so as to change the phase between the coils 22l and 222. This is achieved by using another group of contact fingers 225 adapted to permit current to flow through the condenser 224 when the press button 230 is fully depressed by hand, so that 225 touches the contacts 220A which are connected to the A. C. supply and which will cause the motor 2) to rotate the disc 201 in a reverse (1. e. anticlockwise) direction while the condenser 224 is not being shorted by contacts 208 and 2l2.

If the circuit were left as above, the motor would tend to hunt when the contact edge 215 reached the edge 2? of the metal plate, and to prevent this it is desirable to attach a friction disc device 226 on the motor shaft so as to close a contact 221 when rotating in one direction for example in an anti-clockwise direction. The contact 227 closes a D. C, circuit which may be from a battery H. T, radio or a separate rectifier to operate the magnet 228 to hold the contacts 225 and 220A together until the motor 2I0 stops The contacts H8, 220 and 223 are held closed by the mechanical latch 229 in known manner, and will release the selector contact finger 2l8 when another button is pressed to select another station or to disconnect the control.

The above circuit arrangement functions similarly to that described with reference to Figure 1, as follows. When a station is to be selected and the chosen contact 212 happens to be in the insulated portion of the disc 201, the action of pressing the button 230 closes all the contact fingers 2l8, 220, 223, 220 and 220A, but as there is an open circuit between 208 and 2l2 current only flows between 220, 223 and coil 222 and between 220A, 225, condenser 224 and coil 22! whereby the motor rotates in an anti-clockwise direction and closes contact 221 to energise magnet 228 to keep 220A and 225 closed so that the motor continues to rotate the station selector disc 20'! and tuning element in an anti-clockwis direction until the contact edge 2|! touches the plate edge 216. When this occurs A. C. current immediately flows through the lead 2|! direct to the current coil 22!, thus reversing the motor and opening contact 22! whereby contact fingers 220A and 225 are opened: at the same time the disc 20'! is slightly reversed so that the edge H5 is again on the insulated portion 201 and no A. C. current can then reach the coil 22| through lead 219 or condenser 224 and therefore the motor stops, leaving the disc 20! and the tuning element in the desired tuned position.

Similar arrangements as have been described in connection with Figure 1 to provide rotation of the electric motor in an anti-clockwise direction when the selector member has been rotated to its extreme clockwise position and for breaking of the circuit by means of the insulating zone being shaped as at 56 and 51, Figure 2 may be provided in the modification described in connection with Figure 11 of the accompanying drawings by suitable shaping the insulating and conducting zones of the selector member 201.

The above circuit arrangements should mechanically tune a wireless receiver with sufllcient accuracy for all frequencies below 1500 kc. (above 200 meters), but if higher frequencies are required or if easier adjustment is desired, it is advisable to make use of automatic frequency control" in the radio circuit in addition to the above. I

I claim:

1. In a tuning control for radio receiving apparatus provided with an adjustable tuning element, a selector member having a surface provided with conducting and insulating zones, a plurality of electrical contact members in sliding contact with the surface oi the selector member, a reversible motor for driving both said tuning element and the selector member, a motor circuit for connecting the motor to a source of energizing current including said contact members and a plurality of operable relay devices for controlling the operation of said electric motor so as to adjust said selector member and said tuning element to predetermined positions, said motor circuit being arranged so that when the motor is energized through a selected one of the contact members which is in engagement with an insulating zone of said selector member, the electric motor is rotated in one direction and when a selected one of said contact member i in engagement with a conducting zone of the selector member the electric motor is caused to rotate in the reverse direction.

2..In a tuning control arrangement for radio receiving apparatus as described in claim 1, a pair of voltage windings for said reversible electric motor, said voltage windings being arranged to control the direction of rotation of the motor, only one of said voltage windings being connected in the circuit during any one operation of the motor.

3. In a tuning control arrangement for radio receiving apparatus of the type described in claim 1, a pair of voltage windings for said electric motor to control the direction of rotation thereof, a source of energy for said motor, a condenser and means for applying energizing energy from. said source to the motor through said condenser when the selected contact is in contact relation with an insulating zone of the selector member so as to cause the motor to rotate in a reverse direction to which it is caused to rotate when the selected contact is in contact wlth'a conducting zone of the selector member.

4. In a tuning control arrangement for radio receiving apparatus as described in claim 1, a plurality of selectively operable means corresponding to said electrical contact members and adapted to select upon operation any one of said contact members comprising push buttons any one of which is adapted to be depressed to select the corresponding contact member, latching means for holding the depressed one of said push buttons in a depressed position during operation of the motor tuning means and means for automatically releasing said push button upon completion of the tuning operation.

5. In a tuning control arrangement as described in claim 1, change-over switching means connected in said motor circuit and efl'ective only when a desired predetermined position of the tuning element is approached from one direction, for causing the motor to move the tuning element beyond the desired position and reversing the direction of rotation of the motor so as to move the tuning element back toward the desired position whereby the final rotation in adjusting the tuning element to a required position is always made in the same predetermined direction irrespective oi the initial direction of rotation of the tuning element.

FRANK ALLEN MITCHELL.

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