US2238475A - Tuning device for radio receivers - Google Patents

Tuning device for radio receivers Download PDF

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Publication number
US2238475A
US2238475A US227881A US22788138A US2238475A US 2238475 A US2238475 A US 2238475A US 227881 A US227881 A US 227881A US 22788138 A US22788138 A US 22788138A US 2238475 A US2238475 A US 2238475A
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Prior art keywords
contact
selector
contacts
disc
relay
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US227881A
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English (en)
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Mitchell Frank Allen
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Electrical and Musical Industries Ltd
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Electrical and Musical Industries Ltd
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03J—TUNING RESONANT CIRCUITS; SELECTING RESONANT CIRCUITS
    • H03J5/00—Discontinuous tuning; Selecting predetermined frequencies; Selecting frequency bands with or without continuous tuning in one or more of the bands, e.g. push-button tuning, turret tuner
    • H03J5/02—Discontinuous tuning; Selecting predetermined frequencies; Selecting frequency bands with or without continuous tuning in one or more of the bands, e.g. push-button tuning, turret tuner with variable tuning element having a number of predetermined settings and adjustable to a desired one of these settings
    • H03J5/14—Discontinuous tuning; Selecting predetermined frequencies; Selecting frequency bands with or without continuous tuning in one or more of the bands, e.g. push-button tuning, turret tuner with variable tuning element having a number of predetermined settings and adjustable to a desired one of these settings operated by auxiliary power
    • H03J5/146—Settings desired by a switch controlled together with the tuning member and which stops the control as soon as a desired position is reached

Definitions

  • 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.
  • 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.
  • a tuning device for example, a tuning condenser
  • 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.
  • 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,
  • 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.
  • FIG. 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.
  • FIGS. 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
  • 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.
  • 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.
  • 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.
  • a plurality of contact members A-O 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!
  • 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.
  • 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.
  • 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
  • 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
  • a further relay 32 is provided, associated with contact fingers 40, 4
  • ! is moved out of engagement with contact 4
  • 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
  • Relay 32 controls the direction of rotation of ie motor and when energised opens the circuit of potential coil 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
  • the function of the contacts 5!, 52 and 54 will be hereinafter referred to.
  • the closure of the various contacts controlled by relay 3
  • this action also causes contacts
  • the selector disc is rotating in a clockwise direction and the edge ill of the insulating zone is moving towards contact element M.
  • relay 32 is energised through transformer secondary 25, rectifier 24, relay 32, lead Q, closed contacts 38 and 39, selector switch contacts
  • Energisation of relay 32 causes changeover switch contacts 40, 4
  • 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
  • the effect of this is to transfer control of relays 3
  • 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!;
  • which occurs at the same time as de-energisation of relay 3
  • Relay 32 is thus de-energised since the contacts l5, l8 have opened.
  • 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;
  • 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.
  • , 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
  • when the stationary contact of a selected station bears against an insulating zone of the selector member, relay 3
  • 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.
  • the relay 32 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 is connected to the contact 38 of relay 3
  • 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.
  • 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
  • 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.
  • 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.
  • selector discs and associated contact members may be employed and, furthermore, instead of employing selector discs, drums or cylinders may be used.
  • 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.
  • 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 with a 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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 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.
  • FIG. 11 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 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 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.

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US227881A 1937-09-01 1938-09-01 Tuning device for radio receivers Expired - Lifetime US2238475A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB23864/37A GB501370A (en) 1937-09-01 1937-09-01 Improvements in or relating to tuning devices for radio receivers

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US2238475A true US2238475A (en) 1941-04-15

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US227881A Expired - Lifetime US2238475A (en) 1937-09-01 1938-09-01 Tuning device for radio receivers

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3493830A (en) * 1967-05-03 1970-02-03 Molex Products Co Seeking switch servocontrol including a unique commutator

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2433389A (en) * 1941-09-30 1947-12-30 Int Standard Electric Corp Remote control system for step-bystep adjustment of variable impedances

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3493830A (en) * 1967-05-03 1970-02-03 Molex Products Co Seeking switch servocontrol including a unique commutator

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GB501370A (en) 1939-02-27
FR842875A (fr) 1939-06-21

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