US2112687A - Remote control apparatus - Google Patents

Description

March 29, 1938. L. E. BARTON REMOTE CONTRbL APPARATUS Filed Feb. 28, 1934 3 Sheets-Sheet 1 INVENTOR Lay E. Barton March 29, 1938. L. E. BARTON REMOTE CONTROL APPARATUS Filed Feb. 28, 1934 31/9. Z. jfiga 3 Sheets-Sheet 2 u ucxuxlxlzums "I INVENTOR: Loy E.Bar ton March 29, 193$. 1- E, R- 0 I 2,112,687

REMOTE CONTROL APPARATUS Filed Feb. 28, 1934 a Sheets-Sheet s INVENTOR:

Lo E. Barton HTTOR EY Patented Mar. 29, 1938 Loy E. Barton,

Delaware Collingswood, N. J., assignor to Radio Corporation of America,

a corporation of Application February 28, 1934, Serial No. 713,330

8 Claims.

My invention relates to remote control apparatus and particularly to remote .control systems for radio receivers.

One object of my invention is to provide an improved remote control system by means of which a radio receiver may be tuned to receive any desired incoming signal.

A further object of my invention is to provide an improved remote control system which may be adjusted to tune the receiver to a predetermined number of transmitting stations.

A further object of my invention is to provide an improved remote control system having a small number of control buttons for tuning the receiver to a large number of stations.

A still further object of my invention is to provide an improved remote control system in which a tuning device and a volume control device may be actuated by a single motor.

A still further object of my invention is to provide an improved tuning dial mechanism for use with my remote control system.

In a preferred embodiment of my invention, I provide a motor which is coupled to the tuning condensers of a radio receiver through a friction drive and I further provide the tuning condensers with a magnetic brake for locking them in any desired position. The tuning condenser may be rotated in either direction by means of two push buttons located at a remote control point.

The brake is actuated in response to the tuning condensers reaching a position such that a radio station is tuned in, whereby they are immediately) locked in the correct tuning position and the fricf' 0 tion drive slips until the supply circuit to the motor is opened by releasing the push button in use at the remote control point. Preferably, the brake is actuated in response to the reception of a carrier wave having a predetermined amplitude. By providing the receiver with a sensitivity control, it may be so adjusted that the remote control system willtune the receiver to a selected group of stations, such as local or nearby stations, having the strongest signals. I

The volume control device for the receiver is driven through a second friction drive by'the same motor that drives the tuning condensers. In one embodiment, a magnetic brake is provided for locking the volume control deyice in position while the receiveris being tuned to a station. After the station is tuned in and the tuning condensers locked in position by their magnetic brake, the

volume control brake may be released and the volume increased or decreased by running the motor in one direction or the other. In another embodiment, a single magnetic brake is employed and the volume control device is operated by locking in position one of two discs which are connected through gears for rotation in opposite directions.

Preferably, the'receiver is provided with an improved tuning indicator consisting of two pointers mounted on a dial marked in kilocycles and resembling a clock face. One pointer is geared to rotate through ten scale divisions on a 360 degree scale while the other pointer rotates through one of its scaledivisions. The relative position of the two pointers indicates the station setting of the receiver. Obviously these pointers can be seen from a considerable distance, especially if the dial is illuminated, so that a person tuning the receiver from a remote point can tell what station the receiver is tuned to.

By mechanically connecting the dial pointers and the tuning condensers through a cam, the scale divisions of the dial may be evenly spaced throughout the tuning range of the receiver while employing tuning condensers of the straight-line capacity or modified straight-line frequency type.

Other objects, features and advantages of my invention will appear from the following description taken in connection with the accompanying drawings, in which Figure 1 is a circuit diagram of one embodiment of my invention;

Figure 2 is a' schematic diagram of a modified form of my invention;

Figure 3 is a schematic diagram of tuning apparatus which may be substituted for that shown in Figure 1 and which includes a side-view of my improved tuning dlal;

-to a first detector 1 through aradio frequency transformer 9.

The secondary windings of the transformers 5 and 9 have variable tuning condensers II and I3, respectively, connected thereacross in the usual manner, for-tuning the input circuits of the amplifier l and first detector 1 to the desired incoming signal. i

.circuit of the triode section 4|.

An oscillator I5 is coupled to the first detector 1 for the purpose of heterodyning an incoming signal to a lower intermediate frequency signal. The frequency of the oscillator output may be varied by means of a variable tuning condenser H.

The tuning condensers ll, l3, and I! are preferably units of a gang condenser, and may be varied simultaneously through a common tuning control indicated by a dotted line I 9.

The intermediate frequency output of the first detector is impressed upon the input circuit of an intermediate frequency amplifier 2| through an intermediate frequency transformer 23, the primary and secondary of which are tuned to make the transformer function as a band-pass filter having a pass range of s'ufiicient width to pass the intermediate frequency carrier and at least one signal side band.

It will be understood, of course, that the tuned radio frequency circuits of the amplifier l and detector '1 are also tuned broadly enough to pass the carrier of the incoming radio signal and at least one of its side bands.

The output of the intermediate frequency amplifier 2| is fed to the second detector 25 through an intermediate frequency transformer 21 tuned in the same manner as the preceding trans- I former 23. i

In the particular embodiment illustrated, the

second detector 25 is a diode rectifier which is one unit of a double diode-triode vacuum tube 29.

One terminal of the secondary 3| of transformer 21 is connected to the detector diode plate 33, while the other terminal of the secondary 3| .is connected to the cathode 35 through a re-' sistor 31, the resistor being shunted by means of an intermediate frequency by-pass condenser 99. The triode section 4| of the vacuum tube 29 functions as the first audio frequency amplifier. Its control grid 43 is connected to the plate-end of the resistor 31, whereby any audio signal appearing across the resistor 91 is impressed across the input of the triode section and an amplified audio signal appears in the plate circuit thereof. A resistor 39 reduces the intermediate frequency voltage that may otherwise get to the grid 43.

The amplified audio signal is impressedupon the input circuit of another audio frequency amplifier stage comprising an electric discharge device such as a vacuum tube.45. .The signal is im- 7 pressed upon said input circuit through a coupling system which, in the embodiment shown, includes an audio frequency choke coil 41 in the plate amplified by any suitable audio frequency am-v plifier, generally indicated at 51, and supplied to a loudspeaker 59.

It will be noted that the input circuit of the audio frequency amplifier 45 includes an electric.

discharge device 5| which may be a vacuum tube of the pentode type. The cathode-anode circuit of the tube BI is connected between the cathode 99 of tube 45 and ground to function as a selfbiasing resistor which may be given a very high resistanceto block the amplifier tube 45 when The upper end tuning between stations. In other words, the tube 6| applies noise suppressor control to the audio frequency amplifier tube 45 by functioning as a self-biasing resistor. This feature of my invention is described and claimed in my Patent No. 2,028,859, Serial No. 699,641, filed November 25, 1933, for Radio receivers, assigned to the same assignee as this application, and issued January The noise suppressor control is obtained, in the preferred circuit, through a diode-pentode vacuum tube 55 which is coupled to a transformer 51 sharply tuned to the intermediate frequency. As will be explained hereinafter, the tube 95 also functions to control the remote control circuit for tuning the receiver.

The tube 65 comprises a diode section 79 consisting of a diode plate 59 and a cathode II, and a pentode section 12 consisting of the cathode 1 I, a control grid 13, a screen grid 15, a suppressor grid TI, and an anode 19.

The input circuit of the pentode section 12 is coupled to the resistor 31 in any suitable manner for impressing the low intermediate frequency voltage drop of the resistor across the pentode amplifier input circuit.v In the drawings. this coupling device is shown as a small coupling condenser 9|, having a comparatively low impedance to signals at the intermediate frequency, but having an impedance to audio frequency signals sufficient to prevent appreciable audio signal being applied tothe control grid 19.

v A coupling resistor 93 is provided which is connected at one end to the control grid 13 through a conductor 95, and connected at the other end to the cathode Il through an audio-frequency bypass condenser 91. The coupling resistor 99 is shunted by a variable condenser 99 which may be adjusted for' the purpose of controlling the input voltage to the pentode amplifier l2.

The plate circuit of the pentode section 12 includes the primary winding 96 of the transformer 61 and a resistor 9|, the primary winding and the resistor being connected in series, and the lower end of the resistor being connected to a positive point on the voltage divider 92 of the power supply 95.

The secondary winding 69 of thetransformer 61 is loosely coupled to the primary winding 99,

and both the primary and the secondary are,

I ground to the lower terminal of a resistor III,

(which may have a resistance of the order of one megohm), and through the resistor III to the said other terminal of the secondary 99.

The sole function of the diode rectifier I9 is to increase the negative bias on the control grid I9 of the pentode section upon reception of a radio signal. Since a fiow of current through the diode rectifier 19 causes the upper end of the resistor lill to become negative, the control grid 19 also becomes more negative because of its connection to the negative end of the resistor Ill through a high impedance resistor ill.

Obviously an audio frequency signal will appear in the circuit of rectifier I0 which should not be impressed upon the control grid 13 of the pentode section. This is prevented by the audio frequency by-pass condenser 81.

It will be noted that the self biasing resistor 99, the resistor IOI, and the plate resistor 9I are shunted by the usual intermediate frequency bypass condensers I0'I, I05, and I09, respectively.

It will be apparent from the foregoing description that as soon as an intermediatev frequency signal is impressed upon the input circuit of the pentode amplifier 12, the control grid 13 of that amplifier will become more negative because .of the current flow through the circuit of the diode I0.

It may be noted that the change in bias on the control grid I3 depends; to a certain extent, upon the voltage drop produced in the self-biasing resistor 9-9, since this voltage drop is in series with the voltage drop along the resistor of the diode circuit. That these voltage drops are in series will be made evident by tracing the direct current path of the pentode section input circuit. It may be traced from the control grid 13 through the resistor 83, the high impedance resistor I03, through the diode circuit resistor IN to ground, through ground to the self-biasing resistor 99, and through the self-biasing resistor 99 to cathode II.

When there is no incoming signal, the plate current of the pentode amplifier portion. I2 is large, since the only negative bias on the control grid I3 is that due to the self-biasing resistor 99, and this negative bias is comparatively small. Consequently there is a large voltage drop in the plate resistor 9I, whereby the upper end of the resistor 9I is at a fairly high negative potential with respect to the upper end of the voltage divider 93. Also, the gain of amplifier I2 is low because of the low voltage on its anode l9.

As soon as the receiver is tuned to an incoming carrier wave, amplifier 12 supplies signalenergy to the diode 10, the voltage drop in the diode circuit resistor IOI increases the negative bias on the control grid I3, whereby the plate current of amplifier I2 decreases and the'upper end of the plate resistor 9I becomes less negative and the voltage applied to anode I9 is increased. It is the potential at this end of the plate resistor 9| which is utilized for actuating both the noise suppressor and certain remoteF'control apparatus, this point in the circuit being identified as point A on the drawings.

It should be noted that although the decrease in plate current tends to cause a reduction in the biasing voltage in the self-biasing resistor 99, the increased negative bias provided by the current flow through the diode circuit is much greater than any decrease in bias due to reduction in plate current.

The above described action of the diodepentode circuit whereby the upper end of plate resistor 9I becomes less negative in response to reception of a radio signal is preferably made a trigger" action by giving plate resistor 9I a proper resistance value. This trigger action depends upon the fact that the increase in gain caused by the increase in the plate voltage is greater than the decrease in gain caused by the increase in negative bias on the grid until a more or less definite bias is reached. In practice, a tube of the type known as RCA 237 has been found satisfactory for use as the tube 65.

A trigger amplifier employing a resistor in the plate circuit of a pentode tube is described and claimed in my co-pending application Serial No. 704,510, filed December 29, 1933, and assigned to the same assignee as this application. Y

In order to provide the proper control voltages for the noise suppressor biasing tube SI and for the magnetic brake of the remote control circuit, which is described hereinafter, a potentiometer III is connected between the upper end of the plate resistor 9| and the negative end of the voltage divider 93. This potentiometer consists of three resistor sections, R5. R6, and R1, the sections R5. and R1 having a high resistance value which 'may be of the'order of one megohm, while the resistor section R6 preferably has a lower value of the order of 100,000 ohms.

Referring now more specifically to the biasing tube BI, it has a cathode II3, a control grid II5, a screen grid III, a suppressor grid H9, and an anode I2I.

The anode I2I is connected to the cathode 53 of the audio frequency amplifier 45, while the cathode H3 is connected to ground, and through ground to the lower end of the volume control resistor 49. An audiofrequencyby-passcondenser I23 (preferably having a capacity of from 4 to 8 microfarads) is connected between the cathode H3 and anode I2I for by-passing the audio frequency signal around the plate impedance of the tube BI. Thus it will be seen that the plate'impedance of the tube BI is connected in the oathode circuit of the audio frequency amplifier 45 to act as a self-biasing resistor, while the audio frequency signal appearing across the volume control resistor 49 is impressed upon the input circuit of the audio frequency amplifier 45 through the conductor I25 and through ground and the by-pass condenser I23.

The anode I2I of the tube 6| preferably is connected to apositive point on the voltage divider 93 through a resistor I21 which may have a value of from one-fourth to one megohm. This resistor serves to maintain a high anode to cathode voltage when the tube 45 is blocked because of any leakage current taken by tube 5|. The effect of the use of resistor I21 in the circuit is to make the noise suppressor more rapid and positive in operation.

When there is no incoming signal, the plate impedance of the biasing tube BI is maintained at a very high value by means of the control grid I I5 which has a high negative potential sum'cient. to block the tube. This high negative grid potential is obtained by connecting the control grid I I5 to the lower end of the resistor R1, preferably through a resistor I29, this end of resistor R1 being-identified as point B. Resistor I29 may be given a value of approximately one-half megohm.

The negative voltage applied to the control grid H5 from the point B is not critical in value, approximately 20 volts on the grid, with no incoming signal, having been foundsatisfactory when employing an RCA 57 tube as the tube 6|.

Point B is given the desired negative voltage divider is 150 volts negative with respect to iii ground, while the upper end of the voltage divider is 250 volts positive with respect to ground. With no incoming signal, and a plate resistor 9i having tiometer III (identified as point A) 25 to 50 volts positive with respect to ground. The point B is then approximately 20 volts negative with respect to ground, and the upper end of resistor R5 (identified as point C) is still more negative with respect to ground.

Thus, with no incoming signal, a constant biasing voltage is applied from the point B to the control grid 5 of the biasing tube BI, a by-pass condenser I3I being connected between the control grid I I5 and the cathode II3 for preventing audio frequency'voltages or other ripple voltages from being applied to the grid.

The biasing voltage applied to the control grid III when there is no signal input is sufilcientto block the tube 8|, thereby making its plate resistance so high that the audio frequency amplifier tube 45 is likewise blocked. The blocking potential applied to tube 45 may become as high as 80 volts, this being much higher than necessary I to block a tube such as an RCA 56 which has been found satisfactory for use with the RCA 57.

when the receiver is tuned exactly to an incoming signal, an intermediate frequency voltage is impressed upon the input circuit of the pentode section 12, whereby the voltage drop in the plate resistor 9I is decreased in value, causing the point B to assume a value sufilciently less negative to unblock the biasing tube 3i and greatly lower its plate impedance. This causes a normal biasing voltage to be applied to the grid 53 and the audio frequency amplifier 45 is immediately changed to its normal condition for an amplifier.

It should be noted that in case the point B becomes positive with respect to ground, it will cause grid current to flow through the resistor I29 so that the grid II5 will be maintained ,at substantially zero bias.

As fully explained in my above-mentioned copending application, Serial No. 699,641, filed November 25, 1933, the characteristics of the pentode 6| are such that the plate impedance of the tube remains substantiallyv constant within the range of voltage applied to the control grid during the time the amplifier 45 is effective. This range of voltages is determined by the adjustment of the "trigger amplifier 65. In a preferred adjustment the potential of point B is changed instantly from approximately 20 volts negative to about 3 volts negative upon reception of a signal.

Further slight voltage changes may be caused by variations in the strength of an incoming signal but they will not cause changes in the impedance of tube 3I For example, if the tube 9| is an RCA 57, its plate impedance, will remain substantially constant for control grid voltages ranging from about! volts negative to zero and, since the variation in plate voltage of tube 65 is much greater than is necessary for the control of grid II5, considerable variation in signal may take place without affecting the bias on tube 45.

The remote control circuit for tuning the receiver comprises a control tube I33, a magnetic brake I35, a motor I39 which includes, a plurality of control buttons I4I, I43, I45 and I41. The motor I31 is connected through gears I49 and through a friction drive, such as a belt drive comprising pulleys III,

' current at the same time.

land a remote control unit and I53 and a belt I55, to ashaft I51 for rotating the tuning condensers.

The shaft I51, which is shown broken of! at one endrordinarily would be the rotor shaft of a gang condenser, in the drawings a rigid connection between this shaft andthe tuning condensers being indicated by the dotted line I9.

The motor I31, which is of the reversible type,

may be connected to a power supply ill'through cable conductors iii and I63 for operation in one direction by depressing the control button I to close a switch I65, or it may be run in the opposite direction by depressing the control button 143 whereby a reversing motor winding is connected to the power supply I59 through cable conductors ,I63 and I51 and a switch I59. Thus, it will be seen that the tuning condensers may be rotated to tune the-receiver either up or down the tuning range by depressing either the button I or the button I43. I

In order to stop the tuning condensers at the instant the receiver is exactly tuned to an incoming signal, the tuning condenser shaft III has mounted thereon a disc segment "I. which is positioned between the core I13 and the'shoe' I15 of the magnetic brake I35. The particular mag-.

netic brake illustrated as well as the use of a brake for automatic tuning is disclosed and claimed in my co-pending application, Serial No. 700,471, filed December 1, 1933, and assigned to the same assignee as this application. It should be understood, however, that any electrically operated brake may be employed. a

The brake I35 is actuated to lock the tuning condensers in position in response to the reception of a signal by means of the trigger amplifier circult and the control tube I33.

The control tube I33 includes a cathode I11 which is connected to ground, a control grid I19 which is connected to a point D on the resistor R9 through a grid leak resistor I3I (which may have a resistance of the order of one megohm), and an anode I93 which is connected through a conductor I85, to the magnet .coil I31 of the brake I35, and a conductor I39 to a positive point on the voltage divider 93. The control grid I19 also may be connected to the point a through a condenser I9I, which may have a value of approximately 0.1 microfarad, to increase the speed with which the tube I33 is caused to function when the receiver is tuned to an incoming signal.

It will generally be desirable to have the tube I33 and the biasing tube 5! start drawing plate Therefore, the point on the potentiometer III to which the control grid I19 should be connected depends upon the relative characteristics of the two vacuum tubes. If the tube I33 were the same type as the tube ii, the control grid I19 preferably would be connected to the same point as the control grid of tube 6|, that is, to the point B.

So long asno signal is being received, as when the receiver is tuned between stations, the point D appliesa negative potential to the control grid I19 which is suillcient to block the tube I33 that there is no plate current flow through the brake -winding I91, and the brake I35 is deenergized.

There is, however, a small fiow of current 'the tuning condensers at the right place.

I93 (which may have a resistance of the order of 100,000 ohms) to the conductor I85, and through the magnet winding I81 and the conductor I89 to a positive point on the voltage divider 93.

Assuming that the brake I35 is not energized,

the receiver is tuned by depressing either the tuning button I or I43 to cause a rotation of the tuning condensers and the brake disc or segment "I. The instant the tuning condensers reach a position where the receiver is tuned to the carrier vand the brake is instantly energized thereby clamping the brake disc "I between the brake shoe I15 and the core I13 to lock-the rotors of the tuning condensers in position.

It should be noted that the tuning condenser I are locked in the correct position for tuning the receiver exactly to a desired signal regardless of any tendency the motor may have to-over-run. In other words, it is not necessary to release a tuning button at .a certain time in order to stop This result is obtained by means of the friction drive between the motor I31 and the tuning condenser shaft I51, the, friction drive being so adjusted that it slips as soon as the brake I35 is energized whereby further rotation of the motor has no effect upon the position of the tuning condensers.

In order to tune the receiver to a different station after the brake has been energized, it is necessary to depress the brake release button I45 on the remote control unit. When the brake release button I45 is depressed, a switch I95 is closed whereby the upper end of the potentiometer resistor R1 is connected to ground through a conductor I91 so that a high negative potential is put on the control grid II9 thereby blocking the control tube I33 and releasing the brake I35.

From the above description it will be apparent that the receiver is tuned by depressing either the tuning button I or the tuning button I93, depending upon whether the receiver is to be tuned up or down the tuning range, and by depressing the brake release button M5 momen tarily. Although the brake release button is depressed for only an instant to release the brake, (providing the next incoming signal is to be received), the tuning button is held down until a station is tuned in.

In some cases it may be desirable to have the receiver so adjusted that the remote control cir-.

cult will cause the receiver to tune in only a limited number of stations. Such an adjustment may be made by means of the sensitivity control. If the receiver is adjusted to have low sensitivity the magnetic brake I35 will be operated only in response to the reception of strong signals.

In practice, it is found both difficult and expensive to provide a control circuit for the magnetic brake which is so sharp that the selectivity of the control circuit is itself sufficient to prevent the magnetic brake from being operated too soon if strong signals are impressed upon the control circuit. This will readily be understood since the brake is operated when the plate current of tube 65 reaches a predetermined value; If signals of varying strength are impressed upon the input circuit of tube 65, a very strong signal at a frequency on one side of the resonant curve for the transformer 61 might produce the same plate current flow as a weaker signal at the intermediate frequency which is located at the middle or peak of the resonant curve.

It has been found that the magnetic brake 135 may be made to operate at the proper time when employing a control circuit having reasonably sharp selectivity if the strength of all signals applied to the control circuit is held substantially uniform. A convenient way of accomplishing this is to to provide the receiver with an automatic volume control circuit or AVC circuit which is applied to the portion of the receiver precedinglthe point supplying voltage to the brake control circuit.

While various forms of automatic volume. con trol may be utilized, the circuit illustrated in the drawings is simple and efiective in operation. The AVC circuit includes one of the diode rectifiers I99 of the vacuum tube 29, this diode comprisingjthe cathode 35 and a plate 20I. The plate 20I is connected through a filter resistor 203 and a volume control resistor 205 to ground. The junction point of the resistors 203 and 205 is connected to the control grids of the tubes I, I and 2i through resistors 201, 209, and 2| I, respectively. A filter condenser 2I3 is connected between the'grid end of the filter resistor 203 and round.

The cathode 35 is connected to the negative end of the voltage divider 93 through a cathode resistor 2I5. This resistor is bypassed by means of an audio frequency by-pass condenser 2H.

The operation of the AVG circuit is as follows: Assuming that a strong signal is being received, there is then maximum flow of current through the second detector resistor 31 and the control grid 43 is at a rather high negative potential, whereby the plate current of the tube 29 is small and there is a small voltage drop in the cathode resistor 2I5. Therefore, a large part of the voltage across the lower section 2I9 of the voltage divider 93 is impressed upon the diode rectifier I99. This will be seen by noting that the grounded point of the voltage divider 93 is connected to the plate 20I of the diode rectifier I99 through ground and through the volume control resistor 205, this grounded point being positive with respectto the cathode 35. The voltage across the voltage divider section 2I9 is large compared with the voltage drop in the volume control resistor 2I5 under the conditions assumed, so that although the two voltages are in opposition, the greater part of the voltage across the voltage divider section 2 I 9 is applied to the rectifier I99.

This results in a comparatively large flow of current through the resistor 205, with the result that the voltage drop in resistor 205 maintains the control'grids of the tubes I, I, and 2| highly negative with respect to their cathodes, whereby theirgain is held at a low value. If the strength of the received signal becomes less, the control grid 43 becomes less negative,

the plate current and the voltage drop in the re- I sistor 2I5 increase, and a lower voltage is impressed across the rectifier I99. As a result, the current flow through the volume control resistor 205 decreases and the control grids of the tubes I, I, and 2| become less negative, whereby the- Thus, the tuning condensers will never be stopped by the brake before they have been rotated to the proper position. The above described automatic volume control circuit is described and claimed in my application Serial No. 640,946, filed November 5, 1932, and assigned to the same assignee as this application.

The manual volume control device 55in the receiver may be controlled from the remote control unit by utilizing the motor I31 and a second magnetic brake 23I. The arm 550i the volume control potentiometer 49 is preferably rotatably mounted and connected to a shaft 223, as indicated by the dotted line 225. The shaft 223 is connected to the motor I31 through the gears I49 and through a second friction drive which comprises pulleys 221 and 229 and a belt 23 I. A brake disc 233 is fastened-to the shaft 223 and positioned to extend between the core 235 and brake shoe 231 of the magnetic brake 22I.

A flow of current is normally supplied from' voltage divider 93 through the conductors I89 and 239 to the magnet winding 2 of the brake for locking the shaft 223, and therefore the potentiometer arm 55, in position. It will be evident that so long as the shaft 223 is locked in position, rotation of the motor I31 merely causes slippage of the belt 23I. Therefore the receiver may be tuned to any desired station and the volume control device 55 will not be affected.

After the receiver is tuned to a station, however, and the tuning brake I35 is energized, the volume control device 55 may be operated by depressing the volume control button I 41 whereby a.

switch 243 is opened to break the circuit through the winding 2 of the volume control brake 22I.

-So long as the volume control button I41 is depressed, the volume control device 55 may be operated to either increase or decrease the volume by depressing either the tuning button I or the tuning button I43, since the belt I55 will sliption with Figure 3.

Referring to Figure 2 there is shown a remote control circuit which permits a radio receiver to be set up, for the reception of certain predetermined stations. are indicated generally at 245 have a. pulley 241 mounted upon their rotor shaft 249. A motor 25I of the reversible type is connected to the rotor shaft 249 through gears 253 and through a pulley 255 which is connected to the pulley 24.1 by means of a belt 251.

A remote control unit 259 is provided which has tuning buttons 26I and 263 and a brake release button 265 mounted thereon. The motor maybe run in one direction by depressing the 'tuningabutton 26I whereby a switch 261 is closed to connect a source of power 289 to one of the motor windings through cable conductors 21I and 213. The motor 25Imay be run in the opposite direction by pressing the tuning button 263 whereby a switch 215 is closed to connect the reversing motor winding to the source 02 edge.

An on-off switch of; this type is described hereinafter in connec- The tuning condensers which netic winding 28I, a magnetic core 283, and a brake shoe 285. A sector 281 of a disc, preferably of magnetic material, is mounted upon the condenser shaft 249 in such a position that it extends between the core 283 and the brake shoe 285" whereby. actuation of the brake 219 will clamp it securely in position.

The apparatus for actuating the brake 218 when the receiver is tuned to a desired'station comprises a disc 289 mountedupon the condenser shaft 249, or otherwise mounted for fixed rotation therewith, and a plurality of contact devices 29I clamped to the periphery of the disc 289. Each contact device consists of a U-shaped clamp member having a set screw 293 therein and a contact'member 295 which preferably has a knife By loosening the set screw 293, the contact device 29I may be moved to any desired position on the disc 289 for tuning in a certain station and again clamped in position.

A contact point 291 is fixedly mounted in such position that when a contact member 295 is rotated to a position adjacent thereto, contact is made to complete a circuit through the magnet winding 28I to energize the brake 219. This brake energizing circuit may be traced from the lower terminal of the brake winding 28I.

which is grounded, through the winding- 23I and through a battery 299, the conductor 38I, the contact member 291, and the disc 289, back to ground through the rotor shaft of the condensers 245.

From the above description it will be under-- stood that the receiver may be tuned in one direction by depressing the tuning button 25I, assuming that the brake 219 is de-energized." This will cause the tuning condensers 245 to be rotated until a contact member 295 comesinto contact with the, contact point 291, at which instant the brake 219 is energized to clamp the tuning condensers 245 in position. Further rotation of the motor 25I will have no effect upon the tuning of the receiver since the belt 251 will slip.

To tune the receiver to a different station either the tuning button 28I or thetuning button 2834s depressed, depending upon whether it is desired to tune the receiver up or down the.tun-

ing scale, and the brake release button 285 is I depressed momentarily. By depressing the brake release button 265 a switch 383 is closed to conmeet a resistor 385 across the brake winding 2" whereby the winding is substantially short-circuited and the brake is de-energized' It will be seen that as soon as the brake 219 is released, the condensers 245 and the disc 289 are rotated and the brake circuit is broken at the contact member 295 and the contact point 291. the brake release button 265 has been permitted to move back to its upper position, the brake 219 'will again be energized as soon as the contact point 291 comes into contact with the next contact member 295. Since it may be desirable to operate the receiver at a remote point located where the tuning dial of the main receiver unit cannot be. seen, it is desirable to have an indicator on the remote control unit 259 to indicate the tuning position of the receiver. Such a device is illustrated consisting of a milliammeter 381 having a pointer 389 cooperating with a scale 3i I calibrated in kilocycles, d a var ble resistance device'3l3 and a bat- Therefore, if

tery 3I5 for actuating the milliammeter 301. The resistance device 3I3 consists of a resistor winding 3I1 arranged in the form of a semi-circle and a contact arm 3I9 cooperating therewith and fastened to the condenser shaft 249. The resistor winding 3I1 is connected in series with the milliammeter 301 and the battery 3I5 so that the current flowing through the milliarnmeter, and consequently the position of the pointer 389. depends upon theposition of the tuning condensers 245;

Referring to Figure 3 there is shown remote control, apparatus which may be substituted fcr the corresponding remote control apparatus shown in Figure-. 1. In the two figures like parts are indicated by the same reference numbersl As'will appear from the following description the apparatus shown in Figure 3 .permits remotecontrol of both thetuning and the volume while utilizing only one magnetic brake and only three control buttons} In this case the tuning condensers indicate at 32I are driven from a short shaft 323 through sprocket wheels 325 and 321 and a perforated metal belt 329, the sprocket wheel 321 being mounted ofi center on the tuning condenser shaft=33l, as shown in Figure 4, to act as a cam for purposes which willbe explained hereinafter. The shaft 323 is coupled to the motor I31 through a worm gear 333, and a friction driven device including friction wheels 335 and 331. 1

A volume control shaft 339 is provided upon which the friction disc 331 and a similar friction disc 34I are rotatably mounted. When the friction disc 331 is held in a fixed position by the brake I81, the shaft 339 may be driven through the friction discs 335 and 34I and bevel gears 343, 345, and 341. Gears 343 and '345 are mounted to rotate with the friction discs 34I and 331, respectively. The bevel gear 341, which is positioned between and meshes with 'the bevel gears 343 and 345, is rotatably mounted upon a short shaft 349 extending from a collar 35I locked in position on the shaft 339 by means of a set screw.

It will be seen that if the two friction discs 34I and 331 are free to rotate,'operation of the motor I31 will cause them'to rotate in opposite directions at the same speed whereby the center bevel gear 341 will rotate without causing rotation of the shaft 339. On the other hand, if the friction disc 331 is locked in position there will be slippage between the friction discs 335 and 331, and the friction disc 34I will be the only one which will rotate whereby the'shaft 339 will be rotated through the bevel gears.

The magnetic brake I35 is mounted adjacent the friction disc 331 to lock it in position in response to the reception of an incoming signal. Therefore, if either the tuning button I4I or I43 Jis depressed, assuming that the brake is not clamping the friction disc 331 in position, the two friction discs 331 and 34I will be rotated in opposite directions; the shaft 339 will remain stationary while the tuning condensers 32 I will be driven through the metal belt 329. As soon as the tuning condensers 32I reach a position such .that a signal is tuned in, the brake I35 is automatically energized to prevent further movement of the tuning condensers (as explained in connection with Figure 1) and there is slippage between the friction discs 335 and 331 so long as the tuning button is held down. Therefore. as soon as a station is tuned in, the tuning button should be released immediately, unless it" is desired to change the volume as will be understood from the following description.

Remote control of the volume is obtained by connecting the movable arm of the volume control device to the shaft 339. From the foregoing description it will be understood that, when the friction disc 331 is locked in position, the,

volume may be either, increased or decreased by depressing the proper tuning button. Thus, after a station has been tuned in and the brake I35 energized, operation of either one of the tuning buttons will cause achange in the volume.

In order to turn the radio receiver on or off by actuating the tuning buttons, a switch 353 is mounted adjacent to the volume control shaft 339 for actuation thereby. The switch is of a conventional type pivoted at the point 355 and provided with a spring 351 for moving the switch either to the on or "off position when the switch arm is moved to one side of its center position. A pin 359 on the volume control shaftcooperates with any suitabledevice such as a pin 38I on the switch arm for connecting the switch arm over to its on or off position when the volume control shaft is rotated to predetermined positions. 1

In Figure 3 the apparatus is illustrated in the ofi. position of the receiver. -It will be noted that the volume control device 55 is in its low volume position. It will also be noted that the friction disc 331 is locked in position by means of a spring arm and cam device 363 which is provided for reasons that will be apparent from the description hereinafter. A spring arm 365 is mounted opposite the brake I 35 and provided with a projecting member 361 which is positioned to engage the brake shoe I15. The lower end of the spring arm 365 is provided with a cam member 369 positioned to cooperate with a pin 3'" mounted upon one end of the bevel gear shaft 349. In the off position of the receiver, therefore,the pin 31I forces the projecting member 361 against the brake shoe and locks the friction disc 331 in position.

" Assume now that it is desired to turn the receiving set on. The tuning button marked Up" is depressed and the motor rotates the friction disc 34I in such a direction as to move the pin 31l-off the cam 369, the friction dis'c'331 being ceiver may be tuned either up or down the tuning scale by depressing the proper tuning button since the spring arm 365 has released the brake shoe I15 and friction discs 331 and 3 are free to rotate. As soon as the receiver is tuned to an incoming signal, the brake I35 is automatically f energized and the friction disc 331 is again locked in position. The volume may now be increased by depressing the tuning button marked "Up or decreased by' depressing the tuning button marked Down. v

To tune the receiver to another station, both a tuning button and-the brake release button I45 are depressed, the brake release button being depressed only momentarily if the nextincoming signal is to be received. If it is desired to tune the receiver through a number of stations, the

' rotated to such a position that it will kick the switch arm 353 over to the "off position. It will be noted that in this position the spring arm 7 365 is again forced against the brake shoe I15 to lock the friction disc 331. In the event that it is desired to turn off the receiver when there is no incoming signal, it is merely necessary to. hold down the tuning button until the tuning condensers have been rotated to their limiting position,

at which position further rotation of the friction disc 331 is prevented so that the other friction.

disc 3 will drive the volume control shaft.

While a conventional tuning dial may be employed with my receiver, the type of dial illustrated in Figures 3 and 4 is preferred. This'tuning dial comprises a dial face 313 having two scales marked thereon (as shownin Figure 4) the inner scale being divided into ten equal unitsand the outer scale being divided into a number of units determined by the tuning range to be covered by the receiver. In Figure 4, both scales are shown divided into ten units.

Two pointers are provided, one pointer 315 being connected directly to the sprocket wheel shaft 323 and the other pointer 311 being geared to the sprocket wheel shaft 323, the gear ratio being such that the pointer 311 cooperating with the inner scale makes one complete rotation while the pointer 315 cooperating with the outer ,scale moves through one scale division. In the particular embodiment illustrated in Figure 4, the

pointer 311 which cooperates with the inner-scale makes tenrotations while the pointer 315 makes one rotation.

The dial shown in Figure 4 is calibrated for use with a receiver having a tuning range of from 550 kilocycles to 1500 kilocycles. The numerals on the outer scale represent the first numerals of the kilocycle reading, while the numerals on the inner scale represent the last two numerals of the kilocy'cle reading. Thus with the pointers in the position shown the dial reading is. approximately 608 kilocycles.

It-will be evident that when employing this type of dial the scale divisions should be evenly spaced apart throughout the tuning range of the receiver. Obviously the dial divisions would be so spaced if straight line frequency tuning condensers were employed, the tuning condensers being connected to the sprocket wheel through a simple sprocket wheel and belt mechanism having a 2:1 ratio. In practice, the use of straight line frequency condensers has been found undesirable for various reasons, one reason being that the straight line frequency condenser occupies too much space.

In accordance with one feature of my invention I-utilize either straight line capacity condensers, or preferably, the so-called modified straight line frequency condensers, and shape the sprocket wheel 321 to form a cam. The cam 321 is so shaped that, at the high frequency end of the tuning range where the stations are normally crowded together on the tuning dial, the tuning condensers are rotated only a slight amount during a comparatively great rotation of the sprocket wheel 325 and the tuning dial as in the case of the dial shown in Figure 4, it rotates throughten dial divisions while the main pointer rotates through a single dial division.

pointer 383, however, rotates through 360 and.

The dial illustrated is designed for use with a receiver having a tuning range from 400 kilocycles to 2000 kilocycles. The dial is read the same as the dial previously described, the reading for the dial with the pointers in the positions shown being 1210 kilocycles.

Various other modifications may be made in my invention without departing from the spirit and scope thereof and I desire therefore that only such limitations shall be placed thereon as are necessitated by the prior art and set forth in the appended claims.

I claim as my invention:

1. In a remote control system for a radio receiver having a tuning device and a volume control device, a motor, a friction drive connecting said motor and said tuning device, a second friction drive connecting said motor and said volume control device, a brake for said tuning device, a

brake for said volume control device, means including a switch at a point remote from said receiver for starting said motor, and means including a switch at said remote point for operating said second brake.

2. Radio receiver apparatus comprising a tuning unit, a volume control unit, two coaxially and rotatably mounted drive members, said tuning unit being connected to one of said drive members, means for rotating said drive members in opposite directions through a friction drive, a volume control shaft extending through the axis of one of said drive members and connected to said volume control unit, a gear shaft rigidly secured to said volume control shaft, and at right angles thereto, a gear wheel rotatably mounted upon said gear shaft, a second gear wheel rigidly secured to one of said drive members and engaging one side of said first gearwheel, a third gear wheel rigidly secured to the other of said drive members and engaging the opposite side of said first gear wheel, and a brake for engaging the drive member to which the tuning unit is connected. v

3. In a remote control system for a radio receiver having a tuning device, a motor, a tuning dial having equally spaced frequency markings thereon, a driving shaft, means for coupling said dial to said shaft, means for coupling said motor to said shaft, means for coupling said tuning device to said shaft, said last means including a driving wheel having teeth thereon, a driven wheel having teeth thereon, 'one of said wheels being shaped to act as a cam, and a belt connecting said two wheels, the ends of said belt being connected by means of a connector which is flexiblein a longitudinal direction to permit variations in the length of the belt, means for applying power to said motor in response to the actuation of a tuning control unit whereby said tuning device is moved to tune the receiver, and means includingv a brake for stopping the movement of said driving shaft in response to the receiver being tuned to an incoming signal.

4. Radio apparatus comprising a main receiver unit having a tuning unit therein, a motor, a friction drive for coupling said motor and said tuning unit, a remote-control unit connected to said main unit and including two switches, means for running said motor in one direction in response to closing one of said switches, means for running said motor inthe opposite direction in response to closing the other of said switches, a

brake for said tuning unit, means independent of said first named means for actuating said brake, means provided in connection with said brake actuating means for controlling the latter in response to signal waves having a predetermined strength, and means for controlling the signal level at which said last named means responds.

5. Radio apparatus comprising a main receiver unithaving a tuning unit therein, a motor, a friction drive for coupling said motor and said tuning unit, a remote-control unit connected'to said main unitand including two switches, means for running said motor in one direction in response to'closing one of said switches, means for arrunning said motor in the opposite direction in response to closing the other of said switches, a brake for said tuning unit, means independent of said first named means .101 actuating said brake, and means provided in connection with said brake actuating means for controlling the .latter in response to received signal waves of predetermined strength.

6. Radio apparatus comprising a main receiver unit having a tuning unit therein, a motor, a friction drive for coupling said motor and said tuning unit, a remote-control unit connected to said main unit and including two switches, means for running said motor in one direction in response to closing one of said switches, means for running said motor in the opposite direction in response to closing the other of said switches, a brake for said tuning unit, means independent of said first named means for actuating said brake, in response to received signal of predetermined strength, a third switch at said remotecontrol unit, and means for releasing said brake in response to the actuation of said third switch.

'7. In a remote control system for a radio receiver having a tuning device, a motor, a friction drive connecting said motor and said tuning device, a brake for said tuning device, means including a remote control unit having a pair'of switches, means for running said motor in one direction in response to closing one of said switches, means for running said motor in the opposite direction in response to closing the other of said switches, means for actuating said brake in response to said receiver being tuned to an incoming signal, and means for making said last means effective only when the strength of said incoming signal is above a predetermined value.

8. In a remote control system for a radio receiver having a tuning device and a volume control device, a motor drive means connecting said motor and said tuning device, a second drive means connecting said motor and said volume control device, means for locking said tuning device and volume control device in positions of adjustment, means including a switch at a point remote from said receiver for starting said motor, and means including a switch at said remote point for operating said volume control means.

BOY E. BARTON.

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