US2404101A - Remote control of radio receivers - Google Patents

Description

Qi? 16, 1946'. R. E, scHocK mm REMOTE SQRT-ROL OF RADQ BECEIVERS Filed April l5, 1942 favors cour/ML se/4,4701? #055191 E. Jef/0cm ATTQRNEY July 16, 1946. R. E. scHocK REMOTE CONTROL OF RADIO RECEIVERS Filed April 15, 1942 5 Sheets-Sheet 2 INVENTR ROBERT E. Sch/och BY ATTORNEY My 16,' 194s. R. E. SCHOCK www@ REMOTE CONTROL'OF RADIO RECEIVERS Filed' April 15, 1942 5 Sheets-Sheet 4 Sum; Y

REVERS/@Le July 16, 1946. R. E. scHocK 2,404,101

REMOTE CONTROL 0F RADIO RECEIVERS I 5 SheetSI-Sheet 5 Filed April 15, 1942 INVENTOR /PoE/ir E. cHoc/r ATTO R N EY Patented July 16, 1946 UNITED STATES PATENT OFFICE Robert E. Schock, Riverhead, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application April 15, 1942, Serial No. 438,979

14 claims. 1

My present invention relates to novel and improved methods of remotely controlling a radio receiver, and more particularly to a novel method of, and apparatus for, controlling tuning and/or volume of radio receivers from a remote point.

Certain types of remote control tuning systems, introduced in the past in the broadcast receiver field, use an oscillator at the controlling point. The oscillator is made to send out signal pulses for the purpose of controlling the tuning and/or volume at the receiver. Such systems are not readily adaptable to either push button tuning or continuously variable tuning. The ideal method of remote control should be adapted to either push button tuning, or continuously variable tuning.

Accordingly, it is one of the main objects of my invention to provide a remote control method wherein the remote controlling device is an oscillator whose frequency may be changed at will by the operator, and wherein the controlled device incorporates a frequency discriminator circuit Which detects the frequency changes of the controlling oscillator and causes these changes to direct the operation of the controlled device.

Other features of. my invention will best be understood by reference to the following description taken in connection with the drawings in which I have indicated diagrammatically several circuit organizations whereby my invention may be carried into effect.

In the drawings:

Fig. l shows a remote control oscillator embodying the invention,

Fig. 2 shows a motor control circuit adapted to respond to the oscillator of Fig. 1,

Fig. 3 shows the characteristic of the discriminator-rectiiier of thev control circuit of Fig. 2,

Fig. 4 illustrates a modification of the circuit of Fig. 2,

Fig. 5 shows the operation of the circuit in Fig. 4,

Fig. 6 shows the circuit details of the motor control circuit for tuning and. volume control, and is adapted to be inserted between points P and Q of Fig. 2,

Fig. 7 shows a modified form of remote oscillator wherein separate tuning and volume control push-buttons are used.

Referring, now, to the accompanying drawings, it will be understood thatv like reference characters in the different figures designate similar circuit elements. The control instrumentality is an oscillator, shown in Fig. 1,Y whose circuits may be of any well known form. Merely *25 provided with a drive shaft 25'.

by way of illustration, the remote control oscillator comprises an electron discharge tube having a tank circuit comprising coil 2. The cathode, or lament, is energized by source F, while direct current source P supplies the positive plate potential. It will be recognized that the oscillator is of the well known Hartley type. The coil 2 may be resonated to different control frequencies by choice of a proper tuning condenser. Thus, a desired one of the plurality of iixed condensers c, y, and a may be shunted across coil 2. Push-button control may be had at the oscillator by providing a plurality of normally open switches 3, 4, 5 and 6. Each switch, upon closure, effectively shunts its associated condenser across coil 2, and simultaneously completes the iilament and plate circuits. Of course, each of condensers c, y, :r and a, is of a different magnitude.

Tuning push-buttons 3', 4', 5', 6 areprovided for the respective switches. These buttons 3' to 6 correspond to frequencies fc, fy, fx and fa respectively. In other words, actuation of a button to close its respective switch results in production of constant amplitude oscillations of the selected frequency. For example, depression of button 6' results in production of oscillations of a frequency fa. The control oscillations may be radiated through space to the controlled apparatus, or the oscillations may be transmitted thereto by a transmission line. Let it be assumed that the oscillations are radiated. Furthermore, the frequency of the oscillations can be in any desired frequency band. However, the intensity of the generated control waves should not be such as to cause interference with other receivers in the vicinity.

At the controlled point there may be located a radio receiver which is to be regulated in accordance with the frequency of the control oscillations. The regulation may be with respect to tuning or volume, or any other characteristic. In Fig. 2 there is shown a system for adjusting automatically the tuning of a receiver. The adjusting mechanism is a reversible control motor It will be understood that shaft 25 is mechanically coupled to the receiver tuning device (not shown). The condenser gang shaft (not shown) may be geared to the shaft 25 in any desired fashion.

The motor 25 is supplied with energizing current by leads 30. One of these leads 30 is connected to one terminal of the motor by a switch 3D. The second leadv 36' is connected to the pivoted arms, or contactors, of independent switches "D n 24 and 23. The fixed contact of switch 23 is connected by lead 23 to the third terminal of motor 25, while lead 24" connects the iixed contact of switch 2d to the intermediate terminal of the motor. There will now be described the various high frequency circuits for controlling the diiierent motor circuits.

The receiving system for receiving the control waves is essentially similar to the well known automatic frequency control (AFC) system used for superheterodyne receivers. Thus, the control waves are collected by the collecting device T. The waves are then passed through cascaded amplifiers T1 and T2. These amplify the radio frequency oscillations. The ampliers maybe of well known construction, and need not be described in detail. The resonant input and output circuits S1 and S2 o amplifier T1, and the resonant input and output circuits S3 and Si of amplifier T2, are tuned to pass all the control frequencies which may be employed. In other words, the tuned ampliers will be sufficiently broad up to circuit Si so as to pass efficiently the oscillations of any selected control frequency. The discriminator-rectifier comprises the diodes 9 and I@ whose cathodes are connected by series-related resistors il and l2. Each of the latter is by-passed for alternating currents, while the cathode end of resistor I2 is grounded. The cathode end of resistor il is designated as P; the motor control voltage is derived from point P. The common input circuit of the rectifier diodes consists of a tuned circuit i3, One side of the latter is connected to the anode of diode 9, while the anode of diode it connects to the opposite side of the circuit i3. The numeral 'l denotes the primary winding of the transformer whose secondary is composed of sections i3 and I3 each coupled to the primary. The junction of the sections BSV-I3 is connected by direct current blocking condenser 8 to the high alterhating potential side of circuit S4. The junction of resistors Il and l2 is returned through choke coil I4 to the junction of coil sections ISL-i3.

The plates of amplifiers T1 and T2 are connected by a common lead L to the source of positive potential +B. The circuit i3 is tuned to a frequency which is at the middle of the control fre- 4 quency range. That is to say, the voltage difference between point P and ground is Zero at the -said frequency of circuit i3. It is pointed out that the present discriminator-rectier S4-I3-9-I is essentially of the type `shown by S. W, Seeley in his U. S. Patent No. 2,l2l,l03, granted June 21, l938. The network acts to detect frequency changes in the control waves, relative to the aforesaid median frequency value, and converts such changes into corresponding direct current voltage changes at point P.

` The curve of Fig. 3 shows how the Voltage across the resistors I-i2 (the potential difference between P and ground) varies with control frequency variation. Control frequency as abscissae are plotted against voltage of point P as ordinates. The point B on the curve represents the median frequency point fe. This is the frequency of circuit i3, and, as Shown, the volt age of point P is zero. It will be seen that at frequencies fc and fy the voltages at point P are negative, whereas at frequencies fx and fa the voltages are positive. In other words, actuation of a selected one of the buttons in Fig. 1 will automatically cause pointP to assume a Voltage whose magnitude and polarity are as indicated at Fig. 3.

The point P is connected by resistor I E to the junction of direct current sources I6 and I'I. The right hand end of resisto-r l5 is connected to ground by a condenser l5'. The potentiometer resistor I8 is connected between the positive terminal of source ES and the negative terminal of direct current source i7, and the midpoint of the potentiometer is connected to the junction of the two current sources.

The potentiometer resistor I8 is provided with an adjustable tap Q, and the control grid of tube I9 is connected to the potentiometer adjustable tap. The tap Q is mechanically coupled, by any desired mechanical linkagel to the motor shaft.

Such linkage is indicated schematically by the dotted line 3|. The cathode of tube I9 is connected in common to the cathode of the following tube 20, and the control grid of the latter is connected to the grounded end of the cathode resistor 20. The plates of both tubes I9 and 20 are supplied with positive potential from the plus B terminal of the main direct current source (not shown). It will be noted that the plates of tubes i9 and 20 are connected to opposite ends of the winding of the electromagnet 23 which controls switch 23. In other words, when the winding of electromagnet 23 is energized, then switch 23 is closed.

Switch 24 is controlled by an electromagnet 24. The energization of the electromagnet winding depends on the action of tubes 2I` and`22. The control grid of tube 2I is connected to the adjustable tap Q. Each of tubes 2I and 22 has its cathode connected to ground through a respective cathode biasing resistor. The control grid of tube 22 is connected to the cathode of tube 2 I, and the plates of the tubes are connected to opposite ends of the winding of electromagnet 24. It will be noted that the common lead 22 supplies plate potential to each of the plates of tubes I9 to 22 inclusive. The network I9 to 22 inclusive functions to provide a keyer circuit actuated by the voltage variation of point P. The keying circuit functions to key either of relays 23--23 or 2li-24', as directed, for the purpose of determining the direction of rotation of the reversible motor 25.

A further keyer circuit is provided to close switch 30 whenever there is a control signal at the receiver. Thus, tube 28 has its plate connected to one end of the winding of electromagnet 29, while the opposite end of the winding is connected to the cathode of the tube through resistor 28. The cathode oftube 28 is connected to ground through resistor 28". Resistor 28 together with resistor 28" constitute a Voltage divider by means of which positive voltage is supplied from the direct current source (plus B) to the cathode of tube 28 at a magnitude which will properly bias tube 28. When the winding of electromagnet 29 is energized switch 30 is closed. The control grid of tube 28 has its potential regulated by the diode rectifier 21. The anode of the latter is coupled by condenser 2'I in series with condenser 2'I to the junction of coil sections I3" and I3". The cathode of diode 2'I is connected to ground by resistor R, suitably by-passed for alternating current components. The control grid of tube 28 is connected to the cathode end of resistor R.

A second diode 26 is arranged in parallel with diode 21. The diode 26 is supplied with control wave energy from the input circuit I3 through coupling condenser 21. The resistor 26 functions as a. load resistor for diode 26, the resistor being by-passed for alternating current componente. The anode end of resistor 26 is connected to the low potential end of input circuit S3 through a filter resistor 26". In other words, the diode 26 functions as an automatic volume control (AVC) circuit for the amplifier feeding the dlscriminator-rectifier. The volume level at discriminator input circuit I3 is maintained substantially uniform in this manner. The AVC bias may be applied to tube T1, if desirable.

'Ihe operation of the present remote control system is best explained by first assuming the remote control oscillator as operating at the midfrequency for which the control amplifier and discriminator circuits are tuned. This is represented by fB in Fig. 3. At this frequency the voltages across the discriminator diode resistors II and I2 are equal and opposite, and, therefore, the voltage at point P is zero. For this condition, the motor-driven balancing potentiometer I8 is purposely pre-set so that the voltage on the grids of tubes I9 and 2l (point B in Fig. 3) is also zero, and, therefore, neither relay 23 nor 24 is in operation and the control motor is inoperative. For this specific setting of control oscillator frequency, and of the control motor, assume the radio receiver tuning is at a desired station frequency. It will be understood that an extra button could be provided at the oscillator to produce the frequency fB. It would only be necessary to provide an appropriate condenser, and associated switches as shown in Fig. 1.

Now, to tune to a different station the remote control oscillator is tuned to a new frequency setting, which by previous calibration is known to result in the tuning of the controlled radio receiver to this other station. For purpose of illustration assume the new control oscillator frequency is at point y on the curve of Fig. 3. In other words, push-button 4' has been actuated to initiate generation of oscillations f frequency fy. By inspection of the characteristic curve it is seen that the voltage resulting at point P of the discrlminator circuit of Fig. 2 will now be negative. This negative Voltage on the grids of tubes I9 and 2I causes them to draw less current. Since the current of tube I 9 nows through a cathode resistor common to tube 2U, the decrease of current through this resistor decreases the grid bias of tube 20. Hence, enough plate current flows to operate relay 23, and the switch 23' of relay 23 is closed thus causing the control motor to operate.

However, since the cathode resistor of tube 2l furnishes grid bias for tube 22 the decrease of current through the cathode resistor of tube 2I, due to the negative voltage on its grid, causes its cathode, and therefore the grid of tube 22, to go more negative. Hence, relay switch 24 remains open. The control motor 25 would now operate continuously, were it not for the fact that it immediately adjusts the balancing potentiometer tap Q to a new position which, by virtue of the circuit arrangement, brings the voltage at point Q back to zero. This will, in turn, cause switch 23 to open and stop the motor. In other words, the circuit is so arranged that the potentiorneter tap Q will always be adjusted in a direction and to an extent such as to provide voltage to balance, or buck out, the voltage from point P thereby causing the relay operating the motor (either relay 23-23' or 2li-24') to stop the latter.

If the tuning of the remote control oscillator had been adjusted to a frequency fx, the voltage at point P would have been positive instead of negative. As a result tubes 2l and 22 would have been caused to close relay switch 24 instead of relay switch 23. The motor would now run in the opposite direction causing the balancing potentiometer tap Q to move to a position negative with respect to the voltage at point P. This would stop the motor as soon as this balance voltage were equal and opposite to the point P voltage. The signal-operated relay 29-30 turns the motor on" whenever the control signal is shut off. This prevents the control motor from operating even though the voltage at point Q might not be balanced to zero in the no-signal condition.

It may be seen from the foregoing discussion that for any frequency setting of the control oscillator within the range of tuning of the discriminator circuit I3 (that is from points a to c on the curve Fig. 3) there is a definite position of the control motor (and the balancing potentiorneter tap and receiver tuner mechanically linked thereto) at which the motor balancing potentiometer tap and receiver tuning device will come to rest. This makes it possible to calibrate the controlling oscillator tuning mechanism (either push-buttons or continuous) in terms of definite station tuning positions of the controlled radio receiver tuning by proper alignment of the discriminator tuning, the balancing circuit voltage supplies It and I? of Fig. 2), the balancing potentiometer I 3 and the receiver condenser drive.

The circ-uit of Fig. 4 is a variation of that of Fig. In Fig. 4 the operation is the same, except for the method of balancing the voltage at point Q back to zero for each control frequency position. In the circuit of Fig. 4, the balancing potentiometer circuit between points P and Q is eliminated, and the balancing is done by motordriven tuning of the discriminator circuit. The control motor 25 is mechanically linked to the discriminator circuit tuning condensers, as indicated by the dotted lines marked 3 I The curves of Fig. 5 show how the circuit of Fig. 4 works. Consider curve aBc torepresent the characteristic of the discriminator for normal mid-tuning position where, for a control frequency of fe, the voltage at point P is Zero.

If the control frequency is now shifted in tuning for a different station, to a frequency fy (point y on curve aBc), the voltage at point P will go negative. This will cause the keyer and relay circuit I8-2ll-23--23' to key the motor 25 on as explained in connection with the operation of the circuit of Fig. 2. However, in the circuit of Fig. 4 the circuit is brought to balance and the motor stopped by causing the motor to drive the discriminator tuning condensers I3a and |31) until the discriminator characteristic 4becomes that shown by curve aBc of Fig. 5. At this position of discriminator tuning the frequency fn of the control signal no longer produces a voltage at point P of Fig. 4, and, therefore, the motor keying circuit is released thereby stopping the motor. Since the radio receiver tuning condenser is also mechanically linked to this same control motor it may be seen that the motordriven discriminator tuning, if properly linked and aligned, constitutes a balancing circuit which will accomplish the same end as was achieved by the motor-driven potentiometer voltage-balancing circuit in Fig. 2.

In the circuits so far described, no provision was made for volume-controlling the receiver from the remote control position. This may be accomplished by replacing that part of the circuit of Fig. 2 between points P and Q, with the circuit of Fig. 6. The balancing circuit of Fig. 6 is aligned with respect to the radio receiver tuning and the remote control oscillator so that all of the receiver tuning is now accomplished within that frequency range of the control oscillator lying between f and fc of Fig. 3. This leaves that frequency range of the control oscillator between fa and JB of Fi-g. 3 for use in controlling volume in the manner about to be described.

It will be noted that so long as the control frequency is held within the range fe to fc of Fig. 3, the radioreceiver tuning control range, the voltage at point P in Fig. 6 is negative in polarity. Tubes 5| and 52 of Fig. 6 form a keyer circuit which is so biased that if the control frequency is shifted to the volume control range (fa to JB of Fig. 3) the voltage at point P is caused to go positive. This will result in a shift of the two single-pole, double-throw switches 51 and 50 from the position they were in for the tuning control process, to the opposite side. As a consequence the circuit is set up for the volume control process thereby releasing the tuning control set-up in the following Way.

Switch 51 cuts out the balancing potentiometer circuit |5|8', and connects in a voltage supply source 54 which is of such a value and polarity that it causes point Q to be negative for any control frequency from fis down to a frequency fx midway between fa and je (Fig. 3). For any control frequency between fx and fa the positive Voltage at point P is greater than the negative voltage from source 54, and the point Q will, therefore, be positive. Later it will be shown how this feature renders the circuit usable for volume-controlling. Switch 53, when shifted to the volume control position, opens one relay and closes another relay in a circuit shown in detail in Fig. 6.

The switch 58 in the tuning position actuates relay coil which, acting through an armature |02 pivoted at |08, keeps the receiver tuning drive shaft and balancing potentiometer shaft |06 geared to the control motor 25` through sliding shaft |03, and keeps the volume control mechanism disengaged from the control motor. When switch 58 is shifted to the left, or volume control, position it energizes relay |00. As a result the gear shifting armature |02 disengages the receiver tuning drive shaft |05 and the balancing potentiometer drive shaft |55 from the control motor, and engages the volume control drive shaft |01 to the control motor, The sliding shaft |04 is reciprocated by the lower end of armature |02.. It will be understood that shaft |05 is coupled to the controlled radio receiver tuning shaft (not shown); shaft |05 is mechanically coupled to adjustable tap I8 of Fig. 6; the shaft |01 will adjust the usual volume control device of the controlled radio receiver. The motor feeder leads will be exactly the same as in Fig. 2. At this point it should be pointed out that time constant circuit 55 is so chosen that when the shift is made from the tuning control position to the volume control position the action of keyer tubes I9 and 2| will be so retarded that switches 51 and 58, and their related circuits, will have had time to complete their duties before the control motor is put into action through either tubes i9 or 2| and their related keyer circuits. The relays |00 and |0| are fed with supply voltage by leads 200.

To illustrate the working of the volume conacross the oscillator coil Z.

trol assume that the control frequency is shifted from the tuning range to the volume control range, for instance to frequency jv of Fig. 3. This, of course, makes point P slightly positive thereby biasing tube 5| to draw more current through its cathode. In turn, this biases the grid of tube 52 more positive thereby causing tube 52 to energize relay 53 and operate switches 51 and 58. The operation of switch 58 to this volume control position energizes the gear shifting relay |00 to disengage the tuning and balancing drive shafts and couple the volume control drive shaft |01 to the control motor. The switch 51 acts at the same time to cut out the balancing control circuit (|6-|0) and throws the negative voltage supply source 54 in series with the lead connecting point P and point Q.

Since control frequency jv is between fx and fB (Fig. 3), point Q is rnow negative due to the voltage supply source 54 being more negative than point P is positive at this control frequency. Therefore, tube I9 and its related relay keying circuit (shown in detail in Fig. 2) is actuated to operate the control motor as previously explained for the circuit of Fig. 2. Assume, now, that the motor-driven volume control is so arranged that for the above described condition it is being driven to increase the receiver volume. To decrease volume the control frequency is shifted to a fa (Fig. 3). Since fa is below ,fx the voltage at point P is now more positive than the voltage supply 54 is negative, and point Q is, therefore, now positive. This causes tube I9 and its related keying circuit to be de-energized, and tube 2| with its keying circuit to be energiZed to reverse the direction of the control motor. As a result the volume control device is adjusted to decrease the Volume of the radio receiver. Therefore, operating the control frequency at a frequency fv will increase the volume at the receiver, and operating it at a frequency fa will decrease the volume at the receiver.

Fig. 7 shows the control oscillator circuit of Fig. 1 with provision for remotely controlling the volume at the receiver. To illustrate how the remote control oscillator of this modification works, suppose that it is arranged that buttons 3-fi-55 each correspond to points c-.e-y-B respectively of the curve of Fig. 3. These are the tuning buttons. They actuate the respective switches 3-5--5-6. The buttons 300' and 500 correspond to point o and a respectively of the curve of Fig. 3. Button 300 closes switch 300, while button 400' is adapted to close switch 400. The buttons 300 and 400 are the volume control buttons.

Suppose, now, it is desired to tune in a station for which purpose the circuit of Fig. 2 requires a control frequency of fc (Fig. 3). The push-button 3 at the oscillator in Fig. 7 marked with the station desired is depressed. This operation closes the switch identified in Fig. '1 as 3. One portion of switch 3 closes the lament circuit of tube thus turning on the oscillator. The upper section of switch 3 places condenser c Condenser c is chosen of such capacity as will resonate with coil 2 at the frequency fc which is required byA the circuit of Fig. 2 in order to make it operate to tune in the station wanted. The depressing of any one of the station tuning buttons of the oscillator of Fig. '7 does the same thing as described above, except that each button throws in its own tuning capacitor which is of correct capacity to tune the oscillator to the frequency,

required by the circuit of Fig. 2 to tune the par ticular station called for.

For volume control it is necessary, as explained before, that the circuit-of Fig. 6 be inserted between points P and Q in the circuit of Fig. 2. Depressing volumecontrol button 300 (fv) closes the filament circuit, and puts capacitor o across the oscillator coil 2. Capacitor o is of such capacity as to provide the oscillator frequency fv (Fig. 3) which, as was explained in connection with the volume control circuit, acts on the circuits of Figs. 2 and 6 to cause it to decrease the volume of the radio receiver. Depressing volume control button 403 (fa) turns the oscillator on, and connects a, capacitor a across the oscillator coil 2. This capacitor ais of such value that it causes the oscillator to oscillate at a frequency fa (Fig. 3) which operates, as has been explained, to increase the volume. It will be noted that the oscillator is on for only that period of time required to tune in a desired station, or to set the volume level. Also the only other operation at the oscillator, Kbeside turning it on, is tuning its frequency, and it is not necessary that the push-bottom method be used. A calibrated continuous tuning would also work at the remote oscillator. In that case a continuously variable condenser would be used in place of the plurality of fixed condensers. Of course, my invention may 'be carried out by using permeability inductance tuners in place of condensers. The method described by this disclosure might well be used over long distances for co-ntrol work, as Well as for short distances.

While I have indicated and described several systems for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organizations shown and described, but that many modications may .be made without departing from the scope of my invention, as set forth in the appended claims.

What I claim is:

l. A method of controlling the position of a device from a remote point, which includes generating oscillations of a selected frequency at the remote point, transmitting the oscillations to a point adjacent the device, deriving from the transmitted oscillations a unidirectional control voltage whose magnitude and polarity are dependent respectively upon the mean amount and sense of frequency difference between said selected frequency and a predetermined reference frequency, adjusting the device to an extent and in a direction determined by said voltage magnitude and polarity respectively, producing a second voltage of a polarity opposed to said control voltage polarity in response to adjustment of said devices, and utilizing the second voltage to oppose the effect of the control voltage thereby to terminate said adjustment at a predetermined point.

2. A method of controlling the position of a tuning device from a remote point, which includes generating oscillations of a selected frequency at the remote point, transmitting the oscillations to a point adjacent the device, deriving directly from the transmitted oscillations a control voltage whose magnitude and polarity are dependent respectively upon the mean amount and sense of frequency departure of said selected frequency from a predetermined reference frequency, adjusting the device to an extent and in a direction determined by said voltage magnitude and polarity respectively, producing a sec- 10 `ondvoltage of a polarity opposed to said control voltage Vpolarity in response to adjustment of said devices, and utilizing the second voltage to oppose the effect of the control voltage thereby to terminate said adjustment at a predetermined point.

3. A method of controlling the position of a volume control device from a remote point, which includes generating oscillations of a selected frequency at the remote point, deriving from the oscillations a unidirectional control voltage whose magnitude and polarity7 are dependent upon the mean amount and sense of frequency difference between said selected frequency and a predetermined reference frequency, adjusting the volume control device to an extent and in a direction determined by said voltage magnitude and polarity respectively, producing a second voltage of a polarity opposed t0 said control voltage polarity in response to adjustment of said devices, and utilizing the second voltage to roppose the effect of the control voltage thereby to terminate said adjustment at apredetermined point.

4. A method of controlling the position of a tuning device from a remote point, which includes generating oscillations of a selected frequency at the remote point, transmitting the oscillations to a point adjacent the device, deriving directly from the transmitted oscillations a unidirectional control voltage whose magnitude and polarity are dependent respectively upon the mean amount and sense of frequency difference between said selected 'frequency and a predetermined reference frequency, adjusting the device to an extent and in a direction determined by said voltage magnitude and polarity respectively, and opposing said control voltage with a balancing voltage derived in response to said device adjustment to cause said latter adjusting action to cease.

5. A method of controlling either of the tuning and volume devices of a receiver from a rcmote point, which includes generating oscillations of a selected frequency at the remote point, said frequency being to one side of a predetermined reference frequency for tuning control and to the opposite side for volume control, transmitting the oscillations to a point adjacent the device, deriving from the transmitted oscillations a unidirectional control voltage Whose magnitude and polarity are dependent respectively upon the mean amount and sense of frequency difference between said selected frequency and the predetermined reference frequency, and adjusting either of the tuning or volume devices to an extent and in a direction determined by said voltage magnitude and polarity respectively.

6. A method of controlling the position of a tuning device, which includes generating oscillations of various selected frequencies, each frequency corresponding to a diiferenttuning position, deriving from the oscillations a control voltage whose magnitude and polarity are dependent respectively upon the mean amount and sense of frequency difference between a selected frequency and a predetermined reference frequency, the reference frequency being the median of the range of selected frequencies, adjusting the tuning device to an extent and in a direc,- tion determined by said voltage magnitude and polarity respectively, producing a balancing voltage in response to said adjustment whose polarity is opposite to the control voltage polarity and il opposing the control voltage with the balancing` voltage to nullify the effect of the control voltage.

7. A method of adjusting the adjustable element of a circuit control device of a radio receiver from a remote point, Which includes generating a control wave of a selected frequency at the remote point, transmitting the wave to the receiver, deriving from the transmitted wave a control voltage whose value is dependent upon the amount of frequency difference between said selected frequency and a `predetermined reference frequency, adjusting the adjustable element of said device to an extent determined by said control voltage value and automatically neutralizing the control voltage with a balancing voltage produced during said adjustment.

8. A method of controlling the position of a tuning device from a remote point, which includes generating control energy of a selected frequency at the remote point, transmitting the energy to a point adjacent the device, deriving from the transmitted energy a control voltage whose polarity is dependent upon the direction of frequency departure of said selected frequency relative to a predetermined reference frequency, adjusting the device in a direction determined by said voltage polarity and automatically neutralizing the control voltage with a balancing voltage produced during said adjustment.

9. A method of controlling the position of a receiver control device, which includes generating oscillations of a selected frequency, transmitting the oscillations to a desired point, deriving from the transmitted oscillations a unidirectional control voltage whose magnitude and polarity are dependent respectively upon the mean amount and sense of frequency difference between said selected frequency and a predetermined reference frequency, utilizing the control voltage for adjusting the device to an extent and in a direction determined by said Voltage magnitude and polarity respectively, and reducing the eiect of said control voltage sebsequent to the adjustment of said device by a balancing voltage of opposite polarity and equal magnitude.

10. A system for controlling the position of a frequency adjusting device from a remote point, which includes means for selectively generating various oscillations of desired selected frequencies at the remote point, means for receiving oscillations of one of said frequencies, means for deriving from the received oscillations a control voltage whose magnitude and polarity are dependent respectively upon the mean amount and sense of frequency difference between said one frequency and a predetermined reference frequency, motor means energized in response to the control voltage for adjusting the device to an extent and in a direction determined by said voltage magnitude and polarity respectively, and additional means effective subsequent to a predetermined adjustment of said device, for 0D- posing the control voltage with a balancing voltage thereby rendering said adjusting motor means inoperative.

l1. A method of controlling the operation of a volume control from a remote point, which includes generating waves of a frequency chosen from a range of control frequencies, each of which control frequencies corresponds to a different desired adjustment of said control, transmitting said waves to 'a desired point, deriving from the transmitted waves a direct current voltage whose polarity and magnitude depend respectively upon the sense and extent of frequenN cy difference between the chosen frequency and an intermediate frequency of said range, controllin-g the adjustment of said volume control in response to said voltage, balancing said direct current voltage against a voltage of opposite polarity to provide a resultant voltage, and ending the adjustment automatically in response to a concurrent gradual decrease of the said resultant voltage produced by a balancing voltage of opposite polarity.

12. A system for controlling the position of a motor-operated radio receiver control device from a remote point, which includes means for generating oscillations of a selected frequency chosen from a range of control frequencies, each of said control frequencies corresponding to a different adjustment of said motor, means for transmitting said oscillations to a point adjacent the motor, a discriminatcr-rectifier network for deriving from the transmitted oscillations and at the transmitted frequency a direct current voltage whose polarity and magnitude depend respectively upon the sense and extent of frequency difference between the selected frequency and the median frequency of said range, means energized by the voltage for controlling the adjustment of said motor in response to said voltage, and further means, responsive to motor adjustment, for opposing said direct current voltage with a second voltage of opposite polarity thereby rendering said energized means ineffective subsequent to a period of motor adjustment.

13. A control system comprising means at a remote point for generating oscillations of a selected frequency chosen from a range of control frequencies each of which corresponds to a different adjustment of a control device, means for deriving from the oscillations a direct current voltage whose polarity and magnitude depend respectively upon the sense and extent of frequency difference between the selected frequency and the median frequency of said range, means for controlling the adjustment of said control device in response to said voltage and means responsive to said adjustment means for balancing the said voltage with a second voltage of opposite polarity thereby to terminate adjustment of the control device.

14. A method of selectively controlling the respective operation of a tuner device and volume control from a remote point, which includes generating a wave of a selected frequency chosen from a range of control frequencies, certain of which frequencies locatedon one side of a median frequency correspond to different adjustments of said tuner while others of the frequencies located on the other side of said median frequency correspond to diiferent adjustments of said volume control, transmitting said wave to a desired point, deriving from the transmitted wave a direct current voltage whose polarity and magnitude depend respectively upon the sense and extent of frequency difference between the selected frequency and the said median frequency of said range, and selectively controlling the adjustment of said tuner device and volume control in response to said voltage.

ROBERT E. SCHOCK.

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