June 8, 1943- H. v. ALEXANDERSSON ETAL 2,320,996 REMOTE CONTROLSYSTEM Filed April 14, 1941 ' 4 Sheets-Sheet l . /47 INVENTOR Cowman? Form? HA/GMS June 8, 1943. H. v. ALEXANDERSSON‘ EI'AL 2,320,995 REMOTE CONTROL SYSTEM Filed April 14, 1941 4 Sheets-Sheet 2 F34" D/ 75 (‘w/0:11am ?ora? HA/GLE r97 / / INVENTOR M .44” Z4; 2 I BY W June 8, 1943. H. v. ALEXANDERSSON ETAL 2,320,996 REMOTE CONTROL SYSTEM > Filed April 14, 1941 4 Sheets-Sheet 3 OR M I Z 5'’ ATTURNM June 8, 1943. H. v. ALEXANDERSSON ETALT 2,320,996 REMOTE CONTROL SYSTEM Filed April 14, 1941 / 4 Sheets-Sheet 4 / INVENT R' I Ww?'k? 2,320,996 Patented June 8, 1943 UNITED STATES PATENT OFFICE 2,320,996 REMOTE CONTROL SYSTEM Harald Valdemar Alexandersson, Lidingo, and Carl-Erik Granqvist, Stockholm, Sweden, as slgnors to Aga-Baltie Radio Aktiebolag, Stock holm, Sweden, a corporation of Sweden _ Application April 14, 1941,.Seria-l No. new In Sweden April 15, 1940 (Cl. 172-239) lator il, a discriminator II, a direct current Our invention relates to remote control appa 7 Claims. amplifier 2|, a motor 2i for causing the move ratus. In remote control systems it has been proposed to arrange a transmitter in such a way that it transmits a radio-frequency alternating current the frequency of which is determined by the position of the transmitter control, and to ar range a receiver for the transmitted radio-fre quency alternating current which is provided with automatic arrangements for tuning ‘to the transmitted frequency, the automatic tuning ar rangement being connected to the object to be controlled according to the momentary position ment of the secondary parts, to be controlled, and finally a tuning circuit 22 for the modulator oscillator, said tuning circuit being actuated by the motor 2i together with the secondary part 8. For the sake of simplicity it has been assumed that a common valve of a well known type is used both as modulator and oscillator. This .valve ll contains a cathode 23, an oscillator grid 24, an oscillator anode 25, a, first screen grid 28, a modulator grid 21, a second screen grid 22 and an anode 29. The oscillator tuning circuit 22, consisting of In remote control systems of this kind it is 15 coil 22 and tuning condenser 33, is connected between the grid 24 and the cathode 23 of the suitable to tune the transmitter and the receiver valve it, through a grid condenser 30 and a grid by means of tuning circuits, containing fixed in leak II. The oscillator anode 25 is connected to duction coils and variable condensers, the shafts the plus terminal oi’ the main through a reaction of which are connected to the transmitter con trol and to the object to be controlled, respec 20 coil 34. By this arrangement oscillations are pro duced in the internal system of the valve l8, said tively. . oscillations being modulated by the oscillations Fig. 1 is schematic diagram of the known ar of the transmitter control. > rangement. Figs. 2 and 3 are diagrams illustrating the operation of the system of Fig. 1; Fig. 4 is a schematic diagram of a transmitter embodying the present invention; received from the transmitter which are im pressed on the control grid 21 of the external system to produce an interference oscillation of beat frequency similar to the operation of super heterodyne radio receivers. In the anode circuit of the valve ll is included Fig. 5 is a diagram illustrating the operation a transformer which is tuned to the beat fre of the transmitter of Fig. 4; 30 quency. This transformer is made as a dis Fig. 6 is a schematic diagram of a receiver (or criminator, that is, it is sharply tuned to the beat use with the transmitter of Fig. 4; frequency and passes a current the direction and l"lg.'7 is a diagram illustrating the operation magnitude of which is determined by the varia of the receiver of Fig. 6; tion in signal frequency. One example of such Figs. 8 and 9 are diagrams illustrating a novel a discriminator is shown in Figure 1. The pri form of variometer for usein the receiver of Fig. mary circuit contains the coil 25 shunted by the 6; and condenser 20, which can be adjusted to the beat Figs. 10 and 11 are schematic diagrams illus frequency. The secondary circuit contains a trating further embodiments of the invention. In Fig. 1, 10 is the oscillator valve of the trans 40 corresponding coil 31, shunted by a condenser 30. In addition to the inductive coupling of the mitter. In the anode circuit of the oscillator two circuits a further coupling is provided by valve there is included a coil ii, which is induc connecting the mid point 0! the coil 31 through tively coupled to a coil i2 connected in the grid circuit of the valve Ill, and to a further coil I! connected by a transmission channel II to the receiver. The coil i2 is connected in parallel with a tuning condenser il, mechanically connected to the transmitter control P, shown in the form of a condenser 38 to the high voltage side relative to alternating current, of the coil 25. ‘ The discriminator is completed by two recti ilers l0 and 4|, connected to earth and to the ends of the coil 31 and provided with the shunt resistors 42, 48 and series resistors 44 and 45. a dial. The resonance frequency of the tuned circuit formed by the coil i2 and the condenser 50 For alternating currents the latter resistors are shunted by by-pass condensers l6 and 41. The M will thus vary with the position of the dial. connection between the resistors 44 and 45 thus The circuit l2-H is connected by a grid con is connected to earth while the end terminals of denser ii and a grid leak it to the grid circuit these resistors are connected by conductors l8 of the valve ill to form an oscillating circuit. The principal parts of the receiver are a modu 55 and 49 to the grids of direct current amplifying ,2 2,320,996 electronic valves 50 and 51, respectively. The 0-D of the vectors O--A and O——B. As a result one of the rectifiers 40 or H, for example the rec anode circuits of the valves 50 and 5| are con ti?er 40, receives a higher voltage and the voltage balance between the load resistors of the recti fiers is destroyed. With a greater voltage drop ‘nected in series with counteracting ?eld windings l2 and 53 of the motor 2| to one terminal of the armature 54 of the motor. the other terminal across the load resistor 44 the grid voltage of the valve 5!) falls and the anode voltage of this valve of which is connected to the plus terminal of the mains. The shaft of the motor is connected to the tuning condenser 33 and also to the object also fails. Simultaneously the voltage drop across the load resistor 45 decreases so that the S to be controlled, shown in the form of a dial. The operation of this system is as follows: grid voltage of the valve 5| rises and the anode current of this valve also rises. Unequal cur To start with it will be assumed that the trans:\ rents flow through the windings 52 and 53 and the motor 54 turns in for example counter-clockwise mitter is tuned to a predetermined position on the “ dial P. A frequency dependent upon the position of the control dial P is transmitted through the conductors ll to the modulator grid 21 of a valve ll of the receiver. The oscillator is assumed to direction. - ' - I The motor 54 thus changes the‘setting of the oscillator condenser 33 and gradually brings this to‘ a value such that the beat frequency is restored to theifrequency to which the circuits 35—-36 and 3'I—38 are tuned. In these earlier proposed arrangements, how 20 > circuits 35-36 and 3l—-38 are tuned. ever, certain disadvantages are present. For In Fig. 2' the voltage vector of the circuit 35-36 example, the transmitter condenser can only vary , is indicated by O-A. The voltage vector of they from minimum value to maximum value repre circuit 31-38 is indicated by B-C. ‘It is well known that at absolute. resonance the voltage - senting for normal condensers a mechanical vectors of the primary circuit and of the second 25 range of variation of half a revolution. Often. however, this is not sufficient for obtaining the ary circuit are exactly 90° out of phase relatively desired range of movement or su?icient precision to one another. Due to the coupling through the in the receiver. In such cases it is desirable to condenser 39 the voltage O-A is added to half make the arrangement capable of operating in the voltage 3-0 in positive direction for applica tion to the recti?er l0, and in negative direction 30 such'a way that the control means of the trans mitter can be turned more than half a revolution, for application to the rectifier ll. The former in many cases even a plurality of revolutions, the voltage is thus composed of the vectors O--A and controlled means of‘ the receiver thereby turning 0-0, while the latter voltage is composed of the a corresponding number of revolutions. This is, vectors O-A and O—B. As will be seen from however, as explained below, impossible with an . the diagram in Fig. 2 the two resultants O--D and arrangement of the kind shown above. 0-13 in this case are equal. Consequently both The capacity of a tuning condenser varies dur recti?ers 40 and ll set- up equal but counter-act ing one revolution between a maximum through a ing voltages over their load resistors, which after minimum and back to the same maximum value. ampli?cation in the electronic valves 50 and ii For each revolution of the shaft of the condenser are transmitted to the two windings 52 and 53 of such a cycle of capacity variation is obtained, as the motor 2 I. The latter is consequently in shown in Fig. 3 in which the vertical axis repre balance and does not operate. sents the capacity and the horizontal axis reprea It will now be assumed that the setting of the sents the angular setting of the condenser. It transmitter is changed. The condenser I4 is thus may now be assumed that the arrangement is set shifted and the transmitter frequency is changed in a position corresponding to point 55 in Fig. 3 either to a higher or to a lower value. The?beat and that a movement is begun from this position frequency will therefor differ from its normal in the direction indicated by the arrow 56. The value either in the same direction as the trans mitter frequency or in the opposite direction, 0 change in transmitted frequency produces a cor responding change in its beat frequency which dependent on whether the frequency of the oscil thus increases or decreases, dependent upon lator'tuning circuit 22 is above or below the trans whether the oscillator frequency is above‘ or below mitter frequency. The direction in which the the signal frequency. The change in frequency beat frequency deviates is of no importance as set up an oscillation of a frequency which [com blues with the frequency received from the trans mitter to produce the beat frequency to which the regards the operation, as in every case the direc tion, is dependent upon the direction of’ deviation of the transmitter frequency. The beat frequency, however, after the position of the dial P has been changed, is no longer in exact resonance with the 55 causes an unbalanced voltage to be set up across the two rectiflers, and as a consequence of this , voltage the motor is started. The direction of movement of the motor, however, is determined l circuits 35-36 and 31-33. _,Hence the two vectors O—A and B—C will assume a mutual phase posi tion other than perpendicular to one another, and shifted by an angle depending upon whether the frequency displacement has been inductive or capacitive. With‘reference to the diagram this 65 may ‘-be most easily explained by assuming that one of the vectors, for example the vector O-A, has turned relative to the other vector 3-0 as indicated by the vector O-A’. As will be seen by relation between the beat frequency and the discriminator frequency. It may now be assumed that the oscillator frequency is higher than the signal frequency. The capacity, rising from the point 55, will then cause a decreasing signal fre quency, which will cause an increasing beat fre quency and the motor is rotated in a direction to restore the original beat frequency. After the condenser ll of the transmitter has I passed its maximum, represented by point 51 in Fig. 3, the capacity will again decrease, thereby ‘ from Figure 2 this causes the resultant O—E' of 70 causing an increasing signal frequency. The beat frequency decreases to the value to which the vector O.—A’ and of the vector 0-0 to become greater than the former resultant O-—E of the vectors O--A and O—C, whereas on the other hand the resultant 0-D’ of the vectors O-A' and O—-B become less than the resultant 75 the discriminator is tuned, and thereafter the beat frequency will remain lower than the dis criminator frequency until the condenser M has again ‘reached a reversal point, in this case the 3 2,320,996 minimum point 58. During this period the mo tor in the receiver will continuously rotate in the opposite direction until it reaches its end posi tion. Hence, if the condenser ll should be turned a plurality of revolutions the receiver would follow the movement of the transmitter during the ?rst half revolution only, rapidly moving back mean value when the capacity of the other con denser is a minimum or maximum. , The capacity variation oi‘; the two condensers is shown in Fig. 5, the vertical axis as in Fig. 3 indicating the capacity and the horizontal axis indicating the angular setting of the condenser. The curve ll, drawn in full, shows the variation of the capacity of one of the condensers whereas to its initial position during the second half revo the dotted curve Ii shows the variation of the lution of the transmitter, following the trans in the other condenser. mitter during its third half revolution, again rap 10 capacity A receiver for the signal emanating from the idly returning to the initial position, etc. transmitter in Fig. 4, is shown in Fig. 6, said re The present invention relates to an arrange ceiver being in general substantially the same as ment by which this disadvantage is obviated. the receiver, shown in Fig. l.’ The transmission According to the invention the discriminator is mains are indicated at ‘I! as in Fig. 4. Other arranged in such a way that the control voltage ~ wise the same reference numerals have been used for the remote control motor reverses its direc as in Fig. 1 except that in the two parts of the tion as the capacity curve of the condenser receiver of Fig. 6, the hundreds-figures i and 2, changes from rising to falling or vice versa. The respectively, have been added. reversal of the control voltage or current may The transmission‘ mains ‘I! are connected to take place either in the discriminator or in some 20 both of the receiver units through transformers other place in the control channel. A number of diflerent arrangements of this kind are shown below. At the moment when the control voltage or current reverses its polarity thisvoltage or cur rent will be zero. Hence, at the point of re containing the primary windings I" and 265 and blocking condensers I" and 256. The secondary windings ill and 251 are broadly tuned by the condensers I" and "I to the mean frequency . of the received frequency band. The condenser 33 in Fig. l is replaced in Fig. 6 by two condensers I59 and 25!,‘ and variable condensers I“ and 2","respectively, coupled in This disadvantage is obviated according to a fur parallel. In the discriminators the inductive cou ther embodiment of the invention by providing 30 pling is made variable by means of a variometea, two cooperating transmitter units acting upon For this purpose the primary and secondary cir diii'erent receivers, the discriminators of which cuits are screened from each other by means of I are connected to the same remote control motor. screens iii and 2H, respectively, and the primary The condensers of both of said transmitters, circuits are connected in series with the primary however. are mechanically displaced in relation coils I" and 2", respectively, of variometers, the to each other in such a way that one of the con secondary coils of which are formed by the sec densers is in a position in which good precision ondary coils I31 and, 23.1, respectively, of the dis- ‘ is obtained when the other condenser is in a po criminator. Both of the variometers and both of sition of less precision and vice versa. the condensers are connected to a common me Fig. 4 shows an arrangement of a transmitter 40 chanical control from the motor 54, as indicated for two frequencies, intended to be connected to by the dotted line II. This mechanical connec versal the system loses its power of following the movement of the transmitter with precision. a receiver such as that shown in Fig. 6. The transmitter according to Fig. 4 contains two electronic valves 59 and 60, coupled as oscil lators. The oscillation circuits contain one con denser 6l or 62, respectively, and one coil 68 or N, respectively. The cathodes of the electronic valves are connected to taps on the respective coils, whereas the high voltage terminals of the coils are connected to the control grids of the electronic valves over condensers 65 and it, pro tion is made so that the variometers are at zero coupling when the corresponding condensers pass through their maximum or minimum positions. In Fig. 5 this is indicated by the full line curve ll corresponding to the capacity variation curve 80 of vthe condenser I60, and by the dotted curve N which corresponds to the capacity variation curve ll of the condenser 280. By this arrangement an extremely uniform movement of the receiver is obtained. Assuming vided with grid leaks "and 88, respectively, in that the variometers are moving with pure sine a known manner. variation in coupling, the polar curve for the In the anode circuit of each of the valves 59 variation in coupling will be obtained in the form and 60 is a broadly tuned circuit 89 and 10. re of two circles touching each other. for example spectively, said circuit transferring with substan the circles I5 and II in Fig. '1 for one of the vari tially the same amplitude all frequencies which ometers and, due to the mechanical phase dis may be set up by the oscillator valves. The cir placement of 90°, the circles l1 and 8| for the cuits are coupled to coils ‘H and ‘I2, respectively, other variometer. The sum of ‘the coupling volt which are connected by means of blocking con 60 ages through both of the variometers, which also densers 13, ‘I4 to the transmission mains ‘I! lead determines the current fed to the ?eld windings ing to the receiver. 52 and 53 of the motor 54, is then obtained in - The condensers ‘I and 62 are dimensioned in Fig. 7 in form of the curve "- which varies only relation to the coils ‘I and N to tune to a fre quency which is not substantially higher than the highest frequency which is to be produced by the oscillator. For obtaining a frequency varia tion condensers ‘l6 and 11 are connected in paral lel to the tuned circuits. These condensers are mechanically connected with each other and with . the transmitter control dial 1! as by a common shaft 19. The stators of the two condensers ‘Hi and 11 are displaced in relation to the rotors of the said condensers in such a way that the capac ity of one of the condensers is at or near. its ‘ about plus or minus 15% from a true circle as in dicated by curve 90. The operation of the variometers shown in Fig. 6 may cause certain di?iculties. as sliding con tacts must be avoided due to the small voltages involved, as well as due to the capacity of sliding contacts which may be too high when the higher radio frequencies are used for the control. In Figs. 8 and 9 an arrangement is shown for ob taining a variometer without using movable con tacts. In these figures the coil of the primary 4 . 2,320,090 circuitin the discriminator is indicated at 9| and the condenser coupled in parallel therewith is in_ dicated at 92.‘ In series with the coil 9| there is and the secondary winding I63 of which is cou~ pled,in parallel with a condenser I64 for tuning approximately to the mean value of the trans arranged a coil 93. This coil is wound on a cylin drical coil frame in the interior of which is ar ranged a coaxial cylindrical coil frame carrying a mitted frequency band. The signal is ampli?ed coupling winding 94. arranged on the same shaft as the primary wind nected containing the primary winding I66 and the secondary winding I61. The primary wind ing 95 of the variometer, said last named wind- . ing is coupled in parallel with a ?xed condenser This coupling winding is by means of a standard ampli?er valve I65 in the output circuit of which a transformer is con ing being so arranged that upon the‘ rotation of 10 I68 by means of which this circuit is tuned to a frequency within the transmitted frequency the variometer, a continuous and preferably pure ly sinusoidal coupling variation to the secondary . coil 96is obtained. As a matter of symmetry this last named secondary coil is arranged with a mid point tap and is connected between the two half parts of the secondary winding 91 of the discrim inator. The last named winding is ?nally coupled in parallel with the condenser 98, corresponding to the condensers I38 and 238, respectively. A range. The secondary winding I61 is coupled in parallel with a condenser I69 by means of which said secondary winding is tunable over the same frequency range as the transmitter. Preferably the condenser I69 is so shaped that the receiver during the automatic tuning always turns through the same angle as the transmitter. ' The coils I66 and I61 are connected as de condenser 99 connects the mid-point on the sec 20 scribed above by means of a condenser I10 for obtaining the discriminator action. The termi ondary winding 96 with the primary winding 9|. nals of the coil I 61 are connected to recti?ers I1I In Figs. 10 and 11 two modi?cations of the ar rangement according to Fig. 6 are shown. In - and I12 whichiare connected to load resistors I13 and I14. The connection point between the the arrangement according to Fig. 6 the two di rect current amplifying electronic valves I50 and two load resistors is grounded, whereas the two .I5I and also 250 and 25I, respectively, were so ungrounded terminals are connected to the con connected to the ?eld windings 52 and 53 of/the trol grids of two direct current ampli?er valves I15 and I16 by means of two contact arms I11 and I18. The counter contacts forthe contact motor 54, that the sum of the currents ?owing through the anode circuits of the electronic valves in question passed through the ?eld windings. 30 arms are so arranged that. the contact arms, which are mechanically connected together, when At balance'between these currents no movement in one position connect the resistor I13 with the of the motor was obtained as the two ?eld wind ampli?er valve I15 and the resistor I14 with the ings were opposed. The arrangement according ampli?er valve I16 but when in their other posi to Fig. 10, however, is such that the difference tion connect the resistor I13 with the ampli?er between the voltages created in the two recti?ers valve I16 and the resistor I14 with the ampli?er is fed-to the ?eld windings. In this case the di valve I15. The anode current from the valve rect current amplifying electronic valves can be n5 flows through the ?eld winding I19 01' the‘ omitted as will be evident from the following. motor I80, whereas the’ anode current from the The coupling from the transmitter to the two modulator valves I00 and MI is assumed to be 40 valve I16 flows through the ?eld winding I8I. The shaft I82 ‘of the motor I80 is coupled me made in any manner suitable for the purpose, chanically to actuate the tuning condenser I69 as for example as shown in Fig. 6. The discrimina well as the switching arms I11—I18, so that the tors I02 and I03 are also made in a suitable man arms are switched over from one position to the ner. The discriminator I02 is connected to the two recti?er valves I04 and I05, whereas the dis 45 other each time the condenser I69 passes through maximum or minimum capacity positions. By criminator I03 is connected to the two recti?er this arrangement the receiver is prevented from valves I06 and I01. The direct current voltages reversing its direction at each half revolution of from the recti?ers in question across the resist the transmitter control as in'Fig. 1. ors I00, I09, H0 and III are fed to four resistors Of course the invention is not limited to the H2, H3, H4 and H5, coupled in pairs. The con 50 nection point between the ‘resistors H2 and H4 embodiments shown. Various modi?cations may be made therein as will be apparent to a person and also between the resistors H3 and H5 are skilled in the art. connected to the control grids of ampli?er valves What is claimed: H6 and H1, respectively, provided with by-path condensers H9 and‘ I20 and a common cathode 55 7 1. A remote control system responsive to fre quency variations of a received signal, comprising bias resistor I2I. The anode circuits are con a receiver having a circuit responsive to the re nected in the ?eld windings I48 and I49 of the ' ceived signal, arotatable tuning element pass motor I22. 7 ing progressively through maximum and mini In cases where a high precision is not required this may be substantially simpli?ed. It is pri 60 mum positions during its rotation, said tuning element being connected to control the frequency marily possible to make the discriminator itself response characteristics of said receiver, a re tunable instead .of using a tunable oscillator cir versible motor connected to actuate said tuning cuit to obtain an intermediate frequency adapted element, a motor control circuit responsive to the to a ?xed discriminator. Further only one chan nel may be used from the transmitter to the re 65 relative frequency characteristics of said receiver and of the received signal and connected and ar ceiver instead of two channels and ?nally it is not ranged'to cause said tuning element to follow necessary to make the reversal of the discrimina variations in signal frequency, and a circuit con tor voltage continuous, a mechanical switching arrangement being used. An arrangement, sim nected to cause said motor to continue operation pli?ed in these three respects for receiving a re 70 in the same direction in response to continued unidirectional variation in frequency of the re- ’ mote control signal is shown in Fig. 11. ceived ‘signal as the tuning element passes The transmission mains I1 from the trans through its maximum or minimum position. mitter, such as the transmitter shown in Fig. 1 are connected to a broadly tuned transformer, ' 2. A remote control system responsive to fre the primary winding of which is indicated at I33 75 quency variations of a received signal, compris 4 2,320,996 ing a receiver having a circuit responsive to the received signal, a rotatable tuning element pass ing progressively through maximum and mini mum positions during its rotation, said tuning element being connected to control the frequency 5 response characteristics of said receiver, a re versible motor connected to actuate said tuning element, a motor control circuit responsive to the relative frequency characteristics of said re ceiver and of the received signal and connected and arranged to cause said tuning element to fol low variations in signal frequency, and reversing connections comprising a variometer connected response characteristics of said receiver, a revers ible motor connected to actuated said tuning ele ment, a motor control circuit responsive to the and arranged to automatically reverse the con relative frequency characteristics of said receiver and of the received signal and connected and 10 trol of said motor control circuit as the tuning control circuit passes through its maximum or arranged to cause said tuning element to follow minimum tuning position. variations in signal frequency, and reversing con 6. A remote control system responsive to fre nections connected and arranged to“\automati quency variations of a received signal, compris cally reverse the control of said motor control ing a receiver having a circuit responsive to the circuit as the tuning element passes through its received signal, a rotatable tuning element pass maximum or minimum position. ' ing progressively through maximum and mini 3. A remote control system responsive to fre mum positions during its rotation, said tuning quency variations of a received signal, comprising element being connected to control the frequency a receiver having a circuit responsive to the re ceived signal, a rotatable tuning element passing progressively through maximum and minimum positions during its rotation, said tuning element being connected to control the frequency response characteristics of said receiver, a reversible motor connected to actuate said tuning element, a motor ~ response characteristics of said receiver, a re versible motor connected to actuate said tuning element, a motor control circuit responsive to the relative frequency characteristics of said re ceiver and of the received signal and connected and arranged to cause said tuning element to follow variations in signal frequency, said motor control circuit comprising a pair of inductive quency characteristics of said receiver and of the coupling members connected in cascade, one of received signal and connected and arranged to said members comprising a variometer rotatable cause said tuning element to follow variations in with said tuning element, the other of said mem signal frequency, and reversing connections actu 30 bers comprising coaxial coils the axis of which ated by said tuning element and constructed and coincides with the axis of rotation of said vari arranged to automatically reverse the control of ometer. said motor control circuit as the tuning element '7. A remote control system responsive to fre passes through its maximum or minimum posi-, quency variations of a pair of received signals tion. which are displaced in frequency and are varied 4. A remote control system responsive to fre in frequency in the same sense, comprising a re quency variations of a received signal, compris ceiver having circuits selectively responsive to ing a receiver having a circuit responsive to the the two received signals, a pair of rotatable tun received signal, a rotatable tuning element pass ing elements passing progressively through maxi ing progressively through maximum and mini 40 mum and minimum positions, said tuning ele mum positions during its rotation, said tuning ments being‘ mechanically connected to rotate in element being connected to control the frequency unison and relatively displaced as to their maxi responsive characteristics of said receiver, a re mum and minimum positions, said tuning ele versible motor connected to actuate said tuning ments being respectively connected to control element, a motor control circuit responsive to the frequency response characteristics of said the relative frequency characteristics of said re receiver circuits, a reversible motor connected ceiver and of the received signal and connected to actuate said tuning elements, a motor control and arranged to cause said tuning element to circuit responsive to the combined effect of the follow variations in signal frequency, and revers relative frequency characteristics of said receiver ing connections connected and arranged to re circuits and of the received signals and connect verse the phase of a voltage component of the ed and arranged to cause said tuning elements motor control circuit so as to automatically re to followv variations in their respective signal verse the control of said motor control circuit frequencies, said circuits being connected and as the tuning element passes through its maxi arranged to cause said motor to continue opera mum or minimum position. tion in response to variations in frequency of 5. A remote control system responsive to fre one of said signals while the tuning element co quency variations of a received signal, compris operating with the circuit responsive to the other ing a receiver having a circuit responsive to the of said signals is passing through its maximum received signal, a rotatable tuning element pass or minimum position. ing progressively through maximum and mini- 60 HARALD VALDEMAR ALEXANDERSSON. mum positions during its rotation, said tuning control circuit responsive to the relative fre element being connected to control the frequency CARL-ERIK GRANQVIST.
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