Fell 26, 1946- H. v. ALEXANDERSSON r-:T AL, n 2,395,708 REMOTE CONTROL SYSTEM Filed May 8. 1940 l l l l 4 Sheets~Shee-î 1 I I l n ll i iinNQ| l ^ l-vwx ¿_„ïLMi l uw| L_ ' H_" I ì A"E`TORNEY y Feb. 26, H. V. ÁLEXÄNDERSSÜN ET AL REMOTE CONTROL SYSTEM Filed May 8. 1940 4 Sheets'âheet 2 U V ìNvENTORs Hmmm Wwf/ww mfm/mfßâsow ATTORNEY Feb- 25? 1946- H. V. ALEXANDERSSON ET AL 2,395,708 REMOTE CONTROL SYSTEM Filed May 8, 1940 4 Sheets-Sheet 3 52 »l | j? .4. / ¿M , /á/„M ATTORNEY Feb. 26, 194:6a H. v. ALEXANDERSSON ET AL 2,395,708 REMOTE CONTROL SYSTEM Filed May 8, 1940 4 Sheets-Sheet 4 N + 4U 39I c Vx ‘y Z55 , BY ` Patented Feb. 26, 1946 2,395,708 UNITED STATES PATENT OFFICE 2,395,708 REMOTE CONTROL SYSTEM Harald Valdemar Alexandersson and Carl-Erik Granqvist, Stockholm, Sweden, assignors to Aga-Baltic Radio Aktiebolag, ' Stockholm, Sweden, a corporation of Sweden Application May 8, 1940, Serial No. 333,926 ' In Sweden May 24, 1939 14 Claims. ( Cl. 172-239) In remote control systems of the variable fre tates a further 360°, thereby repeating the same quency type in which the transmitted frequency frequencies, the frequency-meter must again isa function of the position of an object at the be brought into its initial position, a problem transmitter, and in which the receiver contains which is rather difficult to solve, if the frequency a frequency-meter or other similar device which takes a position dependent upon the received frequency, there is diiliculty in obtaining suñi- ‘ meter is also used as driving means for the re ceiver object. During the overlapping move ment in question there is such unreliability in the coincidence between the transmitter and the receiver, that the operation of the receiver may cient precision, particularly in cases where a large angular movement is to be transmitted. In remote control systems of this type, the ob 10 be very inaccurate. ject at the transmitter, the angular movement Furthermore, there is also a risk of error in of which is to be reproduced at a remote posi I tion, is connected toa means to control the fre that it is never certain that the transmitter ob ject and the receiver object have passed through quency transmitted which may, for example, be the same number of revolutions. If, for exam 15 ple, the receiver, for some reason, should become a frequency of the order of radio frequencies. The receiver is provided with‘means selective uncoupled while the transmitter rotates one or for frequencies of different ranges, which, in the more turns, the receiver would, when again simplest case, may constitute frequency-meters coupled in, show the correct angular position, An improved form of receiver includes an 0s but would not have made the correct number cillator together with a tuning circuit the tuning 20 of turns and there would be no possibility of supervision unless the receiver wereI provided also drives the controlled object. A discrimi with an indicator to show the number of turns nator is provided for comparing the received from its initial position. frequency with the oscillator frequency generated The present invention relates to an arrange- ` in the receiver and the motor is connected to 25 ment for overcoming the above disadvantages. tune the oscillator frequency to a value which In accordance with the present invention the is a function of the received frequency. transmitter is arranged so as to sweep over a As frequency determining means, simple os plurality of different frequency ranges, for in stance, two frequency ranges which are sepa cillation circuits may be used. However, these have only a limited frequency range which must 30 rated from each other. In this way a more ac cover the entire range of movement of the trans curate and continuous control is maintained. mitter object. On the other hand, the precision The transmitter may include units responsive to of the system is determined by the frequency the two frequency ranges which are operated re discriminating power of the receiver, which can spectively over alternate half revolutions of the not be made too sharp without risk of over transmitter object or the two units may operate control and hunting and without risk that the simultaneously for fine adjustment and coarse l control Will be unable to follow if there is too adjustment respectively. In the latter Case the great a lag between the transmitter and the re ñne adjustment unit will be connected to have ceiver. Hence, the precision is reduced as the a greater range of movement than the coarse . range of movement of the transmitter object 40 adjustment unit. increases. In the following the invention is described Within certain fields, especially within the with reference to the annexed drawings, in artillery art, it may be necessary to transmit which Fig. 1 is a wiring diagram of a complete angles up to 360°, or even up to a multiple of remote control arrangement according to the in 45 360° with high precision. In such cases the pre vention, Fig. 2 is a diagram for explanation of cision usually becomes too small. The precision the operation of the arrangement according to can be increased, however, by causing the re Fig. 1, Fig. 3 is a wiring diagram of a modified ceiver object to rotate a plurality of times, but form of thetransmitter, Fig. 4 is a diagram, this involves certain disadvantages which make corresponding to the diagram of Fig. 2, for ex such an arrangement impractical. Assume for 50 planation of the operation of the transmitter instance, that the receiver organ is a standard of Fig. 3, and Fig. 5 shows diagrammatically a frequency-meter. During 360° rotation of the receiver to be used with the transmitter of Fig. 3. means of which is controlled by a motor which transmitter object the frequency-meter will, pro The transmitter according to Fig. 1 contains vided it is ,used in the best possible way, sweep two transmitting units S1 and Sz for transmit over its entire scale. If the transmitter object ro 55 ting radio frequency within different frequency 2 2,395,708 quency will be displaced in one direction or the other. Dependent upon the direction in which the intermediate frequency is displaced, there is ranges. The tuning means for controlling the frequency of each of the transmitting units in cludes condensers C1 and C2, respectively. 'I'he obtained a stronger field current through one of two condensers are mounted on the same shaft as the transmitter object. The shaft also car C1 the two field windings of the motor m. which causes the motor to rotate, and to turn the con ries a cam 2 of a switch X, which includes a densers of the receiver units in a direction to contact spring I, arranged to be brought, by the bring the intermediate frequency to the correct cam 2, alternatively in contact with one or the value where both of the fields in the motor are other of two contacts 3 and I. During the rota tion of the shaft, therefore, the contacts I--3 and the contacts I-I are alternately closed to connect the condenser C1 and the condenser C2 alternately into the oscillation circuits of the transmitters S1 and S2. As will be apparent from the following expla nation of the operation of the system, it is ad vantageous, if the Contact arrangement is so made that one of the contacts is closed immedi again in balance and the motor stops.' The operation of the arrangement as a whole is as follows: It is assumed that the transmitting unit of the system is initially in the position shown in Fig. 1. The movement is further assumed to take place `in clock-wise-direction. As apparent from the drawing this rotation of the cam closes the con tacts l-3 of the switch X and the condenser C1 is coupled in, the transmitter unit S1 therefor ately before the other is opened and vice versa, so that the closing of the contacts will always transmitting a frequency which varies with the position of the condenser during the rotational movement. The condenser is cut so that the ca pacity decreases when turned in clock-wise-di rection, and therefor the frequency will increase, as shown in Fig. 2 by the curve a-b. This in overlap for a short time. The two transmitting units S1 and S2 are con nected in parallel by a common line L to the re ceiver, which consists of two superheterodyne units M1 and M2, so arranged that one of the crease of frequency continues during a half rev receiver units M1 has the same frequency range olution, and then the switch X uncouples the as one of the transmitting units S1, and the other condenser C1 and couples in the condenser C2, so of the receiving units M2 has the Asame frequency that the transmitting unit S2 begins to operate. range as the other transmitting unit S2. The re ceiving units are only schematically shown, as 30 The transmitting unit S2 transmits within a fre quency band different from that of the transmit their construction has nothing to do with the ting unit S1. Its frequency thus will vary in the present invention. Concerning the arrangement manner shown by the curve c-d in Fig. 2, until and operation of the receiver it is believed to be after a further half revolution the transmitting unit S2 is uncoupled and the transmitting unit S1 is again coupled in. If the movement takes place very slowly, there is a possibility that the motor M may not start immediately upon switching between the two suiiicient to mention the following: Each of the receivers contains an oscillator, the tuning condensers of which C1111 and C1112, re spectively, are arranged on a common shaft, which also serves as the shaft of the controlled object. The control motor m is arranged on this This motor is provided with two 40 transmitting units. This may be avoided if, as mentioned above, the operation of both of the transmitting units is made to overlap during a motor develops torque in one direction under the short interval. iniiuence of one of the field windings and in the The receiver units are provided with condensers opposite direction under the influence of the 45 C1111 and C1112, respectively, which are cut in such other field winding. a way that they produce the correct intermediate In the intermediate frequency channel of each frequency when the controlled object is in the of the receiving units is arranged a frequency same shaft. field windings, wound in such a way that the same position as the transmitter object. The re discriminator D1 and D2, respectively, of some suitable kind, which after rectifying the inter ceiver condenser C1111 corresponds to the conden ser C1 of the transmitter unit S1, and the receiver condenser C1112 corresponds to the condenser C2 of the transmitter unit S2. Due to the above de scribed operation of the receiver object the re ceiver will therefor always assume the same posi tion as the transmitter object, In order to vary the receiver frequency the mediate frequency, creates voltages which are a function of the displacement of the frequency in the intermediate frequency channel from the frequency to which the channel is tuned. Thus each of the discriminators contains two rectiiiers L11 and L12 and L21 and L22, respectively- The direct current voltages, obtained from the recti fiers, are amplified by means of the amplifier valves R11, R12, R21 and R22, the valves R11 and R21 being connected in parallel to one of the usual methods for frequency calibration, known in the radio art may be used. A very much great er precision may, however, be obtained, if the field windings of the motor m and the two other 60 condenser of the transmitter unit as well as of the receiver unit is designed to cover a greater con of the amplifier valves being connected to the trol angle than 180°, e. g. as shown in the fig other of the two windings. ure, 270°, the condensers being made to give a Due to the above described coupling arrange ment, the superheterodyne receiving units, will logarithmic frequency variation with the angle of convert the frequency received from the trans mitting unit into an immediate frequency, pref rotation, at least within the range which is used. One can then always choose an angle of 180° for the transmitting condensers and a different erably equal to the difference between the signal angle for the receiver condensers, at which the above mentioned frequency relation is present. frequency of the transmitting unit and -the in ternal oscillator frequency of the receiver, al though the sum may be used. If theinternal In this way a simple condenser of the same shape is obtained for the transmitter as well as for oscillatory frequency is correctly tuned, a fre the receiver while maintaining an accurate align ment between the angles of rotation of the trans quency difference will be obtained which is ex actly the same as the tuning frequency of the intermediate frequency channel, but if the oscil lator frequency is wrong the intermediate fre mitter and of the receiver. 75 » It is easy to prove mathematically, that in this asaavos \, 3 case the inductance coils in parallel to the con densers should have inductance values which comes again active, and oscillator 24 is put out of action. are in a proportion to each other as the squares The oscillators 22 and 24 have similar condens ers. because of the fact that the condensers have of the mean frequencies of the frequency bands, respectively. The shunt capacities on the re ceiver and on the transmitter should be as nearly a common rotor. Also the coils 2I and 23 are similar. 'I'he frequencies therefore will vary in equal to each other as possible. ' the manner shown in Fig. 4. The line 30, drawn After this preliminary explanation of the in full, represents the frequency of oscillator 29, operation of a simple system embodying the in and the line 3I represents the frequency of oscil ventlon, the transmitter according to Fig. 3 may 10 lator 22 and the line 32 represents the frequency be described. This transmitter is arranged to of oscillator 24. Parts of the lines 3| and 32, provide a main movement and a movement which which are drawn in full, represent operating pe is subordinated under this main movement, the ' riods of the respective oscillators, whereas the last mentioned movement being here supposed broken parts of these lines represent the time to be a vernier movement. 'I'he shaft of the 15 while the oscillation circuits of the oscillators are transmitter object is referred to as I0. This short-circuited. shaft may for instance be connected to some The receiver for the transmitter of Fig. 3 is, indicator which may be read in a remote place. shown in Fig. 5` The transmission line is also Such an indicator is schematically shown at II. here designated as 25. It is inductively coupled On the shaft I0 there is arranged a‘worm gear 20 through a transformer 33 to the receiver for the ing I2, by which the shaft I0 is connected to an main signal and also through two transformers other shaft I3 in a gear ratio of 100:1, the last 34 and 35 to each of two cooperating receivers named shaft determining the main movement. for receiving the Vernier signal. The main sig The shaft I0 carries a rotor I4 of a double con nal receiver consists of an oscillator valve 35 denser, having double stators I5 and I6. Thus 25 connected in a standard manner to operate as a one condenser is formed between the rotor I4 combined oscillator and modulator. The con and the stator I5, whereas another condenser nections for this valve are here of no importance is formed between the rotor I4 and the stator I6. except as far as this valve converts the main sig A :cam wheel Il, carried by the shaft I0, causes nal frequency to a frequency corresponding to a contact spring I8 to be in contact with the 30 the difference between the main signal frequency contact point I9 during substantially half of a and the oscillator frequency, such as the inter revolution of the cam I1 and with the contact mediate frequency in a superheterodyne receiver. point 2li during substantially the oher half of The transmitter frequency ‘may have a range of its revolution. 15G-200 kcs. and the receiver oscillator frequency 'I'he shaft III is grounded, so that the con 35 a range of 250-300 kcs., producing an intermedi denser I4-I5 is permanently coupled in parallel ate frequency 100 kcs. Of course the invention to the coil 2I of an oscillator valve 22, and the could also ‘be used according to the infrahetero condenser I4-I5 is in a corresponding manner dyne principle, although it has not been found pennanently coupled in parallel with the coil 23 as advantageousof a second oscillator valve 24. The oscilla 40 The oscillator circuit `of the oscillator valve 36 tion circuit, formed by the coil 2| and the con contains the coil 31, coupled in parallel with a denser I4-I5 may, however, be short-circuited trimmer condenser 38 and the tuning condenser by means of the contacts I3-I9 and in a corre 33. Condenser 39, which is thus the main tuning sponding way the oscillation circuit of condenser condenser, is mounted on the same shaft as the> I4-I6 and coil 23 may be short-circuited by con 45 control motor 4I for the receiver object 42, which' tacts I8-2II. The anode circuits of the oscilla is here as a matter of simplicity shown in the form tor valves 22 and 24 are vinductively coupled to of a simple dial. the transmission line 25. The anode circuit of the oscillator valve con-l The shaft I3 carries a further condenser, ln tains a circuit tuned to the exact value of the This con 50 intermediate frequency and containing th'e con- , denser is coupled in parallel to the coil 23 of an denser 43 and the coil 44. Coil 44 is inductively oscillator valve 29, the anode circuit of which is coupled to a second coil 45, tuned by means of also connected inductively to the transmission condenser 46.' Further the coils 44 and 45 are line 25. connected to each other by means of a condenser For explanation of the operation of the trans 65 41, which is connected between the mid-point of mitter, reference is made to Fig. 4. It is assumed one of the coils, for instance, coil 45, and the that the shaft I0 turns a plurality of revolutions high potential end with reference' to alternating in clock-wise direction. Due to its rotation the current of th'e other coil, in this case the coil 44. capacity I4-I 5 will initially increase, so that the This coupling arrangement is sharply tuned and frequency 0f the oscillator 22 decreases succes 60 is known per se. It operates in the following sively. The Áoscillation circit 0f oscillator 24 is manner: short-circuited by the contacts I3 and 20. At the The voltage of a tuned primary circuit and in same time also shaft I3 turns, but due to the a tuned secondary circuit are normally displaced gearing this takes place in counter-clockwise di in phase by 90°. If the primary voltage is added, rection and also at a speed which is assumed to 65 as by the condenser 41, to one half of the sec be only one hundredth of the speed of rotation ondary voltage in positive direction and to the of shaft III.> The capacity of condenser 26--21 other half of the secondary voltage in negative will therefor successively decrease, and the cre direction, due to th‘e symmetry between these two ated frequency will increase. When shaft I0 has voltages the resulting vectors will be exactly equal. turned half a revolution, the short-circuit of con 70 If the frequency differs from that to which the denser I4-I6 is opened, so that the oscillator 24 circuits are tuned, however, the symmetry is de becomes active, and a moment later the oscilla , stroyed. Of course the two half voltage vectors tion circuit of oscillator 22 becomes short-cir of the secondary voltage are still equal, but one cluding a rotor 26 and a stator 2l. cuited, this oscillator thereby becoming inactive. ' After a further half revolution condenser 22 be-~ 75 of them, due to the changed phase relation be tween primary voltage and secondary voltage. will 2,395,708 forman acute angle with the primary voltage At the same time as the frequency 30, Fig. 4, vector, whereas the other one forms an obtuse angle. The former resultant will thereby be es is transmitted, transmission of a further fre quency 3| or 32 from the Vernier transmitter takes place. This is received by means of the receivers which contain oscillator valves |36 and 233, re sentially greater than the latter one, and if both _ of the voltages are _rectified different direct cur rent voltages will be obtained. 'I'h‘e rectifiers, in which the rectification is made, are in the figure shown as valves 48 and 49, which work on the load resistors 50 and 5|, spectively. As a matter of fact, the frequency is received by both of these receivers, but only one of them is in the position to operate. Assume, for instance, that the main receiver has been respectively. The voltages across the respective 10 roughly positioned so that the oscillator |35 op erates, then due to the characteristic of the dis load resistors are fed each to one of two direct criminators of this type a substantial voltage dif current amplifier valves 52 and 53, the anode cir ference may be obtained between the direct cur cuits of which >are connected each to one of the rent voltages created by rectifiers |43 and |43 field windings 54 and 55 of th'e motor 4 |. The coupling arrangement for Vernier recep 15 if th'e shaft 56 is not correctly positioned. This direct current voltage difference influences the tion is arranged in substantially the same man field windings of motor 51, so that an automatic ner as the main receiving system. The only dif ference is that two cooperating receivers are pro vided, cne of which responds to the frequency correction is obtained. .. Meantime, howeverl the oscillator 235 produces 3| and the other to the frequency 32 in Fig. 4. 20 an intermediate frequency with the incoming frequency, but this differs widely from the inter In order to simplify the description the same ref mediate frequency to which the discriminator is erence numerals have been used in the Vernier re tuned. Since discriminators of this kind produce ceivers as in the main receiver, said reference very small or no current deviation, when th'e fre numerals having been increased by one hundred for one of the Vernier receivers and by two hun 25 quency is widely displaced from the dìscriminator frequency, the result is that about equally strong dred for the other. field currents are delivered by the amplifier Valves The two receiver units are provided with con 252 and 253 to windings 50 and 6|1 said currents densers with a common rotor 58, mounted on also being substantially weaker than the currents the common control shaft 56, which' is driven bymotor 51. The shaft 56 actuates the receiver ob 30 delivered by Valves |52 and |53. The fact that the oscillator 236 is allowed to operate at the ject 59, which is shown as a Vernier dial. The same time as oscillator |36 therefore does not anode circuits of the direct current amplifier cause any appreciable disadvantage. valves |52 and 252 are connected together and If necessary, a contact arrangement (not connected to supply field current to the field wind shown) may be provided on shaft 55, by means ing 60 of motor 51, whereas the direct current of which the field windings 50 and 6| are con ampliñer valves |53 and 253 are connected to nected in turn to the valves |52 and |53 and to gether to supply field current to the field winding the valves 252 and 253. 6|. When the system has been out of operation, The operation of the arrangement is the fol lowing: ` 40 one can not with certainty assume that the trans vary as a function of the angular position of the mitter and receiver are in agreement. It thus may happen that the receiver or the transmitter has meantime changed its position, so that a dif ference in position of half a revolution of shaft of the sh'aft l0 a full frequency range, corre within a range of tolerance which is less than When shaft IU in Fig. 3 turns, it causes the transmission of two different frequencies, indi cated by the curves 3| and 32 of Fig. 4, which shaft I0. Another frequency is transmitted by 45 I0 or a multiple of such' a half revolution has oc curred. In order to prevent this, the motor 4| oscillator 29 in the form indicated by the curve may be made strong enough in relation to the mo 30 in Fig. 4, which is a function of the angular tor 51 to always secure correct rough adjustment position of the shaft I3. For each half revolution sponding to the capacity variation during 180° of 50 plus or minus a quarter of a revolution of the shaft I0, or the motor 51 may be cut oi! until the the condenser |4-I5 and |4--|6, respectively, is motor 4| has completed control within the said run through by the transmitter units 22 and`24, tolerance. This may be done by connecting the as shown in Fig. 4 by curves 3| and 32 respec field windings 54 and 55 of motor 4| in series tively. through the windings 62 and 63 of a differential On the receiver side the frequency 3D is re relay 65 having a contact 64. At certain differ ceived by means of the transformer 33 of the main ences between the currents through' said wind receiver, in which it is modulated with’ the fre ings 62 and 63 the contact 54 of the relay opens quency created by oscillator valve 36, so that an the armature circuit of motor 51, which is not intermediate frequency is formed. vIf it now should happen that this intermediate frequency 60 closed until the difference between the two cur rents have decreased to a sufficiently low value. agrees with the frequency to which the discrimi Of course it is possible to utilize additional nator 43-46 is tuned, the reception of th'e fre stages of Vernier adjustment to obtain a still quency 30 does not result per se in the operation more exact adjustment. In this manner it is of the motor 4| of the receiver. If, however, the possible to obtain a precision in the remote con frequency differs from the above, a stronger mag trol which- is only limited by the mechanical pre~ netizing current is obtained through one of the cision of the gearing. If the invention is used to windings 54 and 55 of the motor 4|, which causes control with high precision the position or di th'e motor to operate and the shaft 40 is tuned, rection of some object, for instance, a piece of until condenser 39 has reached -such a position that the correct frequency is restored in the in 70 ordnance, the control mechanism of the piece termediate frequency channel of the main re may be connected with the shaft 56 as indicated by th'e dial 59. ceiver. The dial 42 then will take the position corresponding to that of the main transmitter, What we claim is: but which according to the suppositions may not `1. In a remote control apparatus, a transmit 75 ter including a pair of units each having means _ have sufficient precision. 5 2,395,708 for producing and transmitting signals having powerful to effect control regardless of the ener gization of the fine control motor. 7. In a remote control system according to claim 4 in which the signals are respectively in tended for fine and coarse control, control means responsive to each of said signals and means frequencies variable over a predetermined range and including a control member to control as a function of its position the frequency of said sig nal, and a receiver, including a controlled ob ject, and a pair of units tuned for receiving the rendering the fine control means ineffective ,until signals transmitted from said first units, said last units each having means responsive to variations the approximately correct coarse control is in the frequency of the received signal from the effected by the coarse control means. 8. In a remote control system according to frequency to which said last units are tuned for 10 effecting a control of said object corresponding to claim 4, tuning means for the control channels including variable condensers having logarith the movement of said control member, said con mic capacity characteristics. trol member being connected to cause said first 9. In a remote control system according to units to alternately transmit signals sweeping over their respective ranges, whereby said con claim 4, tuning means for the control channels including variable condensers having logarithmic trolled object is controlled alternately by the re ceiver units cf said pair. capacity characteristics, the, condensers of the respective channels being angularly displaced rel 2. An apparatus as defined in claim 1 includ ing a tuning circuit for each of said units of said ative to each other. 10. In a remote control apparatus, a trans pair, and a variable condenser having two stators 20 mitter including a unit having means for produc and a common rotor, one of said stators being in ing and transmitting a signal having a frequency cluded- in the tuning circuit of one of said pair of variable over a given range anda pair of units - units and the other stator being included in the having means for producing and transmitting tuning circuit of the other of said pair of units. signals having frequencies variable over different 3. A remote control apparatus as defined in ranges and including a contro1 member to con claim 1 in which the signals transmitted by the trol, as a function of its position, the frequencies units of said pair are variable ,over different of said signals within the respective ranges, and ranges. . a receiver, including a controlled object, a unit 4. In a remote control apparatus, a transmit n ,ter including a pair of units having means for 30 tuned for receiving the first-mentioned signal and producing and transmitting signals having fre having means responsive to variations in vthe frequency of said ñrst signal from the frequency quencies variable over a predetermined range and which said unit is tuned to receive for effecting including a control member to control as a func control of said controlled object, and a pair of tion of its position the frequency of said signals, and a receiver, including a controlled object, and 35 units each tuned for receiving said second men tioned signals, and having means responsive to a pair of units tuned for receiving the signals variations in the frequency of said last signals transmitted from said ñrst units, said last units from the frequency which said units are tuned to each having means responsive to variations in the receive for modifying the control of said object. frequency of the received signals from the fre quency to which said last units are tuned for 40 effecting a control of said object corresponding to th'e movement of said control member, said con trol member being connected to cause the fre quency of one of said signals to vary at a rate substantially greater than that of the other of 11. An apparatus as deñned in claim 10 in . which said control memberis connected to vary the frequency of said signals at different rates, the slower varying frequency constituting a coarse adjustment of said object and the more 45 said signals and to cause said ñrst signal to suc cessively sweep over its range while said second signal varies progressively and continuously in the same direction during a predetermined range in movement of said control member whereby said first signal may be used for effecting ñne ad justment of said controlled object and said sec ond signal may be used for effecting coarse ad iustment thereof. 5. In a remote control apparatus according to claim 4 in which the signals are respectively in tended for fine control and coarse control, rotat-~ able tuning means at th'e transmitter and receiver for each of said signals and reducing gears in rapidly varying frequency constituting a fine ad justment of said object. 12._In an apparatus as defined in claim 10.~ means alternately rendering the units ofl said pair operative, said means being connected to said control member to cause the signals from said last units to alternately sweep over their respective ranges in response to continued movement of said control member. 13. In an apparatus as defined in claim 10, means alternately rendering the units of said pair operative, said means being connected to said control member to cause the signals from said last units to alternately sweep over their respec tive ranges in response to continued movement terconnecting the rotatable tuning means for the 60 of said control member, said last means causing the periods of energization of the respective units ñne and coarse' signals >at the transmitter and receiver. of the pair of transmittir g units to overlap where 6. In a remote control apparatus according to by continuous control is effected thereby. »‘~ claim 4 in which the signals are respectively in tended for fine control and coarse control, rotat able tuning means in the respective channels at 14. An apparatus as defined in claim 10 i which said second mentioned signals are variable over the same range as each other, but over a dif the receiver, and motors actuating said tuning ferent range from that of the first mentioned means in response to frequency variations in the signal. received signals, the motor actuating th'e tun ing means for the coarse control being suiiiciently 70 - HARALD VALDEMAR ALEXANDERSSON. CARL-ERIK GRANQVIST.
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