US2237156A - Speed correction for multiplex telegraph and facsimile systems - Google Patents

Description

April 1, 1941. R E, MATHES 2,237,156

SPEED CORRECTION FOR MULTIPLEX TELEGRAPH AND FACSIMILE SYSTEMS Filed Dec. 13, 1953 4 Sheets-Sheet l INVENToR @War/f5.5' BY ATTORNEY R. E. MATHlz-:s 2.237.156r

April l, 1941.

SPEED connEcTIoNloR UUL'TIPLEX 'rELEGRArH AND 'FACSIHILE -SYSTEMS 4 Sheets-Sheet 2 Filed Dec. 13, 193s mvNToR Rl HARD E. mHTHES ,BY

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ATTORNEY n. E. MATHEs 2,237,156

SPEED CORRECTION FOR HULTIPLEX TELEGRAPH AND FACSIIILE SYSTEIS 1"':11edDecLy 13. 1938 4 Sheets-Sheet 5 All uu nhs.

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ATTORNEY April 1 1941' R. E. MATHr-:s 2.237.156

SPEED CORRECTION FOR MULTIPLEX TELEGRAPH AND FACSIMILE SYSTEMS Filed DSC. 13, 17938 4 Sheets-Sheet 4 f C 1'7l 1% I :mama/wim a v v f anni )d M w ASU a #suf/w www /r ,www

INVENTOR ATTORNEY PatentedApr. 1, 1941 A S PATENT OFFICE SPEED CORRECTION FOR MULTIPLEX TELE- GRAPH AND FACSIItIILE SYSTEMS Richard E. Mathes, Westiield, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application December 13, 1938. Serial No. 245,364

20 Claims.

This invention relates to speed` and phase correction in multiplex telegraphy and facsimile transmission operating on the time division principle. In such systems the rotating connectors or distributor arms at the transmitting and receiving ends must run in absolute synhronism and phase. With distributor arms that are run by electric motors, speed control is usually obtained by means of tuning fork mechanisms at the transmitter and receiver that are as identical as it is possible to make them. These control devices will maintain substantial synchronism between the rotating parts of the transmitter and the receiver but it is practically irnpossible to maintain with them alone the exact synchronism and phase necessary for satisfactory operation of the system. It is therefore necessary to use some speed correction mechanism that operates to correct any tendency to deviate from the `synchronous speed. In my Patent No. 2,038,375, April 2l, 1936, I have described mechanism for making this speed correction by utilizing brushes and short-circuiting bars on the rotating mechanism controlling the distributor arm.

It is an object of this invention to correct the speed of motors and other rotating parts without utilizing any brushes and short-circuitlng bars for thisl purpose.

Another object is to combine pulses of the incoming signal with electrical potentials produced bythe rotating distributor in such a way that resultant potentials produced by the incoming signal and the rotating parts initiate movements Athat bring the parts back into synchronism and 2.

phase.

Other objects will appear in the following de-l scription, reference being had to the drawings in which similar reference characters represent similar parts.

In the drawings:

Fig. 1 is a diagrammatic illustration of one form of my invention.

Fig. 2is a diagrammatic illustration of a second form of my invention.

Fig. 3 is a diagrammatic illustration of a third form of my invention. v

Fig. 4 is a series of graphs illustrating the principle of the speed control in Figs. 2' and 3.

Fig. 5 is a series of graphs showing the torque l in the relay of Fig. 1.

Fig. 6 shows the battery connection for applying the voltage to the circuits in Figs. l, 2 and 3. Referring to Fig. l, I indicates radio receiving apparatus consisting of the usual tuning devices,

ampliers,`detectors and tone keyers that produce in line 2 separate pulses of current such as are more particularly described in my Patent No. 1,979,484, November 6, 1934. This station equipment is well known and it is suflicient to state that the received signal exists in line 2 in the form of separated current pulses of irregular length and spacing but the beginning and end of each pulse occur-s at a definite time in respect to the keying speed; The combined signals in line 2 of the receiver are separated by the distributor arm 3 made to rotate in synchronism with'the distributor arm at the transmitter by the electric motor 4 energized in ways well known in the art for maintaining synchronism between the transmitting and receiving distributors. Since any type of control may be used for motor 4 the energizing circuits have not been shown.

The stator frame of the electric motor l is geared to speed correction unit 5 so that the frame is moved forward in the direction of rotation when the speed is slow, and in the opposite direction when the speed is fast. In this way the distributor arm 3 is run in absolute synchronism and phase with the distributor arm at the transmitter.

The rotation of the speed correction motor 5 is brought about by a relay 6 which closes the circuit of the motor to the positive or negative terminal. This relay is under the control of two electromagnetic coils. One 1, of the coils is wound around switch tongue 8 and the other one, 9, is wound on the relay field core. The coil 1 is energized by an inductor generator I0 having the rotor II attached to the rotating shaft of the distributor arm either directly or by suitable gearing. The field of this inductor generator is supplied by coils I2 connected to the terminals of suitable supply such as the battery I3 in Fig. 6. The armature of the inductor generator consists of coils I4, I5, connected to the relay coil I by conductors I8v and I1. The composite signal pulses coming over line 2 are imposed through conductor I8 on the grid of a tube I9, the output of which extends through transformer 20. The secondary of this transformer is connected Vto ground and to a rectifier 'M of any appropriate kind. Of rcourse the transformer will vtransmit a brief potential only at the beginning and close of a signal character while the field is building up or collapsing. That is, there will be a pulse generated only at the change ofsense of the signals. No potential will be generated while the current isV steady. The rectifier 2'I is connected through a coupling condenser 22 and leak drop in grid resistance 33.

resistance 22' with the multi-vibrator generally indicated by reference character 23. This rectier eliminates one of these two pulses; for example, the one at the end of each signal character. This multi-vibrator is of the type described by Abraham and Bloch in An. d. Physique XII, page 252, 1919. It is essentially an oscillator maintaining a frequency that bears a constant ratio to the rate of rotation of the distributor arm vat the transmitter. While this multi-Vibrator is old and well known in the art, its method of operation is somewhat obscure and it, therefore, will be described somewhat in detail.

When the potentials of the battery I3 are rst applied to the terminals 24, 25, each condenser 26 and 21 will commence to charge. Condenser 21 will be charged by current flowing from terminal 24 through one-half of coil 9 to conductor 28, resistance 29, condenser 21, grid resistance 30, vto ground terminal 25. VThe other condenser will charge through conductor 3l, plate resistance 32,

condenser 26, grid resistance 33, to ground terminal 25. It will thus be seen that the charging current from each condenser passes through the grid resistances in'such a direction as to make the grids positive. This has no effect on this initial charge except to cause the tubes 34 and 35 to draw more current and retard the charging operation somewhat by increasing the drop in resistances 29 and 32.

' Theoretically, it would be possible to charge the condensers 26 and 21 to the full line potential of conductors 24, 25, without any oscillating action taking place, but this would require an absolutely steady plate-lament current flowing at all times. It is Well known that the plate-filament current of a vacuum tube is not steady even when no adjustments are being made.. Therefore, the tubes 34 and 35 will draw slightly varying currents. Suppose that after the condensers are initially charged to some potential, tube 34 has a very slight increase in current. This causes aslight discharge of condenser 26 because the slightly increased drop in plate resistance 32 has lowered the voltage impressed on the condenser below the charge in that condenser. This condenser 26 will discharge through the plate filament circuit of tube 34 through conductor 36, resistance 33, and conductor 31. This now of current is in such a direction as to place a negative bias on the grid of tube 35. This causes tube 35 to draw less current'and condenser 21 commences to charge further because of the lessened drop in plate resistance 29. This charging current will pass through grid resistance 30 and increase the positive bias on the grid of tube 34. This causes that tube to draw still more current which causes condenser 26 to further discharge, due to the increase in drop in plate resistance 32. This further increases the negative bias on grid 36 due to the increased This action continues until nally 'tube 35 blocks and no current at.all passes through resistance 29. Condenser 21 then has its maximum charge and condenser 26 its minimum charge.

When condenser v21 obtains its maximum charge, current ceases to ow through grid resistance 30 and the grid of vacuum tube 34 then goes more negative. This reduces the plate current fiowing through resistance 32 and condenser 26 commences to charge because the voltage at its terminals is now increased due to the dimin ished drop in resistance 32. When this condenser starts to charge the current ows through conductor 31, grid resistance 33, conductor 36, to ground terminal 35 and back to the positive ter minal 24. It will be seen that this places a positive potential, or less negative potential, on the grid of vacuum tube 35 and the tube starts to draw current. This increases the drop in resistance 29 and the voltage impressed on condenser 21 is then lowered below the voltage of the charge therein. Condenser 21 therefore discharges through the plate filament circuit of tube 35, conductor 38, grid resistance 3|) and conductor 39. This makes the grid of tube 34 still more negative due to the drop in resistance 30 and conf denser 26 further charges due to decreased drop in plate resistance 32, and this charging current causes tube 35 to draw still more current, as previously explained.V This causes condenser 21 to still further discharge. until tube 34 blocks and a reverse action takes place in respect to the two condensers.

Thus, the unbalance condition of this circuit arrangement causes the multi-vibrator to continue to vibrate or oscillate at a frequency depending upon the charging and discharging times of the condensers which depend upon the constants of the circuits.

The circuits of the multi-vibrator 23 are adjusted so that the frequency of vibration is the same as the frequency of rotation of, distributor arm 3 but it seems to be humanly impossible to cause two oscillators or rotating mechanisms to continue indefinitely at absolute synchronism and tocause absolute synchronism, and occasional correction is necessary. To obtain this correction, Icause the rectified pulses of the signal to be applied at 40 to the grid of tube 35. This pulls the multi-vibrator into step and causes it to osclllate at a frequency that is absolutely the same as the frequency o1'l rotation of the transmitter distributor at the sending station. The operation of my improved speed correction system may now be explained. l

The inductor alternator I0 is generating an alternating potential of a frequency that is the same as, or proportional to. the rate of rotation of the distributor arm 3. Switch tongue 8 is magnetized by a current of this frequency which passes through coil 1. The field of relay 6 is magnetized by the oscillating current that passes al-` ternately through the two halves of the coil 9 to the multi-vibrator 23. This produces a magnetization in the core 4I which changes its polarity with the frequency of the multi-vibrator.

The inductor I I is so positioned on the distribu.. tor shaft that the magnetization of coil 1 is 90 out of phase with the magnetization of coil 9 produced by the multi-vibrator, which is in phase with the distant transmitter distributor arm. With this adjustment the switch tongue will remain in mid position for reasons that will now be explained.

In.Flg 5 a series of graphs H to L inclusive, show the torque or electromagnetic moment of the relay for various differences of frequencies of the For the 'I'hls action continues l vbetween the multi-vibrator and generator I0.

Curve a indicates the flux in field pole 4I' produced by coil 9 and curve b gives the flux in the ymovable pole 4I" produced by the coil 1. The

relay tongue is so damped, mechanically, that it cannot vibrate at theV frequency of the torque indicated by curve c which is twice the frequency of the multi-vibrator. Since the average positiveand negative torque, so to speak, is zero the relay tongue remains motionless.

In graphs I the torque is shown when the generator I lags 45 behind its normal synchronous condition. The average positive torque is greater than the average negativeA torque and the tongue pole 4|"` moves away from field pole 4l'.

In graphs J the torque is shown when the generator I0 is 90"V behind the multi-vibrator. Here curves a and b coincide. The torque shown by curve c is all positive and as before, the tongue pole 4I" moves away from eld vpole 4I'. Thus, for all lagging conditions from 0 to 90 the switch tongue is forced to the left in Fig'. 1 into engagement'with the positive contact.

In graphs K the torque is indicated by c for lead of the generator llover the znulti-vi brator. Here the average torque is negative and the tongue pole 4|" moves toward field pole 4I'.

In graphs L the torque is indicated by c for 90 lead. Under this condition the torque is all negative andthe tongue'pole 4i" likewise moves toward ileld pole 4I'. Itwill be apparent that for all leading conditions'froni 0 to 90 the switch tongue will be forced into engagement with the negative terminal.

The above analysis of conditions between 90 lag and 90 lead' is merely to show how the relay operates. As a matter of fact the receiving distributor never departsl from synchronisrn but a slight amount. switch tongue is thrown into engagement with the positive terminal 42, and current flows through conductor 43 to the correction motor 5 which will rotate the frame of motor 4 in the direction of rotation of the distributor shaft 3. This' will speed the shaft up until it gets in phase with the multi-vibrator and distant transmitter distributor arm..y

If the distributor arm 3 should slightlyvspeed up, that is, lead, the switchmtongue will be thrown into engagement with the negative terminal and the correction motor 5 will be rotated against the direction of motion of switch arm 3. This will slowv down the motor until it is again insynchronism with the multi-vibrator. In this way absolute synchronism and phase is main-` tained by this embodiment of my invention.

In'the embodiment of Fig. 2 the distributor arm is driven by the same kind of motor 4, as in Fig. 1, and its speed is corrected by the same sort of motor 5 as in thatgure though the control of the speed correction motor is somewhat different. The distributor, either by direct connection or by. any type of gearing operates a generator of alternating current shown diagrammatically at 45, which feeds current of frequenwhich is connected between the grids of vacuum tubes 48, 49. The other end ofthe secondary of transformer 45 is connected through'resistance to the neutral terminal of the battery I3 75 Whenever i't lags slightly theY through ground. A second generator 5I directly or otherwise connected to the distributor arm 3 'a differential re1ay,'the tongue 55 of which is connected to the speed correction motor 5. When tongue moves against the positive contact 55 the motor rotates the field frame of the motor 4 in one direction and when in engagement with contact 51 it rotates-the motor 5 and field frame of motor 4 in the opposite direction. Condensers 58, 59, may be arranged to shunt the coils 53, 54,

as shown in the drawings, to integrate the pulses and prevent chattering of the relay. The laments of vacuum tubes 48 and 49 are connected to the neutral point of battery I3 as by grounding.

The incoming signal wire 2 is connected to the distributor arm 3 inthesame way as in Fig. 1 and this wire 2 is also connected through a tube I9, transformer 20, conductor 90, rectifier 2i and condenser 22, to the junction point between resistance 50 and the secondary of transformer 45.

The operation of themodiiication in Fig. 2 is as follows:

The constants of the 'circuits of generators 45 and 5I are so chosen that their combined voltage is insufiicient to operate the relay tongue 55. In Fig. 4, graph F shows the output of generator 45, a half wave only being shown, as this is suiiicient for explanation. Graph F1 represents the voltage of the frequency of generator 5| which in this case is the sixth harmonic of the other frequency. Graph B illustrates the composite voltage produced by the combination of voltages Fand F1.

In this composite voltage it will be seen that at the center'point 62, graph B has the same value as graphF because as4 shown by graph F1 the voltage in generator 5I is zero. At point 83 thecomposite voltage is a maximum 15 to the left of point B2 in this figure. 'I'he voltage at point 55 or B4 in the composite curve is of insufcient value to operate relay tongue 55.

ince the grids of tubes 48 and 49 are arranged in opposition as in push pull tube circuits, the

plate voltage in one tube is 180 out of phase with that in the other as far as the frequency F1 is concerned, but in phase insofar as frequency F is concerned. Therefore, graphs A in Fig. 4 may-be taken as applying to one tube, say, tube 48, and graphs C, as applying to the othertube 49. Since frequency F1 is reversed in graphs C. as compared with frequency F1 of graphs A, the maximum value 63'v occurs at the right of point 62 in Fig. 4 and the values 64 and 65' are also reversed, as compared to similar points in graphs A. Current led in through line from receiving conductor 2 places a drop in resistance 50 that is impressed on the grids of tubes 48 and 49 in the same phase.

e negative bias 66 and 91 placed on the grids of tubes 48 and 49 is sucient to block these tubes or to permit onlya very small current flow in the plate circuits of the tubes even when the signal pulse 68 of graphs D is combined with the other two currents 'at the point 52. At this point the distributor arm 3 is in phase and synchronism with the signal. v

If the receiving distributor arm 3 of Fig. 2 happens to depart from synchronism the graphs A and C will move relatively in respect to signal pulse 58 of graphs D. For convenience of illustration this relative movement will be shown by duplicating the signal pulses in graphs D either to the right or left of the center point 52.

In slowing down of arm 3 let it be assumed that the relative movement is such as to place the signal pulse in the position shown. at 69 in graphs D. In moving from 62 to point 63 the resultant voltage increases because the signal pulse shown at 69 is combined with the maximum voltage 53 of graph A. Tube 48, therefore, draws current, but the tube 49 is still blocked, its grid voltage being the sum of 63a and 69. The plate current of tube 48v is shown by graph E. 'I'his plate current flowing through coil 53 operates the relay tongue 55 which connects the correction motor 5 with the positive terminal 56. The eld frame of synchronous motor 4 is then rotated in the direction of rotation of the motor connected to distributor arm 3 and this brings the distributor arm back into phase to the point 62.

If the distributor arm 3 attempts to speed up it will get out of phase in the other direction, as shown by graphs C and D. The signal pulse is now indicated at 10 in line with the hump 63' of combined frequencies FFi. This produces plate current as shown in graph G which flows through coll 54. Tube 48 is blocked at this time, the combined grid voltage being 63h plus single voltage 10. The tongue 55 is now moved into contact with the negative terminal 51. The correction motor then rotates in the opposite direction and rotates the field frame of the motor 4 opposite to the direction of rotation of the distributor arm 3 and it is brought back into phase at point 62. Thus synchronism is maintained between the transmitter and the receiver without any commutator connections on the distributor shaft.

It will be apparent from an inspection of the graphs in Fig. 4 that the higher the harmonicv used, within reason, for frequency F1, the closer the regulation will be but the sixth harmonic is quite suitable .for the purpose.

In Fig. 3 a further modication is shown. In this modification the current from generators of frequency F and F1 are led into transformers 46 and 41 in exactly the same way as in Fig. 2, but the terminals of the transformer 41 are connected to a multi-vibrator indicated generally at -23 to elongate or fill out the signal pulse coming over conductor 60 before the output of transformer 41 is connected to the tubes 48 and 49. In this way a stronger magnetic pull may be produced by relay coils 53 and 54 through the action of the multivibrator. 'I'his multi-vibrator is biased so that no current flows in the plate circuit except when the maximum voltage f of the crests 63, 63', is impressed on the grids. The multi-vibrator thus does not oscillate continuously but when acting under the voltage crests 53 or 63 it vibrates a number of times, as later explained. In this modification the bias on multi-vibrator tubes 34, 35, is

' such as to block them even with the peak voltages When the distributor arm is in phase with the signal pulses, the relay tongue 55 remains in neutral position because the multi-vibrator tubes 34, 35, and the relay tubes 48 and 49 are still blocked. When the distributor arm 3 retards in phase through a decrease in speed over the synchronous .been charged at full potential of the line.

speed the relative position of the signal pulse will be indicated at 69 in Fig. 4. The resultant pulse 63 impressed on the grid of one of the tubes, for example, that of tube 35, will cause that tube to draw current, but relay tube 48 will not draw current. The drop in resistance 29 causes condenser 21 todischarge because it has previously The charging current will pass through the platenlament circuit of tube 35 to groundup through resistance 50, the primaries of transformers 46, 41, resistance 30 and conductor 39. This instantly places a more negative potential on the grid of tube-49 blocking it still more strongly.

When the signal pulse diminishes tube 35 draws less 'current and condenser 21 starts to charge. This places a strong positive bias on the grid of tube 34 and it starts to draw current. Condenser 25 then startsl to discharge and makes the grid of tube 35 still more negative and so on till the peak 63 passes. All of this, of course, happens practically instantaneously and the net result of the peak voltage applied to grid of tube 35 is to make the grid of tube 49, which has the same potential as tube 34, highly positive for s. sufficient period to pass a strong current through coil 54. In this case the potentials of the terminals of the relay would be reversed so that coil 54 connects to the positive terminal though, of course, the same result could be accomplished in other ways as by reversing the winding of coils 54 and 53, changing the polarity of motor 5, etc.

After the peak voltage 63er 63' passes, both tubes of the multi-vibrator block until another of these peaks occurs.

To explain the expression channel keying frequency used in the claims, it is explained that the smallest marking unit in a Morse code mes sage is a dot. Since a space is required to distinguish this dot from the other characters, the space immediately following the dot is part of the dot cycle. The number of these dot cycles of a y single channel or their equivalent f ed through the multiplex system per second is called the "channel keying frequency.

In a multiplex system of the type described, the Vchannel keying frequency of the various channels is the same and the composite keying frequency" is the sum of all the channel keying frequencies. For example, in a three channel system, if the channel keying frequency is 60 dot cycles per second, the composite keying frequency is dot cycles per second. Both of these terms are used in multiplex telegraphy, but I prefer to use the term channel keying frequency in the appended claims. In equal length codes, the channel keying frequency would have the same significance, but in such codes one cycle would be a mark and a space and the channel keying frequency would be the number of such cycles of a channel sent through the multiplex system per second.

I have shown in the drawings one or more dynamos connected to the receiver distributor to run at a speed proportionally thereto but any other form of generator of alternating potential may be used instead, so long as it has a frequency proportional to the frequency of the receiver distributor. Also, in Figs. 2 and 3 the harmonic frequency may be obtained from the generator of the fundamental frequency by using well known frequency changers. Various other modications may be used without departing from the spirit of the invention.`

Having described my invention, what I claim is:

1. In a telegraph system for receiving multiplex signals having a predetermined channel keying frequency, a receiving line, a distributor connected to said line, means for operating said distributor substantially atsaid channel keying frequency, control means for causing the first means to increase and decrease the speed of said distributor, a generator of alternating electromotive force at the receiver having a frequency proportional to the channel keying frequency, a second generator of alternating electromotive force at the receiver having a frequency proportional to the speed ofsaid distributor and means for causing said control means to increase the speed of the distributor when the frequency of the second generator is below that of the first generator and to decrease the speed when it is thereabove.

2. In a telegraph system for receiving multiplex signals having a predetermined channel keying frequency, a receiving line,- a'distributor connected to said line, means for operating said distributor substantially at a speed of rotation proportional to said channel keying frequency, control means adapted, when connected to one potential to vary the speed of said distributor in one y sense and when connected to another potential to vary the speedy in the opposite sense, a generator of alternating current at the receiver having a frequency proportional to said channel keyingfrequency, a second generator of alternating current at the receiver having a frequency proportional to the speed of said distributor and a relay for connecting said control means to one ptential when the frequency of the second alternating generator is below that of the first generator and to the other potential when it is thereabove. y

3. In a telegraph system for receiving multiplex signals having a predetermined channel keying frequency, a receiving line, a distributor connected to said 1ine,'means for operating said distributor substantially at a yspeed of rotation proportionaly to said channel keying frequency, control means adapted, when connected to one potential to vary the operating rate of said distributor in one sense and when connected to another potential to vary the speed in the ,opposite sense, a generator of alternating curr'entat the receiver having a frequency proportional to said channel keying frequency, a generator of alternating current operated with said 'distributor having a frequency proportional to the speed of said distributor and a relay-for connecting the control means to one potential when the frequenc'y of the second generator is below that of the rst generator and to the other potential when it is thereabove.

4. In a telegraph system for receiving multiplex signals of a predetermined channel keying frequency, a receiving line, a distributor connected to said line, an electric motor operating said distributor substantially at a speed of rotation proportional to said channel keying frequency,

- an oscillator connected to the said line having a frequency proportional to said channel keying frequency, an alternating current generator operated with said( distributor having a frequency proportional to said speedand means for rotating the stator of said motor in one direction when the generator frequency is below that of the oscillator and for rotating it in the opposite direction when it is thereabove.

5. In a telegraph system for receiving multiplex signals having a predetermined channel keying frequency. a receiving line, a distributor connected to saidline, an electric motor operating said distributor substantially at a speed of rotation proportional to said channel keying frequency, an electric motor adapted to rotate the stator of the first mentioned motor both with and against the direction of the rotor rotation, an oscillator connected to said line having a frequency proportional to said channel keying frequency, an alternating current generator operated with said distributorhavingafrequency proportional to said speed and means for causing the second mentioned motor to rotate said stator in the direction of said rotor when the generator frequency is below that of the oscillator and against it when it is thereabove. f

6. In a telegraph system for receiving multiplex signals of a predetermined channel keying frequency, a receiving line, a distributor connected y to said line, an electricmotor operating said distributor substantially at a speed of rotation proportional to said channel keying frequency, an electric motor adapted to rotate the stator of the first mentioned motor in one direction when connected to one potential and in the opposite direction whenconnected to another potential, an oscillator connected to'said line, means for causing the oscillator to operate at a frequency proportional to said channel keying frequency, an alternating'current generator connected to said distributor to operate-at a frequency proportional tosaidspeed,a relay switch having a coil energized by said generator and another coil energized by said oscillatorY for connecting the second mentioned motor to one potential when the generator frequency is below that of the oscillator and to connect it to another potential when it is thereabove. s

7. In a telegraph system forreceiving multiplex signals of a predetermined channel keying frequency, a receivingline, a distributor connected to said line, an electric motor operating said distributor substantially at a speed of rotation prokportional to said channel keying frequency, an

electric motor rotating `the stator of` the first mentioned-motor in one direction when connected to positive potential and in the opposite direction whenconnected to negative potential, an oscillator connected to said line, means for causing the oscillator to operate at a frequency proportional to said channel keying frequency, an alternating current generator connected to said distributor to operate at a frequency proportional to the speed of said distributor, a relay switch having a coil energized by said generator and another coil energized by said oscillator for connecting the second mentioned motor to positive potential when the second generator departs in one sense from the frequency of the oscillator and to `connect it to negative current when it departs in the opposite sense.

8. In a synchronizing device, a generator of a1- ternating electroinotive force, a commutating device having a contact arm and a series of contacts,`means to rotate said arm into successive engagement with said contacts substantially at a speed of rotation proportional to the frequency of said generator, a second generator of alternating `electromotive force operated by said means at a frequency proportional to the speed of rotation of said arm, the second electromotive force being out of phase with the first electromotive force when the two frequencies are identical, and means energized by both of said generators for causing the first mentioned means to increase and decrease the speed of rotation of said arm when the frequency of the second electromotive force respectively drops below and rises above that of the other electromotive force.

9. In a synchronizing device, a generator of alternating electromotive force, a commutating device having a contact arm and a series of contacts, means to rotate said arm into successive engagement with said contacts substantially at a speed of rotation proportional to the frequency of said generator, a second generator of alternating electromotive force operated by said means at a frequency proportional to the speed of rotation of said arm, the second electromotive force being 90 out of phase with the first electromotive force when the two frequencies are identical, and electromagnetic means energized by both of said generators for producing a steady torque in one sense when the frequency of the second electromotive force'drops below that of the other and a steady torque in the other sense when it rises thereabove, and means controlled by said torque for causing the first mentioned means to vary the speed of rotation of said arm. l

10. In a synchronizing device,a generator of alternating electromotive force, a commutating device having a contact arm and a series of contacts, means to rotate said arm into successive engagement with said contacts substantially at a speed of rotation proportional to the frequency of said generator, a second generator of alternating electromotive force operated'by said means at a frequency proportionalto the speed of rotation of said arm, the second electromotive force being 90 outof phase with the first e1ectromotive force when the two frequencies are identical, a relay having a field coil energized by one generator and an armature having a coil energized by the other generator, said armature being damped to prevent its moving at the standard frequency, and means controlled by said armature for causing the first mentioned means to increase and decrease the speed of rotation of said arm.

11. In a telegraph system for receiving multiplex signals, having a predetermined channel keying frequency, a distributor for'receiving said signals, means for operating the distributor substantially at a speed of rotation proportional to said channel keying frequency, a generator of alternating electromotive force, means "operated in response to change of sense in the signal characters for keeping the frequency of said generator proportional to said channel keying frequency, a second generator of alternating elec- `tromotive force operated with the distributor at a frequency proportional to the speed of rotation of said distributor, the second electromotive force being 90 out of phase with the rst electromotive force when the speed ofthe distributor is proportional to said channel keying frequency and means energized by both of said generators for causing the first mentioned means to increase and decrease the said speed when the ratio of the frequency of the second electromotive force to that of the other electromotive force respectively decreases and increases.

12. In a. telegraph system for receiving multiplex signals of a predetermined channel keying frequency, a. receiving line, a distributor conu nected to said line, means for producing unidirectional pulses when a signal character changes in one sense, means for operating the distributor substantially at a speed of rotation proportional to said channel keying frequency, a generator of alternating electromotive force having a frequency proportional to the speed of said distributor, a second generator of alternating electromotive force having a frequency harmonic to that of the rst generator, means energized by the combination of said pulses, and said electromotive forces4 for causing the second mentioned means to increase said' speed when its ratio to said channel keying frequency and to decrease the speed when said ratio increases.

13. In a telegraph system yfor receiving multiplex signals of a predetermined channel keying frequency, a receiving line, a distributor connected to said line, means for producing unidirectional pulses when a signal character changes in one sense, an electric motor operating the distributor substantially at a speed of rotation proportional to said channel keying frequency, a generator of alternating electromotive force having a frequency proportional to the speed of said distributor, a second generator of alternating electromotive force harmonic to the first electromotive force, y.means energized by the combination of said pulses, and said electromotive forces for causing said motor to increase the speed of the distributor when its lratioto the channel keying frequency decreases and to decrease the speed when said vratio increases.

14. In a telegraph system for receiving multiplex signals of a predetermined channel keying frequency, a receiving line, a distributor connected to said line, means for producing unidirectional pulses when a signal character changes in sense, an electric motor operating the distributor substantially at a speed of rotation proportional to said channel keying frequency, a relay having a switch tongue and two contacts of different potentials, means to cause said motor to increase its 4speed when the switch tongue engages one contact and to decrease its speed when it engages the other contact, a generator of alternating electromotive force having a frequency proportional to the speed of said distributor, a second generator of electromotive force having a frequency harmonic to that of the first electromotive force, means energized by the combination of said pulses, and said electromotive forces for connecting said switch tongue to one of said contacts when the ratio of the speed of the distributor to the channel keying frequency decreases and to the other contact when said ratio increases.

15. In a telegraph system for receiving multiplex signals of a predetermined channel keying frequency, a receiving line, a distributor connected to said line, means for producing unidirectional pulses when a signal character changes in sense, an electric motor operating the distributor substantially at a speed of rotation proportional to said channel keying frequency, a switch, a positive and negative voltage source, means to cause said motor to increase its speed when the switch connects it to voltage of one polarity and to decrease its speed when it connects it to voltage of opposite polarity, a generator of alternating electromotive force having a frequency proportional to the speed of the distributor, a second generator of electromotive force having a frequency harmonic to that of the first electromotive force, means energized by the combination of said pulses, and said electromotive forces for connecting said switch tongue of one of said contacts when the ratio of the speed of th distributor to the channel keying frequency deitive and negative voltage source, means to cause said motor to increase its speed when the switch connects it to voltage of one polarity and to decrease its speed when it connects it to voltage of opposite polarity, a generator of alternating electromotive force having a frequency proportional to the operating rate of said distributor, a second generator of alternating electromotive force having a frequency that is a sixth harmonic of the first electromotive force and means energized by the combination of said pulses, and said electromotive forces for connecting said switch tongue to one of said contacts when the ratio of the speed of the distributor to said channel keying frequency and to the other contact when said ratio increases.-

17. In a telegraph system for receiving multiplex signals of a predetermined channel keying frequency, a receiving line, a distributor connected to said line, means for producing unidirectional pulses when a signal character changes in sense, an electric motor operating said distributor substantially at a speed of rotation proportional to said channel keying frequency, a generator of alternating electromotive forcehaving a frequency proportional to the speed of said distributor, a second generator of alternating electromotive force having a frequency that is a sixth harmonic of that of the first electromotive force, two triodes having their input electrodes connected in parallel to receive said unidirectional pulses and the first electromotive force. and in opposition to receive the second mentioned electromotive force, a relay having one coil in the output circuit o f one triode and another coil in the output of the other triade and 18. In a signal system, transmitting a predetermined frequency, a receiving device, means for operating said device substantially at a speed proportional to said frequency, control means for varying said speed, a generator of alternating electromotive force having a frequency propor tional to the first-mentioned frequency, a second generator of electromotive force having a frequency proportional to said speed and 90 out of phase from the electromotive force of the first generator when the two generators have the .same frequency, and means for causing said control means to vary saidrspeed in one direction when y said phase displacement increases and in another direction when the phase displacement decreases.

19. In a signal system, transmitting a predetermined frequency, a receiving device, means `for operating said device substantially at a constant speed proportional to said frequency, control means for varying said speed, a generator of alternating electromotive force having a frequency proportional to the'first-mentioned frequency, a

second generator of electromotive force having speed of said motor.

a. frequency propotrional to said speed and ,out of phase from the electromotive force of the Aa frequency proportional to the first-mentioned frequency, a second generator of electromotive force maintained by said motor at a frequency y RICHARD E. MATHES.

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