US2457790A

US2457790A - Apparatus for sequentially keying and connecting a plurality of oscillators to a common output circuit

Info

Publication number: US2457790A
Application number: US620829A
Authority: US
Inventors: Rudof F Wild; Fred J Curran
Original assignee: Brown Instr Co
Current assignee: Brown Instruments Co
Priority date: 1945-10-06
Filing date: 1945-10-06
Publication date: 1948-12-28
Anticipated expiration: 1965-12-28

Description

19484 R. F. WILD ETAL I 2,457,790

APPARATUS FOR SEQUENTIALLY. KEYING AND CONNECTING A PLURALITY OF OSCILLATORS TO A COMMON OUTPUT CIRCUIT Filed 001: 6, 1945 4 Sheets-Sheet l AAAAAAAA vvv vvvv In I INVENTOR. RUDOLF F. wu 0 FRED J. CURRAN ATTORNEY.

R. F. WILD ET AL v APPARATUS FOR SEQUENTIALLY KEYING AND CONNECTING A PLURALITY OF OSCILLATORS TO A COMMON OUTPUT CIRCUIT Dec. 28, 1948.

4 Sheets-Sheet 2 Filed Oct 6 1945 AT TOR N EY.

R. F. WILD ET AL APPARATUS FOR SEQUENTIALLY KEYING AND Dec. 28, 1948.

' CONNECTING A PLURALITY 0F OSCILLATORS TO A COMMON OUTPUT CIRCUIT 4 She ets-Sheet 3 Filed Oct. 6, 1945 INVENTOR. RUDOLF F. WILD BY FRED J. CURRAN ATTORNEY.

Dec. 28, 1948.

R. F. WILD EFAL APPARATUS FOR SEQUENTIALLY KEYING AND CONNECTING A PLURALITY -OF OSCILLATORS I TO A COMMON OUTPUT CIRCUIT Fild Oct. 6, 1945 FIG. 4

4 Sheets-Sheet 4 FREQUENCY HIGH FREQUENCY LOW V0 LTA 6 E TIME OSCILLATOR n SIGNAL II IIIIIIIIIIIIIIIIIIIIIIIIIII III I IIIII IIIII III II IIII OSCILLATOR I2 SIGNAL (a) INPUT TO RECEIVER (0m) INPUT TO RECEIVER (dJA- COMPONENT OF DISCRIMINATOR OUTPUT u U .3 g A A A V V V V V V I (b) INPUT To DISCRIMINATOR (BU INPUT T0 DISCRIMINATOR 5 5 5 9 I I I I I 9 I TIME I L I I I DISCRIMINATOR OUTPUT DISCRIHINATOR OUTPUT U1 DJ (9 (D E E 9 2 TIME TIME (debA- COMPONENT OF DISCRIMINATOR OUTPUT INVENTOR. RUDOLF F. WILD FRED J.CURR'AN ATTORNEY.

Patented Dec. 28, 1948 AND (IQNNBGWL A) E QS:- GILLABQRS m. At COMMONv QU R 'D' CIR:-

CUIT

Rudolf F; wilfl 'andiFl-ed J. Gurmn, Philadelphia, Pa., assignors v to The Brown; lnstnumentiGom-r pa v; P i adelphia m om mtinnzof P nn.-

sylvania Anolicationociobex 6, Se ialiNo. 620,82

The present invention relates to improvements:

inelectrioal' systems; and more especially; to electrical systemsfor transi'nitting. intelligence from a transmitting station to one or more separate.

and" remotely located receiving stations.

An object of the invention. is to provide im; movements in electrical systems whereby an elec tron discharge device may simultaneously, serve the dual function of keying or intermittently blocking one oscillation enerator while, amplifying the oscillating output signalof. a secondoscil: lation generator.

Another object. of. the invention. is. toIJlKQJ/ide. improvements, in electrical telautograph, systems, to the. end. that a combination of frequencifisbi two. electrical. signals. representative, of the, ins telligenceto be transmitted, may be amplified by the same amplifier. and. transmitted. to. the remote receiving station. or. stations over thelsame transmission circuit. To, this end;. means. are provided at the receiving station or stations as. Well as at thetransniittingstation for separating; the electrical signals received. and; forutilizing. thorn automatically to adjust. areceiver. exhibit;

ing element in accordance with the intelligenceunoler transmission.

Considered. in its more: specific. aspects. the 111+ vention relates to transmission systems; of the.

type in which 'the-pGSlI/mn,Of'wpOintl/QM53215 mitted is cone rectangular or polar coordinates, des lifim. When rectangular coordinates. are employed. the position of the point to be transmitted; i013 83w ample is considered in; terms of. distance between the point and: eachot two mutually penpendicue lar lines comprising the coordinate axes, If the magnitude of the deviation in. position of; the

point from each of the coordinate axes is-transs mitted to. a remotely located receiving station, the

two deviations can be combined at the remotecillating electrical currents each corresponding in frequency to one coordinate of a inarkijngelee ment at the transmitter. Both high, frequencx signals. are amplified, by the same, amplifien and are transmitted by. the same transmission cit. wit to. the remotely located receiving: station ered; in. terms; of the position: of; that point with. respect to; a pairot coordinate; axes. The coordinates employed may be; either- 2. whereav mas-king.- ele ment; isv positioned; in; each coordinate according tothe frequency of: thecoij responding received signals; thereby; reproducing thechanges 01? position. of theimarl zing; element. at thetransmitter;

It is; a specific object of; theinvention, there: fore, to. provide. improvements in. electrical; tel.- autograph system to the end that the high fre.. quency signals. representative of? the position. of. the: marking element at; theitransmitten may. be amplified by a common amplifier and; transmitted over 31.00MB transmission. cincuit. tothe remote reoeivings-tation on stations. It isaspeoifioobv. i801 also; to. providein. conjunction with. such. transmission apparatus; means at: the remotely. located receiving stations or. stations. for separat-.. ingthehigh frequency signals received: and. for utilizing: them totadjostautomatioallyl a receiver marking element to aposition corresponding to. theposition of? the transmitter' marking element;

The various. features of novelty. which charam. terioeour-inventiontare pointed outwith particmlarity in the claims annexed to and forming a H part of this specification. abetter under-.

standingoi the invention, however, itsadvantages, ancl specific obg'ectsattained by its use,- retjeltence shouldbe haci to the accompanying; drawings and descriptive matterin which we have illustrated and described preferred embodi' merits of the invention.

0i thedrawi-ngs:

Fig l illustratesawiring-diagramofthe-transmittee mechanism of apre-ferred embodiment of our invention 2 illustrates a wiring diagram of a preferred form oi receiver mechanism which, may be employedin connection with the transmission mechanism ot'Fig. 1;

Fig. 3* illustrates a modification of" the trans mittermechanism,of'liig, 1'; and;

Fig. 4 shows voltagediagrains illustrating the operation of' the apparatus of Figs. 1;. and

In Fig; 1 there is illustrated a transmitter en bodying the principles of our invention for producing two separate variable frequency high frequency oscillating currents, each corresponding i fr quency t he ev ati n. of a. m rk ng. element from momutuallv p rp ndicu ar. i es 0.1; oordinate. a s whi h hav een esigna ed. b thererf rence cha a ers 2. and 3.. resnee ive a. nd ar drawn a p otting boa or: tab e? The, markin e ement i. may minim se. ther a.

o a emai and: for; succes of lust ation. willb ons dered to e.- a. pencil...

Data is plotted on the plotting board 4 with the pencil I, the latter being suspended by a holder 6 from a so-called transmitting head indicated generally by the reference character 5. The transmitting head 5 has been shown in very diagrammatic manner in Fig. 1 inasmuch as the details of that device comprise no part of the present invention, since that device is the invention of George W. Barnes, Jr., John F. Goetz, and Walter P. Wills and is disclosed in an application, Ser. No. 620,827 filed concurrently herewith. A writing handle is preferably attached to the holdor 6 for the pencil to facilitate the plotting of information to be transmitted on the plotting board 4. The pencil, when not in use, is automatically lifted from the plotting board 4 by spring means located within the holder 6 and disclosed in detail in the Barnes, G-cctz, and Wills application. A switch 'I is provided in the pencil holder 5 for actuation by writing pressure of the pencil on the plotting board for the purpose of actuating a solenoid at the remotely located receiver shown in Fig. 2 so that the marking element at the receiver is adapted to engage the recording chart only when the transmitter pencil is in contact with the plotting board. A knurled nut 8 at the top of the pencil holder is provided to permit the latter to be turned, whereby plotting can be done from any side of the plotting board. After the pencil holder has been adjusted to a desired posi tion, the knurled nut is tightened.

The transmitting head includes certain of the electrical components of the transmitting mechanism and in particular houses variable electrical condensers 9 and I0, and also includes suitable cams and gimbal joints so that the condenser 9 is arranged to be varied in capacity in accordance with the movements of the pencil I along one coordinate, for example, along the coordinate 2,

while the condenser II] is arranged to be varied in capacity in accordance with the movements of pencil I in the other coordinate. The cams referred to serve a compensating purpose required because the angle of the deflection of the pencil holder 6 is not directly proportional to the 7 linear movement of the pencil I along the plotting board. The transmitter head also includes twoelectrical oscillation circuits II and I2, respectively associated with condensers 9 and I0.

Oscillation circuits I I and I2 may be and are shown as being identical to each other, and therefore, only oscillation circuit II will be described. Components of the oscillation circuit I2 corresponding to those of the oscillation circuit II have been indicated by the same reference numeral with a prime figure added.

Oscillation circuit II comprises an electron coupled oscillator and includes a pentode tube I3 which may be of the commercially available type 6SJ7. Tube I3 includes an anode, a suppressor grid, 2. screen grid, 2. control grid, a cathode and a heater filament. The heater filament is connected to and receives energy from the secondary winding I4 of a combination stepup-stepdown transformer I5 having a line voltage primary winding I6 and high voltage secondary windings Il, I8, I9, and 20 in addition to the secondary winding I4. The terminals of the primary winding I6 are connected by conductors 2| and 22 to a commercial source of alternating current 23, through a double pole-single throw switch 24 and a fuse provided to protect the apparatus from damage due to excessive currents resulting from failure of a component of the apparatus. A lamp 24 connected across the terminals of transformer secondary winding I4 is employed to pro vide a visual indication that the switch 24 is closed and the apparatus is powered for operation.

The control grid of tube I3 is connected through a. parallel connected resistance 25 and condenser 25 to one terminal of a parallel circuit 2?, the other terminal of which is connected to ground G. The parallel circuit 21 includes in one branch an inductance coil 28 and includes condenser 9 in another branch. The other branches of the parallel circuit respectively include condensers 29, 30, and 3|. Condenser 3I is shown as adjustable in capacity and is provided for the purpose of providing a fine adjustment for the zero setting of the pencil I along the coordinate 2. Preferably the condenser 3I is provided with a suitable knob or kerf to facilitate its adjustment. Condenser 29 preferably is of the type having a negative temperature coeificient of capacitance and is provided to compensate for the effect of ambient temperature variations upon the frequency of the oscillating current generated by oscillator II.

'The cathode of tube I3 is connected to ground G through an inductance coil 32 which is disposed in inductive relation to the coil 28 and serves the purpose of feeding back energy from the output circuit of the tube l3 to the circuit of the control grid for maintaining the circuit Ii in an oscillat ing state.

As shown, the screen grids of tubes I3 and I3 are connected through respective resistors 33 and 31 to the positive terminal 34 of a filter indicated generally by the reference character 35 and having its input terminals connected to the output terminals of a full wave rectifier designated by the character 36. The suppressor grids of tubes I3 and I3 are connected directly to ground G.

The oscillating circuit of oscillator II includes 7 the control grid circuit of which the parallel circuit 21, including the variable condenser 9, forms a part and also includes a screen grid circuit, which may be traced from the positive terminal 34 through resistance 33, the screen grid of tube I3, the cathode thereof, and inductance coil 32 to ground G, which, as shown, constitutes the negative output terminal of the filter 35. The screen grid and control grid circuits are inductively coupled by the inductance coils 28 and 32 and provide for high frequency operation through a range varying from approximately 390 to 470 kilocycles, depending upon the position along the coordinate 2 of the pencil I. Similarly, the inductance coils 28 and 32' of oscillation circuit I2 provide for high frequency operation through a frequency range varying from approximately 390 to 470 kilocycles, depending upon the position of the transmitter pencil I along the coordinate 3. Accordingly, the oscillation circuits II and I2 each produce a high frequency oscillating current having a frequency Within the range of 390 to 470 kilocycles, depending upon the position to which the pencil I of the transmitter is moved relatively to the coordinates 2 and 3.

Energizing current is supplied the anode circuits of the oscillation circuits I I and I2 from the rectifier 36 and filter 35 through a circuit which may be traced from the output terminal 34 of filter 35 through a conductor 42 to the junction of a pair of

resistors

43 and 44. The other terminal of resistor 43 is connected to the anode of tube I3 of oscillation circuit II, while the other terminal of resistor 44 is connected to the anode of tube I3 of oscillation circuit I2. The cathodes of tubes I3 and I3 are connected through their respectively associated feedback coils 32 and 32 to ground G and-thereby to the negative output of fllter- 38. It is noted that ground G is connected by a resistor 45 to the junction of the transformer secondary windings I8 and I9 whereby the potential of the junction point of windings l8 and I9 is maintained a suitably negative with respect to ground potential.

In order that both of the high frequency oscillating signals generated by the oscillation circuits II and I2 may be amplified by a common amplifier and both amplified quantities may be conducted over the same transmission lines to the remotely located receiving station, the oscillating currents produced by the oscillation circuits II and I2 are alternately interrupted at suitable frequency, and in particular, at the frequency of the voltage supplied by source 23. To this end there are provided keying and amplifying

tubes

38 and 39.

Tubes

38 and 39 also serve as bufl'er tubes to increase the stability of the respectively .assoscreen grid of tube 38 for amplifying and transmission purposes, while the output circuit of oscillation circuit I2 is coupled by means of a condenser 4I to the screen grid of tube 39 for the same purposes.

Energizing current is supplied the anode circuits of the

tubes

38 and 39 from the rectifier 36 and filter 35 through a circuit which may be traced from the positive output terminal 34 of the filter to the junction of resistors 33 and 31. The other terminal of resistor 31 is connected to the anode of tube 38,v while the other terminal of resistor 33 is connected to the anode of tube 39. The cathodes of

tubes

38 and 39. are connected together and to the junction of transformer secondary windings I8 and I9. Since the potential of the last mentioned junction point is negative with respect to ground by an amount determined by the magnitude of resistor 45 and the magnitude of current flowing through it, the anode voltage impressed on the

tubes

38 and 39 is of correspondingly greater magnitude than that impressed on the anode circuits of tubes I3 and I3. Resistor 45, accordingly, is so chosen as to provide the proper operating anode voltages for

tubes

38 and 39.

The suppressor grids of

tubes

38 and 39, as shown. are directly connected to the cathodes of said. tubes. 1

Energizing voltage is supplied the screen grids of

tubes

33 and 39 from the rectifier 36 and filter 3.5 through a circuit which may be traced from the filter output terminal 34' to the junction point of resistors 45' and 46. The other terminals of resistors 45' and 46 are connected to respective screen grids of

tubes

38 and 39.

Separate alternating voltages 180" out of phase with each other are impressed on the control grids of

tubes

38 and 39 from the transformer secondary windings I9 and I8, respectively. Specifically, the cathodes of

tubes

38 and 39, as previously noted, are connected together and to the junction point. of windings. I8 and I9. The other terminal of winding I9 is connected through a resistor 41 to the control grid of tube 38, while. the other terminal of winding 18 isconnected througlra resistor19to the control grid of tube 39. The alternating voltages thus impressed on the control grids of

tubes

38 and 39 are of the proper magnitude to render the

tubes

38 and 39 non-conductive during alternate half cycles of the alternating voltage supplied from the alternating current source 23.

In order to periodically interrupt the oscillating signals generated by the oscillation circuits II and I2. at the frequency of the alternating voltage supplied from source 23, the screen grid of tube I3 is connected to the junction of resistor 33 and the anode of tube 39 and the screen grid of tube [2 is connected to the junction of resistor 31 and the anode of tube 38. When

tubes

38 and 39 are rendered conductive, the potential of their respectively associated anodes decreases with respect to ground potential. The reduced anode voltages are sufficiently low when applied to the screen grids of tubes I3 and I3 to cause the latter tubes to be rendered non-conductive. Hence, tube I3 is arranged to be rendered nonconductive during the half cycle that tube 39 is conductive. During that half cycle tube 38 is non-conductive, and in consequence, tube I3 will be conductive and an oscillating signal will be produced by oscillation circuit I2. In the next half cycle tube 38 will be conductive and the oscillating signal produced by the oscillation circuit I2 will be interrupted. During this latter half cycle the tube 39 will be non-conductive, and as a result the oscillation circuit l I will be operative to produce an oscillating signal. The fluctuating voltages so created and impressed on the screen grids of oscillator tubes I3 and I3 change rapidly from a value at which the oscillators are permitted to oscillate to a value at which oscillation is interrupted, and consequently, the interruption and initiation of the state of oscillation of tubes ['3 and I3 is clean and sharp.

Specifically, assume that the voltage applied to the control grid of tube 38 is traversing its positive half cycle while the voltage applied to the control grid of tube 39 is traversing its negative half. cycle. The amplitude of the voltage applied to the control grid of tube 39 is sufficient to quickly block or cut ofi conduction through tube 39. Therefore, this tube is efiectively eliminated from the circuit and the screen grid of oscillator tube I3 receives its full operating voltage from the output terminal 34 of the filter 35. It. is important to note that during operation of the oscillation circuit II the operating voltages applied to the electrodes of tube I3 are constant for all practical purposes and consequently no frequency modulations occur due to periodically varying values of operating voltages.

During the half cycle under consideration tube 3.8 is conducting and the steady D. 0. component of its anode current effects a sharp decrease in the voltage of its anode, which voltage is also the voltage applied to the screen grid of oscillator tube I3, to such a value that conduction through the oscillator tube I3 is suddenly cut off. It is noted that cut ofi of tube I3 is readily accomplished because the. anode voltage of tube 38 may become zero or even go slightly negative. with respect to the potential of the cathode of tube I3 and still provide an operating voltage for the anode of tube 38 of amount sui'ficient to maintain conduction through tube 38. This operation is made possible because of the negative voltage applied to the tube 38 cathode by virtue of the latters connection to the junction of transformer secondary windings I8 and I9,

which, as previously indicated, is negative with respect to ground potential.

In the half cycle under consideration the tube 38 is utilized as a buffer for the oscillation circuit l2 and also serves to amplify the oscillations produced by that oscillation circuit. To this end, the anode of tube I3 is connected by condenser 49 to the screen grid of tube 38. It is noted that the circuit constants are not critical as long as the most positive voltage which the anode of tube 38 may assume during this interval determined by the direct current and radio frequency voltage drop across the anode resistor 31 is sufficient to prevent oscillation of the oscillation circuit l2. For the next half cycle of the voltage supplied by source 23, the reverse of the above conditions exists. That is to say, tubes 38 and I3 are cut off while tubes 39 and I3 are rendered conductive. Hence, during this half cycle the oscillation circuit [2 produces an oscillating signal and this oscillating signal is amplified by tube 39 which also serves a buffer purpose. To this end, the anode of tube I3 is connected through condenser to the screen grid of tube 39.

As those skilled in the art will recognized, it is possible to utilize in place of the

tubes

38 and 39, tubes such as the commercially available type 6L7, or any other frequency mixer or pentagrid converter tube conventionally used in heterodyne radio broadcast receivers. Such tubes are provided with two control grids, and therefore the oscillating signals from the oscillation circuits H or I2 to be amplified may be applied to one control grid while the keying voltage derived from the transformer secondary windings l8 and I9 is applied to the other control grid. The use of such tubes in place of the

tubes

38 and 39 is advantageous in that the oscillating signals to be amplified are also applied to a control grid, and therefore, will be amplified to a higher degree than they are when applied to a screen grid as shown in Fig. 1.

In Fig. 3 we have illustrated another modification of the arrangement of Fig. l for alternately interrupting the oscillating signals produced by the oscillation circuits II and I2 and for amplifying those oscillating signals. The circuit arrangement of Fig. 3 is substantially identical to that of Fig. 1 with the exception that the keying voltages from the transformer secondary windings l8 and I9 are impressed on the screen grids of

tubes

38 and 39 and the oscillating signals to be amplified are impressed on the control grids of those tubes. Specifically, the voltage of the transformer secondary winding 18 is impressed on the screen grid of tube 39 through a circuit which may be traced from the said control grid through the winding l8 and through a biasing resistor 50 to the cathode of tube 39. Similarly, the voltage of winding I9 is impressed on the screen grid of tube 38 through a circuit which may be traced from the said screen grid through winding [9 and through a biasing resistor to the cathode of tube 38.

The oscillating signals produced by oscillator II are impressed on the control grid of tube 38 through condenser 4 0, while the oscillation signals produced by oscillator l2 are impressed through condenser 4| on the control grid of tube 39. As shown, the control grids of

tubes

38 and 39 are connected by individually associated

resistors

52 and 53 to the negative terminals of biasing resistors 59 and 5|, which terminals are connected together and to the junction of transformer secondary windings l8 and I9.

The manner of operation of this modification of our invention is otherwise the same as that shown in Fig. 1, and hence, further description thereof is believed unnecessary. Here again circuit constants are not critical, as long as the most positive voltage which the anodes of

tubes

38 and 39 may assume during the alternate half cycles that they are conductive is sufficiently low to prevent operation of the respectively associated oscillation circuits 1! and II.

From the foregoing description it is evident that in each contemplated embodiment of my invention, the interruption of the oscillating signals produced by the oscillation circuits H and I2 are timed so that one oscillation circuit ll generates an oscillating signal only when the oscillation circuit I2 is cut off and vice versa. Moreover, the interruption of the oscillating signals from the oscillation circuits I l and 12 occurs at the frequency of the alternating voltage supplied from the source 23. In other words, during one half cycle of the alternating voltage supplied by source 23, the oscillation circuit II is operative to generate an oscillating signal and that oscillation signal is amplified by the tube 38. During the next alternate half cycle the oscillation circuit I2 is operative to generate an oscillating signal and that signal is amplified by the tube 39. Therefore, the

tubes

38 or 39 which generate a voltage for interrupting one of the oscillating signals are also used to amplify the output of the other oscillation circuit during the cut off period of the first oscillation circuit. The

second tube

38 or 39 which generates a voltage for interrupting the other oscillation circuit performs a similar amplifying function for the first oscillating circuit. This amplification

stage comprising tubes

38 and 39, as previously noted, also serves to increase the stability of the oscillation of oscillation circuits II and I2 by reducing fluctuations in the oscillation circuit loads.

In order to further amplify the oscillating signals generated by the oscillation circuits II and I2 sufficiently for transmission of those oscillating signals to the remotely located receiving station or stations, there is provided an additional amplifier indicated generally by the reference character 54. This amplifier 54 also performs the additional function of matching the impedance of the output circuit of the transmitter to that of the receiving circuit to obtain maximum power transference.

As shown, the transmitter amplifier 54 includes a tube 55 which may desirably be of the commercially available type 6A0? and includes anode, suppressor grid, screen grid, control grid, cathode, and heater filament elements. Anode voltage is supplied tube 55 from the rectifier 3G and filter 35 through a circuit which may be traced from the positive output terminal 34 of the filter through a resistor 56 to the anode of the tube 55, the cathode thereof, and through a biasing resistor 51, shunted by a condenser 58, to ground G and thereby to the negative output terminal of the filter.

Energizing voltage is supplied to the screen grid of tube 55 through a circuit which may be traced from the positive output terminal 34 of the filter through a resistor 59 to the screen grid. the cathode and the parallel connected resistor 51 and condenser 58 to the negative and grounded output terminal of the filter. The screen grid is also connected by a condenser 60 to ground.

respective condensers BI and 62 to the control grid of tube 55 which, as shown, is also connected by resistor 62' to ground G, and the cathodes of

tubes

38 and 39 are connected through resistor 45 to ground G and through the parallel connected resistor 51 and condenser 58 to the cathode of tube 55. Tube 55, therefore, operates to amplify the oscillating signals in the output circuits of both

tubes

38 and 39. The amplified quantity derived from tube 55 is resistance coupled by means of a condenser 63 and a resistor 64 to the input circuit of a tube 65 which is provided for the purpose of matching the impedance of the output circuit of transmitter amplifier 54 to the characteristic impedance of a transmission line connecting the transmitter to the remotely located receiver.

Tube 65 may be of the commercially available type 6V6 and includes an anode, a screen grid, a control grid, a cathode, a heater filament, and also a pair of beam forming plates. Energizing voltage is supplied to the anode circuit from the rectifier 36 and filter 35 through a circuit which may be traced from the positive output terminal 34 to the anode of tube 65, the cathode thereof, and through an output resistor 66 to the negative and grounded terminal of the filter. Energizing voltage is supplied the screen grid of tube 65 through the same circuit. The beam forming plates, as shown, are directly connected to the cathode. The control grid of tube 65, as shown, is directly connected to the junction of condenser 63 and resistor 64 and thereby is coupled to the output circuit of tube 55.

While the rectifier 35, filter 35, and transmitter amplifier 54 have been shown in Fig. 1 as being located closely adjacent the plotting board 4, it will be understood that, if desired, these components may be located at a distance with respect to the plotting board and also with respect to the oscillation circuits II and I2. For example, in some applications it may be desired to locate the plotting board 4 and the oscillation circuits II and I2 in one room and to have the rectifier 36, filter 35, and the transmitter amplifier 54 in another room to the end that the transmitting mechanism visible for manipulation by an opera-- tor may be made less cumbersome and bulky.

This feature is also advantageous when the transmission system of the present invention is utilized on shipboard in which the space available is at a premium and would preclude the cation of all of the transmitting equipment closely adjacent the plotting board 4 and overhead transmitter unit 5. In a practical operating embodiment of the present invention, a shielded cable 25 feet long is provided between the plotting board and the circuit components including the rectifier 36, filter 35, and amplifier 54.

Tube 65 is connected to operate as a cathode follower, that is to say, the output signal which is transmitted to the receiver is derived from the resistor 65 connected in the cathode circuit of the tube. Resistor 66 is so chosen as to have characteristic impedance approximating that of the transmission line L connecting the transmitter to the receiver. As shown, the terminal of resistor 66, which is connected to thecathode' 10 of tube 65, is coupled by a condenser 61 to one terminal of the transmission line L, while the other and grounded terminal of the resistor 66 is connected directly to another terminal of the transmission line.

At the transmitter amplifier 54 there is also provided a relay 68, one terminal of the operating coil of which is connected to the ungrounded side of transformer secondary winding I4 and the other terminal of which is arranged to be connected to the grounded side of winding I4 upon closure of the switch I attached to the writing pencil or stylus I. To this end, one terminal of the switch I, as shown, is connected directly to ground G. When the switch 1 is closed, as upon movement of the pencil I into engagement with the plotting board 4, the relay 68 is energized and closes an associated switch 69 to energize a solenoid 10 attached to the recording pen mechanism in the receiving unit to move the pen into engagement with the recording chart. When the switch 1 is open and the relay 68 is deenergized, the switch 69 is also open, and the pen at the receiving unitis moved out of engagement with the recording chart by the action of gravity, the solenoid 10 then being deenergized.

As has been previously mentioned, the apparatus located at the remote station, where the transmitted writing or other data is to be reproduced, is arranged to translate the adjustable frequencies of the oscillating signals generated by the oscillation circuits II and I2 into two coordinates of pen position. More specifically, the receiving apparatus operates to move the recording pen in a vertical direction in accord ance with the variations in frequency of the oscillation signal generated by the oscillation circuit II, and operates to move the recording pen in a horizontal direction in accordance with the frequency variations of the oscillation signal generated by the oscillation circuit I 2. In this manner the changes in position of the pencil or stylus along the plotting board 4 at the transmitter may be exactlyreproduced at the receiving apparatus.

By reference to Fig. 2, it will be noted that two independent receiving circuits are provided. One of the receiving circuits controls the movement of the recording pen in one coordinate, for example, the horizontal coordinate, and the other receiving circuit controls the recording pen in the vertical coordinate. The oscillating signals derived from each of the oscillation circuits I I and. I2 and transmitted to the receiver over the transmission line L are impressed on both of the input circuits of the two receiving circuits. The receiver mechanism is so arranged that one of the receiving circuits is responsive only to the oscillating signal generated by the oscillation circuit H, and the second receiving circuit is responsive only to the oscillating signal generated by the other oscillation circuit I2 to control the energization of individually associated reversible motors, which in turn are linked by suitable mechanical means to the recording pen to position the latter in the two coordinates along the recording chart. The operation of the two receiving circuits is the same, and the following explanation applies to both circuits. One of the receiving circuits has been generally indicated by the reference character II and the other by the reference character H. The elements of "the receiving circuit 1 I corresponding to those of the receiving circuit II have been indicated byv 11 the same reference numerals with a prime figure added.

The receiver ll includes two stages of amplification. the first of which utilizes an amplifying tube 12 of the commercially available type SAC? and. the second of which utilizes an amplifying tube 13 of the type 6V6. In the second stage of amplification the two oscillating signals from the transmitter are separated and one of them is rejected. In other words the second stage of amplification responds only to the oscillating signal generated by one of the oscillation circuits l I or I2 and, for purposes of illustration, will be assumed to respond only to the oscillating signal generated by the oscillation circuit l I. Rejection of the oscillating signal from the oscillation circuit I2 is accomplished in a manner described in detail hereinafter, and generally speaking, involves the application of an alternating voltage derived from source 23 to periodically interrupt the conduction of tube 13. The oscillating signal after rejection of the undesired portion consists of a radio frequency wave which is periodically interrupted at the frequency of the voltage supplied by the source 23 and has been illustrated schematically in graphs (b) and (bb) of Fig. 4 which show the oscillating signal frequency as being higher and lower, respectively, than a frequency value at which the receiving pan is held motionless along the vertical coordinate.

Tube 12, as shown, includes anode, suppressor grid, screen grid, control grid, cathode, and heater filament elements. Energizing current is supplied the heater filament from the low voltage secondary winding 14 of a transformer 15 having a line voltage primary winding 16 which is connected by conductors l8 and 19 to the alternating voltage source 23. To this end the conductors I8 and 19 are included in the shielded cable L connecting the trammitter to the receiver. The transformer 15 also includes high voltage secondary windings 80 and 8 l both of which are provided with a center tap.

Energizing voltage is supplied to the anode of tube 12 from a full wave rectifier indicated. generally by the reference numeral 82 and a filter indicated at B3. The rectifier 82. energized by the transformer secondary winding 80, provides a voltage at the output terminal 84 of the filter 83 which is suitably positive with respect to the potential of ground G to which the negative terminal of the filter is connected. As shown. the positive terminal 84 is connected through a resistor 85 to the anode of tube 12, and the cathode is connected through a parallel connected resistor 85 and condenser 81 to ground G. Energizing voltage is supplied to the screen grid of tube .12 from the positive filter output terminal 84 through a circuit, including a resistor 88, to the screen grid and from the cathode through the parallel

connected elements

86 and 81 to ground G.

As may be seen by reference to Figs. 1 and the output terminal of resistor 66 of the transmitter amplifier 54, which is connected to the cathode of tube 65, is connected by condenser 61 and the shielded transmission line L to the control grid of tube 12. The other and grounded output terminal of the transmitter amplifier 54 is connected through the transmission line L to the parallel connected resistor 86 and condenser 31 and thereby to the cathode of tube 12.

The output circuit of tube 12 is coupled by a condenser 89 and a resistor 90 to the input circuit of tube 13. Tube 13 includes an anode, a screen grid, a control grid, a cathode, a heater filament,

and beam forming plates. Energizing current is supplied to the heater filament from the low voltage transformer secondary winding '14.

Anode voltage is supplied to tube 13 through a circuit path which may be traced from the positive output terminal 84 of the filter 83 through a parallel network including in one branch the primary winding 95 of a transformer 98 to the anode of tube 73, the cathode thereof, and a parallel connected resistor 92 and condenser 93 to the grounded and negative terminal of the filter. The other branches of the parallel network respectively include a resistor 9i and a condenser 94. The transformer 98 comprises a part of a frequency discriminator indicated generally by the reference numeral 91 and includes a split secondary winding in addition to the primary winding 95.

The beam forming plates of tube 13 are directly connected to the cathode, and. the control grid is coupled to the output circuit of tube '12 by virtue of its connection to the junction of condenser 89 and resistor 90.

Alternating voltage is impressed on the screen grid of tube 13, for periodically rendering it nonconductive, from one half of the center tapped transformer secondary winding through a circuit which may be traced from lower terminal of the winding 80, seen in the drawing, through a resistor 98 to the screen grid of tube 13 and through the parallel connected elements 92 and 93 to ground and thereby to the center tap on winding 80. The screen grid of tube 13 is also connected directly to ground G by a condenser 99. The magnitude of the alternating voltage impressed on the screen grid of tube 13 is so chosen as to be sufiicient to cause the tube 13 to be rendered non-conductive or cut oil during those hall cycles of the voltage of source 23 in which the screen grid is driven in the negative direction. Furthermore, the phase of this alternating voltage is such that the tube 13 is operative to amplify the oscillating signals generated by the oscillation circuit I I and transmitted to the receiver "H only during those alternate half cycles of the supply line voltage in which the oscillation circuit II is operative to generate an oscillating signal.

It is noted that the entire transmis receives energizing current from the sin 23 of alternating current. This source. de' scribed, is located at the transmitter amplifier unit and the alternating current utilized for. energizing the receiving units is transmitted from the source 23 by way of the transmitting cable L. This is done to insure synchronism of the keying action of the transmitter and receiver units and also provides the advantage of permitting the installation and use of receivers at locations where there is not available alternating power of the same frequency and phase as that delivered by source 23.

The frequency discriminator 97, previously referred to, includes in addition to the transformer 96 pair of diode rectiflers Hi9 and Iili, which desirably may be contained within a sin le envelope. generally designated at Hi2. One half of the split secondary winding of the intermediatev frequency transformer 96 has been designated 0*! the numeral I03 and the other half by the nu- Ineral I04. The center tap of the split secondary winding comprising the junction of winding sections I03 and I04 is connected through a blocking condenser I05 to the anode circuit of tube 13, and more specifically, to the terminal of the primary winding which is connected to the anode gun-no.

13 of the tube 10.. The center tan of the split secondary winding is also connected to the point of engagement of apair'of resistors ["86 and-N1. The,

resistors I06 and I01 are shunted by a resistor I08 which is providedwith an adiustable tap I09. The usable output voltage from the frequency discriminator is obtained. across the resistor 1.08 which, as shown, is shunted by a condenser H0.

The diode rectifiers I00 and MI may be'contained within a single tube such as the commercial-ly available type. 6H6. Each diode includes anode, cathode, and heater filament elements. The heater filament elements are connected in series with each other and receive energizing current from the transformer secondary winding I4. The cathodes of the'diodes I00 and I0=I are connected through resistors I06 and Ill-I, respectively, to the junction of' the transformer secondary windings I03 and I04. The other terminal of the winding. I03 is connected to the anode of diode I 00, while the other terminal of the winding I04 is connected to the anode of the diode I'M.

For tuning the secondary winding of the transformer 96 to the frequency of the oscillating signals impressed thereon from the output circuit of tube I3, a variable condenser II I is provided. This variable condenser is arranged to be automatically adjusted in capacity as required to maintain the secondary winding of the intermediate frequency transformer 96 tuned to the frequency of the applied oscillating signals. A variable condenser I I2 and a variable inductance H3 are connected in shunt with the secondary winding of thetransformer 96 for a purpose which will be later explained.

The blocking condenser I05 and the condenser H0 are so selected as to present lowimpedance to the radio frequency oscillating currents flowing through them. The condenser 94 and the transformer primary Winding 95 connected in parallel therewith are so' selected as to provide high impedance in order to produce a large'output signal from the discriminator. Preferably the primary winding 95 is tuned to a value which is outside the range of frequency variation of the oscillating signals generated by the oscillation circuit II' at the transmitter and impressedon the receiver circuits. By way of example it is noted that satisfactory operation has been obtained' when the primary winding 95 is tuned to a frequency of'325 kilocycles. The tuning of the primary winding 95 to this value which is below the operating range of frequency variation of the oscillating signals conveyed by the transmission line L to the receiver H consti utes no part of the present invention but is the sole invention of the joint applicant Rudolf 1". Wild and is being dis closed and claimed in. application, Ser. No. 620,831, filed concurrently herewith.

The frequency discriminator 9'! together with the diodes I00 and IN is, provided for the purpose of deriving a voltage having an alternating component of one phase or of opposite phase and of the same frequency as the voltage supplied by source 23 accordingly as thefrequency of theoscillating signal impressed thereon from the output circuit of tube I3 is higher or'lower than the frequency value to which the split secondary winding of transformer 96 is tuned. The details of this frequency discriminator constitute no part of the: present invention. Its manner of operation and arrangement are disclosed in the aforementioned application of R. F; Wild and'also in the copending application, Ser. No. 537,505, filed 14 May 26,1944, of R. F. Wild, and therefore, need be only briefly described herein.

Itv is believed sufficient to note that if the fre quency of the applied oscillating signal is the 3 value towhich the secondary winding of the intermediate frequency transformer 96 tuned, the outputs of the diode rectifiers I00 and IM cancel each other and zero voltage appears across the output resistor I08 of the frequency discriminator circuit 91. If the frequency of the applied oscil-' lating signal is a value other than that to which the secondary winding of the transformer 96 is tuned, the phase relations of the voltages applied to. the diode rectifiers I00 and NH are such that their outputs do not cancel and a direct current voltage appears across the output resistor I08. The polarity of this voltage depends upon whether the frequencyof the applied oscillating signal is above or below the value to which the secondary windingof the discriminator is tuned. The magsince the applied oscillating signal is periodically interrupted at the frequency of the alternating voltage supplied by source 23, the pulsations of direct current voltage produced across resistor I08 have the same frequency as the voltage supplied by source. Graphs (c) and (cc) of Fig. 4 illustrate the voltage output produced across the resistor I08 for the respective cases of high and low frequency of the applied oscillating signal.

The pulsating voltage produced across the resistor I08 may be considered as comprising two components. (1) a steady D. C. component and (2) an A. C. component. The A. C. component obtained when the frequency of the applied 05- cillating signal is higher than the value to which the secondary winding of the frequency discriminator is tuned is shown in graph (d) of Fig. 4 while graph (dd) of Fig. 4 illustrates the A. C. component obtained when the frequency of the applied oscillating signal is lower than the value to which the secondary winding of the frequency discriminator is tuned.

The variable condenser H2 connected in parallel with the discriminator secondary winding is a trimmer condenser and serves to provide for zero adjustments of the recording pen along the vertical coordinate. To this end the condenser H2 is provided with a suitable knob or kerf for facilitating its adjustment.

In order to provide for span adjustment or,

in other words, the extent of variation of condenser Ill required to traverse the entire fre-' quency' range of operation, the variable inductance H3 is provided. Inductance H3 is preferably provided with an adjustable iron core. A suitable knob or kerf is preferably provided on the inductance H3 to facilitate its adjustment.

The zero and span adjustments described comprise no part of'the present invention, but aredisclosed and claimed in the application of R. F. Wild bearing Serial No. 620,832, filed concurrently herewith.

The alternating component of the pulsating voltage produced across resistance I08 is amplifled by a stage of voltage amplification including a tube H4, which stage of amplification incorporates a gain control for manually adjusting the sensitivity of the receiving unit. This gain control comprises the provision of slider contact I09 in association with the resistor I08 for tapping off and impressing on the input circuit of tube H4 a variable portion of the voltage produced across the resistor I08. Tube II4 may be of the commercially available type 6AC7 and includes anode, suppressor grid. screen grid, control grid, cathode, and heater filament elements. Energizing current is supplied the heater filament from the transformer secondary winding '14. Anode voltage is supplied tube H4 from the rectifier 82 and the filter 83 and to this end the positive terminal 84 of the filter 83 is connected through a resistor I I5 to the anode of tube I I4, and the cathode of the latter is connected through a resistor II6 to the grounded and negative terminal of the filter. Energizing voltage is supplied the screen grid through a circuit which may be traced from the positive terminal 84 through a, resistor H! to the screen grid, the cathode, and resistor H6 to the grounded and negative terminal of the filter. A condenser I I6 is connected between the screen grid of tube I I4 and ground, as shown.

The output circuit of tube H4 is coupled by a condenser H9 and a resistor I20 to the input circuit of a motor drive stage indicated generally by the reference character IZI. Motor drive stage I2I is shown as including triodes designated by the numerals I22 and I23, respectively, but it is preferred to utilize a number of such triodes connected in parallel with each other instead of single triodes. For example, in. a practical operating embodiment of the invention, three such triodes I22 and I23 were connected in parallel, thus insuring the derivation from the motor controlled by the tubes of suflicient torque to actuate the recording pen.

As shown, the tubes I22 and I23 each include anode, control grid, cathode, and heater filament elements. Energizing voltage is supplied the heater filament elements in series from the transformer secondary winding 14. Anode voltage is supplied tubes I22 and I23 from the transformer secondary winding BI and to this end one end terminal of winding BI is connected to the anode of tube I22 and the other end terminal of that winding is connected to the anode of tube I23. The cathodes of tubes I22 and I23 are connected together and through a biasing resistor I24 to one terminal of the control winding I25 of a reversible two-phase induction motor I26. In addition to the Winding I25, the motor I26 includes a second winding I21. A condenser I28 is connected in parallel with winding I25 and the other terminal of the latter is connected to the center tap of the transformer secondary winding 8|. Accordingly, energizing current is delivered to the motor winding I25 from the transformer secondary winding BI under control of the triodes I22 and I23. Winding I2I of the motor I26 is connected through a condenser I29 and conductors I8 and I9 to the source of alternating current 23.

Thus, the output current of the tubes I22 and I23 is utilized to deliver ener y to winding I25 of the motor I26, and the power winding I21 of that motor is connected to the alternating current power supply through condenser I29. The motor is actuated for rotation when an alternating current signal of the frequency of the volt age supplied by source 23 is impressed on the input circuits of tubes I22 and I23. For accomplishing this result the control grids of triodes I22 and I23 are conected together and to the junction of condenser H9 and resistor I20.

Referring to graphs (d) and (dd) of Fig. i, it will be seen that the A. C. component oi the dis criminator output voltage reverses in phase when the frequency of the applied oscillating signal changes from below to above that to which frequency discriminator is tuned. This chap phase when applied to the control grids of tri I22 and I23 causes a decrease in the conduc-tiv y of one triode I22 or I23 and a corresponding in crease in the conductivity of the other triode. In consequence, energizing current is delivered to the control winding I25 of the motor I26 which leads or lags by approximately the voltage of source 23 depending upon which triode I22 or I23 has had its conduction increased. Stated differently, this change in phase of the volt {e derived from the frequency discriminator cai: reversal of the direction of rotation oi" the reversible motor I26.

The details of this motor drive circuit comprise no part of the present invention, since that circuit is the invention of Walter P. Wills and is disclosed in a copending application, Ser. No. 421,173, filed December 1, 1941, now Patent No. 2,423,540 of July 8, 1947, and hence, requires no further description herein.

The shaft of motor I26 is geared in any suitable manner, not shown in order to avoid complication of the drawing, to the variable condensel III connected in the frequency discriminator. The shaft of motor I26 is also mechanically coupled to the recording pen of the receiver and adjusts both the condenser I II and the recordin pen until the secondary winding of the frequency discriminator is tuned to the frequency of the applied oscillating signal. Inasmuch as the output of the frequency discriminator is zero Wi'iG'l'l it is tuned to the frequency of the applied 05.... lating signal, the motor then stops and is main-- tained stationary until the frequency of the applied oscillating signal again changes.

In Fig. 2 a portion of the receiving instrument containing the recording chart is broken away to show a pen carriage I30 which has a pen I3I mounted thereon. The carriage I311 is actuated for movement in vertical and horizontal direc tions by bars I32 and I33, respectively. The supporting bars for the carriage have rollers I36 and I35, respectively, on their ends, which ride on individually associated tracks I36 and I3I, which are provided in the base of the receiving instrument. As the rods I32 and I33 are moved, the pen carriage I3I will be moved in any direction underneath the chart indicated generally by the reference numeral I38. If rod I32 only is moved as upon operation of motor I26, the carriage i3I will be moved in a vertical direction only. Similarly, if rod I33 only is moved, as upon operation of motor I26, the carriage I3I will be moved in a horizontal direction only. If rods I32 and I33 are simultaneously moved, the pen carriage I3I will be moved at an angle to both sides of the instrument. Movement is imparted to the rod I32, as previously stated, by the motor I25, which has a drive pulley I39 attached to it. This pulley drives a cable I40 that passes over suitable guide pulleys at opposite ends of the track I 38 and which is fastened to the roller I34. In a like manner motor I26'.is utilized to impart movement to the rod I33, and to this end motor I 26 has a drive pulley I4I fastened to its shaft. As the pulley armies I4 I rotated-it drives' a-"cable l 4-2 anew aroun'd suitabl guiddpulleys the ends smack m and wh-ili is attacnemetnemner m- Iii-consequence; as the mctors -1 2s and-I26 energized forrot'altibrid-ri one' directietr 'or -the other 11 1 responsew dihei rceptioii -of oscillatin signals fromthe trarisiiiitt the en? t3 t avili' be' adi'u's'te d' relativel-y to -the chart -438 'to produc an -exaot 'reproduc'tion crthe' i'novement iniparted to the writing stylusor"pencil at the-transmitter relatively toth' plotting boardl As -previousl I noted; u on' movemen :cr tne writingi'astyius or pencil unto eng'ag'ement with ime plotting board energization of the solenoid for littlri'g' ithe' -m recording ups into engagenie'nt vt'itl'i th re cordingfchart I 38; :In" consequence th' re'cording pen l 3 t is operativeto'ttac'e tnepatn of 'its move ment' on the chart I38 'o'ni'y' when the wr i ting' pen in oil or stylus at the transmitter is in contact with m the? plotting boards: z

This arrangement in which the 'recordingsmeoh ll anism is located entirely beneath the chart and: thereforarleaVes the can or the 'cha'rt iree for: in-

closed in this appiication'iandarelat-ingto' an elec i Serial Number 12,873, filed March 3, 1948$ Whileiin' accordanceiwith the provisions of the statutespwe 'ihaiie illustrated and described the best forms of the invention now known to us, it will be apparent 'to -those skilled in the art that changes may be madecinitheeform-of-ithe. appa-- ratus disclosed without departinglfrom the spirit in of the invention as set forth in'theappended claims, and that in-some==caseseertain' features of the inventi n may sometimes-bowsed to advan zz' tagewithout-a corresponding usewof other ifea sl turesi Having nowdescribed our invention, what wve clairn as newand desire to secure by Letters? Patent, is; a

1. In an electrical transmission' s'ystem;'i'first and second oscillation generators for producing 15 separate electrical signals to be transmitted, each oscillation generator having an output circuit and an input circuit for adjusting the oscillation generator to its oscillating and non-oscillating condition, a common transmission circuit for both 5' of said signals, first and second electron discharge devices each having an input circuit and an output circuit, means to alternately render each of said electron discharge devices inoperative, means connecting the output circuits of both of said no electron discharge devices to said transmission circuit, means connecting each of the output circuits of said first and second oscillation generators to a respectively associated input circuit of said electron discharge devices, and means connecting each of the input circuits of said first and second oscillation generators to a respectively associated output circuit of said electron discharge devices whereby said first oscillation generator is operative and the signal produced thereby is relayed by one of said electron discharge devices to said transmission circuit only when the other of said electron discharge devices is inoperative, and said second oscillation generator is operative and the signal produced 7 thereb y is relayed-by said -other-electron dis chargddev'ice to said transmission circuitonly when said one electron discharge device is inoperative.**

2. In an electrical transmission -system, first and second oscillation generators" forproducing separate electricalsignals to be t-ransmitted; each oscillation generator havingamoutputcircuit'and' an input circuit for adjus'tingthe" oscillation genorator-to its 1 oscillating and "non oscillatfing' conditi om -"a commontransmission"circuitfor both i of said signals; first "and-second electron dis charge iievices each having andnputcircuit andan output circ'uit; means to alternately *render each-of said electron discharge devicesinoperm five-means connecting the'output circuits of both of an electronfdischarge devics to -said-=transmission-circuit} means connecting eacirof the" outputcircuits of said first and second oscilla tion generators tothe input circuits of said first f and second electron discharge -device's, respec tiv'elyyandmeans connecting each of theinput circuitsof-s'aid "first andsecond o'sciilation generators to the output circuits of said "second and first electron dischargedevices; *respectively, whereby said first -oscillit't'ion'generater-is 'ope'rative and the signal produced" ther'ebyis relayed by said first electron'di'scharge"deviceto said transmission circuit-only When=saidsecond electron 1 discharge device is inoperative, and said second o'scillatioii"generatof is operative *and the signal producedthereby' is' -relayed by'said" second electron" discharge device'ftdsaid transmission circuito'nly whens'aidflrst'electrondischarge de--' lis vic'e is inoperative- 3. In an" electrical transmission-system, "first and 'second="dscillation generators "for producing 1: separate electrical signals to be transmitted; each oscillationgenerator' having'an output circuit and an input circuit "for adjusting the oscillation L 1' generator to as *oscillating""and" non-oscillating condition?" a "common" transmission 1 -circuit for both of'said signals,"first and second electrondise;

charge deviceseach-havinga screengrid cir-' cuitga controlgrid -circuit,""and ani'outputi circuity'means to "apply' alternating voltages m0? out or phase to "the control grid circuits of "said electron-- discharge devices "to alternately render both of said electron discharge devices to said transmission circuit, means connecting each of the output circuits of said first and second oscillation generators to a respectively associated one of the screen grid circuits of said first and second electron discharge devices, and means connecting each of the input circuits of said first and second oscillation generators to a respectively associated output circuit of said electron discharge devices whereby said first oscillation generator is operative and the signal produced thereby is relayed by one of said electron discharge devices to said transmission circuit only when the other of said electron discharge devices is inoperative, and said second oscillation generator is operative and the signal produced thereby is relayed by said other electron discharge device to said transmission circuit only when said one electron discharge device is inoperative.

4. In an electrical transmission system, first and second oscillation generators for producing separate electrical signals to be transmitted; each oscillation generator having an output circuit and an input circuit for adjusting the oscillation generator to its oscillating and non-oscillating condition, a common transmission circuit for both of said signals, first and second electron discharge devices each having a screen grid circuit, a control grid circuit, and an output circuit, means to apply alternating voltages 180 out of phase to the screen grid circuits of said electron discharge devices to alternately render each of the said electron devices inoperative, means connecting the output circuits of both of said electron discharge devices to said transmission circuit, means connecting each of the output circuits of said first and second oscillation generators to a respectively associated one of the control grid circuits of said first and second electron discharge devices, and means connecting each of the input circuits of said first and second oscillation generators to a respectively associated output circuit of said electron discharge devices whereby said first oscillation generator is operative and the signal produced thereby is relayed by one of said electron discharge devices to said transmission circuit only when the other of said electron discharge devices is inoperative, and said second oscillation generator is operative and the signal produced thereby is relayed by said other electron discharge device to said transmission circuit only when said one electron dis charge device is inoperative.

5. In an electrical system including two oscillation generators each having an output circuit and an input circuit for adjusting the oscillation generator to its oscillating and non-oscillating condition in response to a keying signal, an electron discharge device having an output circuit and a pair of input circuits, means to impress a keying signal on one of said input circuits of said electron discharge device to produce an amplified keying signal in the output circuit of said electron discharge device, means connecting the output circuit of said electron discharge device to the input circuit of one of said oscillation generators, and means connecting the output circuit of the other of said oscillation generators to the other input circuit of said electron discharge device for transmission of the applied oscillation signal to a utilization circuit.

6. In an electrical system including two oscillation generators each having an output circuit and an input circuit for adjusting the oscillation generator to its oscillating and non-oscillating condition in response to a keying signal, an electron discharge device having an anode circuit, a screen grid circuit and a control grid circuit, means to impress a keying signal on said control grid circuit of said electron discharge device to produce an amplified keying signal in the anode circuit of said electron discharge device, means connecting the anode circuit of said electron discharge device to the input circuit of one of said oscillation generators, and means connecting the output circuit of the other of said oscillation generators to the screen grid circuit of said electron discharge device for transmission of the applied oscillation signal to a utilization circu'it.

7. In an electrical system including two oscillation generators each having an output circuit and an input circuit for adjusting the oscillation generator to its oscillating and non-oscillating condition in response to a keying signal, an electron discharge device having an anode circuit, a screen grid circuit and a control grid circuit, means to impress a keying signal on said screen grid circuit of said electron discharge device to produce an amplified keying signal in the anode circuit of said electron discharge device, means connecting the anode circuit of said electron discharge device to the input circuit of one of said oscillation generators, and means connecting the output circuit of the other of said oscillation generators to the control grid circuit of said electron discharge device for transmission of the applied oscillation signal to a utilization circuit.

RUDOLF F. WILD. FRED J. CURRAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS