US2044519A

US2044519A - Automatic idle time keying unit

Info

Publication number: US2044519A
Application number: US711764A
Authority: US
Inventors: Usselman George Lindley
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1934-02-17
Filing date: 1934-02-17
Publication date: 1936-06-16
Anticipated expiration: 1953-06-16

Description

fume E6, i936. G, USSELMAN AUTOMATIC IDLE TIME KEYING UNIT Filed Feb. 17, 1934` 5 Sheets-Sheet 1 INVENTOR G. L. USSLMAN ATTORNEY G. 1 UssELMAN 2,044,539

AUTOMATIC IDLE TIME KEYING UNIT Filed Feb. 17, 1954 5 sheets-sheet 2 J l e i6, 3936.

june 3.5, 1936. G.- L USSELMAN 2,044,539

AUTOMATIC IDLE TIME KEYING UNIT Filed Feb. 17, 1954 5 Sheets-Sheet 5 ATTORN EY G L USSELMAN AUTOMATIC IDLE TIME KEYING UNIT ATTORNEY Patented June 16, 1936 PATET AUTOMATIC' EDLE TME KEYING UNIT Application February .17, 1934, .Serial No. 711,764

'15 Claims.

This invention relates to .telegraphy signalling means and in particular to keying control switching for radio transmitters, said keying control switching means being automatic in operation.

Transmitters of this type in general comprise a line for incoming control or keying impulses or source of keying impulses, and a transmitter adapted to signal at different frequencies, including an oscillation generator, the necessary amplifiers and radiating means coupled therewith, and keying means interposed between the signal line or source and one or more stages `in the transmitter. The signals from the source, or on the line from the remote point, key the transmitter to send out signals.

In transmitters of this type vknown in the prior art it has been the practice to send out Vs or "a-b-d between messages in order ,that vthe receiving apparatus destined to receive said messages may be kept in tune and ready for the next message. This continued operation of the transmitter in sending out these Vs or a-b-c is wasteful of power because these idle signals used up as much power as is used by signals in a useful message. One of lthe .objects of the present invention is to eliminate or at least reduce materially this waste of power.

Briey, attain the object Ymentioned above by the use of a novel device for automatically switching the transmitter over to a source of signals of relatively short duration. These signals require less power to transmit and serve the same purpose as the Vs or a-b-c of normal length transmitted heretofore. The control impulses may be Vs or any other desired characters oi reduced length. These signals may have wider spaces as well as shorter dots and dashes. For example a dot or dash one-third as long and spaces that much longer may be used and the utilization or dots and dashes of reduced length and spaces of increased length will require only about one-third as much power as is required to send out the control or tuning impulses sent out heretofore at normal spacing.

The source of Vs or other characters of 4reduced length and the increased spaces may be sent out by means of a wheel. The characters may be arranged on the periphery or on the face oi the whe-el which when Arotated will in accordance with the present invention transmit the dots and dashes of reduced length and the spaces oi increased length. The wheel may also include call letters or character-s which identify the particular channel on which signalling is going on. The wheel will for convenience be termed a V (Cl. Z50-17) wheel throughout kthis specication. It will be understood, however, that other means may be used 4tofsend out the signals of reduced length and spaces of increased length without departing from the spirit of the present invention. Of course 5 each transmitter may send out signals-on several channels, and the frequencies of the waves used .on the various channels may be different. In my .inventionl provide a V wheel as described above for each channel, and the V wheels may be thrown in or out of circuit, by switching means which is operated simultaneously with and by the device used to change the frequency of the signals worked with.

Where the keying control is operative during extended no-signal periods as described above, the telegraph line may become open-circuited or inoperative for some other reason without the operator at the .receiver end being aware of Vsuch in- ,operativeness The open circuit would merely 20 connect the selected V wheel to the keying tube to send vout the Vs or other short pulses for tuning purposes and the identifying signals.

vAnoloject of the present invention is to provide :means whereby the operator at the receiving station will Yknow whether the operator at the transmitter .is still in control and when such control is relinquished. This is accomplished in accordance with the present invention by providing a simplied means whereby the transmitter may be disconnected from the channel andconnected to one of the sources of Vs or other characters of reduced length and spaces of increased length by the presence of a continued marking character on the line, and disconnected from the V wheel 1 and connected to the message line in the absence of said continued marking current.

Briefly the object mentioned above is accomplished in accordance with applicants Ynovel .invention by interposing the contacts of a relay between the V wheels and the keying apparatus in the transmitter and interposing a thermionic relay between the source ofsignal and the armature in said relay as in the prior modications and operating said thermionic device in such a manner that as long as normal message characters separated by normal spaces or intervals are coming in over the line or yfrom the source the transmitter will be co-nnected with said line or source, vbutas soon as a signal character of -continuous duration is put on the line the transmitter Will be disconnected from the message or line and connected to the selected V wheel. This action takes place slowly so that there is no danger of the transmitter being disconnected 55 from the message line or source as long as messages are coming in. When messages are again started the thermionic relay is actuated to permit the contact of the relay to close the circuit between the message source or line and the tran,.- mitter. This operation takes place quickly so that the transmitter is connected to the message line or channel immediately so that no messages are mutilated.

The novel features of my invention have been set forth in detail in the claims appended hereto.

The nature of. my invention and the manner in which the same may be carried out will be best understood by the detailed description thereof which follows and therefrom when read in connection with the attached drawings throughout which like reference characters indicate like parts insofar as possible and in which:

Figure l illustrates a circuit arrangement including the essential elements of my novel automatic idle time keying unit. In this circuit the essential elements only of the transmitter keyed by my novel circuit are shown;

Figure 2 shows modification of the arrangement of Figure 1, While;

Figures 3, 4, and 5 show a modification or" the arrangement of Figure 2. In the circuits of Figures 3, 4, and 5 however, the operativeness of the transmitter to send signals or tuning impulses is determined by the presence or absence `of signals or a pulse of continuous duration on the line.

Referring to all of the gures, the keying unit is indicated at A, a thermionic relay which controls the mechanical relay is indicated at B, the mechanical relay is indicated at Z, the transmitter keyed stage is indicated at E, the transmitter keying stage is indicated at D and the source of characters of. reduced length and increased spaces for tuning purposes at the receiver and channel identifying symbols is indicated at C by the V Wheels v1 and v2.

In Figure 1 keying unit A has its output connected to the control grid 2`of thermionic tube V1 and also to contact I3 of relay Z as shown. The cathode 3 of tube V1 is grounded. The anode I of tube V1 is connected to the positive end of a source B1, while the negative end of B1 is connected to the grid 5 of tube V2, and also to ground by way of a resistor R1. The cathode 6 of tube V2 is connected to ground as shown. The anode 4 of tube V2 is connected to the positive terminal of a high voltage source HV by way of resistor R4 and to the grid 8 of tube V3 and to one terminal of a condenser I0, the other terminal of which is connected to ground. The cathode 9 of tube V3 is connected to the positive terminal of a source B2, the negative terminal of which is grounded. The anode II of the tube V3 is connected to the coil I I of the relay Z and by way of the coil I I of the relay Z to the positive terminal of a high potential source. All of the high potential sources mentioned above may be replaced by a single source when desired. Furthermore this source may be obtained from a generator or by way of rectifiers from an alternating current source. The tongue I2 of relay Z is connected to the grid electrodes of a pair of thermionic tubes V4 and V5 as shown in the keying stage D of the transmitter. A spring I5 retains the tongue I2 of, relay Z pulled over against contact I3 when there is no current flowing in coil II. Contact I4 is connected to a brush on one of the V Wheels. To simplify the description of applicants device it will be assumed that wheel V2 is connected in circuit by contact K. The other brush on V wheel Z is connected as shown to a source of negative potential. Contacts' I3 and Ie are also connected to a source of 10W positive potential through resistors Rs and RF1. The tongue I2 is connected to a low positive voltage by Way of a resistor R7 of high value.

The stage D, that is the keying stage of the transmitter, and the stage E of the transmitter form no part of the present invention. However, it may be said that the tubes V4 and V5 of stage D and the tube Vs of stage E all derive their anode voltage and current by way of a resistance R5 from any source of high voltage HV. If the control grids of tubes V4 and V5 are maintained at positive potential or a small negative potential tubes V4 and V5 are conductive and draw anode current. In this manner they divert current and potential from the anode electrode of the transmitter tube in E and decrease the amplitude of the oscillations produced by E. In this manner the transmitter is keyed. The thermionic tube E may be an amplifier, a frequency multiplier or a relay and may have its control electrode excited or energized by a source of oscillations as shown. The output circuit of E may be coupled to a utilization circuit directly or by way ot ampliers or frequency multipliers or both. The utilization circuit may be an aerial system or a transmission line.

In the operation of Figure 1 it will rst be assumed that there is no signal being sent from the telegraph oice to the vacuum tube keying unit at A, which may be located at or near the transmitter. Under these circumstances the output voltage of unit A is zero and the grid 2 of tube V1 is made positive by the current through Re. The tube V1 is then conductive and current flows through the resistance R3. Because of the drop of current in the resistance R3 the grid 5 of. tube V2 becomes sufciently negative to out off the ow of anode current in V2. This permits the condenser IU to charge up slowly to a higher positive value through resistance R4 which is connected to the high voltage source HV. When the charge in condenser Ill has reached a suiiiciently high value the grid 8 of tube V3 Will be made suciently positive in respect to cathode 9 to cause current to flow in the anode circuit thereof. This current passing through coil II of relay Z produces a magnetic eld which attracts the armature I2 to overcome the bias supplied by the spring i5 and to pull the armature I2 over to make contact with the contact point I4. The V wheel V2 is now connected to the control grids of the keying tubes V4 and. V5 in the transmitter and when said V Wheel is rotated current impulses representative of the signal on the periphery thereof or on the face thereof are impressed on the control grid of the keying tubes V4 and V5 for transmission.

The V wheel operates as follows:

When the brush I6 passes over the conducting segment, on the rotating V Wheel, negative voltage is impressed on the grids of tubes V4 and V5, which causes these tubes to be non-conductive. The anode potential of tube Ve is sufficiently high to allow this tube to function as an amplifier or a relay or as a frequency multiplier so that carrier energy is impressed on the following stage and passes on through the transmitter to the antenna or transmission line. Likewise, when brush I il passes over a non-conducting segment on the V wheel, the grids of; tubes V4 and Vs of stage D become slightly positive because of the current through resistor Rs. This causes tubes' V4 and V5 to conductv current which is drawn through resistor R5. This extra current causes a much: greater voltage drop in R5 so that the anode; potential of tube: Ve in stage E is too low to conduct suiicient current and the carrier energy is cut oi from the. remaining stages of the transmitter and no signal is transmittedV at this moment. The characters onthe V Wheel may be of any desired length and may as indicated above be very short while the spaces may be of greatly increased length.

Now assume that a signal or message comes in over the telegraph line. This. message causes keying unit A to send out a series of negative potential. pulses. The first negative pulse cuts oi the current in tube V1 and the,- grid 5 of tube'Vz changes toground. or cathode potential because there is no current flowing in. Ra.- This causes tube Va to become conductive so that current flows. in the anode circuit thereof. Con-denser l0 quickly discharges. by way olthev path of low resistance in tube V2, which lowers the potential on the grid 8 of tube V3 with respect to the cathode 9 thereof. The tube V3 immediately becomes non-conductive thereby deenergizing the winding ll of relay Z. This allows the field of the magnet to fall and permits the-spring I5 to pull the tongue i2 over against contact I3 which connects the transmitter keying stage D to the vacuum tube keying device A. Keying is accomplished in the-same manner described in connection with the V wheel. The negative impulses of high potential from the output of A, biases the control grids of Vl andVtV negatively so that their anode circuits are non-conductive. This causes a potential on the anode of Vs to increase and transmission of oscillations takes place. When the potential from A to the control grids of V4 and V5 is zero or less negative the keying tubes become conductive thereby lowering the potential on the anode of Vs to cut off oscillations in the transmitter. If the signals from A should stop for, say, ten seconds then condenser I0 will have time to charge up sufficiently to cause the control grid of tube V3 to become positive enough to start a flow of current in the anode circuit of V3. This current energizes H and actuates relay Z to connect the transmitter keying stage D to V wheel V2.

The overall operation would be that as long as the telegraph ofce is sending the transmitter will respond, but if the telegraph ofce stops sending for several minutes or for aV period longer than a pre-arranged time delay, the transmitter will be idle until the time delay is up and then the V wheel will be automatically switched on. This is where the saving in power occurs. The V wheel dots and dashes are shorter than normal, while the intervals between dots and dashes are longer than usual.

This requires less transmitter power than normal keying requires and yet serves to keep the receiving stations tuned to the transmitter frequency. The change from the V wheel to the message line control is almost instantaneous, but a comparatively long period is required toautomatically switch from the message channel to the V Wheel.

The V wheel may be made so that any ratio of length between dots and spaces can be obtained by moving the brush near to or further from the center. The number of dots or spaces per time intervalv maybe controlled by controlling the speedofi rotation oi the wheel.

theA modification. ofY Figure 2.1 have climi.- nated the necessityof; the separate; sources B1 B2, To; accomplish thisY l1 interpose a resistance R2 between the anode of V1 and the control grid of V2. Positive potential for the anode of V1 is Asupplied byY way of a resistance R1 from any source of: high potential. Biasing potential for the control grid ot V2 may besupplied by way of a resistance. Rs connected to a negative point on asource. The. current for the cathode ofVa may be supplied from an alternating current source andi the: cathode 9 of; V3` may beconnected to a source of positive potential. Figure 2 otherwise operates in the same manner in which the. modification of Figure l operates as described in detailhereinbefore. For this reason. it is thought unnecessary to repeat the op eration of the circuits at this point. howeventhat'the action of. Vrcauses through the networkV of resistors R1 Rz, and Ra-potential changes on the grid 5 of V2 as in Figure l.

When it is desired. to control the relation between the transmitter and the message channel or the V Wheel from. the message source the keying device may be made. to function from an extended dash put on the message line at the source or telegraph oiiice. When the keying control is so operated the receiving operator is conx scious of the fact that the telegraph operator still has the transmitter under his control. If the automatic keying control is made to function by the extended no-signal period, as in the .prior modifications, the telegraph control line rangement of Figure 2 disclosed hereinbefore.

The operation of this device is the same as the operation of the prior arrangements except as indicated hereinafter.

At the end of a message or group of messages -the telegraph operator sends a prolonged dash over the line to the vacuum tubekeying unit A. This causes the vacuum tubekeying unit A to maintain a. steady negative potential in its output. rihegridl 5 of tube V2 is in this case made suciently negative to block the anode current in the tube. Condenser l0 then slowly charges through resistor R4 andcauses the grid 8 of tube V3 to become suiciently positive with respect to the cathodef whichv is already positive to some extent topermitanode current to flow in V3. This anode current passes through the coil Il of the relay Z tocause the relay tongue I2 to make contact withv contact I4 which connects the se- -lected V wheel. to the control grids of the tubes V4 and V5 of the transmitter keying unit D. As long as the dash is maintained on the telegraph control line. the V wheel will continue to key the transmitter. l

Now if a telegraph message is started the long dash istaken oi the control line. No voltage appears on the output of the vacuum tube keying unit AY and the grid 5 of tube V2 assumes practically ground potential because of its connection to ground through resistor Ra. TubeVz quickly discharges.condenserv l0.- andalso draws. more cur- The modification of It is noted,

rent from the positive source through the resistor R4, so that the potential drop in this resistor R4 prevents further building up of positive potential on condenser I9 and grid 8 of tube V3. This causes grid 8 to be sufciently negative with respect to the cathode 9 of this tube to block the anode current. Consequently relay Z is deenergized and the relay tongue I2 is pulled over by spring I5 to make contact with contact I3. This in eilect connects the keying stage D of the transmitter to the vacuum tube keying unit A. When the next dot or dash comes, condenser I starts to charge slowly through resistor R4 but before it is charged is suciently high to cause relay Z to operate, the next space between signals causes it to quickly discharge through tube V2 so that as long as signals or prolonged nosignal periods are maintained the transmitter keying stage will remain connected to the signal line or telegraph channel.

Very briey, when the telegraph operator wishes to put on the economy Vs he holds a continuous dash on the control line. After a certain adjustable time delay the automatic control device switches the transmitter keying control to the V wheel. When the operator wishes to start a message he may start immediately and the automatic control device very quickly `switches the transmitter keying control to the telegraph control system.

In a modification the automatic keying control device described above may be used on the extended dash while the extended no-signal period may be used through another and somewhat similar control system to stop and start the transmitter.

The apparatus may be simplied in practice. For example, I may utilize the arrangement shown in Figure 4. Here the cathodes of the tubes V2 and V3 may be both heated by alternating current supplied from any alternating current source. Furthermore, the secondary windings of these heating circuits need not be centertapped but may be grounded at one side as shown. Cathode 6 may be maintained at the desired potential by connecting one side of the heating circuit thereof to the terminal of resistance R3 which is grounded. The desired positive potential for the cathode 9 of tube V3 may be obtained by connecting one side of the heating circuit for cathode 9 to the tap on a potentiometer P connected as shown between the positive terminal of the direct current source and ground which is also connected to the negative terminal of the source of direct current. Here, as in Figure 3, the charge on the condenser If! is determined by the amount of current flowing in the anode circuit of tube V2 and in turn determines the bias of the control grid 8 of tube V3. The conductivity of tube V3 determines whether or not the winding II of relay Z is energized. 'I'he keying of the transmitter by the V wheel or by messages from A is accomplished here in the same manner in which it is accomplished in Figure 3` and it is thought unnecessary to describe in detail the operation of the arrangement in Figure 3. The V wheels V1 and V2 here as in the prior modifications may be rotated in any manner as for example by means of a motor. The motor in turn may be energized in any manner and may be energized as shown by alternating current from the same source used to energize the cathodes of the tubes V2 and V3.

In arrangement of Figure the output of the vacuum tube keying device A is connected to contact I3 and to oneterminal of Rs, the other terminal of which is grounded. The electrical center oi' the heating circuit of V2 is connected to ground while the electrical center of the cathode heating circuit of V3 is connected to a point on a potentiometer P connected between a high potential source and ground. The lower potential N of potentiometer P may be shunted by a capacity as shown and in the operation of the arrangement shown in Figure 5 as in the prior modications the conductivity of V3 is determined by the charge of condenser I0 which is in turn determined by the conductivity of V2.

The transmitters of each modification are usually provided with wave changing devices in one or more stages to permit signalling on a plurality' of different frequencies or channels. Each channel is kpreferably identified by its own call letters or symbols. In my invention I provide a V wheel for each channel. Each V wheel may carry channel identifying letters or symbols in addition to the Vs or tuning signals. The desired channel may be selected by a wave change switch WC. VThe particular V wheel that carries the identifying letters for the selected channel may be thrown in circuit by a switch VS which may be connected to the control for the wave change switch WC as shown.

Having thus described my invention and the operation thereof, what I claim is:

l. A signalling system comprising a transmitter of the thermionic type including a source of signais, keying means interposed between said source of signals and said transmitter, and means for sending out controlling signals of reduced length between messages, comprising, a control signal producing device, a relay, and thermionic means coupled to said source of signals on the one hand and to said relay on the other hand, said ther- -mionic means being responsive to the presence or absence of signals in said source to disconnect said source from said transmitter between messages and to connect said control signal produ-cing device to said transmitter.

2. A signalling system comprising, a transmitter including a thermionic keying tube, a source of signals, a source of control impulses, a relay including contacts for connecting said keying tube to said source of signals or said source of control impulses, and a thermionic device interposed between said source of signals and actuating means in said relay, said thermionic device responding to a constant signal from said signal source to actuate said relay to connect said source of control impulses to said keying tube. l

3. A signalling system comprising, a transmitter including a thermionic keying tube, a source of signals, a source of impulses of short duration separated by intervals of long duration, means for connecting said keying tube to said source of signals or said source of short impulses including, a thermionic relay device interposed between said source of signals and said keying tube, said thermionic device responding to a constant signal from said signal source to actuate said relay to connect said source of short impulses to said keying tube.

4. A signalling system comprising, a transmitter of the thermionic type, a source of signals, keying means interposed between said source of signals and said transmitter, and means for sending out controlling signals of reduced length sepa.- rated by spaces of increased length between messages, comprising, a control signal producing device, a mechanical relay including a movable contact connected to said keying means, and xed contacts connected to said source of Signals and' Y in said source to move said movable contact against one or the other oi said fixed contacts.

5. In a signalling system, a transmitter of the therrnionic type, a source of signals, a thermionic keying tube connected with said transmitter, a

` magnetic relay having a movable contact and a pair oi xed contacts, a connection between said keying tube and one of said contacts, a source of control' signals connected with another of said contacts, a connection between the remaining one of said contacts and said source of signals, a

thermionic tube having output electrodes con# nested with the energizing winding in said relay, said tube having input electrodes, and a coupling between the input electrodes of said thermionic tube and said signal source.

6. A signalling system comprising, a transmitter of the thermionic type, a source of signals, keying means interposed between said source of signals and said transmitter, and means for sending out controlling signals of reduced length between messages comp-rising a controlling signal producing device, a mechanical relay, and thermionic means coupled to said source of signals on the one hand and to said mechanical relay on the other hand to disconnect said source of signals from said transmitter between messages and to connect said controlling signal producing device to said transmitter, said operations taking place slowly and means for quickly disconnecting said transmitter from said control signal device and connecting the same to said source of signals.

7. In a signalling system, a transmitter of the thermionic type including a keying tube, a source of signals, a wheel having conducting segments connected to a source of potential and separated by non-conducting segments, a relay having a movable member connected to said keying tube and a pair of contacts, a connection between a brush on said wheel and one of said contacts, a connection between the other of said contacts and said source of signals, a thermionic tube having an output connected with an energizing winding in said relay, said tube having an input circuit, and a coupling between the input circuit of said thermionic tube and said signal source.

8. A signalling system comprising, a transmitter of the thermionic type, a source of signals, a keying tube interposed between said source of signals and said transmitter, and means for sending out controlling signals of reduced length and increased spaces between messages comprising a controlling signal producing device, a mechanical relay having an armature connected to said keying tube, said relay having a pair of contacts and a winding, a connection between said source of signals and one of said contacts, a connection between said controlling signal producing device and the other of said contacts, thermionic means coupled to said source of signals on the one hand and to said winding on the other hand to disconnect said source of signals from said transmitter when signals from said source are interrupted and to connect said control signal source to said transmitter said operations taking place slowly and for quickly disconnecting said transmitter from said control signal source and connecting the same to said source of signals when signals are resumed.

9. A signalling device comprising, in combina-A tion carrier wave producing and keying means,l

wave length changing means `connected therewith, a source of messages, a plurality of sources of short impulses and wave length identifying symbols, a device for selecting one of said last named sources, common control means for sai-dwave length changing means and said source selecting device, and a relay for connecting either said source of messages or said selected short impulse and wave length identifying symbol source to the keying means in said transmitter.

iQ. A signalling system comprising, a wave `re-V laying circuit of the thermionic type, wave changing means connected to the relaying circuit, a source oi signals, a thermionic keying tube connected with said relaying circuit, a relay having a plurality of contacts, a connection between one of said contacts and said keying tube, a plurality oi sources of control signals and wave length identifying symbols, a switch for selecting one of said sources and connecting the same to another of said contacts, a connection between athird one of said contacts and said source of signals, therinionic means connected with an energizing winding in said relay, a coupling between the input circuit of said thermionic means an-d said signal source, and a common control for said switch and said wave changing means.

l1. A signalling system comprising, carrier wave relaying means and wave length changing means, a source of signals, keying means interposed between said source of signals and said carrier wave relayings means, means for sending out controlling signals of reduced length separated by spaces of increased length between messages and wave identifying symbols, comprising, a plurality of control signal producing devices, there being a device for each wave length, means for selecting a particular one of said devices, a mechanical relay including a movable contact connected to said keying means, and xed contacts connected to said Source of signals and to the selected one of said devices, thermionic means coupled to said source of signals on the one hand and to said mechanical relay on the other hand, said thermionic means being responsive to the presence or absence of signals'in said source to move said movable contact against one or the other of said fixed contacts, and a common control for said wave length changing means and said device selecting means.

12. In a signalling system, a wave relaying circuit, wave changing means connected to said relaying circuit, a source of signals, a thermionic keying tube having a plurality of electrodes, a connection between a pair of said electrodes in said keying tube and said relaying circuit, a magnetic relay having an energizing winding and a plurality of contacts, a connection between one of said contacts and one of the electrodes in said thermionic keying tube, a plurality oi sources of control signals and wave length identifying symbols, a switch for selecting one of said last named sources and connecting the same to another of said contacts, a connection between a third of said contacts and said rst named source of signals, a thermionic tube having input and output electrodes, resistive means connecting the input electrodes of said thermionic tube to said source of signals, an additional thermionic tube having input and output electrodes, resistive and capacitive elements coupling the input electrodes of said additional thermionic tube to the output electrodes of said preceding thermionic tube, and a circuit connecting the output electrodes of said additional tube in series with said energizing winding of said relay.

13. In a signalling system, a wave relaying circuit, a source of signals, a keying tube having a plurality of electrodes, a connection between a pair of the electrodes in said keying tube and said relaying circuit, a magnetic relay, having an energizing winding, a movable contact and a pair of xed contacts, a connection between said movable contact and one of the electrodes in said keying tube, a source of control impulses, means connecting the source of control impulses to one of said fixed contacts, a connection between the other of said xed contacts and said source of signals, a control tube having input and output electrodes including a cathode, an impedanace connecting the input electrodes of said control tube to said source of signals, an impedance cori-i nected between said fixed contacts, a connection between a point on said impedance and the cathode of said control tube, an additional tube having input and output electrodes, an impedance and a capacity coupling the input electrodes of said additional tube to the output electrodes of said control tube, and a circuit connecting the output electrodes of said additional tube with said energizing winding of said relay.

14. A signalling system as recited in claim 13 wherein all of said imp-edances are resistive in character.

15. A system as recited in claim 13 in which the input and output electrodes of said additional tube includes a cathode and in which the cathodes of said control tube and said additional tube are 15 heated by alternating current.

GEORGE LINDLEY USSELMAN.