US2019166A - Electric train signaling system - Google Patents

Description

Oct. 29, 1935. L. D. WH-ITELOCK ELECTRIC TRAIN SIGNALING SYSTEM Filed Feb. 175-1954 R v. 0% m H%. 0 m E .nb n MW mw W A 1 y. S d 1 km wg ws m H l e A V L Y -\%\-.-%.V-W% L R xN HVBK EQ KQSEQQ I: w kmxww m k M m kmx gwwwk i i i J l, .S i %B MWM Q n H E u mm? 1 Patented Oct. 29, 1935 UNITED STATES acialtc PATENT OFFIQE ELECTRIC TRAIN SIGNALING SYSTEM Application February 17, 1934, Serial No. 711,788

19 Claims.

My invention relates to signaling systems for railway trains, and particularly to systems for telephone communication for railway trains.

An object of my invention is the provision, in systems of the type here involved, of novel means for transmission of signaling currents between spaced points on a train, or between two trains, or between a train and a wayside station. Other objects and advantages of my invention will appear as the specification progresses.

I will describe certain forms of apparatus embodying my invention, and will then point out the novel features thereof in claims.

In the accompanying drawing, Fig. 1.is a diagrammatic view showing one form of signaling apparatus embodying my invention. Fig. 2 is a diagrammatic view of a modified form of the signaling apparatus of Fig. l and which also embodies my invention. Fig. 3 is a diagrammatic view of a wayside station equipped with apparatus embodying my invention.

Similar reference characters refer to similar parts in each of the views.

My present invention is an improvement on the invention disclosed and claimed in application for Letters Patent of the United States, Serial No. 450,135, filed May 6, 1930, by Lars O. Grondahl for Electric train signaling systems.

Referring first to Fig. l, the reference characters i and l designate the trafiic rails of a stretch of railway track which is occupied by a railway train designated as a whole by a reference character TN. The forward vehicle of the train TN is indicated at 2 and the rear vehicle is indicated at 3, for example, the vehicles 2 and 3 may be the locomotive and caboose of the freight train, respectively. This particular make-up of the train TN has no significance, however, in so far as my present invention is concerned, and the vehicles 2 and 3 may be any two vehicles of the train. Furthermore, as will appear hereinafter, the vehicles 2 and 3 may be vehicles of two separate trains, respectively.

When my invention is to be utilized for signaling between two spaced points on the same train, for example, between the locomotive and caboose of a freight train, one equipment will be mounted on the locomotive and a second and similar equipment will be mounted in the caboose. Each of such equipments preferably comprises a transmitter, a receiver, a coupling transformer, a circuit controller for connecting said transformer with either the transmitter or receiver and an electrical conducting member or counterpoise. The transmission circuit between the two spaced locations preferably includes the traffic rails in a manner to more fully appear hereinafter. The transmitter T of the locomotive equipment includes a source of alternating current, such as a generator G. One terminal of the generator G is connected with a contact 8 of a manually operated circuit controlling switch SW, while the opposite terminal of the generator G is connected with a second contact 9 of the switch SW, the secondary winding ill of a transformer Ti being interposed in the connection between the generator G and the contact 9. The primary winding ll of the transformer TI is included in a circuit which also contains a battery I2 and a control device, such as a microphone M. It follows that sound impulses produced by speaking into the microphone M will cause variations in the current flow in the primary winding I I of the transformer T! which will induce an electromotive force of corresponding frequencies in the secondary winding NJ with the result that the alternating current supplied by the generator G will be modulated by the voice frequencies. It will be understood that the microphone M may be a control device adapted to produce a single given frequency of variation of the current flow should it seem desirable. In this latter case, the alternating current will be modulated by a single frequency corresponding to the frequency produced by the control device.

The receiver R of the locomotive equipment includes in this instance a demodulator-amplifier DA and a signaling device shown as a loud speaker LS. The upper right-hand input terminal of the demodulator-amplifier DA is connected with a contact l3 of the switch SW and its lower right-hand input terminal is connected with a second contact M of the switch SW. The output of the demodulator-amplifier is connected with the operating winding of the loud speaker LS over wires I5 and Hi. The demodulator-amplifier DA may take different forms several of which are well known to the signaling art, and as'its specific structure forms no part of my present invention, this device is shown conventionally only for the sake of simplicity. It is deemed sufilcient for the present application to say that this demodulator-amplifier DA demodulates alternating current modulated by voice frequencies or modulated by a given single frequency when such currents are applied to its input circuit and causes to appear in its output circuit the voice frequencies or the single frequency only greatly increased in amplitude. As stated above, the output circuit of the demodulator-amplifier DA is connected with the operating winding of the loud speaker LS, and hence alternating current modulated by the voice frequencies of a telephone message and applied to the receiver R will be reproduced by the loud speaker LS. The loud speaker LS may be a signaling device selectively responsive to a single given frequency should it seem desirable. In this latter case, alternating current modulated with the given single frequency and applied to the receiver R will be effective to operate the signaling device.

The contact members I! and N3 of the circuit controlling switch SW are connected with the opposite terminals respectively, of the winding IQ of a coupling transformer T2. Consequently, when the switch SW is set in the position illustrated by the full lines in Fig. 1 and the contact members H and I8 engage the contacts I 3 and I4, respectively, the receiver R is connected with the winding [9 of the transformer T2. When the switch SW is depressed to the position illustrated by the dotted lines in Fig. l and the contact members H and ill make engagement with the contacts 8 and 9, the transmitter T is connected with the winding IQ of the transformer T2.

A second winding 20 of the coupling transformer T2 is included in a circuit connection extending from the traffic rails to an electrical conducting member or counterpoise. This circuit connection extends from the lower terminal of the winding 26 over wire 2| to the traffic rails I .and l in multiple through the medium of the wheels and axle 4 of the locomotive or vehicle 2. The electrical connection of the wire 2| with the wheels of the locomotive may be through the journal boxes or may be through a contact ring mounted on the axle and a contact brush adapted to engage therewith, as may be desired. Furthermore, the wire 2| may make connection with the rails i and P through the medium of a pair of contact shoes, one riding on each rail, if found desirable to do so. The specific manner of connecting one terminal of the locomotive circuit with the traffic rails forms no part of my invention, and the form here shown will serve to illustrate the many ways direct-connection with the trafiic rails may be made. This circuit connection on the locomotive extends from the top terminal of the winding 20 of the transformer T2 over a wire 22 to one end of an electrical conducting member A-B, the other end of which is dead-ended and is free from connection with the equipment and from the metallic parts of the locomotive. The electrical conducting member A-B may be a single wire of some length, a loop of several turns, a network or a metal sheet of considerable area as desired, one terminal of which, as stated above, is dead-ended. This conducting member A-B may be located .at any convenient place on the locomotive and preferably is located below the body of the locomotive and relatively close to the road bed. It is clear that the conducting member A-B serves as one plate of a condenser of which the earth is the other plate, and also serves as one plate of another condenser of which the traffic rails is the other plate. This latter capacity, however, will be relatively small in comparison with the capacity between the conducting member A--B and the earth, and hence the conducting member AB serves as a counterpoise for .a circuit which includes the above traced circuit connection and the trafiic rails in multiple extending in either or both directions from the locomotive.

A tuning condenser 23 is preferably connected across the winding 20 of the transformer T2 to tune this circuit connection. The condenser 23 may be used in series with the Winding 20 if found desirable.

From the foregoing description it is to be seen that with the switch SW on the locomotive set in the position illustrated in Fig. 1, alternating current picked up from the trafiic rails will be impressed upon the receiver R through the medium of the transformer T2, and that with the switch SW depressed, alternating current will be supplied to the trafiic rails from the transmitter T of the locomotive equipment through the medium of the coupling transformer T2 and that this alternating current may be modulated with voice frequencies by speaking into the microphone M.

The equipment mounted on the caboose or vehicle 3 of Fig. 1 is similar in all respects to the equipment mounted on the locomotive and it is thought unnecessary to repeat the description. It will be noted that as long as the manually operated switch SW on the caboose occupies the position illustrated by the full lines in Fig. 1, its receiver R is connected with the winding 26 of the caboose coupling transformer T3 and hence is coupled with the circuit connection extending between the trafiic rails and the caboose counterpoise .AB. With the switch SW on the caboose depressed, the winding 26 is disconnected from the receiver R and is connected with the caboose transmitter T which is now coupled with the circuit connection between the traffic rails and the counterpoise through the medium of the transformer T3.

When the switch SW of either the locomotive or the caboose is reversed and its transmitter T is connected with the winding of the coupling transformer, an electromotive force of corresponding frequency will be induced in the winding of the transformer interposed between the member AB and the traffic rails with the result that an alternating difference of potential is created between the counterpoise on that vehicle and the traific rails, and a corresponding current is supplied to the rails which returns in part through the distributed impedance between the rails and ground, the ground and the capacitance existing between the counterpoise and earth. A portion of such current flowing in the traffic rails will be picked up by the wheels of the other vehicle and will flow through the circuit connection between the rails and the counterpoise on that vehicle, thence over the capacitance between the counterpoise and earth, the ground path and the capacitance existing between the counterpoise and earth on the sending vehicle. Such current flowing in the coupling transformer winding interposed in the circuit connection on the second vehicle will induce a corresponding electromotive force in the other winding of the coupling transformer with the result that energy of corresponding frequency will be applied to the receiver of the second vehicle. It is to be seen, therefore, that a transmission circuit between the equipment on the locomotive and the equipment on the caboose is provided through the medium of which energy corresponding to that supplied by the transmitter of the sending vehicle is impressed upon the receiver of the second vehicle. Furthermore, this transmission circuit will be effective to transfer energy between the two equipments in either direction.

To aid in visualizing this transmission circuit between the two vehicles, fictitious condensers 21 and 28 are shown by dotted lines in Fig. 1 between the counterpoise AB and ground of the two vehicles, respectively; and arrows have been added to the drawing to indicate the. flow of current at some particular instant. To be explicit, this transmission circuit can be traced as consisting of the following element: counterpoise AB of vehicle 2, wire 22, winding 20 of the transformer T2, wire 2|, wheels and axle 4 of vehicle 2, rails l and l in multiple, wheels and axle 6 of vehicle 3, wire 25, winding 24 of transformer T3, counterpoise AB of vehicle 3, capacitance between counterpoise AB and earth (fictitious condenser 21), ground and capacitance between counterpoise AB of vehicle 2 and earth (fictitious condenser 28). It is clear that when an electromotive force is induced in the winding 20 of the transformer T2 of vehicle 2, a corresponding electromotive force will be induced in the winding 26 of the transformer T3 on the vehicle 3, and conversely, when an electromotive force is induced in the winding 24 of the transformer T3 of vehicle 3, a corresponding electromotive force will be induced in the winding l9 of the transformer T2 on the vehicle 2.

In the event the locomotive operator desires to telephone to the operator in the caboose, he will depress his switch SW and speak into the microphone M. An electromotive force corresponding to the alternating current of the locomotive generator G modulated by the voice frequencies will be induced in the winding 20 of transformer T2 and a corresponding current will be supplied tothe trafiic rails. A portion of this modulated current will be picked up from the traiiic rails .by the wheels of the caboose and will flow through the connection between the rails and the counterpoise on the caboose and thence back to the locomotive through the capacitance and ground path. An electromotive force of corresponding frequencies will now be induced in the winding 26 of the transformer T3 which will be applied to the input circuit of the demodulator-amplifier on the caboose. After demodulation and amplification, the voice frequencies will be caused to appear in the output of the demodulator-amplifier and the telephone message will be reproduced by the caboose loud speaker LS. Totelephone from the caboose to the locomotive, the operator at the caboose will depress his switch SW to couple the caboose transmitter with the transmission circuit and he will speak into his microphone. This modulated alternating current will induce a corresponding current in the winding 24 of the transformer T3 and current will flow in the transmission circuit to induce a corresponding current in the winding IQ of the loco-motive transformer T2. The locomotive operator having subsequently restored his switch SW to its normal position, this modulated current induced in the winding I9 will be applied to the locomotive receiver, and, after demodulation and amplification, the telephone message will be reproduced by the locomotive loud speaker.

While, in the particular adaptation of my invention here disclosed, telephone communication is provided, it is apparent that by coding the alternating current supplied by the transmitters according to a prearranged code, code impulses of alternating current will be transmitted between the two vehicles over the transmission circuit. By further providing the receivers with decoders and signaling devices responsive to the prearranged code, control between the two vehicles may be established as desired.

The frequencies of each generator G may be of any suitable value, and is preferably high enough to avoid interference due to currents of commercial frequencies. Each receiver R will, of course, be provided with a filter so proportioned and adjusted as to pass the frequency sent out by the transmitter at the other location and to substantially suppress all other frequencies.

In order to signal between two trains, each train may be provided with one or more equipments located at any convenient location or 10- cations on the'trains. For example, the vehicle 2 of Fig. 1 and its equipment may be included in one train and the vehicle 3 and its equipment may be included in another train. With this arrangement, communication between the operators on the two trains may be carried on in exactly the same manner as described above between the locomotive and the caboose of a freight train. In. the case of two trains, the transmission circuit passes over the traffic rails in multiple and returns to the sending vehicle through the capacitance and ground path. In this latter case, however, it will be understood thatthe two trains are within reasonable distance of each other.

When it is desired to signal between a train and a wayside station along the track, the train may be provided with one or more equipments in the manner previously described, and another equipment maybe located at some convenient point along the track. The equipment located along the track may, for example, be constructed as illustrated in Fig. 3. As here shown, the wayside equipment is provided with a receiver and a transmitter which are preferably the same as the corresponding devices provided on the train and are selectively connected with the winding 29 of a coupling transformer T4 over a manually operated circuit controlling switch SW. The second winding 3i] of the coupling transformer T3 is included in a connection extending from the rails l and l over a resistor 32 to its mid point, wire at, winding tilandthence to a ground electrode 33. Assuming the vehicle 2 with its'equipment occupies the traffic rails i and l within reasonable distance of the wayside station of Fig. 3 and that communication between the operators is desired, the operator on the vehicle 2 by depressing his switch SW will supply alternating current to the traffic rails which will flow over the rails in multiple to the station equipment and thence it will pass to ground through the connection including the winding 30 of the transformer T 3 and back to the equipment on the vehicle 2 over the ground and counterpoise path. A corresponding electromotive force will be induced in the winding 29 of the transformer T4 which will be applied to the receiver of the wayside station equipment. It is. clear that alternating current may be transmitted from the wayside station transmitter to the vehicle 2 by the operator at the wayside station depressing the switch SW to connect his transmitter with the winding 29 of the coupling transformer T4.

Since the impedance of the circuit connection between the traffic rails and the counterpoise on a, vehicle contains capacitance, it may be tuned by means of an inductive reactance in series with the connection as well as by a condenser. In Fig. 2, the condenser 23 of the locomotive equipment is replaced by an inductor 34 which is interposed between the winding 29 of the coupling transformer T2 and the counterpoise AB. It is clear that the equipment of Fig. 2 will function in exactly the same manner as the locomotive equipment of Fig. 1.

Although I have herein shown and described only certain forms of apparatus embodying my invention, it is understood. that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. A signaling system comprising in combination with the traific rails of a stretch of railway track and a train adapted to travel thereon, an electrical conducting member mounted on the train in a horizontal plane to form one plate of relatively large area of a condenser of which the earth is the other plate, sending means located on the train connected between said conducting member and the traflic rails and including a source of periodic current for supplying such current to the rails which flows from the point at which it is supplied to the rails and returns partly through ground and the capacitance between earth and said conductor, and receiving means remote from said sending means controlled by the current in the rails due to said sending means.

2. A signaling system comprising in combination with the traffic rails of a stretch of railway track and a train adapted to travel thereon, an electrical conducting member mounted on the train in spaced relationship with ground and rails to form a counterpoise with respect to said rails, sending means located on the train connected between said conducting member and the traffic rails and including a source of periodic current for supplying such current to the rails which flows from the point at which it is supplied to the rails and returns partly through ground and the counterpoise, and receiving means remote from said sending means controlled by the current in the rails due to said sending means.

3. A signaling system comprising in combination with the traffic rails of a stretch of railway track and a train adapted, to travel thereon, an electrical conducting member mounted on the train in spaced relationship with ground and having one end free, sending means located on the train having connection with the other end of the conducting member and with the traffic rails and including a source of periodic current for supplying current to the rails which flows from the point at which it is supplied to the rails and returns partly through the ground and the capacitance between ground and said conducting member, and receiving means remote from said sending means controlled by the current in the rails due to said sending means.

4. A signaling system comprising in combination with the traffic rails of a stretch of railway track and a train adapted to travel thereon, an electrical conducting member mounted on the train to form an electrostatic coupling with ground, a circuit connection for connecting said member with the traffic rails, means on the train including a source of periodic current interposed in said circuit connection for supplying a periodic current to the rails which flows from the point at which it is supplied to the rails and returns partly through the ground and the coupling between ground and said member, and receiving means connected with the rails at a remote point controlled by said periodic current.

5. A signaling system comprising in combination with the traflie rails of a stretch of railway track and a train adapted to travel thereon, an electrical conducting member mounted on the train in spaced relationship with ground and having. one end free, a circuit connection for connecting the other end of the conducting member with the traffic rails, means on the train including a current source interposed in said circuit connection for creating an alternating difierence of potential between the conducting member and the rails for supplying a periodic current to the rails which flows from the point at which it is supplied to the rails and returns partly through the ground and the capacitance between ground and the conducting member, and receiving means connected with the rails at a remote point controlled by said periodic current.

6. A signaling system comprising in combination with the trairlc rails of a stretch of railway track and a train. adapted to travel thereon, an electrical conducting member mounted at one location on the train in electrostatic relationship with ground, a circuit connection for connecting said member with the trafiic rails, means on the train including a current source interposed in said circuit connection for supplying periodic current to the rails which flows in the rails in multiple from the point at which it is supplied to the rails, another electrical conducting member' mounted at another location on the train in electrostatic relationship with ground, a cir-- cuit connection for connecting said other member with the traffic rails, receiving means interposed in the last mentioned circuit connection influenced by the periodic current picked up from the trafiic rails, and signaling means controlled by the receiving means responsive to such current.

7. A signaling system comprising in combination with the traflio rails of a stretch of railway track and a train adapted to travel thereon, an electrical conducting member mounted at one location on the train in spaced relationship with the ground and the rails to form a counterpoise with respect to said rails, a circuit connection for connecting said member with the rails, mean on the train including a current source interposed in said circuit connection for supplying periodic current to the traffic rails which flows from the point at which it is supplied to the rails and returns partly through ground and the counterpoise another electrical conducting member mounted at another point on the train in spaced relationship with the ground and rails to form a counterpoise with respect to said rails, a circuit connection for connecting said other member with the rails, receiving means interposed in said last mentioned circuit connection influenced by the periodic current picked up from the trafiic rails at said other point and which returns through the last mentioned counterpoise and ground, and signaling means controlled by the receiving means responsive to such current.

8. A signaling system comprising in combination with the traiilc rails oia stretch of railway track and vehicles adapted to travel thereon, an electrical conducting member mounted on one vehicle to form one plate of a condenser of which the earth is the other plate, a circuit connection for connecting said member with the rails, means on the vehicle including a current source interposed in said circuit connection for supplying periodic current to the trafiic rails which flows in either direction from the point at which it is supplied to the rails and returns partly through ground and the capacitance between earth and said member, another electrical conducting member mounted on a second. vehicle to form one plate of a condenser of which the earth is the other plate, a circuit connection for connecting said other member with the traific rails, receiving means interposed in said last mentioned circuit connection influenced by the periodic current picked up from the rails at said second vehicle and which flows to ground through the capacitance between earth and said other member, and signaling means controlled by the receiving means responsive to the current in the rails due to the source on said one vehicle.

9. A signaling system comprising in combination with the trafiic rails of a stretch of railway track anda train adapted to travel thereon; a transmission circuit including a conducting member mounted on the train in electrostatic relationship with the earth and having connection with the traffic rails, the trafic rails in multiple and a remote circuit connection between the rails and ground; means on the train including a current source for supplying said circuit with periodic current, and signaling means interposed in said circuit connection responsive to the current flowing in said circuit due to said current source.

10. A signaling system comprising in combination with the trafiic rails of a stretch of railway track and a train adapted to travel thereon; a transmission circuit including a conductor located on the train in spaced relationship with ground having one end electrically connected with the rails and its opposite end free, the traffic rails in multiple and a remote connection between the rails and ground; means on the train including a current source interposed between said conductor and the trafiic rails for supplying said circuit with alternating current, receiving means interposed in said remote connection influenced by such current, and signaling means controlled by said receiving means responsive to said alternating current.

11. A signaling system comprising in combination with the trafiic rails of a stretch of railway track and a train adapted to travel thereon; a transmission circuit including a conductor mounted on the train to form a counterpoise, connection between said counterpoise and the trafiic rails, the traiiic rails in multiple and a remote connection between the rails and ground; means on the train including a current source interposed in the connection between the counterpoise and the rails for supplying said circuit with periodic current, and signaling means interposed in said remote connection responsive to such current.

12. A signaling system comprising in combination with the tramc rails of a stretch of railway track; a transmission circuit including a first conductor mounted at one location in spaced relationship with the track and in a horizontal plane to form one plate of relatively large area of a condenser of which the earth is the other plate, a first connection extending between said first conductor and the traffic rails, the traiiic rails in multiple, 2. second conductor mounted at a second location in spaced relationship with the track and in a horizontal plane to form one plate of relatively large area of a condenser of which the earth is the other plate and a second connection extending between said second conductor and the traffic rails; means including a current source interposed in said first connection for supplying said circuit with periodic current, and signaling means interposed in said second connection responsive to such current.

13. A signaling system comprising in combination with the traffic rails of a stretch of railway track and vehicles adapted to travel thereon; a {5 transmission circuit including a conductor mounted on one of the vehicles with one end connected with the rails and its other end free, the traflic rails extending from the vehicle and a conductor mounted on another vehicle with one end nating current.

14. A signaling system comprising in combination with the traffic rails of a stretch of railway track; a transmission circuit including a conductor mounted in spaced relationship with said track for movement along said track and positioned in a horizontal plane to form one plate of relatively large area of a condenser 01 which the earth is the other plate, contacts movable along the rails for connecting said conductor with the traffic rails in multiple, the trafiic rails and a remote connection between the rails and ground; means including a current source interposed between said conductor and said movable contacts for supplying said circuit with periodic current, and signaling means interposed in said remote 3 connection responsive to such current.

15. A signal system comprising in combination with the traffic rails of a stretch of railway track and vehicles adapted to travel thereon, an electrical conducting member mounted on each of 40 two vehicles in spaced relationship with the track each having one end free and its other end connected through a circuit connection with the traific rails, a transmitter on each vehicle including a source of periodic current, a receiver on each vehicle including a signaling device responsive to such periodic current, and a manually operable circuit controller on each vehicle for selectively coupling the transmitter and receiver into the circuit connection between the conducting member and the rails for operating the signaling device on either vehicle by current supplied by the source of the other vehicle.

16. A signal system comprising in combination with the traific rails of a stretch of railway track and vehicles adapted to travel thereon, an electrical conducting member mounted on each of two vehicles in spaced relationship with the track each having one end free and its other end connected through a circuit connection with the trafiic rails, a transformer on each vehicle having a first winding interposed in the circuit connection, a transmitter on each vehicle including a source of periodic current, a receiver on each vehicle including a signaling device responsive to such 05 periodic current, and a manually operable circuit controller on each vehicle for selectively connecting the transmitter and the receiver with a second winding of the transformer for operating the signaling device on either vehicle by current supplied to the second winding of the transformer on the other vehicle.

17. A signal system comprising in combination with the trafiic rails of a stretch of railway track and vehicles adapted to travel thereon, an electrical conducting member mounted on each of two vehicles in spaced relationship with the track each having one end free and its other end connected through a circuit connection with the trafiic raiLs, a transformer on each vehicle having a first winding interposed in the circuit connection, a. transmitter on each vehicle including a sourceof alternating current and telephone means for modulating said current with voice frequencies, a receiver on each vehicle including a demodulator and a loud speaker, and a manually operable circuit controller on each vehicle for selectively connecting the transmitter and the receiver with a second winding of the transformer whereby two-way telephone communication between the two vehicles can be accomplished.

18. A signaling system comprising in combination with the trafiic rails of a stretch of railway track, a wayside equipment including a receiver adapted to receive a telephone current and a transmitter adapted to supply such telephone current, a resistor connected across the trafiic rails adjacent said equipment, a circuit connection between a mid-terminal of said resistor and a. ground electrode and including a winding, and means including a manually operated circuit controller efiective to couple said winding to either said transmitter or said receiver to supply such telephone current to the rails which flows in the rails in multiple in both directions from said 'resistor and returns through the ground when the winding is coupled with the transmitter and to supply such current from the rails to the receiver when the winding is coupled with the receiver in response to such telephone current flowing in the rails. I

19. A signaling system comprising in combination with the trafiic rails of a stretch of railway track, a wayside equipment including a receiver adapted to receive a telephone current and a transmitter adapted to supply such telephone current, a resistor connected across the traffic rails adjacent said equipment, a transformer, a circuit connection between a mid-terminal of the resistor and a ground electrode and including a first winding of said transformer, and means including a manually operated circuit controller effective to connect a second winding of said transformer with either the transmitter or the receiver to supply such telephone current to the rails which flows in the rails in multiple in both directions from said resistor when said second winding is connected with the transmitter and to supply such current from the rails to the receiver when said second winding is connected with the receiver in response to such telephone current flowing in the rails.

LELAND D. WI-IITELOCK.

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