US2484680A

US2484680A - Railway train communication and alarm system using modulated carrier currents

Info

Publication number: US2484680A
Application number: US575311A
Authority: US
Inventors: Paul N Bossart
Original assignee: Union Switch and Signal Inc
Current assignee: Hitachi Rail STS USA Inc
Priority date: 1945-01-30
Filing date: 1945-01-30
Publication date: 1949-10-11
Anticipated expiration: 1966-10-11

Description

P. N. BOSSART RAILWAY TRAIN COMMUNICATION AND A Oct. 11, 1949;

LARM SYSTEM USING MODULAI'ED CARRIER CURRENTS 3 Sheets-Sheet .1

Filed Jan. 30, 1945 mg 5 Q Q My I Q NN INVENTQR Paul M flossar'. BY aim H117 A'ITORNEY P. N. BOSSART I 2,484,680 RAILWAY TRAIN COMMUNICATION AND ALARM SYSTEM USING MODULATED CARRIER CURRENTS 3 Sheets-Sheet 2 I N kw wmmmw R A% Oct. 11, 1949.

Filed Jan. 50, 1945 Oct. 11, 1949. P. N. BOSSART RAILWAY TRAIN COMMUNICAT ION AND ALARM SYSTEM USING MODULATED CARRIER CURRENTS v 3 Shee ts-Sheet 3 Filed Jan. 30, 1945 NB gwmmmmw Q NQ U INVEN'TOR.

Paa! M flassap.

AS SN U HIS ATTORNEY Patented Oct. 11, 1 94 9 -RAI'LWAY TRAIN COMMUNICATION ALARM SYSTEM Union Switch & Signal Company,

AND

, USING MODULATED panama :CUR It ENTS Paul N. Bssart, Cheswick, Pa., assignor to The Pa., a corporation, of Pennsylvania Application January .30, 1945, Serial '19 c ai s. (01. 179-82) My invention relates to railway train communication systems, and more particularly to multiple channel train communication systems.

When train communication is installed on, all or nearly all of thetrains of a railway division and also at one or more gwayside stations, some form of selection is necessary. That-is to say, ;if end to end communication is being carried on by the crew of one train the train crewof asecond nearby train should be able to carry on come munication without interference between the two trains. Also an operator at a Wayside ,station should be able to communicate with a train without interfering'with end to end" communication of other trains. Furthermoraif the ofiic'eopera-. tor or any other station should wish to break in on a conversation to issue train orders,.such should be permitted. In other words, when an entire railway division is equipped for train communication, a, plurality of different communication channels and a break in feature are essential.

Accordingly, a feature of my-inventi'on is the provision of novel and improved apparatus for a multiple frequency channel train communication system.

Another feature of my invention is the provision of railway train communication apparatus incorporating novel means for selecting a particular frequency channel of a plurality of different channels for communication. I

Still another feature of my invention is-the provision of railway train communication apparatus incorporating novel means for calling a train or station on each one of a plurality of dif ferent frequency channels. j

Again, a feature of my invention is theprovie sion of apparatus of the type here contemplated for calling a station that is already in communica-e tion and for cyclically calling a station on'each of aplurality of different channels. r

A further feature of -my invention isthe "provision in apparatus of the type here involved. of novel means to reduce the receiver sensitivity for the channel in use during a; conversation sothat the integrity of the transmitter and receiver may be checked by side tones from-the receiver." 1

Another feature of my invention is the'provi-J sion of train communication apparatus incorpo rating novel means t'o'suppress background noises and to 'pIOVide We...

Swissvale,

No. 575,311 I '2 Again, a feature of my invention is the provision of improved railway train communication apparatus using frequency modulation with a trackway transmitting circuit which includes the trackrails and line wires and other conductors extending parallel along'the railway.

Other features, objects and advantages of my invention will appear as the specification progresses.

I attain the aforementioned features, objects and advantages of my invention by the provi-' sion of transmitting apparatus capable of being conditioned to supply frequency modulated carrier telephone current of any one of a plurality of difierent carrier frequencies, and receiving apparatus responsive to each of said frequency modulated carrier telephone currents. That is, each such carrier serves as a frequency channel. The receiving apparatus is-normally conditioned to receive a calling current on any one of the channels, but thetransmittingapparatus is excited and made active only during periods current is to be sent out; Preferably the receiving apparatus includes an individual or independentreceiver for each channel, the different'receivers being connected in multiple to a loud speaker. to sound a calling tone signal received on any one of the channels, each channel having its individual tone. Through the hook switchoi a telephone hand set and other manually operable switches, the hand set when removed from the hook switch is connected to the channel of which a calling signalhas been received, but the loud-speaker is left connected to the other channels to sound a calling signal if it is found'necessary'to break in onthe conversation being carried on through the selected channel. That is, when the hand set is hung on its hook switch, a calling signal or speech on any one of the frequency channels is received in the loud-speaker, but when, the hand set is off the hook the channel selected for conversation is connected to the hand set only and the other channels are connected to the loud-speaker.

,In addition, each receiver includes-ineansto check the operativeness of the transmitter and of the receiver of the channel in use. To this end the receiver of the channel in use is kept active during transmission but itssensitivity is greatly reduced because of the very strong energy it will pick" upifrom'the local transmitter. This reduction in sensitivity is made only during the talking period. Thus there is sounded in the local earphone at a normal energy level the conversation that is being sent out. Reduction in the sensitivity of the receiver during the transmitting period prevents overloading of the receiver and permits self-monitoring at a comparatively low energy level.

The transmitting apparatus is preferably of the reactance-variation type of frequency modulating transmitter, and: its various elements are,- provided with different capacitors through which the transmitting apparatus can be selectively condir. tioned for any one of a plurality of different frequency channels.

On railway trains there exists ,a large amounts of background noise which if transmitted may be objectionable, and to overcome this I provide, an

adjustable microphone circuit'network whose;

sensitivity can be set so that the usual background noise is ineffective to operate the transmitter. This requires the speaker to speak 'rela-' tively loud and close to the microphone. In connection with such sensitivity adjustment of the microphone I provide the transmitting apparatus with indication means sothatthe speaker can readily tell when he is-talking loud enough'to cause the proper frequency swing of the transmitting apparatus. Such indication means preferably includes a gas discharge type of lamp connected to the-microphone circuit through an amplifier to flash'the lamp when the speaker is speakin at the-correct loudness.

Pro-emphasis is of a considerable help inimproving the signal noise operate at times near the noise level, and pro-- emphasis-is provided in the apparatus by -a resistance-capacity circuit in the microphone network; In adjusting the microphone network,--it isimportant that the amount of pro-emphasis does not change and a resistance pad is used-to accomplish such results.

I provide a calling current by impressing an audio frequency on the modulator through contactsrof. a calling relay, a different pitch-being used for each channel. Such calling frequency is attained through the use of an adjustable-elem; tron tube oscillator and preferably I switch an amplifier: tube of the indication means to an os-- cillator to. serve as a tone generator. Also--the secondary winding of the microphonetransformer ispreferably switched -to serve-asthe induc tance of the oscillating circuit'of thetone gen orator- Separate oscillatortubeand inductance can be used, if desired.

I provide a special control unit together with control relays to govern the condition of;--the transmittin apparatus for-operation-at the dif-- ferent channel frequencies and to efiect the differentcalling conditions. This control means also includes an emergency calling meas which when set into operation functions to send call-1 ing pulses cyclically on each of the frequency channels.

Atwayside stations I preferably couple the apparatus to the trackwaytransmitting circuit by connection to a line wire extending along the railway. Switching means is used to increase the voltage applied to the line wire at the lowercarrier frequency.

I shall describe one form of apparatus embody ing my invention, and shall then point out,the novel features thereof in claims.

In the accompanying drawingsLFigs. 1 and .2

with Fig. l placed above Fig. 2 are diagrammatic ratio in systems which \on .v hicles .of

views showing one form of apparatus embodying my invention when used with a train carried station of a two frequency channel train communication system. Fig. 1 discloses the transmitting apparatus, certain control relays, and a source of power, and Fig. 2 discloses the receiving apparatus and a control unit. Figs. 3 and 4 are diagrammatic views showing wayside station line wire connections for the apparatus of Figs. 1 and 2.

In each of the several views like reference characters are'used to designate similar parts.

Referring to Figs. 1 and 2, the reference character CO designates a vehicle of a railway train ,on, which theicomm-unication apparatus is mounted; This vehicle. CO may be the caboose of a freight train; for; which two way communication with remote stations is provided, such remote stations being on another vehicle of the same train,

other trains and at wayside stations. Eachsuch remote station will of course be provided with. communication apparatus simi- 'lar tothat disclosed in Figs. 1 and 2.

The caboose CO is provided with a source of power, such as the usual 32 volt car lightin system theterminals of this source being designated B32 and AN32L' The -32 volts of this source are converted into a voltage-suitable for use with electron tubesthrough-a motor generator MG, a motor lll :of whichis-connected-to the 32 volt source and a generator I of which is provided with terminals B lflflt'and. N400 from which a relatively: high voltage is obtained. The positive terminal B32t'and the. negative terminal N Q93 are connected to: aground electrode I 2." The caboose. is alsoiprovided with a series of control-relays. l9, 25.,.'50:-"and.16,= and..a control .unit indicated aswa whole byta dashiand dot rectangle CU; which relays andunit will be referred to from time. to time .as. the specification progresses.

A dashand dot rectangle v TA -.(Fig. 1) designates -theatransmitting apparatus. This trans mitting. apparatus vTA comprises as essential .ele'-.

ments a :microphonecircuit network including a transformer'Tl and a. potential divider Mt, a reactancemodulating tube. VI; san oscillator :tube V2, a driver amplifier tube V3,:a power-amplification stage including tubes ya and, V5, indication mplifier tubes VBand-VLand ;a calling means which includes tube V6 as an oscillator. and a windingof .thetransformer T! as .5 the inductance of the associated: oscillating circuit; 1'

A primary-winding l 4 of transformer ,I i is connected (to themiorophone circuit in a manner'to appear hereinafter, and secondary winding i5 oi the transformer is included 1 1113, controlgrid circuit for the, reactancatube l. This grid circuit extends; from control id wil through choke coil, 23 and either ofytwo alternativemaths, to cathode I8 of the tube The first path includes back contact l4 3 -.of-;rel-ay 56 -tobe referred to later,- adjustable terminal .-I 44. of potential divider I4fl,,.wire Jl, winding 15-, back contact it of relay |9v also to bereferred, to later,-ground electrodes 20 and 2| and, biasing unit =2 2, a The, second path includes frontcontact, I42 ofrelay, 50, wire 1| andthen-ce thesameasthexfirst path. The plate. circuit for tube-Vi is-provided with power from terminalB400Hof theigenerator 1 I, through front contact 24, .of. a directional relay. 25 governed in a mannendescribed later..wire 26,.resistors 21,an d .28; 'mpe dance,29,.plate, 30, and tube space v The oscillator tube V2 has associatedithere with an oscillating circuit comprising. inductance 33 and capacitor 34. Aphase shifting networkv comprising capacitor '35 and resistance 36 in series is connected across theoscillating circuit and assures the correct phasing of the reactance mod ulator tube Vl. Cathode 31 .of tube-V2 is connected to an intermediate terminal of winding 33 of the oscillating circuitQandplate 38 ofthe tube V 2 is provided with power from terminal B400 of the current source through a circuit including front contact 24 of relay 25, wire 26, andresistors 21 and 9. The parts are so proportioned that oscillations of a preselected carrier frequency which I shall call frequency I are produced, an adjustment of the inductance of the coil 33 for such frequency being provided through anfiadjustable core structure asindicated in Fig. 1.

The control grid circuit and-plate circuit of tube VI are coupled through capacitors 3i and 32 to the oscillating circuit with the .result tube Vl serves as a variable reactance for the oscillating circuit. Thus voltages applied to the control grid of tube Vl cause variations in the reactance of the tube as it appears to the oscillating circuit and in turn cause corresponding frequency variations of the oscillations created'by the oscillating circuit, with the result the oscillations are frequency modulated according to the voltage ap plied to the grid of reactance tube VI. 7

The plate circuit of oscillator tube V2 is resistance coupled toa control grid circuit of amplifier tube V3 through a capacitor 39. The plate circuit of the amplifier tube V3 is'powered from terminal B400 through primary winding 40 of 'a coupling transformer T2. Primary winding 40 and secondary winding 4| of the coupling transformer T2 are normally tuned to resonance at the frequency fl by capacitors I04 and I; respectively, and by adjusting variable iron'cores. Secondary winding 4| of transformer T2 has-its outside terminals connected'to control grids 4'2 and 43 of tubes V4 and V5, respectivelyfiof the power amplification stage, 'and'itsmid terminal is connected to the negative terminal N32 of the power source through a biasing unit 44 so that each control grid 42 and43 is provided witha preselected bias voltage. The plate circuits of tubes V4 and V5 include primary winding 45 of an output transformer T3 in a push-pull arrangement. A first preselected portion of secondary windin 46 of the output transformer T3 is connected through a back contact of the relay 50 to a sending loop circuit the lead wires I38 and of which loop circuit are connected tothe pairs of wheels 4'! and 48 of the caboose. Such sending loop circuit is tuned to resonance at the frequency fl through the use of a variable capac- 1?;1 5i connected across the lead Wires I38 and Relay 50 serves as a frequency change-over unit for the transmitting apparatus TA, the apparatus being conditioned to supply a ifllll'il'. telephone current of the channel frequency fl when the relay is released and the transmitting apparatus being conditioned to supply a different and a lower channel frequency which I shall'call frequency f2 when the relay is picked up. When relay to is released the various elements of the transmitting apparatus are tuned in the manner described hereinbefore and the apparatus is conditioned to supply the channel frequency fl; but when the relay 50 is picked up in 'a' manner to appear hereinafter, an -adjustable capacitor 52 is connected through frontcontaot-53of relay-5M0 mitting apparatus TA it is apparent that when the the 'oscillating circuit and the" oscillations are shifted to the carrier frequency f2. .:The primary winding 40 andsecondary winding 4| of: coupling transformer T2 are shifted in their tuning to the. channel frequency f2 by means of anxadjustable capacitor connected across winding 40through front contact 55 of relay 50, and an adjustable capacitor 56 connected across winding 4 I through front contactv 51 of relay 50. Also, an adjustable capacitor 56 is connected across primary winde ing 45 of the output transformer T3 through front contact 59 of relay 50, an adjustable capacitor 60 is connected across the sending loop cirr-x cuit through front contact 6| of the relay, and a second portion of the secondary winding. 46 of the output transformer is connected to the sending loop through front contact 62 of the relay to condition the circuits for the channel free-i quency fZ. t: Fromthe foregoing descriptionof the transfrequencychange-over relay 50 is released, trans mitting apparatus TA is conditioned to operate. on, the first channel frequency fl and when relay 5 0 is picked up the transmitting apparatus is con-a ditioned to operate on the second channel fre: quency f2. It is also apparent that-voice frequency voltages appearing in the secondary winding l5 -of microphone transformer TL cause through the reactance tube Vl, a corresponding frequency modulation of the carrier created by the oscillating circuit for tube V2, and such free quency modulated carrier current is amplified; to a predetermined energy levelandapplied to:.the sending loop circuitof the caboose, such sending loop circuit including the track railsbetween the wheels 41 and 48 withtheresult that the com-1 munication current is made to flow in a'track-t way transmitting circuit or channel including the rails and paralleling line wires in the well-known manner. Since a smaller per cent frequency-swing is needed for the same absolute frequency-swing at the higher channel frequency, and since less .oscillator capacity is used, the potential dividerl40 is interposed-in the gridcircuit of tube VI when relay 50 .is released to condition thetransmitter for the higher frequency fl and it is by-pass'ed when relay 50 is picked-up to condition the trans-, mitter for the lower frequency f2." Inthis manher the same voice current produces the same ab solute frequency swing for both channel fre;

quencies. v r I shall now describe themicrophone circuit network with the sensitivity adjustment ,pre emphasis, and modulating indicationfeatures.

A microphone 63 of a hand set HS of the con-, trol unit CU has one terminal connected, to ground electrode 64 and its other terminal connected through wire 65 to a so-called L-pad66, the pad 66 being connected to ground through an impedance unit consisting of a capacitor- 61 and a resistor 68 in multiple, and beingconnected through a circuitconnection including choke coil 69 to the terminal N32 of the current source, Consequently the microphone network isf ener gi'zed from the 32 volt current source, the proper value of microphone current being obtained by the correct value of the resistance of choke coil 69. Primary winding I4 of the microphone transformerTl is connected to a terminal of the pad 66 through a back contact 10 of the relay Hand to one terminal of coil 69. This L'-pad 66 is so constructed that it' presents a substantially con stantresistance to the "audio frequencyfcurre nt fl w n n-the-m crophone circuit networkg" nae impedances: of .the' pad :66 and capacitor -61 rot the impedance unit:are chosen tobe of.susbtan-.-. tiallygthe'. same .order' at theshigher voicev fro-.- quency-of say 2400 cycles per second. Then for a lower voice frequency the impedance of capaci-- tor 61. becomes relatively greater-than the resist-' ance componentof the impedance of the. microphone circuit and thecurrents flowing .are pro-- portionately reduced at the lower voice frequency. Thus at,600 cycles, the impedance of capacitorfi'l would be about four times as great as the resistancelcomponents of the circuit and the current flowingwould be proportionately reduced. Re sistor 68 having about the same impedance as capacitor vElfat 600.cycles, is shunted around capacitor Bl hand the sensitivity is maintained relatively constant at the reduced level for the low voice-frequencies. Since pad 66 is chosen to have a constant input impedance, changes of ad:- justmentiwill not change the pre-emphasis characteristic of the microphone circuit network.- Thus-.voice frequency voltages created in the microphone network are applied to the controlgridof the reactance-tube VI at a preselected amplitude such that an operator speaking very loud into the microphone will not over swing the oscillations of the oscillating circuit for tube V2.

The --modulation indicating feature includes tubes V6 and-V'l and an indication-lamp 11 located in the control unit CU. The tube V6 receives. power from the microphone circuit net work, a connection extending from the high voltageside of the secondary winding l through wire .'|'l and grid leak unit 12' to control grid 13 of tube V6, cathode M of tube V5 being -connectedto groundelectrode 20. The plate 75 of tube. V6 receives power from terminal B400 through'front contact'24 of directional relay 25, wire 26, resistors 21 and 28, wire 18 and resistor 19; The plate circuit of tube VB is'resistance coupled to the control grid 88) of tube V! through capacitor 8i and the plate 82 of tube V1 receives power from the power source through abranch connection from wire l8, -resistor 83 being interposed in the connection. Lamp 7! is preferably a glow discharge tube, such as a neon tube, and it has one terminal grounded and its other terminal connected to the plate 82 of tube V! through wire l3 and a blocking capacitor 84. It follows that voice frequency voltages appearing in the input-circuit of the'reactance tube V! are also applied to tubes V6 and V1 and a corresponding amplified voltage is applied to the lamp 11. The parts are proportioned so that a voice volt age-of a predetermined magnitude sufiicient to satisfactorily modulate the carrier generatedby the oscillator tube V2 causes the lamp 11. to flash. Voltages below such predeterminedmagnitude will leave the lamp 17 dark. Thus, the sp eal ier by observing lamp ll can tell whenhe isspeak-. ing atthe correct loudness. It is tobepointed out that the .microphone circuit network is ad: justecl at pad. Bliso thatthe background noiseof usual magnitude will notcreate voltages suflicient to properly modulate the carrier frequency, but that voice frequencies above the energy level-of the backgroundnoise causes proper operation'of the'transmitting apparatus and such magnitude of voice frequencies is required, to flash the am flt.

A calling voltage is-applied to the input of the reactance tube VI for modulating thecarrier, by the calling means,.th'e calling voltagebeing of afrequency preselected to be of a diiferent tone iqr ucha pgl- Th tub V6 no ma ly sedtq amplify theindication' energy is switched to serve as arr/oscillator. for-. ;the. calling. means. When calling relay l9:is energized in a. manner to later appear,.-the..=circuit for. primary winding [4 of transformen-Tlis; opened at back .contact 10 sov that thesecondary winding l5 of the transformer may have maximuminductance and minimum powerv factor. An oscillating circuit network is formed by the .t.op.; terminal of winding l5 being connected throughwire H and grid leak unit 72 to,.,the.controlagrid .13 of tube. V6, cathode It beingv connected to an intermediate terminal of winding l5 .throughfront contact 88 of relay l9, platel5 :of .tubeVB being connected to another intermediate; terminal of winding l5 through blocking...capacitor 81; and front. contact I06 of relay .l9,;.and acapacitor 86 being connected between the gridandcplate leads through front contact 85 of relay. l9 to form an oscillator tank circuit. Also, anadditional capacitor is connected in multiple with capacitor 86 through back contact 9t of thefrequency change-over relay 56. That :is, capacitors 86, and90 are connected in multiple in. the tankbircuit .when the channel selector relay 50 isreleased andcapacitor 90 is removed from the tank .circuit when the relay 5!] is pickedup. It isv to be seen from this descrip tion thatwhen calling. relay I9 is picked up and thefrequencychange-overor-channel selector relay 50 is released, thetube V6 functions as an oscillator to apply-oscillations of a preselected tone frequency to the reactance tube VI and the carrier is frequency modulated according to this tone frequency to provide a calling current which is suppliedtothe .trackway transmitting circuit through the sending loop circuit; When relay l9 isipickedup and the relay 50 picked up, the tube V6 is caused to serve as. an oscillator to supply a tone frequency for modulating the second channel frequency .f2,:the second tone frequency being different from that-supplied for the first channel. It is, to be..-noted that during such calling conditions, the .voltage appearing at the plate of tube V1 would be sufficiently high to excite the indication; lamp 11, causing a constant illumination thereof.- However,- under such conditions, illumination of the. lamp is not detrimental.

.Theemergencycalling means for alternating switching tube V6 to serve as an oscillator to provide the .callingtone for the first channel fl and therrto provide the calling tone for the second channel f2 and to alternately repeat such operation will bemore-fullyexplained when the operation of the apparatus is described.

The. receiving apparatus comprises two complete receivers designated receiver Fl and receiver.F2; respectively,-receiver- Fl being used for reception of .current of the channel frequency II- and receiversFz being used to receive current of the second channel frequency f2, These receivers-are alike except for'the tuning and each may beof-any one. of several well-known arrangements; Each of the. receiverspreferably includes as essentialelements a high frequency amplifier, a converter,.an intermediate frequency amplifier, a limiter, anda discriminator. Each of these essential. elements, of the receiver is shown in block-form for. the sake .of simplicity because the specifiostructure of each of these elements forms noupart. of my. invention and they may be of any one ,ofisevera-liwellsknown arrangements.

Two pick-yup coils:.92.:and.93. are mounted on the caboosefor inductive relation with the trackwaytransmittingcircuit to pickup frequency 7 modulated carriericurrentiapplied to such trackway circuit at a remote station. -These twopickup coils 92 and 93 are connected to the input side of the high frequency'amplifiers of the receivers Fl and F2, respectively.

The output of each discriminator of the two receivers is connected to a control grid of one section of a duo-triode tube V8, as willbe readily understood by an inspection of Fig. 2. The plate circuits of the two sections of tube V8 are pow ered from the terminal B400 of the current source through proper resistors aswill'bealso'readily understood by an inspection of the drawing. The two plate circuits are coupled in multiple through capacitors 98 and Illl' to a control grid 94 .of a loud speaker amplifier tube V9, such connections of the plate circuits being described more fully shortly. Cathode 95 of tube'V9 is connected to ground through a biasing unit 96, and the plate circuit of tube V9 includes a winding of a transformer T4 to a secondary winding of which transformer a loud-speaker LS is connected.

When the hand set HS ofthe control unit CU is placed on the hookfswitch Sl to close contact 97 and a triple-pole.double-throw switch S2 is thrown to the left, that is, to theposition illustrated in the drawing','j;the couplingconnection from the plate circuit'of the "right-hand section of tube VB as viewed in the drawing'iscompleted through capacitor 98 contact blade 99 of switch S2, contact 91 of switch S'l, a'pre s'elected portion of a volume controlresistor I90, andcontrol grid 94 of tube V9. Also, the coizplingponhection for left-hand section tr mps; V8... can ,betraced through capacitorIULcontact [blade I02 of switch S2 and volume control resistor.v I09 tocontrol grid 95 of tube V9. When the switch" S2, is thrown to the right the connection of the left-hand section of tube V8 to tube V9 is, then through contact blade 99 of switch s2 and'thecontact 91 of the hook switch SI, andjthe connection of the righthand section of tube V9 to tube V9is' through the contact blade I02 of switch S2. Consequently when calling current is picked up by either pickup 001192 or 93, such calling Icurrent is amplified and demodulated and the respective tone frequency current is applied to .the loudspeaker, the tone sounded by the loud-speaker depending upon the channel frequency. When the switch S2 is thrown to the. left and the hand set'HS is removed from the hook/switch vtheleft-hand section of tube V8 remains connected to the tube V9 to sound a calling: current sent on the'channel frequency f2 but the outputof the receiver Fl is disconnected from the tube V9 and is connected to the earphone lll'l of the hand set,this connection being completed'through the .contact I03 of the hook switch and a volume control resistance let. Similarly, when the switch S2 is thrown to the right and the hand set, is removed from the hook switch the receiver Fl remains connected to the loud speaker to sound'a callingcurrent sent over the frequency channel f-I .but'the output of receiver F2 is disconnectedfromtheloud-speaker and the earphone of the hand set is connected to the output of this receiver F2, the connection now including the contact I93 of the'hook switch and the volume control resistor I ll8.j The volume control resistor I99 is preferably provided with stop i539 so that the sensitivity of the loud-speaker cannot be reduced below a desired limit.

The switch S2 also serves to determine the frequency channel of the transmitting-apparatus.

When switch S2 'is thrown to'the'left a circuit is prepared for terminal N32 through contact blade I 10 I I l-, wire I ll, front contact I I8 and transfer contact II5 of a continuity transfer type of contact of relay 15, wire H6 and winding of frequency change-overrelay 50 to ground, and relay 59 is normally deenergized to condition the transmittingfor channel fl. The relay 59 can be picked up and the'transmitter conditioned for channel )2 by the energizing of relay 16 when switch S2 is thrown to the left. With switch S2 thrown to the right a circuit is formed from terminal N32 through'blade Ill, wire lI3, back contact H4 and transfer contact I I5 of relay 16, wire I I5 and winding of relay 5D to ground, and relay 5!] is normally picked up to-condition the transmitter apparatus for channel f2, but relay 50 can be released and the transmitter conditioned for channel fl by th picking up of relay it.

Also, when the frequency control switch S2 is thrown to the left to establish channel fl, current flows from terminal N32 through blade III and lamp III! to ground and lamp III] is illuminated to indicate the use of channel fl. Similarly, with switch S2 thrown to the right, current flows through lamp 2 and that lamp is illuminated to indicate the use of channel 2.

It follows that switch S2 serves as a frequency channel control device, the'left and right-hand positions of switch S2 selecting channels fl and f2; respectively. Such selection can be reversed, however, by relay I6.

I will next point out the circuits which reduce the sensitivity of the receiver of the channel in use during the time of transmission at the same station. Assuming that communication is being carried on through channel fl, a shunt circuit is formed across the" output side of the high fre- 'quency amplifier of receiver Fl, such shunt circuit being traced from one output terminal of the high frequency amplifier through resistor H9, wire I20, back'contact I2l of relay 50 and front contact I22 of relay 25 to ground, the other output terminal of the high frequency amplifier being also grounded. The-resistor H9 is proportioned so that during the sending period of the trans- Initter TA, the energy picked up by the coil 92 and'applied to the receiver Fl is shunted sufficiently for the energy heard in the earphones tobe at about thesa'me level as that during the transmission from a remote station. In a similar manner if communication is being carried on through channel f2, a shunt circuit is completed across the output side of the high frequency amplifier of the receiver F2 during the sending period of the transmitter; this shunt circuit extending from one output terminal of the associated high frequency amplifier through resistor 123; wire I24, front contact I25 of relay 50, front contact I22 of relay'25 and to ground, the other output terminal of the respective high frequency amplifier being grounded, It is clear, therefore, that'these shunt circuits cause a reduction in the sensitivity of the receiver during transmission and each receiver will provide a satisfactory tell-tale sound in the earphones of the hand set, such sound serving to indicate the operativeness of the transmitting apparatus' and of the receiving apparatus then in use.

Referring to Fig. 3, there is disclosed means for coupling the transmitting apparatus TA and the receiving apparatus RA of a wayside station WS t'o'th'e transmitting channel. The transmitting apparatus TA andthe receiving apparatus RA are shown in Fig.v 3- in block form, "each of these apparatuses being similar to the corresponding ppafhtus of Figs. 1 and 2. A line wire Ll extends along the railway in eit-her or bothdirections from station WS and thisline wire may be an existing wire included in some present circuit or-it may be a wire placed on a pole line to serve as a part of the transmitting circuit. 7

' Secondary winding 46 of output transformer T3 of apparatus TA is connected between line wire LI and ground through "contacts of the frequency change-over relay 50. Substantially the full winding is included-in this connection when relay 56 is picked up to close front contact 62 and a preselected portion ofwinding 46 is included in the connection when relay 50 is released closing back contact 49. Thus a larger voltage is applied to the transmitting circuit at the lower channel frequency f2. I

Since noise level is higher and- Government regulations permit a given strength of-energy at a greater distance from the line wire carrying the current for the lower frequency, more turns of the A output Winding can be used at the lower frequency. It is not necessary ordinarily to tune this output circuit at a wayside station since the line wire presents an'impedance with a relatively large resistive component. "Tuning can, of course, be used if desired.

The receivers ;FI and F2 are coupled to the transmitting circuit through pick up coils 92" and 93 which are disposedin inductive relation to line wires L I.

Fig. 4'discloses a'second form of coupling the apparatus of'wayside station WS to the trackway transmitting'circuit, Line'wires L2 and-L3 extend along the railwayin either or both'directions from station WS and serve as elements of the transmitting circuit in the usual manner. These line wires L2 and L3'may be used in some other existing circuit. Two capacitors I45 and H are connected inseries-across wires L2 and L3,'the full winding 46 of output transformer T3 is connected between the'junction terminal of capacitors J and I46 and ground through front contact 62 of frequency change -over relay 50, and a preselected portion of winding 46 is included in this connectionthrough back contact 49 of relay 5%. Thus the voltage applied to the transmitting apparatus TA of the transmitting circuit is of a value preselected according to the channel frequencyused.

In Fig. 4 theinput terminals of receivers Fl and F2 are connected between the junction terminal of capacitors I45 and I46 and ground. It is clear that in Fig; 4 the wayside apparatuses are capacity coupled to the transmitting circuit. It-is apparent-that-inductive coupling can be used in Fig: 4 either by inductive coilswound in'inductive relation towires-LZ and L3'or another wire extending some distance-parallel to wires L2 and L3. 1 A g In; describing the-operation of the apparatus, I shall first consider Figs. 1 and- 2 and shall assume that the apparatus occupies its normal position, that is, the position illustrated in the drawings. At the start it is to be observed that the filaments-of the various tubes are all heated through suitable filament circuits notshown. Under this normal condition calling current may be picked up by coil92 due to some remote station sending out a calling current of the channel frequency fl. -Theenergy thus picked up is supplied to the receiver Fl and after amplification and demodulation, the tone frequency current is -applied to tube V8 and thence to tube V9- and to the loud-speaker whichsounds the calling tone to-inform' the operator that communication is desired on the-channel frequency fl. -Similarly, if energy is picked up by the coil 93 due to a 'remote stationsending a calling currentof the channel frequencyf2 the pickedup energy is applied to the receiver F2 and after amplification and demodulation :the tone current is applied through tubes V8 andVS to the loud-speaker and the-operator is-in'formed that communication is desired on channel f2; the operator distinguishing between the channlsby the different tones of the calling currents.

Assuming first that thecalling tone is for channel fl, the operator would set switch-S2 to the left if it is not already in that position and would remove the handset HS from the hook to connect the hand set to the output of the receiver Fl leaving the receiver F2 connected to the loudspeaker. The operator after removing the hand set from the hook'switch presses the press-totalk switch 5 on' the: hand set and'speaks an agreed salutation into the microphone 53. The closing of the press-to-talk switch 5 completes the connection for current to flow from battery terminal B32 to ground electrode 64 switch 5, wire E25 and Winding of directional relay 25 to battery terminal'N32; and the directional relay 25 'is picked up. The'picking up of relay 25 to close front contact 24 applies plate voltage to the tubes of the transmitting apparatus, and the closingof front contact I22 of'relay 25 applies the shunt circuit across the receiver Fl, so that the transmitting apparatus excited and the receiver Fl is'reduced insensitivity. With the tubes 'of the transmitter energized voice frequencies created by speaking into the microphone 63' are applied to tube Vl with the result a frejquency' modulated carrier telephone current is applied-to the loop circuit and thence to the trackway transmitting circuit for transmission to remote stations. Such energy is also picked up by pick-up coil 92 and applied to respective receiver'Fl' and the voice frequencies are reproduced at a reduced energy level in the respective earphone 101 of the associated hand set to check the operation of the apparatus. From this point ontwowaycbhvzrsation can be carried on between'the operator of the caboose and the remote station by the operator properly operating the press-to-talk switch 5.

It is clear that during sucha conversation through the communication channel fl, calling current can be received on the channel f2 and such calling tone 'soundedby the loud-speaker, such calling serving as a break in.

Assuming next "that the calling current picked up is that 'for the channel f2,' the operator to answer such call would first throw the switch S2 to" the right and then remove'the'hand set HS from the hook. The throwing of the switch S2 completes the"circuit for the frequency change-over relay 50 andthat relay picks up and conditions the "transmitting apparatus for operation' on-the "channel frequency f2. The removal of the handset 'from'thehook connects it to the output of the receiver F2- leaving the receiver Fl connected to the loud-speaker for sounding any call that may be thereafter received on that channel. From this point on the caboose operator can answer the call and carry on a conversation with a remote station through the channel f2 in substantially thesame manner as explained in connection with the communication on the channel fl.

In connection with communication on either channeL-thespeaking at proper loudness by the 13 operator will be indicated by the flashing of lamp TI in the manner explained hereinbefore.

If a conversation is being carried on through one channel and a call is received through the other channel, such call can be immediately answered by the reversing of the switch S2. Also, the channel in use will be indicated through the lamps III) and II2 of the controlunit In the event the operator on the caboose desires to initiate communication, he first sends a calling current corresponding to the channel through which he wishes to communicata-selection of the channel being effected bythe proper position of the switch S2. The operator would then depress a push button KI of the control unit to close contacts I2! and I28. The closing. of contact I21 of push button KI completes the circuit for energizing relay 25 and that relay on picking up applies power to the tubes of the transmitting apparatus. The closing of contact I28 of the push botton KI completes a circuit for current to flow from battery terminal B32 through ground electrode I29, winding of relay I9, wire I30 and contact I28 to battery terminal N32, and relay I9 is energized. The picking up of relay I9 switches tube V6 to serve as an oscillator and oscillations of thecalling frequency for the channel selected are applied to the reactance tube VI to modulate the carrier and. a corresponding calling current is applied to the trackway circuit through the caboose loopcircuit. Subsequent to the proper answer back of such a calling current the operator would remove the hand set of the hook switch and carry on a conversation in the manner previously explained.

In the event the caboose operator wishes to send an emergency calling current, that is, a calling current alternately on each of .the two channel frequencies, the operator depresses: a push button K2 Of the control unit closing contacts i3I, I32 and I33. The closingof contact I3I completes the circuit for relay I9 and relay I9 on picking up switches the tube V6 to serve as an oscillator. The closing of contact I33 of the push button K2 completes the circuitfor relay 25 and that relay on picking up applies power to the transmitting tubes. The closing of contact I32 of the push buttonKZ completes a circuit for relay 16, the circuit for relay 16 extending from positive terminal B32 through" ground electrode I34, back contact I35 of relay I6,winding of that relay, wire I36 and contact I32 to terminal N32. A capacitor I3! is connected across the winding of relay Iii to cause this relay to beslow acting. Since relay IE is controlled throughits own back contact I35, this relay will alternately be energized and deenergized. The circuit for changeover relay 53 is controlled through the contacts H4, H5 and H8 of the relay I6 and thus with relay I3 alternately energized and deenergized, the relay 5!! in turn is alternately picked up and released, and relay 50 when released conditions the transmitting apparatus to operate on channel frequency f I and when picked up conditions the transmitting apparatus to. operate on the channel f2. It follows, therefore, that as'long as the push button K2 is held depressed, the'relay 16 causes the transmitting apparatus to be alternately conditioned for sending a calling current first on the frequency channel fl and then on the'frequency channel f2. Such emergency callingi'condition would be useful when it is desired tocall all trains with some of the trains carrying'on a communication through channel fl and'other' trains carrying on a communication through'channelifil.

- Communication between an operator at. the wayside station of either Fig. 3 or. Fig. 4 and a train would be carried on in substantially. the same manner as just explained in connection with the station in caboose CO.

Apparatusv such as here disclosed has the advantages that trains can carry on a conversation on the different channels without interference between different trains. A call can be received on a train on any one of the channels and a call can be received on a train on the channel not in use to serve as a break in. Also, any station can call all the trains irrespective of what channel they may be at the time carrying on communication through the emergency calling condition which alternately sends pulses of calling current on the two channel frequencies. Furthermore, the usual background noise created at locations on a train is suppressed and preemphasis is provided by adjustment of the microphone circuit. Proper speaking during a conversation is indicated to the operator. Checking of the integrity of the transmitting apparatus and of the receiving apparatus is provided and the use of frequency modulation assures that noise created by static conditions is avoided.

Although I have herein shown and described but one form of railway train communication systems 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 .iHaving thus described my invention, what I claim is:

1. In a railway train communication system for communication between the trains of a division of the railway through a common transmitting medium and by use of currents of different carrier frequencies, a plurality of stations at least one for each train, each said station provided with communication equipment and which equipments are substantially alike for all stations; each said equipment including transmitting apparatus, re 'ceiving apparatus, a frequency selector means and a telephone set; said transmitting apparatus having elements electrically coupled to said transmitting medium and including means capable of being differently conditioned to supply carrier telephone" current'of different carrier frequencies, said receiving apparatus including an individual receiver for each of said different carrier frequencies, each said receiver including an element electrically coupled to said transmitting medium and each having means operable to demodulate carrier telephone'current of the respective carrier frequency, each said receiver normally active for 'each station to be ready to'receive on any one of said carrier frequencies, and said selector means including circuit controllers operable to different positions and circuit-s connected to the transmitting and receiving apparatuses to preselect the condition of the transmitting apparatus and to effectively connect said telephone set to the receiver for the carrier frequency corresponding to the selected condition of the transmitting apparatus; whereby each station is enabled to communi'cate with any one of the other stations on any one of said plurality of carrier frequencies and a plurality'of noninterfering two-way communication can be carried on simultaneously between a plurality of different pairs of said station's.

In a railway train communication system for communication between the trains of a division o'f t'he' railwaythrough a common transmitting medium'arld" by use ofcalling and' telephone "currents of a plurality 'oi different carrier frequen cie's, a plurality orstations at least one for each train; each said-station provided with communication equipment and all of which equipments are substantially identical; each said equipment including transmitting apparatus, receiving apparatus; control means -a loud-speaker"and" a telephone hand set; said transmitting apparatus having elements electricallycoupled to said transmitting medium and including" means capable of being"difi'erentlyconditioned to supply a carrier telephone current of a-first or a'second carrier frequeh-cycr a calling current of either said carrier frequencies modulated by an individualtone frecru'ency;v said receiving apparatus including: an independent receiver for each of said carrier fre quenciesweacli said receiver including a' pick-up element electrically coupled" to said transmitting medium and each-having means which'is normally active-fordemodulating the telephone and cal-ling currents of the respective carrier frequency; andsaid control means including contacts operable to dififerent circuit arrangements tomor-m-ally -connect said receivers in multiple to said loud-speaker at a given normal arrangement or itsccontacts and toselectively condition the transmitting apparatus to supply calling and telephonecurre'nts of apre'selected one of the carrier frequencies 'and'connectth-e telephone set to the receiver ofsuch selected carrier frequency and the-loud=speaker-to -the receiver of the non selected carrier at diiTerentgiven operating ar rangements of-its-contacts', whereby each station can be called by any one of the other stations through its loud-speaker on either ofsaid carriers andcommunicate by telephone through its telephone'set with-the calling-station and at the same time beincondition to'receive a call or message through its loud-speaker from any one of the otherstations.

'3. 'In arailway train communication system for communication 'betweenthetrains of a division of the railwaythrough a common transmitting medium, a 'pluralityof stations at least one for each train; a plurality of substantially like commu-nication equipments one at each of'said-statiohs and each of' which equipments includes a multiple frequency channel transmitting apparatus; a, multiple frequency channel receiving apparatus, a-telephone set and a channel selector means; said transmitting apparatus having elements-electrically coupled to said transmitting medium and including devices which are capable of-beingdifierently-conditioned to supply carrier telephone current of any one of the channel irequencies; said-transmitting apparatus at each station being normally inactive, said' receiving apparatus-including an independent receiver for each "of-said channel frequencies, each said 'receiver'having an element electrically coup-led to saidtransmitting medium and including devices which are operable to detect thetelepholie current of therespective channel frequency, each said receiver at each station being normally active,- said selector means including controllers operable todifferent positions anda circuit-network ha-ving connectionsto the transmitting and receiving apparatuses to preselect the condition of-saidtransmitting apparatus and to efiectively connect said telephone set to the transmitting apparatus and to the receiver of the channel frequency corresponding to the selected condition ofthe transmitting apparatus, and a push-to-talk means at each said'station operable to selectively actlVatethe transmitting apparatus and the re ceiver with which'the telephone set is connected, whereby a plurality "of two-way telephone communications canbe-carried on simultaneously between different pairs or said trains without in terferen'ce between the different conversations.

i. In a railway train communication system the combination comprising; an electron tube oscillatorincluding an oscillating circuit and an electron tube provided with input and output electrodes, said tube electrodes connected to the oscillating circuit in such amanner as to generate a carrier frequency current, a, reactance electron tube provided with output electrodes and a control electrode, said output electrodes connected to the oscillating circuit of'said oscillator to frequencymodulate the carrier according to voice frequenciesapplied to the control electrode of said reactancetube; a circuit network including a microphone, aresistance pad and a transformer and connected'to said control electrode of the reactancetube to apply voice frequencies to said control electrode; 'saidbircuitnetwork proportioned to suppress background noise below a given level, and indication means including a voice frequency energy responsive device and connected to said circuit network to indicate when the energy applied to said control electrode is above said given level to indicatecor'rect loudness ofspeaking into'sai'cl microphone for satisfactory transmission of the corresponding frequency modulated carrier telephone current.

5. In combinationjrailway train communication receiving" apparatus-Tor reception of the telephone and "calling currents of a plurality of different carrier fre uency channels, said receiving 'apparatus comprising an independent receiverfor eachof's'aid channels, aloud-speaker, an earphonegeachsaid receiver having input and output circuits" and-including a demodulating device capable of demcidulating the telephone and the'calling currents'of therespective carrier frequency channelg-and manually operable switching' means having a first-position to connect the output circuits of said receivers in multiple to said loud=speaker-tosouhdthe calling tone of the calling currentor the speech of the telephone current of any of said channels, and saidswitching"means having other positions to connect the output circuit of any selected one of said receivers to said earphone with the output circuits of the remaining receivers connected to the loudspeaker only to permit telephone communication through the channel of the selected receiven'the calling tone and spe'ech of any of the other channels being sounded at the loud-speaker.

6-. -In railway traincommuhication apparatus for reception- 0f a'plurality' ofdifferent carrier telephone currents, the combination comprising, a plurality of difierent-receivers one for each of said different telephone *currents, each said reoeiver'having input and output circuits and including means capable of'demodulating the respective carrier telephone"current, pick-up elements one connected'to the input circuit of each of said receivers, a loudespeaker, a telephone handset having a hook switch, and manually operable switching meansto cooperate with said hook switch to normallyconnect in multiple the output circuits of-said receivers to said loudspeaker and to selectivelyeonnect the earphone of the hand set to the output circuit of any one of said receivers andthe output circuits of the remaining receivers'in multiple to'th'e loud speaker. 7..*Incombination;transmitting apparatus ill-'- eluding a modulator-oscillator, a microphone and a calling tone generator and which modulatoroscillator and tone generator are capable of being differently conditioned to supply carrier telephone current of any one of a plurality of different carrier frequencies and a calling current for each of said carrier frequencies, each said calling current being the carrier modulated with a predetermined tone frequency, a first manually controlled means having circuits connected to the transmitting apparatus to govern the conditions of the transmitting apparatus to preselect the carrier telephone current to be supplied, a second manually controlled means having circuits connected to the transmitting apparatus to govern the conditions of the transmitting apparatus to preselect the calling current to be supplied, and a third manually controlled means having circuits connected to the transmitting apparatus to govern the conditions of the transmitting apparatus to cause the calling currents to be supplied in a cyclic manner.

8. In combination, transmitting apparatus including a modulator-oscillator a microphone and a calling tone generator and which devices are capable of being differently conditioned to supply carrier telephone current of either a first or a second carrier frequency and a calling current of either of said carrier frequencies, each said calling current being the carrier modulated by a predetermined tone frequency, a first control relay operable to a first and a second position to govern the conditions of the transmitting apparatus to preselect the carrier frequency to be supplied, a second control relay operable to a first and a second position to govern the conditions of the transmitting apparatus to preselect the supplying of telephone current or'of calling current, and a third control relay capable of code operation to govern the conditions of the transmitting apparatus to supply the calling currents alternately.

9. In combination, an electron oscillator tube having input electrodes and output electrodes which are connected to an oscillating circuit to generate a carrier frequency current, an electron reactance tube having a control electrode and output electrodes and which output electrodes are connected to said oscillating circuit to frequency modulate the carrier according to the voltages applied to the control electrode of the reactance tube; a circuit network including a microphone, a resistance pad, and a'trans'former connected to said control electrode to apply voice frequency voltages forfrequency modulating said carrier; said circuit network proportioned for only voice currents above a predetermined energy level to be effective for modulating the carrier to suppress background noise, and indication means includin an amplifier and an indicatorconnected to said circuit network to indicate voice currents above said predetermined energy level.

10. In combination, an electron tube oscillator having input and output electrodes which are connected to an associated oscillating circuit to generate oscillations of a predetermined carrier frequency, an electron reactance tube having a control electrode and output electrodes and which output electrodes are connected to said oscillating circuit to frequency modulate the oscillations according to voltages applied to the control elec-- trode of said reactance tube; a circuit network including a microphone and an impedance unit connected to said control electrode to apply voice frequency voltages for supplying in the output of said oscillator a frequency modulated carrier telephone current, and indication means including an amplifier electron tube and an indicator lamp connected to said circuit network to illuminate said lamp only when the voice current of the network is above a predetermined energy level.

11. In combination, an electron tube oscillator having an electron tube which is provided with input and output electrodes that are connected toan associated oscillating circuit to generate oscillations of a predetermined carrier frequency, an electron reactance tube having a control grid and output electrodes and which output electrodes are connected to said oscillating circuit to frequency vary the oscillations according to voltages app-lied to the control grid of the reactance tube; a circuit network including a, microphone, a resistance pad, an impedance unit and a transformer connected to said control grid to apply at times voice frequency voltages to said control grid for supplying in an output circuit of said oscillator tube a corresponding frequency modulated carrier telephone current, and said resistance pad and impedance unit proportioned to pro-emphasize the higher voice frequencies.

12. In combination, transmitting apparatus including an electron tube oscillator having an electron tube provided with input and output electrodes and an oscillating circuit, said oscillating circuit connected to said tube electrodes in such a manner as to generate carrier frequency current, said oscillator capable of being differently conditioned to supply carrier current of either a first or a second frequency, control means having connection to said transmitting apparatus to govern said conditions, an electron modulator tube having a control electrode and output electrodes, said output electrodes being coupled to said oscillator to frequency modulate said carrier frequencies according to the voltage applied to the control electrode of said modulator tube, a circuit network including a microphone connected to said control electrode to apply voice frequency voltages thereto to frequency modulate whichever carrier is being supplied, and a potential divider including resistance interposed in said circuit network and governed by said control means to control said voice frequency voltages to effect substantially the same absolute frequency swing in the modulations of said carrier frequencies.

13. In a railway train communication system for communication between a wayside station and trains operating over a given territory of said railway through a transmitting circuit which includes a line wire extending along the trackway, the combination comprising, a wayside transmitting apparatus including means' capable of being differently conditioned to supply carrier telephone current of a first or a second carrier frequency, said transmitting apparatus coupled to said transmitting circuit by being connected to said line wire and ground, and control means interposed in said connection to apply to the transmitting circuit a voltage predetermined for each said carrier frequency and which voltage is larger for the lower of the two carrier frequencies.

14. In a railway train communication system for communication between a wayside station and trains operating over a given territory of said ing means capable of being differently conditioned to supply carrier telephone current of a apparatus including means operable to demodulate such carrier telephone currents, two capacitors connected in series across a pair of said line wires, a first connection to connect input terminals of said receiving apparatus between a junction terminal of said capacitors and ground, a second connection to connect output terminals of said transmitting apparatus between said junction terminal and, ground, and said second connection including control means to apply to the transmitting circuit a voltage predetermined'for each condition of the transmitting apparatus and which voltage is larger for the lower of the two carrier frequencies.

15. In a railway train communication system which provides equipment on all or nearly all of thetrains of a division for telephone communication on either a first or a second frequency channel and for each of which channels a carrier telephone current and a calling current are provided, each said equipment including transmitting apparatus and' receiving apparatus, each said transmitting apparatus havin means capable of being conditioned to supply the'calling current for each said frequency channel with each said calling current having an individual characteristic, each said receiving apparatus including two independent receivers one for each said frequency channel, each said receiver having means for detecting the calling current and the carrier telephone current of the same channel, the receivers of each of said trains normally active to detect the calling current of the respective frequency channel and each receiver capable of being conditioned to receive the telephone current of the respective frequency channel, control means for each such train, and each control means having circuits connected to the transmitjting apparatus and including a controller operable to' at times'condition' the transmittin 'apparatus of the same train to supply the calling currents of said first and second frequency channels alternately to call all trains when some of the trains are telephoning on one frequency channel and others on the other frequency channel. 16. In combination, transmitting apparatus including means capable of being conditionedto supply telephone current of any one of a plurality of different frequency channels and a calling current for each said channel and also an emergency calling circuit, each said calling current having an individual characteristic, a first control means including a controller and circuits connected to the transmitting apparatus and operable to different positions to control said trans mitting apparatus to preselect the frequency channel, a second control means including a controller and circuits connected to the transmitting apparatus and operable to different positions to control said transmitting apparatus to supply the calling current for the channel preselected by said first control means, and a third control means including a controller and circuits connected to the transmitting apparatus and operable to control the transmitting apparatus to supply an emergency calling current of a distinctive characteristic irrespective of the position of said first control means.

17. In a railway train telephone system for two-way communication between different train carried stations each of which stations is equipped with a telephone transmitter and a receiver using a carrier frequency telephone current, the combination comprising, push-to-talk receiver of the station for reception and to deenergize the transmitter, generating means at a station capableof supplying oscillationsof a preselected tone frequency but normally inactive, circuit connections to connect said generating means to the transmitter of the same station to modulate the carrier by said oscillations, a circuit interrupter device normally deenergized, means including contacts of said interrupter device connected with said generating means to cause the generating means to recurrently supply said oscillations to create a distinctive signaling current of the modulated carrier, and control means having circuits and a circuit controlling switch operable to at times energize said transmitter, to render said generating means active and to energize said circuit interrupter device to sound at the receiver of each of the associated stations a distinctive signal.

18. In a railway train communication system for telephone communication between the trains and selected wayside offices of a railway by use of a common transmitting medium and by the use of calling and telephone currents of a plurality of different carrier frequency channels, a communication station on each of the trains and at each of the ofiices, each said station provided with communication equipment all of which are substantially alike to enable any one of the stations to communicate with any other one of the stations; each said equipment including transmitting apparatus, receiving apparatus, selector means, a control circuit means, a loud-speaker and a telephone set; each said transmitting apparatus including a transmitter having means capable of being difierently conditioned for supplying calling and telephone currents of any one of the plurality of different carrier frequencies, each said transmitter having an element coupled to the transmitting medium but normally inactive, each said receiving apparatus including an individual receiver for each of the different carrier frequencies, each said receiver having -means operable to demodulate the calling and telephone currents of the respective carrier frequency, each said receiver having an element coupled to the transmitting medium and normally active, the receivers of each station having their outputs connected in multiple to the loudspeaker of the same .station to enable each station to receive a call from any one of the other stations on any one of the carrier frequencies, each said selector means including a controller operable to different positions and circuits connected to said transmitter and receivers to select by its position and condition of the transmitter of the same station and to connect the telephone set to the receiver of the station for the carrier frequency corresponding to the carrier frequency of the selected condition of the respective transmitter, the loud- =speaker being disconnected from the selected redifferent carrier frequency channels to enable 'each vehicle to telephone to any other vehicle by use of a common transmitting medium, communication equipment on each said vehicle and all of which equipments are substantially alike; each said equipment including transmitting apparatus, receiving apparatus, a telephone set and selector circuit means; each said transmitting apparatus including means capable of being difierently conditioned to supply carrier telephone current of any one of the plurality of difierent carrier frequency channels, each said transmitting apparatus having elements disposed for communication relationship With the transmitting medium but normally inactive, each said receiving apparatus including an individual receiver for each of said different carrier frequency channels, each said receiver including means capable of demodulating carrier telephone current of the respective carrier channel and having elements disposed for communication relationship with the transmitting medium in a normally active condition, each said selector circuit means including circuits connected to said transmitter and receiving apparatuses and operable to different conditions to select by its condition the condition of the transmitting apparatus of the same vehicle and to 22 effectively couple the telephone set to the transmitting apparatus and to the receiver of the carrier channel corresponding to that selected for the transmitting apparatus.

PAUL N. BOSSART.

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

UNITED STATES PATENTS Number Name Date 1,821,758 Konn Sept, 1, 1931 2,064,639 Whitelock et a1 Dec. 15, 1936 2,064,641 Bossart Dec. 15, 1936 2,064,958 Taylor et al Dec. 22, 1936 2,090,088 Whitelock Aug. 17, 1937 2,124,450 Shaver July 19, 1938 2,143,563 Levy et a1 Jan. 10, 1939 2,176,868 Boswan Oct. 24, 1939 2,272,106 Ash Feb. 3, 1942 2,419,593 Robinson Apr. 29, 1947 Certificate of Correction Patent No. 2,484,680 October 11, 1949 PAUL N. BOSSART It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 19, line 52, for the word circuit read current;

and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office. Signed and sealed this 31st day of January, A. D. 1950.

THOMAS F. MURPHY,

Assistant Commissioner of Patents.