US1902817A - Communication with moving trains - Google Patents

Description

March 22g-'1933. H, A. AFFEL ET AL 1,902,817

COMMUNICATION WITH MOVING TRAINS Filed oct. 2, 1929 2 sh'ts-'shgxlfl L Fixed stamm ATTORN EY March 28, 1933. H. A. AFFEL.` Er A1. 1,902,817

COMMUNICATION. WITH MOVING TRAINS Filed oct. 2, 1929 2 sneetssheet 2 6 7 1 T l Mij-i] 15P;

Fzxed Statc'on/ ml Z-IL ATTORN EY Patented Mar. 28, 1933 UNITED STATES PATENT. ori-ICE HERMAN A. AEEEnoE EIDGEWoon, AND ESTILI. I. GEEEYN,v-or EAST ORANGE, NEW JERSEY, AssIGNoRs To AMERICAN TELEPHONE AND TELEeRAPH COMPANY, A

CORPORATION OF NEW YORK coMMUNIoATIoN WITH MOVING TRAINS Application mea member` 2, 192e.` seriai Nofaeasa.

for communicating-with vehicles in motion,

such, for example, as moving railway trains. One purpose of the invention is to make it possibleto communicate simultaneously with a considerable number of trains on the same track and to do so with the minimum amount of apparatus and .with a minimum use of the frequency spectrum. Another purpose of the invention is to increase the reliability* of such communication. Still another purpose is tov make the maintenance of the transmission equivalent's between the land station and the train automatic and not requiring the special attention of an operator either on the train or the land station.

Briefly, the invention consists in using the existing communication lines,l such as telephone or telegraph' lines, or other circuits which extend along therailway,and connect-V ing with the moving train by inductive or capacitive coupling across the air gap. The communication line is divided electrically into separatesections of suitable lengths and fixed stations, each transmitting in twodif rections. The signaling is effected by means of a carrier frequency in order to afford better coupling between the vehicles and the line, and preferably one pair of frequency bands is assigned to each train. The same frequency bands may be employed for trains which do not run simultaneously in the same section.

. By locating the division between two sections at appropriate places, such as importantcities, it becomes a relatively simple matter to provide telephone connections between a train and any subscribers station in an expansive telephone system. This meansa two-wire termination at the land station but on the trainit would be feasible to provide a four-wire sub-set termination, this being possible in view of the limitedv number of vsub-sets involved.

' in connection with the accompanying drawings, in which Figure l shows the manner in which a railroad route might be divided into sections; Figs. 2 and 3 show the manner in which a plurality of telephone or telegraph lines along the right of way may be associated in groups for the transmission of signals;

Fig. 4 shows one specific arrangement for transmission between a moving train and the parallel line, `making use of combined loop and antenna; Fig. 5 shows in greater detail the arrangement of basic apparatus at afiXed station and a cooperating train station; Fig. 6 is a modilicationof Fig. 5;-Fig. 7 shows provision for compensatingfor distance of thetrain from a fixed station; and Fig. 8 gives a schedule arrangement of communica@ tion witha large number of trains 4on the same track with a minimum use of apparatus and frequencyspectrum. Y

- The method of transmission which we have. n. found most suitable for such communication is to transmit at carrier frequencieszover the telephone line lparalleling the track and to use inductive or capacitive coupling for the connection to the train.,` Such an arrangenient' is indicated in Fig. l in which the line along the track is electrically divided into Separatesections a, b, cof reasonable length, say of about 200 miles, it being of course desirablethat the various sections shall be of about the same length, although'no severe restrictions in this direction arenecessary. AtA orinear the center of each of these sections there is 'located a fixed station, such as A, B, C,- adaptedto' communicate with trains in that section but 4with, no other trains." This 'station A' would provide communication in the section between pointsuD and E,station B between points E and F, and station C between points .F and Gr. It will be `noted i that this arrangement does `not provide'any-'- y repeaters 'along'the sections but instead of this the sections are made sufficiently short" so that any fixed station. I iiay communicate directly in both directionsiwith trains in that section. This. evidently covers the :distance with a minimum amount of apparatus, and

circuit arrangementl since it provides at'all times a carrier circuit to the neares'tvfcity along the route and rfrom this point voice.

ka5 we consider this. an important featureof our'` invention. It also Vfurnishes a, convenient 50, be desirablel touse a combined loop and ancircuits can be built up to distant subscribers stations without difficulty.

In order to avoid confusion during the period when the train is approximately equidistant from two terminals, it may be desir.-

able that the transmitting and receiving fre'- quenciesl be inverted at alternate stations. l

There are a number of ways in which the telephone lines may be associated or used for the presentl signaling purposes but there are two which we nd particularly advantageous. In the one we transmit between two separated wires or groups of wires, and inthe second we transmit over a wire or group of wires with ground return. Fig. 2 shows the first Vof these methods. In this figure it will be seen that the wires l, 2, 3 and 4 are adapted for -ordinary telephonie purposes, .being associated further for phantom operation. The same is true of the group of wires 21 to 24. yFor the purpose of the high frequency V signaling now proposed thehigh frequency Vcurrent maybe sent from either the Xed or the moving. station over a metallic circuit, one side of this .metallic circuit comprising the lines l to 4 and the other side comprising the wires 2l to 24. 'Suitable high pass and low pass filters are shown in the figures, and by means of these, proper separation is maintained between the high frequency and the low frequency signal channels.

In Fig.r3 a group of wires 31Yto 34 isused as one side of the high frequency circuit and the ground is used for return. Again suitable high pass and low'pass filters are provided to maintain separation between the different signaling channels.

v In order that the message shall not be picked up unnecessarily by other telephone or telegraph lines adjacent to those which are being used, it may be desirable to introduce into these additional lines suitable loading or choke coils which will prohibit the flow of the high frequency signals. l

As stated above, we employ some form Aof inductive or capacitive coupling with the train. We have found that approximately the same transmission loss is involved with either form of coupling and it maytherefore tenna, thatV is, to use the inductanceof a loop for the transmittercoupling and its capacityto ground for the receiving coupling, or

the reverse. Such an arrangement is shown Y in Fig. 4, in whichtransmission from the 1train takes place vover a loop, that is, by inductive coupling, whereas reception takes place over the loop considered as an antenna,

lthat is,by capacitive coupling.l This mode of yoperation .has an advantage in that it.

greatly reduces the transmission loss which would otherwise berequired in the receiving filterto discriminate against the transmitting frequency range.

i kA more detailed drawing of the arrangement of apparatus at the fiXed station and the train station is shown in Fig. 5. The" line L is connected with any remote subscribers station, and by means of the hybrid coil II is adapted in the well known manner for two-way communication. Incoming low frequency signals over the line L are used to modulate a carrier frequency f2 and, on suit- Y For signaling in the reverse direction the microphone currents at the train station -are impressed upon la modulator supplied with'v carrier frequency f1 and after transmission through suitable protecting filters and amplifiers is impressed on the loop 4. The signals being picked up by the line 3 are then amplified and impressed on a demodulator supplied with a carrier frequencyv f1 and theV demodulated product is then transmitted overthe. line L. v

As the train travels along there will be large and often very sudden-changes in trans-A mission dueto the following causes :v

(l) Changes in separation v,between the train and the paralleling line.

(2) Changes ina vertical direction in the position of the couplingt device withy refers.

ence to the line. .A f l f (3) The presence of another train vbetween the coupling device and the line.Vv

(4) Varying distance from the fixed station. Some of these variations may be eliminated or reduced by using two collectingv sources on' the train, one at the front yand one at the rear. This is especially helpful in the case of thershort departures of the line from the track'such as when the line enters a dispatchers station. In any event, however, we find it important that a pilot channel shall be provided tor stabilize' the transmission. Fig. G showsa fixed anda moving station with a schematic pilot channel for the purvpose described. In this figure there is shown a twoewire termination for the land station, the hybrid coil H makingit possible to carry on two-way signaling with a remote subscribers station. The low frequency incoming Asignal is modulated against alocally generated high frequency carrier, the modulated signal then being amplified at the transmitter-amplifier 6 and impressed on the transmission line through the: high pass filter 7.

Modulatedhigh frequencyssignals coming amplifier 9, thereafter being demodulated and impressed on the line L. A Vprecisely similar equipment is provided on the train station.

In order to obtain transmission level con-` trol we provide a pilot channel consisting of a carrier frequency transmitted from the one station to the other and preferably of a frequency near but not in the signaling band. fo' In F ig. 6 there is shownat the train station at a pilot control transmitter consist-ing of means for impressing on theline the pilot signal. This signal is picked up at the fixed station and transmitted throughsuitable fil- 1*5 ters and a detector-amplifier 11, the output ofthis amplifier being used to control the gain in the amplifiers 6 and 9 by any suitable means. While this pilot 'signal has been shown as being transmitted from the train 2o station, it is obvious that it might be transmitted inthe reverse direction but we'iind itV preferable to have most of the apparatus .for the pilot channel located at the fixed station ,n since itis desirable to have as little apparatus as possible on the train, and it is thus described in the figure. It should be pointed out, however, that with several fixed stations it may be more advantageous to locate the Y `pilot channel receiving apparatus on the ltrain. We do not here describe the operation of the pilot channel control in detail, any appropriate apparatus being permissible such, for example, `as that described in pat- Vent to Clark, No. 1,438,219, of December 12, 351922. However, because of the speed of the train the pilot channel should have almost instantaneous response to large transmission changes and `this we find can best be obtained Aby varying either the B battery on the am- 4oplifier tubes or the grid voltage on the modulator tubes, or both. This may be accoma' plished in any well known manner, such, for instance, as by adding to the regulation batp tery supply a variable positive potential ap- --plied to the grid or a varying negative potential applied to the plate, these potentials varying directly with the rectified current received on the pilot channel. Such methods vof control are described in patents to Affel, 1,511,015, of October 7, 1924, or 1,574,780, of

March 2, 1926.

The pilot channel arrangements thus described are intended primarily to .take care of the variations coming Aunder items 1, 2

and 3 of page 6. It mightalso be used for taking care of the variations coming under item 4; that is, the changes dueto varying distance between the train and a fixed station, which changes will occur gradually. Since it may be difi'icult to take care of all variations with the pilot channel, it will be desirable to relieve the pilot channel as much as feasi-v ble and to this end we nd that the varia tion in transmission level due to varying distance between the train and the fixed station may be compensated by an arrangement simi'-l lar to that shown in Fig. l7. 4This arranger;

ment provides, on the train, transmitting and receiving potentiometers 18 and 19 whichare mechanically connected to a device which in turn is geared to the wheels. This device is;

arranged to make contact at various intervals along the route and-thus move the potentiometers up orfdownone step according to whether the train is leaving or :approaching the fixed station. The points 1, 2 and 301il the path of the vehicle are so spaced that the distance between points equals the total span covered by a single station divided lby the` total number of potentiometerV steps;` A switch or other device set at the beginning of the trip will arrange it so that the gain is increased or decreased as desired. Obviously, many variations on this .may be conceived, for example, instead ofV being operated on ai mileagerbasis yby virtue of being geared to the wheels, the potentiometervcontrol might be operated by fixed devices set at suitable points along the road bed, these taking the 'Y i form of projecting arms, third rails, or vother special arrangements. i

.'The system as described may be operated y with a single carrier frequency for both transmission and reception or with two different carrier frequencies f1 and f2', one for transmission and the other for reception. The second method has the advantage of moredefinite separation of thetransmitted and the received signals,`with corresponding simplification of the terminal apparatus, but it uses twice as much of the frequency spectrum. j Thus far the description of our invention With a `plurality of trains. One method which we contemplate is that of providing a number of differentcommunication channels and arranging for each train to selectan idle channel. The procedure would be analogous to that in general telephone practice where a group of circuits is` provided between two cities, from which the operator selects an idle circuit.' In our system, for example, if coni'- munication were desired wit-h twenty trains,

The system thus far described ico .116 ods are available for such communication iis" it wouldbe necessary to establish four or five communication channels. It is evident, how` ever, that this arrangement requires elabo-l rate and expensive equipmentv on each train in order to make it possible to select any one of the available channels. ForV example, the equipment needed for ringing individual trains we find becomes rather complicated. A second method which We contemplate for our invention, and which provides'for better economy and simplicity, would make use of a different pair of frequencies for each train. Vrlhis method is practicable for 5 a small number of trains, but as-the total number of trains on a given line is increased, the problem yof finding suitable frequency bands ysulliciently separated in that portion of the frequency spectrum where the attenur4 ation would not be excessive, becomes diiiicult. Further1nore,the apparatus at the fixed stations ywould become complicated ifeach of them is equipped to signal on so large a number of carrier frequencies. y A .third and preferred method which we 'ind'especially well adapted for the case-of a large number of trains is to assign each train one, and only one, pair of frequencies, butto use the same pair of frequencies for several different trains. It will be clear that any two trains which do not runsimultaneously in the same line section `can use the same pair of frequencies Without mutual infterference.v Hence, the total number of pairs `of frequencies necessary in any line section "is equal to the maximum number of trains running simultaneously in that section at a given time, and the assignment of frequencies to the. dierent trains then becomes a 80 relatively simple matter. f

' y Consider, for example, the illustration in Fig. 8. This represents a diagram of the ruiming schedule for a theoretical railroad line covering a distance of 600 miles between Y two cities A and B. Let us assume that -twelve trains a day are run in each direction between these two towns, the trains leaving the terminals on the even hours. The running time foreach train is taken as twelvehours.

40 The schedule is drawn by plotting distances traveled as abscissae, and times as ordinates. In the diagram, the twenty-four hour period is assumed to be divided into a period from 8:00 A. M. to midnight during which communic'ation is provided, and the periodV from midnight to 8 :00 A. M. during which.V communication is unnecessary. The exact length of this period is, of course, immaterial. total distance of 600 miles is divided into Y .six sections of 100 miles each, and it is as- Vsumed that each of the fixed stations located at C, D and Ewill maintain communication for 100 miles on either side.

In this simple. illustration none fof the trains going from A to B runs simultaneously Nin the same section with the preceding or the following train. Hence, all the twelve trains in the A-B direction can use the same pair of frequencies f1 and f2. Similarly, all of the trains running in the B-A direction may use a common pair 'of frequencies, but since these vtrains run simultaneously in the Y same section with trains going in the A-B direction, this must be a new pair of frequencies f3 and f4. At each of the lixed sta- The channel at, all times and the apparatus atV the fixed stations used with maximum etliciency. lt may be noted in comparison that the second method proposed above would re-.

quire a total of fortyeight different frequency bands. y

lf the total number of trains in the assumed system were double-d, one train leaving each terminal every hour, then successive trainsV in each direction would Vrun simultaneously in the same line section. ln this event it would be necessary to use Yadierent pair'of frequency bands for alternate trains, and the total number of pairs ofbands required would be eight instead of four. As an alternate solution of thislast situation it is evidentthat the fixed stations, could be placed closer together in order tov avoid the contingency of two trains, with which communication is to be maintained, being in the same section. I

lnV general, the procedure would be to set up a diagrammatic schedule of the type illustrated in Fig. 8 and from this determine for each direction of travel the trains which run simultaneously in any one section. The proper assignment of frequencies for one direction then becomes obvious. A certain factor of safety may be required because the trains cannot always run on schedule,but this means only the addition of a small number of frequency hands or a reduction'in the length of the sections. Y y o Whilethisrsystem of communication has been describedY in a certain specific manner, it

- is t-o be understood that the scope of the invention covers many Vvariations therefrom.

,F or example, while it has beenrspecilica-lly stated that a pair of frequency bands is preferred for eachtrain', one for transmission and one for reception, it is to be understood that such twoeway signaling may be maintained on one frequency band. Also, while in Fig. 8 the trains are indicated as running lthrough the length ofthe railway line with uniform speed, such will frequently notbe the case, and a correct diagram for any train would show a slope of the line which changes from one portion to'anotherinaccordanceV with the speed fof the train overa given portion of the line.

What is claimed is:

l. ln a signaling systemto and from moving trains, a transmission line along the route of the trains, means-for electrically dividingV said line into a plurality of sectionsa fixed carrier frequency signaling station near theV middle of each section and associated for twoway signaling with the transmission line, and a plurality of trains each provided with inductive lmeans, for two-way signaling with ico moving trains, a transmission line along the said line, eachV train a section being provided for' signaling on a different pair of carrier frequencies and each fixed station being equipped for signaling simultaneously on the pairs of carrier frequencies associated With the plurality of trains.

2. In a system for signaling to and from ni'oving trains, a transmission line along the route of the trains for transmitting signal current, means for electrically dividing said line into a plurality of sections, a fixed ca rrier frequency signaling station near the-middle of-each section and associated for tvvo-Way signaling With the transmission line on a plurality of carrier frequencies, means thereat for modulating the carrier frequency With the signal current and aV plurality of trainsv provided with means for two-Way signaling with said line, means at each fixed station .to provide a separate pair of carrier transmission frequencies for each train Which may simultaneously be in its section. Y

3. In a system for signaling to and from moving trains, a transmission line along the route of the trains, means for electrically dividing said line into a plurality of sections, a fixed carrier frequency signaling station near the middle of each section and associated for two-Way signaling with the transmission line, a train provided With means for two-Way signaling with said line, and means for controlling the transmission level of the signals in accordance With the distance to the fixed station and in accordance with variations in the coupling between the train and the transmission line.

4. In a system for signaling to and from moving trains, a transmission line along the route of the trains, means for electrically dividing said line into aplurality of sections, a fixed carrier frequency signaling station near the middle of each section and associated for two-Way signaling with the transmission line, a train provided with inductive means for two-Way signaling with said line, a pilot signaling channel for indicating the transmission level of the communication circuit,

and means responsive to said indications for controlling the gain.

5. In a system for signaling to and from moving trains, a transmission line along the route of the trains, means for electrically dividing said line into a plurality of sections,

. a fixed carrier frequency signaling station near the middle of each section and associated for two-Way signaling With the transmission line, a train provided With inductive means for two-Way signaling with said line, and means at the train for controlling the gain in accordance With the distance to the fixed station and means at the latter to control the gain in accordance With the variations in coupling.

6. In a system for signaling to and from route of the trains, meansforelectrically di-` viding said line into a plurality of sections, a fixed carrier` frequency signaling station near the middle of each section and associated for two-Way signaling with the transmission line, a train provided with inductive means for two-Way signaling With said line, a pilot signaling channel for indicating-the trans-l mission level of the communication circuit, means at the fixed station to control'the transmission gain. in accordance With the variations in coupling, and further means at `the train for controlling the gain in accordance with the distance to the fixed station.

7. In a system forsignaling to and from moving trains, a fixed signaling station at one point along the route adapted fortwo-` route of the trains, a fixed Vsignaling station at one pointalong said route adapted for;

tWo-vvay signaling with the transmission line, a trani provided with means for two-Way signaling with said line, a pilot signaling channel for indicating the transmission levell 0f the communication circuit, and means responsive to said indications for controlling the gain of said communication circuiti.,

9..In a system for signaling to and from moving trains, a section, of transmission line along the route of the train, a fixed carrier frequency signaling station near the middle thereof and associated with the transmission line for signaling,'a` train provided with means for signaling with said line, and means for controlling the transmission level of the signals in accordance With the distance to the fixed station and in accordance with variaifo,

` 9o l from ,moving trains, a transmission line along the tions in the coupling between the train and the transmission line.

10. In a signaling system to and from movingl vehicles and comprising a transmission line along the route of vehicles, the line being electrically divided into a plurality of sections, 'a fixed carrier frequency signaling` quencies one for incoming and one for out? going signals, means for adjusting the carrier frequency so that each train in any one section operates on a pair of carrier `frequencies different from that forthe other trains in that section, the trains in anyl other section being adapted to use the'sanie 'sets of carrier frequencies as in the first named section.

11. In a signaling system to and from moving vehicles and comprisinga transmission-line along the route of vehicles, the line being electricallydivided into a plurality of sections, a'iixed carrier frequency signaling station near the middle of each section and associated for two-way signaling with the transmission line and inductively coupled to the vehicles, carrier frequency transmitting and receiving appara-tus on each train, each train operating on a pair o-f carrier frequencies one for incoming and one for outgoing signals, means for adjusting the carrier frequency so that each train in any one section `operates on a pair of carrier frequencies different from that forV the other trains lin that section, the same pairs of carrier frequencies being used on all sections and each section being electrically isolated from the other sections for carrier frequency signals. 12. In a system of signaling toand from moving trains comprising a transmission line along the route of the trains for audio frequency signaling between widely separated points and fixed signaling stations along the line, thev method of signaling which consists in sending the audio frequency message along the transmission line to the fixed station nearest the train, converting the message to a `modulated carrier wave, impressing this carrier wave on the transmission line, receiving the message inductively` on the train, and converting it to normal audio frequency.

13. In a signaling: system to and` from moving Vehicles, a transmission line along t the route of the vehicles, means for electricallydividing said line into a plurality of sections for frequencies above the audiofrequency-range, a ixed carrier frequency signalingstation near'the middle of each sec-V tion, means for two-way transmission ofr audio frequency messages on said transmis sion line between any fixed station and a remote point, means at any one of thel fixed stations for converting the message to a carrier frequency wave and for impressing the wave on the section of the transmission line adjacent the fixed station for reception by a train in that section. f

14;. In a signaling system to and from moving vehicles, a transmission line along the route of the Vehicles, means for electrically dividingsaid line into aplurality of sections for frequencies above thev audio-frequency range, a fixed carrier frequency signaling station near the middle of each section, means sof for two way transmission of audio frequency messages onsaid transmission line between any fixed station and a remote point, means at any one of the fixed stations for converting the message to acarrier frequency wave and for impressing the wave on the section -of the transmission line adjacent the xed station trolled automatically by the rota-tion of thev train wheels to adjust the gain in accordance with the distance from. the nearest fixed station. i

In testimony whereof, we have signed our names to this specification this 27th day of September, 1929. Y

HERMAN Y A. j AFFEL. ESTILL I. GREEN.

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