|Publication number||US2399738 A|
|Publication date||May 7, 1946|
|Filing date||Mar 29, 1944|
|Priority date||Mar 29, 1944|
|Publication number||US 2399738 A, US 2399738A, US-A-2399738, US2399738 A, US2399738A|
|Inventors||Winthrop K Howe|
|Original Assignee||Gen Railway Signal Co|
|Export Citation||BiBTeX, EndNote, RefMan|
|Referenced by (15), Classifications (5)|
|External Links: USPTO, USPTO Assignment, Espacenet|
May 7, 1946. w. K. HOWE CENTRALIZED TRAFFIC CONTROLLING SYSTEM FGR RAILROADS Filed March 29, 1944 2 Sheets-Sheet 1 i QED hup snzd a m a 5m v Zsuventor attorney May 7, 1946. -w, HOWE 2,399,738
CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Filed March 29; 1944 ZSheets-Sheet 2 Snnentor LNIIIIIF- n u u u u u w n u Ill .31 4 mi N u my .P m .r
Patented May 7, 1946 csn'mamznn 'msrnc cou'rnonusd SYSTEM FOR nsmaosns Winthrop K. Howe, Rochester, N. Y., assignor to General Railway Signal Company, Rochester,
Application-March 29, 1944, Serial No. 528,528
' 3 Claims. (Cl. 111-353) Thisinvention relates to the communication 1 part of a centralized traffic controlling. system f used for governing traillc on railroads, and more I particularly. pertains to a coded type communi cation system employing direct space radiation of energy.
- plied with only sufficient ated transmitters are in operation to cause a'normal reception.
energy when its associ- This is accomplished by the p1acing of an artificial load on the receiving antennas The usual centralized traffic control system I provides for the remote control of the switches and signals located at various points along a railroad, in such a way that the operator in thecentral offlce may change the position. of the switches and signals, subject to suitable approach locking, detecting locking and the like to prevent unsafe operation of any switch, and may hold at stop any of the signals or allow them to clear. dependent upon thev positions of their associated switches and dependent upon trafllc conditions in advance. Such a centralized trafllc controlling system also provides for the transmission of indications to the central oiilce to inform the operator of trafllc conditions along the trackway throughout the territory under his supervision as well as to advise him of the position and condition of the various switches and signals under his control.
For convenience in the practical application of such a system. those switches and signals which are located adjacent or near each otherare usually considered to comprise what is conveniently termed a field station, and a communication system is provided to transmit controls to each of these field stations and to transmit the indications from each of the field stations to the central oiilce.
The present invention contemplates the use of a code type communication system, such as dis.-
closed in the prior patent of Hailes and Brixner Pat. No. 2,368,826 dated February'li, 1945, organized to provide for communication by direct space radiation instead of b carrier current as disclosed in such prior patent. The present invention therefore relates more particularly to the adaptation of such a code type system to the problems of space radiation and reception.
Since the control oillce of such a system must communicate with the most distant field station, its transmitters must be sufliciently powerful to radiate the proper energy level, but it can be seen that such an energy level will be entirely too strong for reception by the local receivers which are responsive to energy impulses of the same frequencies. For this reason special means are provided to be controlled by the code transmitting means to desensitize the local receiving means at the control office so that it will be sup.
so controlled b the code system as to apply and artificial load at the proper times. Similar desensitizing means is also provided at each of the field stations especially organized to resensitize the receivers coincidentally with the cessation of the energy, impulses transmitted from the associated transmitters so as to be in readiness for the retransmitted impulses from the control office as employed in such a code sysm. i Various other objects, purposes, and characteristic features of the present invention will be in "part obvious from the accompanying drawings and in part pointed out as the description of the invention progresses.
In describing the invention in detail, reference will be made to the-accompanying drawings, in which those parts having similar features and functions are designated throughout the several rilgures by like letter reference characters which are generally made distinctive either by reason of preceding numerals representative of their location or by reason of exponents representative of the order of their operation, and in which:
Fig. 1 illustrates in a diagrammatic manner the apparatus provided in accordance with the present invention to adapt a code type communication system to transmit energy impulses by direct space radiation as associated ceiver; and
Fig. 2 illustrates ina diagrammatic manner the apparatus necessary to adapt a code type field station organization to communicate by direct space radiation as proposed in accordance with the present invention.
In order to simplify the disclosure, the organization proposed by the present invention has been shown very diagrammatically as directly v iii/lug reference characters.
applied to the above mentioned Hailes and Brlxner Patent N 0. 2,368,826 granted February 6, 1945. For this reason, many of the details of the code communication system have been omitted from the present disclosure, but reference can readily be made to such prior disclosure for such details and only those parts of such prior disclosure have been shown in the present disclosure, as are necessary for an understanding of the present invention. For convenience in referring to said prior patent. those parts which are common with the prior disclosure have been with a sensitive re- 3 given correspond- Although the present invention is in the nature of an improvement over the prior Patent No. 2,368,826 granted February 6, 1945, it is to be understood that no claim is made herein to any subject-matter found in such prior patent.
For purposes of simplifying the illustration and facilitating the explanation, the various parts and.circuits constituting the embodiment of the invention have been shown diagrammatically and certain conventional illustrations have been employed, the drawings having been made more with the purpose of facilitating the disclosure as to the mode and principles of operation than with the idea of illustrating the specific construction and arrangement of parts that would be employed in practice. Thus, the various relays are used to indicate the connections to the terminals of batteries or to other sources of electric current instead of bringing all of the wire connections to those terminals. The symbols and are employed to indicate the positive and negative terminals respectively of suitable, batteries of other sources of direct current; and the circuits with which these symbols are used always have current flowing in the same direction. When alternating currents are used in place of direct current, the particular symbols employed should be considered to represent the relative instan taneous polarities. 1
With reference to Fig. 1 of the present disclosure, it will be seen that a transmitter unit with a suitable antenna and ground system is supplied with frequencies f and f from suitable generators or oscillators designated j -GEN. and I -GEN. The generator units for producing these frequencies f and f are respectively controlled by transmitter relays T and T so that when either transmitting relay is picked up the corresponding frequency is produced by the associated generator and caused to be transmitted by direct space radiation.
The transmitter relays T and l? are controlled over bus wires i5 and it in the same manner as described in the above mentioned prior Patent No. 2,368,826 so as to transmit controls to remote field stations upon the positioning suitable control levers and the actuation of a start button for the corresponding field station. These controls have been diagrammatically shown the same as in the prior patent and have been given the same reference characters for the purpose of readily identifying the corresponding parts.
The control office is also provided with two receiver and amplifier units for the two difierent frequencies f and I which are capable of receiving and amplifying energy impulses received from the various field stations and effecting the energization of the receiver relays F and F3. These receiver relays F and F act through suitable circuits to cause the stepping relays V to operate and the decoding means to control the indication relays such as relay lm in a manner fully disclosed and described in detail in the above mentioned prior patent. It is suflicient to know for the purposes oi the present disclosure that the step-by-step operation is governed by the operation of these code impulse receiving relays F and F thrbugh a suitable repeater relay FA (not shown) and a half step relay VP (not shown) in a manner now well understood in the art.
These receiver relays F and F also act to govem the transmitter relays T and T for causing the retransmission of impulses as dictated from the field stations, as will be discussed more in detail as the description progresses. Also, it
aeea'zss might be mentioned at this time, that the various auxiliary control circuits for the relay '1 are also provided in this disclosure the same as in said prior disclosure for the purpose of producing the permission impulse at the end of a cycle of operation.
The antenna system for each of the receiver units is provided with a suitable artificial "load" controlled by its respective relays A and A, in
*such a way that when the load is applied to the antenna system, the associated receiver is proarepreferably so constructed and associated with the antenna system that the radio frequencies in the antenna system are not unduly affected by the capacitance of the relays and their connections to the rest of the system. In other words these relays A andA serve to electrically isolate the rest of the system from the antennas systems.
Each field station, as typically illustrated in Fig. 2, is provided with a receiver and amplifier unit for the frequencies f and j which operate their respective reoelver relays. In Fig. 2; the apparatus is assumed to be located at the first field station and hence the receiver relays have been given the reference characters IF and IF. These receiver relays through suitable repeaters and control circuits (not shown, but disclosed in the prior Patent No. 2,368,826 govern the operation of the stepping relays W W W IV and ILV. These receiver relays 1F and IF also act through suitable station selecting means to cause the selection of the station when its code is received and to then effect the positioning of the control relays for the remaining steps of the system. This has been merely indicated by dotted lines and the illustration of contacts on the stepping relays as leading to the typical control relay ISMR, which causes the operation of the switch machine ISM for the track switch ITS when such relay lSMR is operated to its opposite positions.
With reference to Fig. 2 as typical of the various field stations, it will be seen that the transmitter unit is provided with a suitable antenna system, and is supplied with frequencies f and I from the generator or oscillator units f -Gen. and j -Gen. These frequency generators are selectively controlled through the transmitting relays IT and IT as well as by the receiver repeater relay IPA and the slow acting relay ILON for reasons later discussed. The transthe transmission of its station code call and its indications, continues transmission only so long as its station selecting relay ISI is maintained energized by the reception of retransmitted impulses from the control oflice corresponding to its station code call. Since the control office determines the relative superiority between the two frequencies employed in the present system,
only that field station is selected having the most superior code call when a plurality of field stathe dotted line indicated controlggfrom' the receiver relays Ii and IF;
Associated with the antenna system for thereceiver of each frequency, is a :suitablemrtlficial load" whichis applied when .the respective relays IA and IA are deenerglzed and these relays control the application of these artificial loads in a way as to electrically isolate the antenna systems from the rest of the circuit organization. The application of these artificial loads is required to be controlled by certain coding control relays which has beenindicated in the iorm of written circuits by only the contacts of these relays being shown in connection with the load applying circuits, but it is to be understood that the contacts of these relays and the connections thereto are so made as to maintain the electrical isolation of the high frequency currents of the antenna system with respect to the capacity characteristics of therest of the system. Operation 'from the central oflice to the remote field stations; or is set into operation for the transmission ofindications from any field station to the control ofilce. be employed-so as to avoid the continuous active condition of the frequency generators and amplifying units, it is assumed for convenience in the disclosure that such units are in a continuous active condition ready for transmission 'or reception as the case may be when the codlngportion oi'the system is ready to/initiate a cycle of operation. For this reason, an operator merely actuating a start button causes the immediate transmission of energy impulses to cause the coding apparatus at the central ofllce and at the remote field stations to be initiated into a cycle of operation. Similarly, a change in indication conditions at a field station can cause immediate transmission, subject to an interlock with other field stations on the basis 01 a superiority of code, as briefly described above.
While the system is at rest most or the relays and are thus organized to save energy while the system .is not in operation. However, the re-'-' lays L and R in the control ofilce and at the field stations are normally energized by circu'its which have not been shown in detail, being understood that their control is the same as shown in the above mentioned prior application The relays A and A of Fig. 1 are energized in multiple from through a circuit including back contact 5 of relay T back contacts 6 of relay T windings oi. relays A and A in multiple, to Similarly the relays IA and IA of Fig. 2 are normally energized in multiple through back contacts I and 8 of relays IT Although suitablemeans might the relay C. The closure of front contact 64 of relay C causes a circuit to be closed for the transmitting relay T from through a. circuit in.
cluding a back contact 83 of relay SC, front con tact 84 of relay C, wire 65, back contact 66 of relay LV, back contact 81 of relay V back contact 68 or relay V back contacts of is of relay V back contact 10 of relay V to the bus wire Ii, wlndings of transmitting relay T to The picking up got the relay T closes front contacts Tito cause the frequency generator f Gen. to be set into operation to effect the transmission of impulse energy of frequency 1, while the opening of back contact I of relay T deenergizes the relays A and A. It is to be understood that suitable time constants are included in the generator units so that the impulse en- 'ergy isnot radiated by the transmitting antenna and circuits of the code system are deenergized IA remain picked up and the receiver units at each oi? the field stations remain capable of resystem until the relays A and A have dropped away closing their back contacts 9 and I 0 so as to apply their respective artificial loads to their antenna systems. Thus, the control ofllce radiates impulse energy of frequency f for the conditioning period to initiate the field stations and the control oflice into operation.
After this conditioning impulse has persisted for a time in which the-relay repeating the receiving relays may be picked up, the initial circult for relay T is opened at back contact of transmitterrelay T or the transmitter relay T upon each energization of the impulse relay E closing front contact m depending upon the station code and the controlto be transmitted for that station as the cycle of operation of the system progresses.
It is believed to be unnecessary to specifically point out how the transmitter relays are selectively energized for each impulse of the different codes, it being sumcient to understand that each time atransmltter relay is picked up, the opening of its back contact releases the associated relays A and A so as to protect or desensitize the associated receiving apparatus. However, each impulse transmitted from the oifice is also received at the control oflice at a proper level because of the proper choice of the associ ated artificial load, and is also received at the various field stations. The conditioning impulse inltiates the code receiving apparatus both at the control ofiice and at the several field stations; while the successive impulses of the cycle cause the stepping operation and a suitable station selection for the reception of controls.
It will be obvious that during the reception of such controls, the transmitter relays such as relays IT and iT at. the field station shown in Fig. 2, are inactive, so that the relays IA and ceiving the energy impulses as transmitted from the control oillce. At'the conclusion of the transmission oi the control impulses, a permission ir'npulse is transmitted from the control oflice, un-
less a successive control cycle is to immediately follow.
More specifically, a field station cannot initiate a cycle of operation for the transmission of indications either during a control cycle or between successive control cycles because the relays R and L at each station are picked up only in response to a permission impulse, and such a permission with that station which eiiects the picking up of impulse is transmitted by the control ofilce only providing there are no more control cycles to be initiated as stored in the code determining bank in response to the actuation of several start buttons for the several field stations. Thus, when all of the stored control cycles have been transmitted, the relay C at the control oiilce is deenergized so that a circuit is closed for causing the transmission of a permission impulse.
This circuit for causing the transmission of a permission impulse following the clear out period at the end of a control cycle is effected by the energization of the transmitter relay T by a circuit closed from through back contact I53 of relay SC, back contact I52 of relay C, back contact l| of relay R, windings of relay T to The energization of the transmitting relay '1' closes front contact H to effect the transmission of impulse energy of the frequency f". This continues until the relay R at the control office is picked up, and since the relay R at the control oillce is somewhat slower acting than the corresponding relays at the field station, it is thus assured that the control oilice and all of the field stations have been restored to normal conditions in readiness for an initiation 01 an indication cycle of operation. It is noted that the energize.-
1 tion of these transmitter relays "1 and T either for the transmission of a conditioning impulse to cause initiation of an operating cycle, the transmission of code impulses during a cycle, or the transmission of a permission impulse at the end of a cycle of operation is effective to deenergize .for the reception of the next impulse.
Transmission of indications-When a change in indication conditions occur at a field station, such as the dropping of a track relay IT, or the deenergization of a signal repeating relay IM, such change effects the picking up of a change-relay CH to initiate a cycle an operation by energizing the transmitter relay IT by suitable circuit (not shown) but which has been disclosed and described in detail in the above mentioned prior patent. The picking up of the transmitter relay I'I' closes front contact Hi and sets the generator .f -Gen. into operation for transmitting a start pulse to the control offlce. This start pulse is also received at the local field station, but it is to be understood that it is at a reduced level proper for its local receiver because the relays IA and IA are deenergized as soon as the relay IT is picked up. In other words, the generator units at the field station also have suitable time constants similar to those provided at the control oillce, so that energy is not radiated by the transmitter unit antenna system until the relays IA and IA have released to effectively protect the associated receiver units by closure of back contacts I2 and I3.
As soon as the receiver relay IF has picked up in response to the start pulse, it is repeated by the relay IFA which opens back contact 222 and stops the transmission of the start pulse. At the same time that back contact 222 of relay IFA is opened, the back contacts H and I5 of relay IFA are also opened to remove the artificial loads from the receiver antenna systems. This immediately conditions the receivers to receive the conditioning impulse transmitted from the control a so that the receiver relay IE is maintained energized. Referring to Fig. 1, it will be seen that the start impulse is repeated by the receiver relay F in the control ofilce which causes relay T" to be picked up by a circuit close through front contact 232 of relay L, back contact 233 of relay SC, back contact 234 of relay EP, back contact l6 of relay F front contact I! of relay F, Windings of relay T to The picking up of this relay T closed front contact II to cause the frequency generator f -Gen." to start operation and transmit the conditioning impulse which is of course received at the field station as well as the control oillce, as just described.
At the end of the conditioning impulse, which is determined by the picking up of the relay EP and the deenergizatlon of the relay transmitter T'-. of! period occurs and the next step in the stepping operation is effected at each of the field stations. On the next impulse period, the transmitter relay IT or IT is picked up in accordance with the station code for that station. This picking up of the selected transmitting relay of course causes the transmission of an energy impulse ofthe selected frequencies but such energy is of course not radiated from the transmitting unit until the protective relays A have their artificial loads applied. It is of, course to be understood that the application of the respective artificial loads by the relays IA and IA cause the receiver and amplifier units to be desensitized so as to operate at a reduced level, but this reduced level of operation is proper to cause the operation of the relays IF and IF in response to the locally transmitted impulses to effect the proper operation of the apparatus at the field station. In other words, these artificial loads are properly chosen to give protection to the receivers from overloading due to the proximity of the local transmitter, and yet provide for the proper reception under such conditions, the same as explained in connection with the control ofilce. The impulses throughout the cycle are repeated at the control oilice, and each time an energy impulse is received, a circuit is closed from through front contact BIB of relay'CF, front contact 3|! of relay 00, back contact 234 of EP, front contact 16 of relay F or front contact i! of F to the corresponding transmitter relay T or T to This causes the retransmission of each impulse in an overlapping relation to the one transmitted from the field station.
It is noted that each impulse transmitted by a field station is terminated by the picking up of its receiver repeating relay, such as relay IFA at the first field station diagrammatically shown 'in Fig. 2. This picking up of the relay IFA, for
example, not only terminates the impulse by opening back contact 222, but also at the same instant removes the artificial load from the respective receivers by opening back contacts l4 and 15. In this way, it is possible to maintain energized the proper receiving relay IF or lF because of the retransmitted impulses from the During the indication portion of each cycle of operation, indications are not only transmitted in accordance withtheproper selection of one of two frequencies, but indications are also transmitted in accordance with the length of such impulses, that is, one indication will be transmitted if the pulse is short, but a different indication will be transmitted if the impulse is long. This is accomplished by the selective control of a timing relay such as relay lLON shown in Fig. 2, which is picked up only-if the impulse is to be long. l
For example, let us assume that a long impulse is to be transmitted and the relay ILON has been picked up closing front contact 340 to shunt the back contact! of relay IFA. The impulse is initiated in the usual way by the picking up of either the transmitter relay IT or 'lT to cause the corresponding frequency f or f to be transmitted by the associated transmitter unit. The picking up of the selected transmitter relay of course deenergizes the protective relays [A and lA but that energy which is received by the associated receivers acts to pick up the particular receiving relay corresponding 'to the frequency of the impulse.
This picking up of the receiving relay 1P 01'.
U5 is repeated by the relay IFA which would normally act by the opening of backcontact 22". to cause the cessation of the impulse but the front contact 340 provides a shunt so that the impulse is continued until the relay ILON drops away. As soon as the relay IFA picks up, the circuit for the relay ILON is opened, so that the impulse is increased in duration by the length of the drop away period of the relay ILON. Not
only doesthe relay ILON cause the impulse to be prolonged, but its contacts I8 and lilrespectively shunt the back contacts l4 and 0f the relay lFA so that the associated receivers are protected throughout the transmission of energy during the prolonged impulse. In other words, the artificial loads placed upon the associated receiver units are selectively controlled in aci is made superior to the frequency Fbecause the reception of the frequency f in the control office closes front contact l6 and opens back contact [6 to prevent front contact I! of relay F from acting on the transmitter relay T.
The selection circuits for the relays SI at the several field stations are so organized that the relay SI remains picked up at the field station having the most superior code call while at the other field stations, such relay SI is dropped out and renders the associated transmitter inactive until some subsequent cycle of operation during which its station selecting code isthe by the retransmitted impulses.
From the above discussion it will be seenthat the present invention contemplates a centralized traiiic' control of the coded type employing direct space radiation in which the local receivers are protected from their associated transcordance with whether the impulse is to be short or long. At the instant the relay ILON releases and opens front contact 340, the back contact 2220f relay IFA still being open, the energized circuit for the frequency generators is opened and causes the impulse to cease, the front contacts l8 and I! of the relay ILON also open to remove the artificial loads from the associated receiver units. Thus, the receiver units are resensitized for the retransmitted impulse from the control oilice, as previously described.
The system of the present invention contemplates that a plurality of field stations will be associated with the control office, and due to the nature of the indications which must be transmitted to the control office, it may happen that a change in indication conditions will occur in several field stations at the same time. In such a case, the several field stations will 7 begin transmitting at the same time, but only one field station will be selected because the system operates upon the principle that the reception of two different frequencies by the control ofiice for an impulse period results in the retransmission of but a single frequency. This. arbitrarily renders one frequency superior to the other. With the proper assignment of code characters to the field stations, they are given relative superiority so that the retransmitted impulses result in the selection of only one field station of the several field stations which may be transmitting at the same time. In the present disclosure, it will be seen that the frequency mitters, and which protection is more, particu-r.
larly needed in a system where the receivers are for the same frequencies as provided by their associated local transmitters. It is to be understood that it is desirable to employ the same frequencies at the control office and the field stations for transmission in opposite. directions employ the principle of retransmission to facilitate in, the application of the principle of superiority of code to provide for selection between a plurality of field stations which are ready to transmit their indications at the same time- Having thus described a centralized trafllc control communication system of the code type employing space radiation as one specific embodiment of the present invention, it is desired to be understood that this form is selected to facilitate in the disclosure of the invention rather than to limit the number of forms which it may assume; and, it is to be understood that various modifications, adaptations and alterations may be applied to the specific form shown to meet the requirements of practice, without in any manner departing from the spirit or scope of the present invention except as limited by the claims.
What I claim is:
1. In a communication system for the transerning the associated transmitter to transmit different series of energy impulses by space radiation, means at the control ofilce and at the field station controlled by said code control means at the corresponding location to apply an artificial load to the antenna system of the associated radio receiver when the radio transmitter a that station is rendered active to transmit an energy impulse, said artificial load being of such character as to protect the receiver from excessive'energization without rendering the receiver totally inactive, and means associated'with each receiver receiver means at the beginning of the transmission of each impulse from that station, said nection and governed by its associated step-bystep means when it is initiated into operation for transmitting a series of energy impulses of distinctive carrier frequencies to forma code for a that station, radio transmitting and receiving means at the control omce responsive to each energy impulse of any series transmitted by any given field station i'or'retransmitting an energy impulse ofthe same carrier frequency to prolong the length of that impulse for a predetermined time interval only, radio receiving means at each field station having its individual antenna and ground connection and responsive to the energy impulses transmitted from the control ofllce and from its ownstation, means at each station controlled by its associated radio receiving means for causing the operation of the associatedstep-bystep means and acting during local reception to terminate each impulse transmitted by its radio transmitting means, code responsive means at each field station governed by the radio receiving means and said step-by-step means at that station so.as to be selectively conditioned only in accordance with energy impulses of distinctive carrier frequencies received from the control ofllce during the prolonged time interval of each impulse period, means at each field station efiective to connect an artificial load between the antenna and ground connection for its associated artificial load acting to desensitize its receiver only to that extent to give proper local reception,
and means at each station'eiiective to disconnect said artificial load from the antenna of its associated radio receiving means coinciding with the cessation of each impulse transmitted by its associated transmitterto thereby render the associated radio receiving means responsive at once to impulse energy transmitted from the control ofllce during eachprqlonged impulse period.
3. In a communication systemior the trans- -mission of impulses of radio carrier frequencies to provide two-way communication between a control oflice and a field station, a radio transmitter and a radio receiver at the control oflice, a radio transmitter and a radio receiver at the field station, each of said transmitters and receivers having an individual antenna and a ground connection, and all of said transmitters and receivers being adapted to operate on the same radio carrier frequencies, code control means at the control ofiice and at the field station for governing the respective radio transmitter to cause it to transmit different series of radio energy impulses, means at the control office and at the field station including a separate relay governed by its associated code control means for connecting an artificial load between the antenna. and ground connection of the associated radio receiver to protect such receiver from excessive energization during each impulse transmitted by the associated transmitter, whereby said relays serve to electrically isolate the respective receivers from their associated code control means, and means at the control ofllce and at the field station causing the operation of its associated code control means during the transmission of any particular series of impulses from that station.
- WINTHROP K. HOWE.
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|US2487102 *||May 2, 1947||Nov 8, 1949||Gen Railway Signal Co||Code communication system|
|US2489638 *||Mar 20, 1945||Nov 29, 1949||Ipsophon Patentgesellschaft A||Arrangement for switching on and initiating processes by means of telephone calls|
|US2501091 *||Jun 26, 1946||Mar 21, 1950||Gen Railway Signal Co||Station selective radio communication system|
|US2535162 *||Aug 4, 1945||Dec 26, 1950||Philco Corp||Position indication and control system for moving objects or vehicles|
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|US2577751 *||Mar 24, 1945||Dec 11, 1951||Farnsworth Res Corp||Remote supervisory radio signaling system|
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|US2900498 *||Aug 2, 1955||Aug 18, 1959||Gen Railway Signal Co||Fail-safe protection for code communication control systems|
|US2907980 *||Jun 5, 1953||Oct 6, 1959||Gen Railway Signal Co||Multiple station code communication system|
|US5092544 *||Dec 22, 1989||Mar 3, 1992||General Railway Signal Corp.||Highway crossing control system for railroads utilizing a communications link between the train locomotive and the crossing protection equipment|
|US5098044 *||Jul 15, 1991||Mar 24, 1992||General Railway Signal Corporation||Highway crossing control system for railroads utilizing a communications link between the train locomotive and the crossing protection equipment|
|U.S. Classification||340/12.5, 455/701|