End to End Communications for Trains
October 1944 Radio News

October 1944 Radio News
October 1944 Radio News Cover - RF Cafe[Table of Contents]

Wax nostalgic about and learn from the history of early electronics. See articles from Radio & Television News, published 1919-1959. All copyrights hereby acknowledged.

Special Insert: Radio-Electronic Engineering Department

Here's a good article for the train lovers out there (of which there are many). According to an article I found in the Allentown Morning Call, the world's first radio broadcast from a moving train took place on Sunday, March 27, 1932. The feat was accomplished by radio station WJZ out of New Jersey, while aboard a Baltimore and Ohio (B&O) train. As reported in Radio News magazine a decade later, radio was being used for reliable communications between not only the attached cars (which also often had some wired interconnections), but between other trains and between the train and depots and switch yards. Given the era, no doubt the accomplishment relied at least partly on technology developed during World War II. Radio facsimile allowed printed messaging to replace the previous method of using a hook to snatch rolled up paper messages hanging on poles as the train rolled by.

See also this 1960 Railroad Radio article.

End to End Communications for Trains

Quarter-wave whip antenna installed on top of locomotive - RF Cafe

Quarter-wave whip antenna installed on top of locomotive used to handle freight.

By Ernest A. Dahl

Electronic Eng., Rock Island Railroad

Operating procedures and results of the radio communications system installed by the Rock Island Railroad to facilitate handling of traffic.

On April 1, 1944, the Rock Island Lines started a radio development program designed to develop and prepare material to be used as the basis for communication systems to be installed on the Rock Island Lines. In all, front-to-rear communications, yard operation, dispatcher to caboose operation, and the so-called "walkie-talkie" units were to be studied,

Power Supply Problem

In all train communications, the first problem that presents itself is the standardization of equipment, and second, the problem of securing operating voltages from different types of primary power supplies. Diesel locomotives have a 64 volt battery which increases to 72 volts when the Diesel is running. Steam locomotives have a 32 volt d.c. power supply which is supplied by a steam driven turbine, while the caboose has no power source of any type.

Thus, it was decided to use all 110 volt, 60 cycle equipment, with the power supply, in all cases, built right on the transmitter or receiver combinations. Therefore, every transmitter and receiver would be interchangeable. Servicing would be easy since a.c. is available at all servicing points.

Hence, if trouble developed in the converter itself or motor generator set, the. power unit could be changed instantly, or if trouble should develop in the receiver or transmitter they could be interchanged with spare units available at all times.

For steam units a steam turbine connected directly to an a.c. alternator was designed. The a.c. alternator has a constant speed of 3600 revolutions per minute. Direct connection to an a.c. alternator provides 110 volts at 60 cycles at all times. This solved the power supply problem on the steam type of railroad locomotive.

Engineer of one of the Rock Island Lines - RF Cafe

Engineer of one of the Rock Island Lines' 5400 series freight diesels gets his "go ahead" or "hi-ball" orders by means of two-way FM radio.

Mobile electronics field laboratory built into an all-steel caboose - RF Cafe

Fig. 1 - Mobile electronics field laboratory built into an all-steel caboose. Tests and repairs can be made anywhere on the company lines.

The power supply on the Diesel locomotive, since 64 volts d.c. power was available, warranted the use of a converter unit designed to give 115 volts output with 70 volts on the primary. Therefore, while the Diesel is running, the battery voltage rises to 72 volts, the a.c, voltage rises to 118, and when the Diesel is standing still, the voltage drops to 64, and the a.c, voltage drops to 108. Any change in frequency due to the change in speed of the generator is not critical, as the power transformer will operate efficiently on as low as a 50 cycle power main.

The caboose power supply is designed around a 12 volt d.c. battery which is charged off a belt driven generator. The 12 volt batteries supply primary power for a 12 volt d.c, to no volt 60 cycle a.c. converter. Under normal operating conditions at a train speed of about 15 miles per hour, the wheel generator starts charging the batteries. On transmit, when the load is at maximum, the generator supplies enough power to float the battery, thus, under normal usage for train operation, the battery supply will stand up. With extended operation at a permanent location, the batteries must be replaced after every 15 hours of continuous use.

Laboratory Set-Up

In order to check various systems of operation, including microwave sets, 157 megacycle, 40 megacycle, and 80 kc., a field laboratory was set up. This laboratory is a new, all steel caboose. (See Fig. 1.) The caboose is equipped with a 1000 watt a.c. generator mounted on the roof directly behind the cupola. A five gallon gas tank is built-in to give 24-hour operation. The motor generator set and the gas tank are covered by a shield which gives a weatherproof covering from rain, but permits free air circulation for cooling. (Fig. 2.)

A work bench is built-in on one side of the caboose. The lower section of the work bench is equipped with storage batteries to provide 30 volts d.c. for the operation of airborne 157 megacycle equipment. The second half of the lower shelf is equipped with a 40 megacycle FM transmitter-receiver combination. This unit is used as a standard for office communication, securing materials, expediting materials, tuning antennas, and communication for comparing field strength measurements on other types of equipment.

Gasoline driven motor-generator - RF Cafe

Fig. 2 - Gasoline driven motor-generator unit installed on top of mobile laboratory.

Engineer in direct communications with dispatcher - RF Cafe

Inside of locomotive cab. showing engineer in direct communications with dispatcher.

Located on the top of the bench is a Hallicrafters FM-AM S-36 receiver covering the frequency range from 27 to 143 megacycles, which is used for checking frequency, checking interference with other stations, and general communication work. A Hallicrafters communications receiver S-39 covering the frequency range from 0.55 to 30 megacycle, AM only, is installed here. (The receivers are shown on top of the bench in Fig. 6.)

In one clothes closet at the rear of the caboose, equipment shelves were built and an 80 kc. low frequency radiating system was installed, which, in turn, was connected to a loop which completely encircled the field laboratory. This loop is used in conjunction with producing a magnetic field which is induced in the telephone wires for dispatcher communications. A high frequency 157 megacycle transmitter-receiver combination as shown in Fig. 5 was also installed in the clothes closet. This unit contains both a receiver and a transmitter assembly and is connected by means of a coaxial cable to a quarter-wave ground-plane antenna mounted on the roof.

Two sets of controls are provided for all operation. All measurements are taken on the work bench itself by means of a vacuum tube voltmeter which provides a relative measure of signal strength by measuring the avc voltage in all receivers. Talking points for communications are set up in the cupola of the caboose itself, Fig. 7. The unit on the right hand side is connected to the 80 kc. low frequency radiating system. The telephone set and small loudspeaker in the center of the picture are connected jointly to both the 157 megacycle equipment and the 40 megacycle equipment.

This field laboratory was tied on a switching engine and pulled through the Burr Oak yards on the south side of Chicago in order to take measurements from a master control station operating from a control tower. The caboose is also used for line service to check the low frequency radiating system between Chicago and Rock Island, a distance of about 180 miles.

Master Control Station

The master control station itself is installed at the base of 100 foot lighting tower which is in the center of the Burr Oak yard. Two types of antennas were installed on top of the tower, a 40 megacycle coaxial antenna, and a "J"-type 157 megacycle antenna. Each antenna feeds directly down the tower into its respective transmitter-receiver combination.

Fig. 3 shows the case installed at the bottom of the tower which holds all equipment. The upper shelf contains a 40 megacycle FM transmitter combination. The maximum power output of the transmitter was 50 watts, but arrangements were made so that the power could be stepped down from 50 to 25 to 15 and to 10 watts so that an analysis could be made as to the maximum amount of power needed for dependable yard operations. The middle shelf contains a monitoring amplifier which bridges the telephone line which handles the signal for communication purposes. This provides a means of monitoring and servicing equipment while it is in yard operation. Also mounted above the middle shelf is a line-controlled relay circuit which provides, by means of d.c. voltage, a method for single telephone line operation for transmitting and receiving from remote control stations.

In normal operation the receiver output is fed through a relay into the telephone lines, over the telephone lines to a loudspeaker at a remote control point. When a signal comes in, the operator, if he is called, takes the telephone off the hook and pushes a button to answer. When the button is pushed it allows d.c. to flow in the telephone line which pulls in a relay at this control panel and turns the transmitter on. The operator at the remote control point thus disconnects the receiver, connects the telephone line to the transmitter, and turns the transmitter on. After sending his message he releases the button, and the receiver is again connected to the telephone line so he can hear the incoming message.

Equipment of the master control station installed at the base of yard antenna - RF Cafe

Fig. 3 - Equipment of the master control station installed at the base of yard antenna.

In addition, a polarized relay was inserted which under normal conditions, when positive voltages were used, was connected to the 40 megacycle equipment, and when negative pulses were used was connected to the 150 megacycle equipment.

It was possible. therefore, to operate two different sets of equipment in direct comparison without going out to the signal box to change units, and a direct comparison of frequencies may be obtained using the same amount of power.

Yard Operation

For yard operation, each one of the switching Diesels is equipped with 40 megacycle equipment. This equipment is installed directly behind the engineer's operating position. The original operating power was a gasoline driven generator which was mounted on the rear of the engine. This was later replaced by a permanent converter set which runs off the 64 volt Diesel battery power. A quarter-wave whip antenna is mounted on the hood of the Diesel locomotive and fed by means of coaxial cable run under the floor and through the cab of the engine. This locomotive on field tests showed that communications could be maintained for 15 miles between this locomotive, No. 700, and the central control point.

Fig. 4 shows a graph of the signal to noise ratio measured in the locomotive during this test.

In addition to the various means of communications discussed thus far, it was thought necessary to have continuous communication between the engineer and conductor in order to expedite the handling of trains.

Curves showing the radiation and field measurements - RF Cafe

Fig. 4 - Curves showing the radiation and field measurements made on equipment installed in locomotive at the Burt Oak Yard, Blue Island, Illinois.

Two types of front-to-rear communications have been tested: one type consisting of 1 watt, FM 40 megacycle pack sets. These sets gave perfect transmission from engine to caboose and were used by a brakeman who got off a train to inspect a hotbox and to give the engineer orders as to the handling of the removal of the car with the hotbox. The other units were 40 megacycle permanently installed transmitter-receivers mounted in the engine and caboose. These units were installed in the Silvis Yards, Moline, Illinois, and operated on a 160-car freight running from Chicago to Silvis to Kansas City. In three test runs, a very material saving at time was made in breaking up and handling the trains during these runs.

The 157 megacycle equipment was also installed and checked on this same run. Operation under viaducts, through bridges, and around curves with the FM unit seemed less noisy in extremely noisy yards than the AM unit, which was expected. The comparisons, of course, were made between FM and AM on 40 megacycles. The AM on 157 megacycles was considerably less noisy than the AM on 40 megacycles.

Long Distance Service

An installation of low frequency long distance service was tried and proved very satisfactory. A 76 kc. transmitter-receiver combination was installed in the caboose and connected to the wire loop which extends completely around the caboose. Two similar units were installed in both the Blue Island station and the Bureau, Illinois, station of the Rock Island Lines. These units were approximately 100 miles apart. One of the dispatching units was connected directly to the telephone lines through a condenser, and superimposed the carrier on the telephone lines to the ground. The loop on the caboose picks up the field from the telephone lines and brings it in to the receiver, a reverse operation is used for caboose-to-dispatcher transmission.

157 megacycle transmitter-receiver installed in laboratory - RF Cafe

Fig. 5 - High frequency 157 megacycle transmitter-receiver installed in laboratory.

This system operates extremely well and provides communication at all times over this distance. During an intense electrical storm in the middle of July, a slight amount of noise was encountered but it was not great enough to interfere with operational characteristics of the system. General operation of this system is considered satisfactory. Generally speaking, a satisfactory system of train communication is maintained by means of radio waves, both 40 megacycles and 157 megacycles, from caboose to engine, which gives the conductor complete control of the train at all times and allows the conductor to advise the engineer of any changes to be made. Then, by using the 80 kc. induction system it is possible to communicate with wayside stations or division points. This system fills all the basic requirements of a general communications system for railroads.


Investigation has been made by the Rock Island into the possibilities of the use of facsimile in conjunction with both radio and carrier type of communication. A facsimile printer and transmitter unit was secured from the Faximile Company, Inc. This unit is used in conjunction with both the Aircraft Accessories' 80 kilocycle induction system and the Motorola 40 megacycle F.M. system. The original installation consists of the Faximile recorder installed in the Blue Island Station, Blue Island, Illinois. The printer, or receiver, is installed in the caboose of a high speed freight train. Provisions are made for switching both the printer and transmitter to either carrier or 40 megacycle F.M. The 40 megacycle F.M. has a usable range of about 15 miles, while the carrier system has a usable range of approximately 50 miles.

The present method of transmitting information to a conductor on a train in motion, is by means of a message tied to a wax string which is held on a bamboo pole. As the train passes the wayside station the conductor reaches out and hooks this "train order." The apparent use for a facsimile system is only in replacing the bamboo rod. The wayside station operator takes the message off the telegraph or telephone, types it, and places it in the transmitter. When the transmitter is turned on, the carrier automatically opens the squelch circuit in the receiver and starts the printer in operation and the train receives the order. When the carrier is turned off at the completion of the message, the squelch circuit, in closing, triggers an alarm circuit which rings until the message is taken from the facsimile receiver. If at that time there are any questions about the received message, the operator can contact the wayside station by means of his radio or carrier telephone circuits. The distinct advantages of this system are:

1. The conductor does not have to stop the work he is doing to accept the message.

2. A written form of message is handed him which may be kept as a record.

3. He is automatically notified when a message is on the machine.

4. He can confirm this message by reading it back over the radio or carrier telephone circuit.

Hallicrafters S-36 and S-39 communications receivers - RF Cafe

Fig. 6 - Test bench installed in the mobile field laboratory, showing Hallicrafters S-36 and S-39 communications receivers. At the right is shown a 40 megacycle FM transmitter-receiver combination used as a standard for office communications.

Telephone and small loud-speaker are connected jointly to the 157 and 40 megacycle equipment - RF Cafe

Fig. 7 - Talking points for communications set up in the field laboratory. The upper unit is connected to the 80 kilocycle radiating system while telephone and small loud-speaker are connected jointly to the 157 and 40 megacycle equipment.

Power supply shown is used for radio equipment - RF Cafe

Power supply shown is used for radio equipment installed on steam locomotives. A constant speed, 3600 rpm alternator driven by a steam turbine supplies 110v. at 60 cycles.

The actual system which is being used was designed by Mr. J. V. L. Hogan. The transmitter unit has only one moving part, which is driven by a synchronization motor which drives a lead screw and rotates the message. Drum scanning is accomplished by means of a photo-electric cell. The receiver unit is very similar in mechanical construction. The actual printing is done by means of a low voltage applied across an electrolytic paper. This then discolors the paper which gives the printed matter. The actual synchronization between the transmitter and the receiver is done by means of tuning forks. The station transmitter is synchronized by the 60 cycle power line. The receiver unit has an 1800 cycle tuning fork which triggers a multi-vibrator, whose frequency is 60 cycles per second, therefore a rephasing of the tuning fork circuit would affect 60 cycle synchronization. Once this synchronization was locked, the phasing of the signals hold constant and the equipment works satisfactorily.

All of the forms of communication mentioned in this article have been used in experimental installations for trial handling of freight over sections of the company lines. Much work has already been done toward adapting available communications equipment to the needs of the railroads, but more work remains to be done in the laboratories and engineering departments of the nation's electronic manufacturers. The experiment has proven conclusively that railroad radio communications is possible and practical. 

At the present time the Federal Communications Commission has the railroad operating companies' petitions for frequency allocations under advisement. From their decisions will arise a new and expanded industry in the field of such communications, should their decision favor the petitions.

Facsimile equipment located in the dispatching office of the Rock Island Railroad - RF Cafe

Facsimile equipment located in the dispatching office of the Rock Island Railroad.



Posted March 11, 2021