Trainphone was adopted by PRR as a result of the railroad industry in general losing the rights to 'service' radio bandwidth frequencies early in the century, due to apparent lack of interest, or the inability to find tube equipment durable enough to survive any length of time in on a jolting steam locomotive. Due to Pennsy's huge traffic, it found itself with the need for voice communication between trains and block stations, and between trains themselves. Train orders, telegraphy and the like weren't cutting it on PRR, yet it couldn't use radio for communication with trains.
Trainphone used the track and/or lineside telegraph wires to convey voice messages between loco and cabin car, between trains, or between trains and block stations. The PRR promotional film Progress on the Rails has a segement on the train phone system with some animated graphics that explains how it works and what the PRR used it for.
It accomplished its task by inducing a varying current into rail or wires via an energized coil -- something akin to a radio signal -- essentially turning rail or telegraph wire into a broadcasting antenna. However, it needs to be emphasised that it was an inductive system and not radio. Sort of like the inductive intercom and remote stereo speaker systems that were popular in the 60s and 70s where the signal was imposed on your house wiring. The train phone voice signal (down in the hundreds of kilohertz range i.e. very low freguency) from the towers was imposed on one of the line side wires. This induced a signal of the same frequency on the 'antenna' on the engine or cabin car (more like a signal probe than an antenna). The coil looking device tuned the 'antenna' to the low frequency signal. The coil allowed the 'antenna' to be shorter than really needed for the frequency. The message broadcast could then be picked up by antenna-equipped trains or block stations -- the pickup antennae on moving equipment were the large 'handrail' structures on the tenders of steam locomotives, atop diesel locomotives, and virtually surrounding the longitude of a cabin car.
The same worked in reverse. The trains inductive 'antenna' induced the signal on the line side wires. Since the wires were long enough, tuning coils would not necessarily be needed in the towers. However, not sure how the PRR exactly had the towers set up. Equipment in the tower would have included an isolation transformer to separate the voice signal from whatever else the wire was being used for.
Application of trainphone antennae had to vary, of course, with the application. Pennsy Power I showed some of the original oddball trial applications -- including atop the boilers of steam locomotives. For some reason, diameters of the receiving antennae might have varied -- regular pipe stock was used for receivers, and the smaller diameter "pipes" may have been solid rods. Ken McCorry adds, "It was 1 inch conduit that was insulated from the carbody. Inside was the actual antenna wire. The piping was protection from the elements to preserve the antenna."
The large "handrail" antennae were used to "induce" the current into the lineside wires, or rails (wires carried the induced current farther). The small disc devices "received" the signals, and they were in pairs so one could receive the high band frequency, and one for the low band frequency.
Block cabins and other lineside structures simply had their trainphone devices attached to the lineside wires or rails, and received the signal that way. The wires and rails were the "receiving and broadcasting antennae' for fixed structures, and so there was no need for a separate inducer/receivers as appeared on moveable equipment.
The 'user-interface' was a typical telephone handset, hung on a box-like instrument next to the engineer's seat on locomotives -- probably above the conductor's desk in a cabin car. There was a speaker to get the user's attention (i.e. "MG tower to engineer LCL-1") and the handset was used to allow easier hearing and speaking on a noisy locomotive.
The train phone system used two channels. They were designated 'H' and 'L'. One was for engine-to-cabin (or vice versa) communication, and one for train-to- train or train-to-block cabin communications.
Trainphone was originally used on PRR's busiest lines, such as the Pittsburgh division, as enhancing the ability to move trains in dense traffic was its reason for being. It probably was eventually used system-wide, except for the electrified zones.
TrainPhone was not used in the electrified zone, due to interference from the 25 cycle overhead current, and 'noise' from the locomotives' internal electrical equipment and traction motors. This was unfortunate, as the New York Zone had PRR's highest train density, and one assumes, could have used TrainPhone the most.
Anyone know how on-train telephones used in some passenger trains fit into this system, or if they used another system altogether? The antennae seen on the roofs of some passenger cars would be for the on-train telephone.
Trainphone equipment is one of the things that made Pennsy equipment distinctive, and is indicative of how the railroad coped with the huge traffic it carried.
For further reading, please visit Trains Magazine Online page at http://www.kalmbach.com/trains/. From there, click on "Search", then enter "communications". You'll get several choices. Read the article from the August, 1997, Trains Magazine.From the "PRR-Talk" mailing list: Stephen Bartlett, Chris Brandt, Doug Drew, Ken McCorry, Drew McGhee.
Copyright 1996 - 2008
Last modified: November 23 2007.
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