In old photos I have seen cars and engines (mostly Pennsy, I think) with what appears to be a row of stanchions on the centerline of the roof. They appear to be connected by either heavy wire or rod/tube.
My two theories have always been that they are:
1) somehow radio-related, or
2) it's merely a handrail for maintenance personnel who need to be on top of the cars or engines (which may have curved, unsafe-to-walk/crawl-on roofs).
Here's a photo: https://ogrforum.ogaugerr.com/fileSendAction/fcType/0/fcOid/39582004903544964/filePointer/40849088187154493/fodoid/40849088187154483/imageType/MEDIUM/inlineImage/true/Pennsy%2520E8%25201812.1377656167.jpg
And another: http://bcoolidge.com/PRR%20Pix/Lounge%20Observation%201132%20at%20Chicago%2011_12_66.jpg
What's the story?
Still in training.
I'm pretty sure that they're antennas. Only the Pennsy had them, so I wonder why all railroads didn't use them. Or am I wrong about that?
PRR Trainphone: https://en.wikipedia.org/wiki/Trainphone
Not radio, but electric induction.
There were also "things" on top of most UP lightweight food service and club cars. I lean towards them being radio antennae for "entertainment systems". Called "radio" at the time.
Ed
NorthWest PRR Trainphone: https://en.wikipedia.org/wiki/Trainphone
Trainphone was rumored to come about because US military would not release research on FM radio until way after WW-2 . Believe trainphone was an AM type transmission that would not work under PRR's 25 hZ CAT and transmission lines ?
E.H. Armstrong patented FM in the 1930's and FM broadcast stations were set up before WW2. For what it is worth, FM is a form of spread spectrum modulation.
Note that the Trainphone worked on inductive coupling to the lineside wires and thus did not have the line of sight limitations as with VHF radio. Since the PRR ran though some rugged terrain, the ability to communicate beyind line of sight would have been a great advantage.
Commercial FM broadcasting began to really take off in 1947.
Johnny
That's not too right. The Trainphone idea, as the 'grasshopper telegraph', has a very old history; Frank Sprague commented on it before he got into elevator-control design. Not difficult to filter out the 25Hz and any harmonics from the 'phone transmission, too.
As you probably know, the initial spec for the railroad radio service in 1945 involved FM radio channels. What changed was the channel bandwidth (to allow more channels in the same spectrum) and of course improvement in equipment -- but there was nothing exotic or difficult about FM even in the immediate postwar period.
erikemNote that the Trainphone worked on inductive coupling to the lineside wires and thus did not have the line of sight limitations as with VHF radio.
Since the inductive coupling had a lateral range measured in no more than a few tracks, perhaps a couple of hundred feet, I doubt there was much line-of-sight impairment in normal practice. What I think you mean is that because the lineside antenna run followed the tracks, communication both 'between ends' and to wayside points was always reasonably assured regardless of topography -- which is true. Also, if I remember correctly, energy required was massively lower than for omni RF, and there was inherent separation of transmissions from multiple trains using the common infrastructure simply by dividing the antenna runs into 'blocks'. (Incidentally, 'security' against unwanted eavesdropping is greater for inductive, and I think I remember one '40s or '50s source discussing this 'feature'.)
There are some fun illustrations of the system in the trade press and ISTR in some advertising to the 'general public'.
Thanks, folks.
Overmod Since the inductive coupling had a lateral range measured in no more than a few tracks, perhaps a couple of hundred feet, I doubt there was much line-of-sight impairment in normal practice. What I think you mean is that because the lineside antenna run followed the tracks, communication both 'between ends' and to wayside points was always reasonably assured regardless of topography -- which is true.
Since the inductive coupling had a lateral range measured in no more than a few tracks, perhaps a couple of hundred feet, I doubt there was much line-of-sight impairment in normal practice. What I think you mean is that because the lineside antenna run followed the tracks, communication both 'between ends' and to wayside points was always reasonably assured regardless of topography -- which is true.
Exactly.
If even a couple of lineside wires were routed through tunnels, then there's a chance that communication could have been maintained in tunnels...
One other plus for inductive coupling is that it didn't need to have a frequency allocation from the FCC, much the way that carrier current communications on high tension lines avoided the issue. IIRC, both used carrier frequencies in the 100 to 200 kHz range.
- Erik
erikemOne other plus for inductive coupling is that it didn't need to have a frequency allocation from the FCC, much the way that carrier current communications on high tension lines avoided the issue. IIRC, both used carrier frequencies in the 100 to 200 kHz range.
Power Line Carrier systems work in the 40-200 KHZ range. There were some threats to that spectrum when the Navy wanted to put some high power transmitters in Wisconsin (Why Wisconsin I have no clue) to talk to submarines.
The railroads also used open wire carrier systems to add voice, telegraph, and data (data was new then) circuits between wire centers. This was before microwave systems were developed. In the late fifties, when I worked on the PRR, a number of times, I used (after dinner) an open wire circuit that connected me from the camp train in Greenfield IN to Colunbus OH where the operator would patch me onto a carrier circuit to Cincinnati where the operator would connect to the Bell system to talk to my girlfriend. There were separate wire circuits for the dispatchers and other business but the ones I used were not used much after hours. On a later assignment, I was assigned to Columbus OH, and I would just go down to the switchboard (a three position plugboard with only one operator on duty after hours) and use an idle position whare I could see the carrier circuits which were mostly idle and make my connection to Cincinnati. Saved long distance costs.
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