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W.U. transmission question [Telecom]

I wonder if there is an old Western Union hand in the group. I'm looking at a diagram for an operating table which says it is Class C, and I see there is a Class CT for use over telephone circuits, so I assume that Class C is a particular transmission scheme. I can see that there is a single wire line, and that the table transmits positive for mark and negative for space. I see the receiving relay has a bias current at all times. I don't know what goes on at the other end of this circuit, what it transmits and how it receives. I see that this can be a terminal station at the end of the wire or an intermediate station in series with the wire.

I guess I need to find a W.U. relay and do some experiments to figure out the meaning of D, U, circle-D, circle U, A, O, A' and O'

-- jhhaynes at earthlink dot net

***** Moderator's Note *****

I think we need some more detail to help you, but I'll publish this in hopes that someone from WU will recognize the device and/or system you're working on. It sounds like a duplex circuit, but I'll defer to the WU veterans.

Bill Horne Temporary Moderator

Please put [Telecom] at the end of your subject line, or I may never see your post! Thanks!

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Reply to
Jim Haynes
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I don't have the URL handy, but there is a Western Union retirees website out there; perhaps some of the people who work on that might have some insights.

Reply to
hancock4

Good suggestion - I've seen that web site and will try it.

I think I have it figured out, as there seems to be only one possible way it could work. The line is looped through the out stations if there are more than one. The out stations transmit polar through a relay to ground at the head end. The head end sends make-and-break keying.

-- jhhaynes at earthlink dot net

***** Moderator's Note *****

You've piqued my curiosity, so please let the Digest's readers see the plans. I'm not sure that I understand what you're descxribing, and I'm going to ask that you photograph the drawings you've been looking at, and either post them on your own website or send them to me for posting on the digest's site.

I know it can't be a Polar duplex set, since they are only usable from point-to-point - they're not multipoint devices. If that's what you're looking at, it wouldn't have served more than two stations, but let's see the pictures and take a trip down memory lane.

Bill Horne Temporary Moderator

Please put [Telecom] at the end of your subject line, or I may never see your post! Thanks!

We have a new address for email submissions: telecomdigestmoderator atsign telecom-digest.org. This is only for those who submit posts via email: if you use a newsreader or a web interface to contribute to the digest, you don't need to change anything.

Reply to
Jim Haynes

Sounds like standard 60 mA current loop to me?

--scott

Reply to
Scott Dorsey

What I've been able to figure out from the schematic and doing some testing on polar relays is this. There is a single wire ground return loop from the main office through zero or more intermediate out stations to the terminal out station. The outstations transmit polar, and contrary to the usual Western Union usage it is + for mark and - for space. This presumably goes through a polar relay to ground at the main office. The main office apparently transmits make-and-break to the outstations, as their receive polar relays are biased.

I guess it would also work if the main office transmits polar, - for mark and + for space. But I don't see any advantage in that, for then the main office receive relay would have to be biased and that seems to defeat the purpose of using polar transmission.

Reply to
Jim Haynes

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