-------- In message <df7c7705-b1cc-4b8d-8bac-d471e2ab5...@bardagjy.com>, Andy Bardagjy w rites:
>Does anyone know any other history about that particular piece of equipment? I seriously doubt those claims of precision. At datamuseum.dk we did a small booklet about the history of paper tape as a storage medium some years back, and the Great Nordic Telegraph Company was roughly half of the material. The first thing to notice is that most cables were simplex, you could only transmit in one direction at a time. The turnaround was suprisingly slow. Because of the dielectric absorption in many miles of cable you had to disconnect your (relatively high voltage) transmitter, short the cable for some time, before you could attach your (incredibly) sensitive receiver to the cable. "Some time" depended on cable type and length of cable, but up to five minutes were not unheard of. (The exact duration were often determined by the clerk putting his moistened finger across the terminal.) Needless to say this made it a paramount matter of efficiency to minimize turn-arounds, and therefore the general scheme of operation was that one side would transmit until they had cleared their backlog or until a certain maximum amount of time since last turnaround had elapsed. Some high-traffic cables ran on "clockwork" (minutes 0-15,30-45 A to B, minutes 15-30,45-00 B to A) -- this made it possible to predict how much papertape would be required. During each "turning", the transmitter would be driven by papertape, each roll as large as physically practical, but there would still be a gap between individual messages on the tape and a longer gap between tapes. It was not uncommen for a high speed relay station to go through five miles of papertape a day at rates of several inches per second. This is even more astonishing when you realize that many of these relay stations were remotely situatated, like for instance the "Eastern & South African Telegraph Companys" station on the island Bawe outside Zanzibar. For particular long cables repeater stations were necessary and since they only had two cables, there were never any doubt where the messages would go. Most, but not all of these skipped the paper-tape step, and had the receiving "undulator" drive the transmit relay directly. This is likely the kind of "syncronized" table described in the text. The majority of stations had more than two cables and therefore needed to make routing decisions, but messages would be batched as early as possible to minimize the number of paper tape splices required. Anyway... What all this boils down to is that the syntonization requirements were nowhere as dramatic as that text claims: +/- 5% were a very common specification. Driving the 30Hz reed with a pendulum clock would trivially do this. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.