The 50 baud may of had something to do with sync speed of the motors as uk mains is 50 Hz , the land based (GPO) telex machines ran at 50 baud , but the navy used 75 bauds .ship a/c 60 Hz . I did have a creed 75 telly printer and 3 sets of gears , 75, 50, 45.45 baud , with the 240v/50hz sync ac motor it was noise free , electricslly that was !
G .. --- In digitalradio@yahoogroups.com, "W5XR" <w...@...> wrote: > > Very interesting bit of history. I had to ask, as I used some of that old > equipment back in the 50's. > Thanks. > > Bob, W5XR > > > _____ > > From: digitalradio@yahoogroups.com [mailto:digitalra...@yahoogroups.com] On > Behalf Of jhaynesatalumni > Sent: Thursday, February 26, 2009 3:04 PM > To: digitalradio@yahoogroups.com > Subject: [digitalradio] Re: on another note > > > > --- In digitalradio@ <mailto:digitalradio%40yahoogroups.com> > yahoogroups.com, "W5XR" <W5XR@> wrote: > > > > I'm asking. :) > > > > Bob, W5XR. > > O.K. > > For START-STOP synchronization to work the receiving shaft (selector > or distributor) has to stop between characters. The Morkrum Co. > (ancestor of Teletype Corp.) had the sending and receiving distributor > shafts running at different speeds, so the receiving distributor > completed its rotation part way through the STOP pulse and was > held there until the next START pulse. the STOP pulse was the > same length as all the others, so it was 7.0 unit code. > > Western Electric had built some teleprinters of their own, and > in theirs the transmitting and receiving distributors were on the > same shaft. So to give the receiver a chance to stop they had to > stop the transmitter between characters. They did this by adding > a relay to operate the transmitting distributor clutch. At the > speed they were running at the time, something like 45 wpm, > the relay added a delay in milliseconds that was equal to 0.42 of > a pulse duration. > > When Western Electric discontinued making their own teleprinters > and started buying from Morkrum they insisted on interoperability > with the W.E. machines. Morkrum didn't want to use a relay in > the transmitter clutch, so they simply elongated the STOP segment > on the transmitting distributor to 1.42 times the length of the > other segments and changed the shaft speed to keep the pulse > duration the same. So we got 7.42 code; and this continued as > speeds were increased and after the Western Electric equipment > had all been phased out. > > Western Union didn't have the problem of interoperability with > old Western Electric designs, so they insisted on 7.0 unit code > because of the slightly higher speed that gives, roughly 65 wpm > instead of 60. For many years Teletype had to make equipment > that could transmit either way, by supplying the appropriate > transmitter cam and gear. The printers all had no trouble copying > 7.0 unit code. > > At 100 wpm, 7.42 unit code gives a speed of 74.2 baud. At some > point the U.S. military decided to round that up to 75 baud, > and then to standardize on speeds that are 75 multiplied by a > power of two, so we got 75,150, 300, 600, 1200, etc. for our > terminals and modems. > > For some reason Europe standardized on 50 baud and 7.50 unit code; > I can only assume that some equipment manufacturer had trouble > with a unit-length STOP pulse and needed extra time to get the > receiver stopped. >
