[GreenKeys] do the length of stop bits affect clutch wear?

[Duncan Brown]

Jim,

Thanks for your 7.42 code explanation (again - more detail this time!) 
It is always amazing how some old ideas hang on, long after they are needed.

At some point in the mid 1960s, both Teletype Corp & KLI started  
supplying TTYs with 7.00 code transmitters to the military. Some KLI 
machines were set up for 8.00 from the keyboard and 7.00 from the tape 
reader. Was this for AUTODIN, or some other computerized system that 
couldn't handle the fractional bits?

have fun,

Duncan
K2OEQ

On 11/23/2018 11:21, Jim Haynes wrote:
> Here's a little-known bit of trivia that I have posted before but
> worth posting again I guess.
>
> The question is, why 7.42 unit code (1.42 unit STOP pulse)?
>
> Western Electric developed some teleprinters which used faceplate
> receiving and transmitting distributors, and they had both distributors
> running on the same shaft.  That obviously prevents stop-start from
> working, since the receiver is ready to begin the start segment as soon
> as the transmitter finishes the stop segment.  So they put a clutch on
> the transmitting distributor, and used a relay to operate the clutch.
> This added a little time after the transmitter had finished its rotation
> before it could start off again.  Empirically they found that the relay
> added 0.42 pulse duration to the process, so it effectively had a 1.42
> unit stop pulse.
>
> Now Morkrum (ancestor of Teletype) had solved the problem a different 
> way,
> by running the receiving distributor shaft faster than the transmitting
> shaft.  So that when the transmitting shaft had completed a rotation the
> receiving shaft had finished early and was held back by the clutch.  This
> continued through the whole life of the Teletype product line and 
> meant that a Teletype printer could work satisfactorily on 7.00 unit 
> code.
>
> The Bell System early on wanted interoperability between the Morkrum and
> the Western Electric printers, so they demanded that the Morkrum
> transmitters should generate 7.42 unit code.  And this they continued
> ever after, even though the Western Electric printers were long extinct.
> And for some reason was applied to the machines sold to the military and
> other non-Bell customers.  Only Western Union got 7.00 unit code 
> keyboards.
>
> So the 7.42 code is ultimately the result of a design short-sightedness
> at Western Electric.
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