[GreenKeys] Model 15 Keyboard

[Nick England]

A look at the archives will turn up the history of 7.42 vs 7.00.

7.00 has a stop pulse the same length a start and data pulses. 7.42 has a
longer stop pulse (1.42) but the baud rate is the same since baud rate is
determined by the shortest pulse. Obviously the total character time is
different so one complete keyboard cycle is shorter for transmitting 7.00.
The motor pinion/gear determine the baud rate (main shaft speed) and the
keyboard gears determine the transmitted character time.

Disclaimer- I have probably screwed up this explanation, but most of the
basic facts are right.



Nick England K4NYW
www.navy-radio.com


On Fri, Feb 28, 2025 at 1:12 AM steve bennett via GreenKeys <
greenkeys at mailman.qth.net> wrote:

>
> Jim,
>
> Yes you are correct about the cams.
> I did a search in the document to see if the term "Bell System Standard"
> appeared anywhere else
> and the other place it showed up was on the cam. They list two part
> numbers for the cam.
> One for 7.00 and one for 7.42.
>
> -Steve
> On Thursday, February 27, 2025 at 10:51:18 PM EST, Jim Cooper <
> jim.w2jc at gmail.com> wrote:
>
>
> On 28 Feb 2025 at 2:48, steve bennett via GreenKeys
>
> wrote:
>
> > Just counted the keyboard gear teeth
> > on my M15. Machine was a RO for
> > Associated Press so it didn't even
> > have a keyboard originally but for
> > what it's worth the keyboard gear on
> > the main shaft is 21T which is what
> > the manual calls Bell System
> > Standard. That is in agreement with
> > the gear on the keyboard John sent
> > me. Also a bell system standard.
> > Whatever that means.
>
>
> You are lucky that you have the gears for
> the "Bell system standard" ...
>
> as you typed earlier but did not realise it,
> there are two TYPES of baudot signals ...
>
> 7.00 and 7.42 ...  first is common on WU gear;
> second is common for everyone else !!
>
> has to do with the length of the STOP pulse...
> 7.42 allows time for the rotating shafts to
> complete and stop before the next start pulse.
>
> 7.00 runs with the same length stop pulse
> as are all the other bits of the code, thus no
> 'catchup' time ...  WU thought they would be
> cute and 'faster' by cutting down the stop length.
>
> The kbd gears have to account for that timing,
> as do the cams, etc.
>
> w2jc
>
>
>
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