[GreenKeys] Model 15 Keyboard

[Nick England]

Note. I understand that a 7.42 (60 wpm) printer will copy a 7.00 (65 wpm)
character OK (with a little range adjustment) because the main shaft
actually turns faster than one rotation per character.

And Disclaimer - I’m a M28 guy with no M15 experience. And I’m just a
hobbyist, never a trained military or civilian teletype tech.

Nick England K4NYW
www.navy-radio.com


On Fri, Feb 28, 2025 at 6:07 AM Nick England <navy.radio at gmail.com> wrote:

> 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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