[GreenKeys] Precise baud timing

[Harold Hallikainen]

The long stop bit is interesting. I THINK (but do not know) that the
selector does something like this:

1. Detect mark to space transition of start bit

2. 33 ms later, detect D0, the least significant bit. This would be at the
center of the bit time since we allowed 22 ms for the start bit plus 11 ms
to get half way through D0.

3. 22 ms later, detect D1 in the middle of the bit.

4. 22 ms later, detect D2 in the middle of the bit.

5. 22 ms later, detect D3 in the middle of the bit.

6. 22 ms later, detect D4 in the middle of the bit.

7. 22 ms later, stop shaft rotation if we detect a mark stop bit.

The timing of step 7 is my GUESS as to what happens. If the transmitted
stop bit is 22 ms long, we are detecting the stop bit in the middle, which
seems appropriate. If indeed this is the case, it SEEMS that a 22 ms stop
bit will always work. However, if the printer loses sync, it seems like
the 31 ms stop bit allows the printer to resync more quickly than a 22 ms
stop bit.

My newswire feeds ( https://w6iwi.org/rtty/audio/ ) are currently using a
22 ms stop bit (for 60 wpm) and seem to work fine with my model 15.

On a side note, the DSP TU (https://w6iwi.org/rtty/DspTU3/ ) generates an
error report if you type !ER . The error report counts the number of valid
start bits we received (both the mark to space transition AND still being
space at the center of the start bit) and the number of invalid stop bits
(stop bits that are not mark). An error percentage is calculated as
BadStop/GoodStart. It is a MEASURE of receive quality, though not as good
as a bit error rate which we cannot calculate without knowing what was
transmitted. But we do know that the stop bit should always be mark, and
if it is not, there was an error.

Harold
https://w6iwi.org


On Wed, November 12, 2025 9:09 am, Paul Heller via GreenKeys wrote:
> Ah, those are the seven bits! Sorry for my confusing email.
> Paul
>
>
>> On Nov 12, 2025, at 5:08 PM, John, W9DDD <w9ddd at tapr.org> wrote:
>>
>>
>> Start and 5 data bits are 22ms long, stop bit is 31 ms for most
>> machines, but some newer ones only use 22ms long stop bit.  So a
>> complete character is either 7.42 x 22ms = 163.24 ms  or 7.0 x 22ms =
>> 154ms
>>
>>
>>
>>> On 11/12/2025 9:57 AM, Windows XD wrote:
>>> Dear all,
>>>
>>>
>>> I'm working on an adapter which sends out the 7 bit baudot serial
>>> signals in software to a teletype and I would like to check that I
>>> have my timing correct for each bit. If anyone can find a resource
>>> which says or knows of the precise duration of each bit in 45.45 baud
>>> serial I would greatly appreciate it. I've looked, but haven't found
>>> anything definitive. My program currently works for a period of time
>>> but seems to "lose sync" for lack of better words and I think its the
>>> timing.
>>>
>>> Any help is appreciated!!
>>>
>>>
>>>
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>>>
>>>>>> Jordan Spencer Cunningham's GreenKeys Search Tool:
>>>>>> https://teletype.net/gksearch
>>>>>> 2002-to-present greenkeys archive:
>>>>>> http://mailman.qth.net/pipermail/greenkeys/
>>>>>> 1998-to-2001 greenkeys archive:
>>>>>> http://mailman.qth.net/archive/greenkeys/greenkeys.html
>>>>>> Randy Guttery's 2001-to-2009 GreenKeys Search Tool:
>>>>>> http://comcents.com/tty/greenkeyssearch.html
>>>>>>
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>>
>> --
>> ---
>> ----
>> The above comments or recommendations are SWAG. Use at your own risk.
>>
>>
>> John, W9DDD
>>
>>
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>>
>>>>> Jordan Spencer Cunningham's GreenKeys Search Tool:
>>>>> https://teletype.net/gksearch
>>>>> 2002-to-present greenkeys archive:
>>>>> http://mailman.qth.net/pipermail/greenkeys/
>>>>> 1998-to-2001 greenkeys archive:
>>>>> http://mailman.qth.net/archive/greenkeys/greenkeys.html
>>>>> Randy Guttery's 2001-to-2009 GreenKeys Search Tool:
>>>>> http://comcents.com/tty/greenkeyssearch.html
>>>>>
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
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>>
>
> ______________________________________________________________
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> Post: mailto:GreenKeys at mailman.qth.net
>
>
>>>> Jordan Spencer Cunningham's GreenKeys Search Tool:
>>>> https://teletype.net/gksearch
>>>> 2002-to-present greenkeys archive:
>>>> http://mailman.qth.net/pipermail/greenkeys/
>>>> 1998-to-2001 greenkeys archive:
>>>> http://mailman.qth.net/archive/greenkeys/greenkeys.html
>>>> Randy Guttery's 2001-to-2009 GreenKeys Search Tool:
>>>> http://comcents.com/tty/greenkeyssearch.html
>>>>
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to harold at w6iwi.org
>
>


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