[GreenKeys] Bit rate question

[Brooke Clarke]

Hi Sam:

When a teletype machine is just sitting there waiting there's loop 
current that holds the clutch in the disengaged position.
At the start of a character the "start bit" opens the loop for one bit 
time.  the data bits follow sequentially (5 and 8 are common numbers of 
data bits, but there can be any number) then a stop bit.  The width of 
the stop bit can be either 1 bit time or 1.5 bit times.  To convert 
between characters and words you can use 5 characters/word as an average.

1 divided by 61.1 baud = 16.367 ms for a bit time.  For a 5 level (data 
bit) character there are 7.5 bit times per character, or 122.75 ms per 
character.
1 divided by 122.75 ms = 8.14 characters per second or 488.8 characters 
per minute or 97.7 WPM.

If the stop bit was 1 bit, then 16.367 times 7 =114.5 ms per character.
1 divided by 114.5 = 8.7 char/sec or 523 char/min.  divided by 5 
char/word = 104 WPM.

The Western Union 5A stock ticker runs at 20 ms bit times, see:
http://www.prc68.com/I/WU5A.shtml#Tim
Note: there were two possible coding schemes for the 5A.  In one scheme 
there were start and stop bits and in the other scheme there were no 
start or stop bits.

Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.End2PartyGovernment.com/


Sam Etler wrote:
> Robert, Did they use start bits? I'm going by what Jim Haynes wrote about
> deriving words per minute rates from baud rates and he makes no mention of
> start bits. Only stop bits that had varying lengths depending on the
> equipment and the network operator.
>
> Rice, Thanks for the scans, I'll have to take a more in depth look. A quick
> skim didn't clear anything up but I'm new at this.
>
> sam
>
> On Wed, Sep 14, 2011 at 8:44 AM,<WA5CAB at cs.com>  wrote:
>
>> Sam,
>>
>> You forgot the Start bit.
>>
>>
>> In a message dated 09/14/2011 10:04:25 AM Central Daylight Time,
>> etler at cs.wisc.edu writes:
>>
>> Playing around with some math there's two possibilities I found for this.
>> First, if you used a 6.5 unit code per bit (five data bits plus a 1.5 unit
>> stop bit) you end up with almost exactly 564 characters per second which
>> works out to 94 words per minute. Sort of an odd speed. It also sort of
>> works if you just use a 6.0 unit code (1.0 unit stop bit). Then you get
>> almost exactly 611 cps or 101.83333... wpm. Doesn't work quite as nicely
>> though the 611 is pretty clean. It's possible there's other data bit + stop
>> bit + ??? bit combinations I didn't think of that would work equally well.
>>
>> Or maybe I'm way off here and it's something completely different.
>>
>> So does anyone know what the deal is with this?
>>
>> sam
>>
>>
>>
>> Robert&  Susan Downs - Houston
>> wa5cab dot com (Web Store)
>> MVPA 9480
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