[GreenKeys] 7.00 vs 7.42 unit code

[Duncan Brown]

The extra 9ms on the stop pulse (to make 7.42) was a requirement for an 
early Western Union machine that was obsoleted 80-90 years ago. Most (if 
not all) "modern" machines (designed since about 1925) should copy 7.00 
with no problem.

Computer TTY software is typically "tuned" to a specific data rate. I 
know that MMTTY will not copy 66wpm when set for  60wpm. (I finally 
found the hidden control on MMTTY that lets you change the speed). Don't 
know how stop bit length would effect it.

Have fun,

Duncan
K2OEQ

On 8/7/2019 10:41, Nick England wrote:
> Doing some machine shuffling this week made me think about this - 
> please steer me back on course if my thinking is off.....
> Truth-
> 7.42 unit code has a start bit and 5 data bits of equal length (1.00 
> unit each) and a stop bit 1.42 units long.
> 7.00 unit code has a 1.00 unit stop bit.
> 45.45 baud code can be either - each 1.00 unit data bit is 22ms.
> So 7.42 unit at 45.45 baud is 60 wpm
> and 7.00 unit code at 45.45 baud is 65 wpm
> There's a chart at http://www.navy-radio.com/tty/speed-feed.gif
>
> Consequences-
> These two do require different gear sets - you can't just put 60wpm 
> gears (368 opm) into a 7.00 unit machine (390 opm) - that would make 
> the baud rate wrong and your selector and keyboard transmitter timing 
> would be off.
> A 7.00 printer can copy a 7.42 keyboard or 7.42 TD no problem.
> A 7.42 printer can copy a 7.00 keyboard if you don't type at max rate
> A 7.42 printer probably cannot copy a 7.00 TD
>
> What about sending RTTY with a 7.00 keyboard or TD? - will the 
> computer software RTTY folks copy it OK? I assume so, but don't know 
> for sure.
>
> Comments welcome.....
>
> best regards,
> Nick England K4NYW
> www.navy-radio.com <http://www.navy-radio.com>
>
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