In article ,
Bill Horne wrote:
I'm sure your explanation is correct, but it leaves me confused: I know
bps baud, but they're close, and the Model 15 Teletype I used to own
operated at 45 baud. It seems illogical that Morse would be so high in
the bps count.


Your Model 15 Teletype at the nominal 60 wpm speed, which is actually
368 chars/minute and 45.45 baud works out like this. The character
length is 7.42 bits long (for ancient, interesting reasons I won't go
into right now) and the bit duration is 22 milliseconds. The character
duration is therefore 7.42 * 22 = 163.24 milliseconds, and that works out
to 6.12595 characters/sec = 367.55 characters/minute. To convert that
to words you have to figure 6 characters per word because the space
between words is also a character. So the speed is actually 61.26
words/minute.

Teletype speed is sometimes confusing because there are a couple of
other speeds out there. Western Union liked to use a 7.00 unit
character rather than 7.42. With 45.45 baud, or 22 ms pulses, this
gives 154 milliseconds/character, or 6.49 characters/second, 389.6
character/min and hence 65.9 words/minute. This is completely
compatible with 7.42 unit code because the baud rate is 45.45 for
both. But then there is European 50 baud Telex using a 7.5 unit
code. This is a 20 millisecond bit for a character length of 150
milliseconds, 6.67 characters/second, 402 chars/minute, 67 words
per minute. This is not compatible with the other two codes because
the baud rate is different; but if you say something like "66 wpm"
you could be talking about either scheme.

Now when you get to ASCII, the old Teletype machines transmitted 8
data bits per character and used an 11.0 unit code. This makes 100
wpm work out to 110 baud. Electronic terminals don't need 11 unit
code; they can do just fine with 10. Thus the words-per-minute is
numerically equal to the baud rate. 100 baud - 10 ms/bit -
100 ms/char - 10 chars/sec - 600 chars/min - 100 wpm.

Morse has already been explained. A Morse dot is actually two bits,
since there is the dot followed by the space that makes it distinguishable
from what comes next. A Morse dash is four bits, counting the space,
and the word space is three dot times or 6 bit times. Then the
word PARIS contains 50 bit times counting the space. So one word
per second is 50 bits per second and 60 wpm. As an aside, the
military sends a lot of encrypted 5-letter code groups, so instead
of PARIS the Signal Corps uses CODEZ as a test word more statistically
correct for their kind of traffic. And CODEZ contains 60 bits.