On Mar 18, 3:30 pm, Bill Horne wrote:
wrote:
Here is how Morse speed is usually calculated:

It turns out that the word PARIS and one word space equals exactly 50
"dit times", with a dit time being the length of time the key is
closed for a dit.

So if the word PARIS is sent 50 times in 1 minute, that minute is
divided into 2500 dit times. Which is 41.66 bps.

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.

The difference has to do with how the coding is done. The following is
all from memory:

60 wpm Morse works out to 3000 bits per minute or 50 bits per second
using the "PARIS" formula.

Your 45 baud Model 15 Teletype was in all probability what hams called
a "60 wpm 5-level Baudot" machine. We had similar machines at the
University. (In this post I use the term "Baudot" to mean the 5-level
TTY code US hams used for many years until FCC allowed us other codes
like ASCII in the early 1980s)

"Baudot" takes 7 bits to send a character: one start bit, five data
bits, one stop bit. A space between words is a character, so to send
the word "PARIS" would take six characters including the space
character. That's only 42 bits, rather than the 50 bits that Morse
requires. Thus the difference - the Baudot machine uses 16% less bits
to send the same message. The speed difference works out to about 10%
because the Baudot stop bit was longer than the others in the machines
US hams typically used.

So you don't get the full 16% advantage that you'd expect from the raw
numbers. But since only six of the 42 bits are stop bits, the
difference is small.

To make it even more of a sporting course, the above WPM advantage of
the Baudot machine is message-dependent, same as for Morse. In Morse,
the message-dependency comes from the different characters being of
different length; a five-letter word like "TENET" takes a lot less
time to send than one like "JUICY", while in Baudot they both take the
same time to send.

But in the Baudot code the numbers and some other characters are sent
by shifting from "LTRS" to "FIGS", (letters to figures), so sending
mixed groups could take a lot of extra characters that Morse does not
require.

For example, in Morse you could just send the group "6A8G7" as 5
characters, but to send it on a Baudot machine you had to send
"figs6ltrsAfigs8ltrsGfigs7", which is 10 characters.

So the WPM are really approximations, and the BPS/baud measures took
over.

73 de Jim, N2EY