Jim Haynes posted on Tue, 18 Mar 2008 19:47:44 EDT:

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.

For what it is worth, my paper reference on TTYs is NAVSHIPS
0967-255-0010 "Principles of Telegraphy (Teletypewriter)" from
Department of the Navy Electronic Systems Command. I bought it
from the US Government Printing Office back in the early 1970s as
a reference. [I am an Army veteran, not Navy] The first chapter of
Part A in that TM has a nice historical record of 'telegraphy'
(which includes teletypewriting). It says only "60 WPM" but mentions
other Baud rates.

As far as we in Army communications of the mid-1950s were concerned,
all the teletypewriters that the Army used were called "60 WPM" and
only the teletypewriter maintenance people (and a few carrier systems
types) cared about many numbers. We did have Distortion meters used
to determine irregularities in a circuit.

BTW, the Army and the rest of the military used Teletype Corporation
Model 15s through 19s, variation being only the paper tape punch
and transmitting distributor (P-tape reader).


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.

OK on that. Teletype Corporation Model 28s (explained in intimate
detail in the NAVSHIPS TM I referenced) would easily do 100 WPM
equivalent 24/7 as long as supplied with paper, ribbon, and oil. :-)


...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.

I never encountered any test word 'CODEZ' 1953 to 1956, nor
elsewhere in the Signal Corps or in DoD contracts after that. In
the mid-50s we simply used a continuous 'R-Y' generator (from
Teletype Corporation) for circuit checks with the old 60 WPM
equivalent machines. Teletype Corp. also made a 'fox test'
generator consisting of a half dozen cams operating as many
switches to generate "The quick brown fox jumped..." sentence
(with Tx station ID at the end) for radio circuit checks.

Electromechanical teletypewriters are now rather passe' in the
military and government (I use a French word to replace Obsolete
which so many have trouble with). It is all electronic and, for
permanent installations, over the DSN (Digital Switched Network)
anywhere...including interfaces with the regular civilian telephone
infrastructure. The DSN allows encryption on-line as per protocol.
For field radios, the electronic data protocols are compatible
with hard-wired ones and also allow encryption on-line. It was so
in the first Gulf War (1990-1991) which 'battle tested' the whole
military communications network DX to no-DX via TDRS (Tracking
and Data Relay Satellites) and other military commsats from/to
Florida to/from the Middle East.

Not having any access to the DSN or intimate details of military
cryptographic equipment now, I have no exact knowledge of what is
used for a test word, sentence, or whatever. For the OLD electro-
mechanical teleprinters, I'd say the specifications for a
specific TTY Distortion Meter would tell the exact story on
timing for both polar and non-polar TTY circuits and equipment.

73, Len AF6AY