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From: morris@jade.jpl.nasa.gov (Mike Morris)
Newsgroups: comp.dcom.telecom
Subject: Technical Specifications of TTY Machines
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Date: 22 Sep 89 16:31:37 GMT
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(Nickolas Landsberg) writes:
>
>	In the above mentioned article, you mentioned that the speed
>was around 60 baud.  Well, it was actually something called "75-speed"
>which indicated a maximum speed of 75 WPM, transmitted in 5-level
>"baudot" encoding.  After doing all the mumbo-jumbo af adding start/stop
>bits, etc. this translates to an equivalent bits-per-second of 56.83
>or thereabouts.  A system I worked on once had to monitor transmissions
>from a telco switch which also used this.  An interesting sidelight is
>that they could transmit the full upper-case character set, the numerics
>and a goodly supply of punctuation using just 5 bits.  (Actually, they
>used a "switch" character to flip-flop between meanings of particular
>bit patterns.  The "alternate" set would continue to be used until
>the "switch" character was seen again.)

A bit of nit-picking here: the upshift character was called FIGS (for
FIGureS, and the downshift character was called LTRS.  All the machines
had a feature called USOS for UnShift On Space, and sometimes a message
would have to be resent because an inexperienced operator would send
a message with a lot of numbers on a machine that would drop back to
letters and be received on a machine that wouldn't.  Smart operators
sending strings of numbers would send a FIGS after any space character
just in case.

As a side note, the standard speeds were 60, 75 and 100 words a minute,
using either a standard length stop pulse or a 1.5 length stop pulse.
There are electronic speed converters around, most machines came geared
for 60, or 66 (WU's own speed).  The type-15 and type-19 machines could be
geared for 60, 66, or 75, but had maintenance problems at 75.
The later type-35 machines could be geared for 60, 75, or 100 wpm, or have
a 3-speed gearbox.

5-level machines are still in use in the amateur radio field, and still
passing traffic - the name there is RTTY for Radio TeleTYpe, sometimes
called "Ritty".  Here in Los Angles, much of the local activity is on
146.70 Mhz, and some of the stations are quite sophisticated, using
selective call (imagine a answering machine), and answer-back, etc.
Bless the man that designed the first UART chip with 5,6,7 and 8 bits/char!

Teletype has discontinued parts availability for the Type-15 and Type 19
(which I have in my station) and for the Type-28 (which I may upgrade to
soon- for hauling it away!) - all 5-level).  BTW, my type-15 is
manufacture-dated 1933, and is still in full working condition - I
had to replace the internal wiring as the cotton insulation had
hardened and cracked, and become oil-soaked.  I saw a picture of a
type 20 - it was a 6-level machine used in typesetting - the brief
story said it was a 5-level unit with a case bit.  The type-26 was a
light-duty printing drum machine (like the later 32/33 line) - the
ones I worked on were just not designed for 8-hours-a-day use.
I was told that there was a type 29 and 30, but sever saw literature or
any machines.  The Type 32 is the last of the mechanical 5-level machines,
(I was told it was a redesign of the 26) and it interestingly came in a 3-row
and a 4-row configuration.  The famous type 33 is the common 8-level
machine that I learned BASIC on, interestingly it's stiff keyboard is
blamed for the "tersenes" of UNIX (tm).  The type 35 is the standard
8-level heavy duty machine.  The 37 was an attempt at a upper/lower case
8-level machine - I've only seen 3 in my life, and one of those was in
a scrap heap - supposedly it was a maintenance nightmare.  The 40 was
an attempt at a do-all-end-all integrated system that never made it - I
saw only a few in use, and those were used as dumb terminals.  The
saving grace was the printer - it was built like a mini-IBM-1403, a
train mechanism and was almost indestructible.  I saw several in use
on minicomputer systems, running day in and out with no downtime.  The
type 42 is a 5-level version of the 43 8-level dot-matrix machine - the
one with the strange paper size (8.5 inches wide, _including_ the
perforations!).  If anybody wants a 43, let me know - I've access to 70
in excellent condition in a warehouse - make offer!.  I know several local
amateurs that use 43s as logging printers, and as _quiet_ RTTY stations (with
UART-based 8-level-to-5-level converters).  8-level RTTY is legal in the
amateur service, but is (naturally) incompatible.

Packet is slowly replacing RTTY for message handling, due to it's natural
connectivity (it's X.25 based) but there are still a lot of people using
the old mechanical marvels.

Amateur radio has many facets: voice, television (yes, you can own a TV
transmitter!), radioteletype, packet, radio astronomy, satelites, and more.
If you're interested, look at rec.ham-radio or rec.ham-radio.packet.

Sorry if I got off the subject of FIGS & LTRS, but I happen to like
the old machines.  I spent 13 months working for a TTY sales & service
shop, and still dabble a bit.

Mike Morris                      UUCP: Morris@Jade.JPL.NASA.gov
                                 ICBM: 34.12 N, 118.02 W
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