[GreenKeys] Teletypes round 2

[Harold Hallikainen]

> Some of that transition depended on the wire service and the state.
>
> As for The Associated Press in North Carolina, the only dot matrix
> printers, specifically, the Extel units, were installed in customer
> operations where the customer paid extra for the printers - 1978
> timeframe.
>
> All the slow speed wire printers were either Model 15 units (5-level code)
> or Model 20 printers (6-level code).
>
> Some/many/all of the UPI radio stations in North Carolina were Extel
> printers in 1976.


Speaking of model 20, my school newspaper had one with a tape punch. At
the beginning of each wire service story, a bunch of garbage was printed.
this was the story number in readable form on the 6 hole tape. The
newspaper staff would go through the punched tape looking for the story
number, then tear the tape off to isolate that story. They'd then walk
across the hall and feed the tape into a Linotype machine. The resulting
lead type was then put in a proof press and a proof made. The story proof
was then placed on the page paste-up. When the page was complete, it would
be photographed, then a plate burned from the negative. Finally, the plate
would be put on the offset web press. Quite a process!

The Linotype was eventually replaced by a couple photographic typesetters.
One had a drum with all the characters on it. The drum rotated until the
right character was in position to expose the film. A light would then
flash to expose that character onto the film for the page. The film for
the page would then move to be ready for the next character.

Another photographic typesetter had all the characters arranged on a sheet
of film in a square matrix. A series of mirrors, each representing one
bit, could be flipped to one of two positions. This would place the image
of the desired character in the right position to expose the film for the
page.

Printing in general is quite interesting! Stuff like the Teletype model 15
was definitely designed around a classic typewriter. Then there were daisy
wheel printers (I had one of those!). And the IBM Selectric (to me,
amazing mechanics!). Then impact dot matrix. The Extel was mentioned
above. I also sold a lot of Teletype model 43 printers as part of a
logging system for radio stations. The first ink jet printer I saw was an
Olivetti that had a single nozzle. The print head scanned back and forth
very quickly. Then there are the thermal printers, some with ribbons so
they would not require special paper. Most fax machines used thermal
printers until ink jet came along. Other fax printers (and similar)
included the DeskFax that Western Union gave to customers to send their
telegrams to the local office. It had a classic spinning drum for
scanning. While in high school, I met a short wave listener who "listened"
for "wire photos." He had a rotating drum receiver that exposed
photographic film. He got some very high quality photos. More in the fax
area were the weather map receivers the FAA used in the 1970s (I used to
maintain one for the FAA). I think these were made by Alden (
http://www.alden.com/about - Looks like they were acquired by Morcom ).
These printed by passing current through soggy paper turning it from white
to brown. Horizontal scanning was provided by a drum with a helix on it.
The drum and helix were behind the paper and a "blade" was in front of the
paper. When the helix was in the right position, a voltage would be put on
the helix causing a current through the soggy paper turning that spot
brown. The helix drum was driven by a 60 Hz synchronous motor. The 60 Hz
was derived from a crystal oscillator and a digital divider. At the
beginning of each weather map, a sync sequence consisting of a short
period of white followed by a full line of black was sent for several
lines. The divider would change the motor frequency slightly so the
vertical white bar would skew to the left until it lined up with the left
edge of the image. The motor was then changed back to 60 Hz. I think an
optical interrupter on the drum detected the drum position and compared
that with the received signal. The images were sent over a phone line
using FM with one frequency representing white and another representing
black.

This FAA flight service station also had a bunch of Teletypes. The staff
would do weather observations, punch a paper tape, then load it into a
tape reader. The reader would be polled by some FAA center and the tape
read.

All amazing technology.

Harold




-- 
http://w6iwi.org