[GreenKeys] Police teletype

[Nick England]

There’s a good explanation/example of stunt box selective calling in the
Stunt Box brochure.
http://www.navy-radio.com/manuals/tty/dc/28_stunt_Box001.pdf

Cheers
Nick


On Wed, Dec 18, 2019 at 9:49 PM Jim Haynes <jhhaynes at earthlink.net> wrote:

> On Wed, 18 Dec 2019, Jim Cooper wrote:
>
> > were detected mechanically in the local stunt box
> > and a switch closed to activate something like the
> > solenoid, which would then disable the print
> > suppression (double negative!) ...  local reperfs
> k
> But that's not quite how it worked.  Remember the engineers
> at Teletype were (some of them anyway) prima donnas at mechanical
> design.  Selective calling was done entirely mechanically, with
> stuntbox parts moving a code bar to enable or disable the printing
> clutch.  And I'm sure they could have made some entirely mechanical
> way of enabling or disabling print suppression with a manual
> control.  But for some reason they put in the solenoid to prevent
> print suppression from happening when it was not desired.
>
> As I recall the code bar that made selective calling work was the
> same one used for automatic carriage return and line feed, so you
> couldn't have both of those features on the same typing unit.
>
> Selective calling is pretty complicated.  You have to have a state in
> which, with the machine non-printing, it responds to selective calling
> turn-on codes.  Then you have to put the machine into a state where it
> is not sensing the selective calling codes, so it doesn't respond to
> them during traffic with the machine printing or non-printing.  And
> then an end-of-message-text sequence puts it back into the state of
> sensing turn-on codes and not printing.
>
> Model 28 had a big impact on FAA stations.  Previous to Model 28 they
> had a little box with a 6 by 6 array of pushbuttons that could connect
> any of up to six machines with up to six circuits.  All it switched
> were the signal lines.  With Model 28 they had the stunt box controlling
> all kinds of things, so the little pushbutton box turned into a seven
> foot rack with panels that could switch I don't remember how many wires
> in addition to the signal circuit.
>
> Previous to Model 28 there was a machine called SOTUS which could do the
> kinds of things that the stuntbox does, detecting characters or sequences
> of characters mechanically and closing switch contacts.  That's all it
> did - nothing connected with printing.  Model 28 made that machine
> unnecessary, provided the stunt box was big enough for everything you
> wanted to do.  Later on there was a machine called the Model 28 Sequential
> Selector.  This was basically a typing unit with the front plate and other
> printing parts omitted, so it just operated the stunt box.  This was a
> replacement for the SOTUS when some existing systems were upgraded to
> 100 wpm operation.  There was also an LRXD, a 28-line replacement for the
> FRXD typing reperforator transmitter distributor.  The preferred sort
> of machine for new projects was the R-T stand which accomodated 3000 foot
> paper tape reels.  But the LRXD was exactly the same size and form factor
> as the FRXD for direct replacement in existing systems.
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-- 
Nick England K4NYW
www.navy-radio.com
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