[GreenKeys] More 28ASR K-KT-T madness

[Nick England]

There were TSEC/KW-7 crypto units aboard and I know that had a step pulse
output to synchronize the TTY characters.

A quick explanation for folks not familiar with step control of the M28
keyboard and TD.
This style keyboard had a sync switch that made contact when you pressed a
key and the code bars were released - but the keyboard drive clutch was not
engaged yet. That sync switch enabled a step pulse from the crypto unit to
activate a clutch magnet located on the right side of the keyboard. That
magnet allowed the keyboard drive clutch to cycle, only then transmitting a
character to the crypto unit.
http://www.navy-radio.com/tty/sync.htm
(there is a lever to permanently engage the magnet armature, defeating this
synchronization)

Similarly for the TD, the tape would be read and transmitted only when the
TD received a pulse from the crypto unit. If you didn't want this, the TD
clutch would be wired to an AC or DC supply.

Not having a manual for the crypto equipment (ha!) I assume that this had
something to do with traffic control - this style crypto unit would be
constantly sending characters so that real messages were hidden in the
continuous stream. You didn't want anything to alert interceptors that
actual messages were being sent for two reasons - one that would give them
a particular set of characters to concentrate on breaking, and two, it
prevented traffic analysis (knowing something was up if there were a lot of
messages going out).

Cheers,
Nick



On Tue, Feb 18, 2020 at 10:08 PM Duncan Brown <duncanancy at earthlink.net>
wrote:

> Nick,
>
> Does the USS Iowa gang know what crypto gear was used that required it
> to step the tape reader?
>
> Thanks,
>
> Duncan
>
> On 2/18/2020 17:41, Nick England wrote:
> > I've been helping (via phone & email) the USS Iowa gang with their
> > AN/UGC-48A which is a TEMPEST 28ASR with low-level in/out plus step
> > input to sync the keyboard and TD with a crypto machine.
> > Here's how it works according to the wiring diagrams -
> > K - keyboard and TD on line, printer on line
> > KT - keyboard and TD off line, printer off line, keyboard mechanically
> > punches tape
> > T - keyboard off line, TD on line, printer on line
> >
> > I'm beginning to think that for each model, the K-KT-T switches were
> > wired up by throwing darts at a dartboard........
> >
> > Nick England K4NYW
> > www.navy-radio.com <http://www.navy-radio.com>
> >
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