[GreenKeys] TTY Patch panels

[Nick England]

This message or one like it was found in military training and equipment
manuals -
"NOTE: Anyone patching or unpatching circuits from a TTY panel must be sure
to pull the plug from the looping jack (LPG) before removing the other plug
from the SET (machine) jack. Pulling the SET jack first interrupts all TTY
message traffic on that channel. IT ALSO PRODUCES A DANGEROUS DC VOLTAGE ON
THE EXPOSED PLUG!"

I have diagrams of several military patch panels here -
http://www.navy-radio.com/rtty-patch.htm

Some FSK demodulators switch the signal line to ground for mark. So they
need to be placed in the loop next to the supply negative. Also some demods
only work on positive loop voltage. So:
++ >> resistor >> LPG >> LPG >> SET >> SET >> demod >> --

And of course some demodulators have a built-in loop supply.

And some teletypes are polarity sensitive so you need to hook up the SET
jacks correctly. If you do that, you should be able to patch a SET into LPG
on another loop.

Nick England K4NYW
www.navy-radio.com


On Tue, Aug 11, 2020 at 1:22 PM Bruce Gentry via GreenKeys <
greenkeys at mailman.qth.net> wrote:
>
> As I am getting a TTY setup together, with several different ASRs, KSRs,
TDs and reperfs.� I want to have maximum flexibility in interconnections,
which means a patch bay is probably the best way.�� However, how was
safety addressed with them? I have a military surplus RTTY hut that uses a
standard patch bay, each device� going to a two conductor tip-sleeve
jack.� We know what� can happen when a patch cord is plugged in at one
end and the other end has two live surfaces that will get touched with
fingers or touch something grounded sooner or later. Did industry practice
simply expect common sense? Many older patch cords have an exposed screw
that holds the insulated sleeve on the metal body of the plug that offers
another chance for contact. Did anyone ever consider the consequences, or
did everyone get zapped at one time or another?� Were loop supplies
floating, or one side grounded? ��
>
> ���� Bruce Gentry, KA2IVY
>
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