[GreenKeys] new list member and teleprinter question

[Bill Allen Jr]

Hi all,

i have an old teleprinter with an rca logo on the front that is sitting on an
extel interface box.

the extel model is AN 11R 155

it was used with a upi or api wireline.

the interface has a crystal selector switch and i have no idea what that is for or why it used xtal's on wireline.

the printer is dot matrix but not 9 pin.

What two wire interface and protocol did this use?

i'm thinking eather 20 ma current loop or some odd subcarrier audio line.

anyone know?

Bill