[GreenKeys] Introduction - And Looking for Sagem TX20 information

[Malcolm Macleod]

Greetings,

 

I am new to your list.  It is great to see such an active list for these
lovely old machines.

 

I have a couple of old teleprinters (Models 15 and 100) put away for future
restoration, but my short-term project involves a Sagem TX20 Telex machine I
acquired here recently in Melbourne, Australia.  I am interested in driving
it with a microcontroller board to effectively create a telex simulator
(basically a simulator that can exchange messages between the TX20 and a
locally-connected PC).  I want the simulator to be capable of
generating/decoding the original dialing, negotiation and answer-back
protocols etc, as well as the exchange of data.

 

My first challenge though is getting information about both the interfacing
_and_ day-to-day use of the TX20.  Does anyone know of any relevant
resources that may be available on the web relating either specifically to
the TX20, or to the FSK/PSTN telex interface generally?  If possible, my
plan is to build an interface that connects directly to the TX20's modem
(possibly using an old PC external modem in a direct-connect loop?).  If
that is technically too complicated, I am hoping it might be possible to
connect to a current-loop interface within the TX20 (if it exists!).

 

Any thoughts? In particular, are the Telex mark/space frequencies compatible
with those used in PC external modems?  If they are not compatible, how
complicated is it to decode the frequencies by using a PLL detector driven
from a 600 ohm isolation transformer on a local loop?

 

Malcolm.