Unit Telegraph No. 55A

[M1ECY]

A very long shot.

Has anyone here come across these before?

As far as I can tell they are for converting from the later UK PSTN type connection (Possible V.21) to Double Current.

Any information will be helpful

[DF3OE]

Yes, it looks like something similar to our German (and Austrian) AGTs.
It looks like a double current to V.21 transverter/modem to use older DC machines
with the V.21 FSK network.

[M1ECY]

Handy, this might be a simpler way to get older machines onto the network if the V21 problem can be resolved.

I guess this will also need to be used without FSG, so perhaps a FW change will be needed

[DF3OE]

Use of an FSG (dialling unit) is always the better solution.
I am unsure if the British DC machines have FSG functionality implemented.
Maybe you can find some old Telecomms technican who have knowledge and
perhaps even old manuals of that stuff.

I am working on the V.21 problem.
This weekend is a "long weekend" in Germany with two public holidays and
I will try to test the modified V.21 board.

[M1ECY]

Hi Henning, really no rush, I have lots to do.

I am trying to find the correct manual for this device - it looks like this switches the power to the teleprinter as well, but I cannot be certain.

The Cheetah Plus has no provision for FSG type equipment - it just plugs into the phone line. Perhaps there is some kind of internal device - you dial from the keyboard, and the machine drops into standby after 20 mins idle time.

[DF3OE]

FSK (V.21/ED1000) line connection is like a direct point to point connection, no FSG functionality.
Signalling is made by switching the correct tones.

[M1ECY]

Ive taken a closer look inside the box - The mains connection to the machine is permanent.

So I think any switching is done from inside the teleprinter.

I have posted a query on the Telecommunications Heritage Croup website to see if anything is known about the actual operation of these systems.

[M1ECY]

I've just read the technical handbook and training notes I have for the Super Cheetah - there is no reference to the need for any form of "FSG" so I can only assume that the V.21 enabled machines do not work like that.

So I think in reality, these units are only to convert double current machines to V.21.

This means that the machine is powered all the time, but in standby mode, when a call is incoming, the change of state is signalled in the usual way of current reversal.