Telephone Switching > Strowger (Step by Step) Switching

Elektrisk Bureau PAX SXS with drums

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The PAX was saved from a container, and yes it works.
Much about this in another thread:


Just a little more.
Diagram, and how I made one line to be an outbound trunk line.

Not easy to keep it running as I want, the trunk has had trouble with releasing the line. I replaced the zener and diode in series with the dial repeat (and release) relay with a resistor.

Now I have to try it out.


Does this PAX require ground start trunks or loop start trunks?

It is loop start.
Ground start has not been used here as far as I know.
This PAX does not have a trunk line at all.
I figured out:  due to the simple common bridge for powering both ends, dialing in on telephone caused a voltage rise for each break, and on hang up, and the connection stay until both ends hangs up.
This was used to sense the voltage rise, and give pulses on the POTS side of the trunk. (Relay D, and contact set d1)
When hanging up, the voltage rises, and D opens the POTS circuit....

Another problem are to connect a dtmf to pulse converter, the original dial tone (buzz) disturbs any receiving of dtmf. I will have to put in a SMART1 adapter who makes its own dial tone, and then you will loose the original tone
The dial tone is a constant tone of this busy tone. (horrible)  It sounds some different in the phone.



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