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Ericofox PABX with main frequency ringing

Started by dsk, April 24, 2022, 12:10:53 PM

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Some photos and short films:
The main frequency is 50 Hz, the phone with reverse dial is a Norwegian 167 model from Elektrisk Bureau.
The ringing phone is the Swedish sister from L. M. Ericsson  :)


Interesting! Is that an analog device? What year might it be?
I'm still using an ISDN PABX that I bought in 2000 after remodeling the house. ISDN (= early digital) was heavily promoted by German Telekom in those days and was cheaper than 2 analog lines which I needed. Plus the PABX became affordable.
I never got to the point of buying an ISDN telephone, but always used analog ones behind the PABX.
My internet router today provides an ISDN bus besides 2 analog ports. I hope it will last long, from what I've heard ISDN interfaces will eventually fade out soon.


Absolutely analog! You may use a DTMF phone as the programming phone for where it shall ring etc, but not needed. The voltage is so low that e.g. a W28 will never work well. The ringing is mains frequency and around 48V at 50 Hz.   Dialgizmo does not understand the pulses on the trunk line.

Here in Norway the copper lines is fading out, so my parents in law even lost their DSL and had to start with internet over mobile network  (4G). Works well for the pair in an age of mid 80ies :-)


I've heard *) it is possible to connect a normal LB magneto phone to the office line ("input terminals") of some analog PABX.
When the magneto is cranked, this is registered as an incoming call and the CB phones on the "private" side of the PABX ring as programmed. A conversation can be made and the call can even be transferred to another extension depending on the PABX' functionality. Only thing is, the LB phone cannot be called.
This obviously will only work when the PABX needs no DC feed from the office. This seems to be the case on many models.

*) the author of this posting may not be held liable for any damages or malfunctions  8)


Yes that is generally possible if you may add a voltage to the line, I will recommend a battery in series with a transformer on the pabx side of the transformer.  A typical one could be the "Schnurlose Übertrager" as pictured. I will suggest at least 24V in series with a 660 ohm resistor and a 2-5 uF capacitor across as on the sketched example.