Identify purpose of this phone related (filter?)

I have been extending the phone system into the second building using only a pair from the bunch of twisted pairs for the network, but it seems the old corded phone doesn't ring even though it has dial tone and can dial out. When I plug this box in line with the phone it will ring.

It appears there is only a 470k resistor and a 1.8uF capacitor in it (see pic), I tried making another circuit so I can have two phones in there but it blocks out the dial tone.

I tried a cordless phone without this box connected and that will ring perfectly fine. I don't understand why one phone works and the other doesn't.

Thanks,

Jules

Is DSL internet being transmitted along the same phone line?

Modern phones may have built-in filters (going out on a limb here) but older style corded ones usually need a line filter to separate out the DSL signals from the phone signals.

Matt: The UK and US systems are like night and day.


The BT system is a little wierd. In the UK you have A, B, Earth and Ring. The US has TIP and Ring.


I would read this article first: http://www.rob-r.co.uk/other/UKphonecatwiring.htm

I can answer that one.

You need to connect pin 3 in the master box to pin 3 in the extension, the ring voltage goes through pin3 so some phones wont ring without it.

The reason why the cordless rings is that some cheaper non bt approved phones dont use pin3, the ring volatge is decoupled internally instead of the 1.8uF cap in the master box throughpin 3.

I think that's about right.