Re: BT Talk



Nigel Cliffe wrote:
Custard wrote:


Thanks for everyones help Ive got the problem fixed.
For some reason the problem seemedto be in the Microfilter. I changed
it for a new one and Bingo the phone rings ??
Weird.


Wierd indeed. Never met that one when talking to the test team when I was at BT.


- Nigel


I think you will find that it is because the original filter didn't have the 'ring capacitor' in it that separates the 25Hz ringing that comes down the line and connects it to the 'bell' in your phone.

The signal is normally separated in the Master socket and fed to all the phones and just passes through the filter.
Some installations (see the very good writeups as linked to above) don't have the 3rd wire connected and rely on a capacitor in the filter.

However many 'cheap' filters don't have the capacitor and so the phone won't ring. To be sure, always use the one that came from your ISP or a 'proper' one costing about £10 from Maplin.

The phone would have worked in the router as that derives the 25Hz ringinging and distributes it. If the router came with an RJ11 (US phone) plug to BT socket adaptor, that would also put the pin connections right.

US phones keep the 25Hz on the internal wiring on just 2 wires which go in a simple parallel connection to all sockets. UK phones have the third wire as a hang-over from old 'pulse dialling' systems to prevent 'bell tinkle' when dialling on parallel connected phones. The system was introduced about the time when it became possible to buy and install phones oneself - and do ones own internal wiring rather than have GPO to do it for you and when people wanted more than just the phone on the hall table!!
The original GPO wiring required extra wires in both the cabling and the lead to the phone so that all the bells were in series and lifting any receiver disconnected the lopp with the bells in.
The speech and dialling wires were in parallel to all phones.

Mike

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