"Dave Liquorice" wrote in message
ll.co.uk...
On Sun, 30 Dec 2012 11:12:47 +0000, David Hill wrote:

I posted about the problem I had with my phone over Xmas, internet OK
but the phone was dead.

A "phone line" uses a single pair of wires from your property to the
exchange.

For the phone to work there needs to be a DC path up one wire and down
the other, this is for on/off hook signalling, pulse dialling and power
to the phone.

The ADSL signal is an RF signal using lots of individual carriers space
about every 4kHz from about 30kHz up to 1.1MHz (up to 8Mbps servive) or
2.2MHz for the up to 20Mbps service.

If there is a small break in one or even both wires the lack of DC path
stops the phone working but the RF ADSL signal can jump across the break
and continue working, though it may well be degraded.

Well BT found a line fault away from the property and fixed it without
a home visit,

Presumably you told faults that the broadband was still working and the
phone not. If this information was passed to the engineer all they would
have to do would be to find you pair in the exchange, attach their
time-domain reflectometer (TDR) and measure how far away the break in the
cable is. He'll know the physical cable routes and location of junction
boxes and given the distance will know which one to visit to fix the
fault. Presumably they rang you up to check the line was back working...

http://en.wikipedia.org/wiki/Time-domain_reflectometer

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Cheers
Dave.

Dave that was a brilliant explanation and it sounds to me as if you are a BT
Engineer. Any relation to a Bill Liquorice I worked with on the then GPO in
Leicester in the 60's?

Mike

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I'm an Angel, honest ! The horns are there just to keep the halo straight.

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