[Gllug] ADSL on BT phone wires

[Ryland, Peter]

On Wed, 2006-08-09 at 10:40 +0100, Chris Bell wrote:
>    The ADSL must be tapped off using at least one capacitor, rather than
> just a transformer which would act as a DC short circuit, and I assumed that
> non-electrolytic capacitors would be physically larger but more reliable. It
> then depends on whether the signal polarity really matters, and that would
> require deeper knowledge of the system.

The capacitance is likely to be 1.8uF to provide a UK REN of 1.0 which
is likely to be electrolytic and hence care about polarity, just like a
phone.  Mind, I'm just guessing, as whilst I know about phones, I only
know the basics of how ADSL modems do their thing.

>    The problem occurred on an existing phone line that was upgraded for
> testing connections to AOL, not the main BT ADSL, and is connected via an
> extension. It worked at one end of the extension, not the other end. I was
> not involved, but am suspicious about the explanation given.

Worth checking if there's too much extra line impedance on the
extension.  If a phone works, the polarity is correct, so that can be
discounted.  You could then check the quality of the phone connection at
the extension.  Perhaps also there were unfiltered phones disconnected
in one test, but when testing the other extension, the phone was plugged
back in unfiltered, which would still work, but not as well.

Pete


*****************************************************************************
This communication is confidential and is intended solely for 
the use of the individual or entity to whom they are addressed. 
If you are not that person you are not permitted to make use of 
the information and you are requested to notify 
postmaster at squaregain.co.uk immediately that you have 
received it and then destroy the copy in your possession. 
Squaregain Ltd is authorised and regulated by the 
Financial Services Authority and is a member of the LSE.
******************************************************************************

-- 
Gllug mailing list  -  Gllug at gllug.org.uk
http://lists.gllug.org.uk/mailman/listinfo/gllug