Re: Noise on handset when ADSL has synched (continued)


On 6-May-2006, jdr.smith@xxxxxxxxxx wrote:

Everyone is pretty certain that its nothing inside my house and that
its somwehere between my external connection and the exchange..they
don;t think its a problem back at the exchange.

Anyone have any ideas that I can bounce off the Openreach team ?

BT engineers have a test jack/plug that they can use to isolate your
line at the exchange and test there. If it is ok then the term is
"It's ok leaving us"
Then the do the same at your local roadside cabinet.
If it is sick there then it is, as you say, between the exchange
and the cabinet.
BT universally seem to use Krone IDC strips for connections
and Krone make test plugs to access the line, either in
shunt or to break in.
BT have (expensive - so not many kits around, and you
need two, one at each end) line test sets. The BT (Bristol)
troubleshooter came in with a Consultronics (Google for
Consultronics, although there are other makes).
It graphs the line against international templates M1020,
M1025, or M1040, showing on screen the frequency response,
plus phase noise, phase jitter, impulse noise, and pretty
well everything else that can be wrong with twisted pair
copper circuits.
The nitty gritty:-
There can be split pairs somewhere along the route, where
some caghanded linesman got a wire from one pair, paired
with a wire from another pair, over part of the route.
A right pain in the arse to find. How much trouble it
causes varies, if it's the nominal ground wire, probably
not much. But it can cause cross talk, how bad depends
on how far, and the useage of the pair it is crossed with.
If it is someone elses phone, you probably don't use your
phones at the same time, so the problem is pretty
well hidden. The pain in the arse effect.
Water in a street cable causing leakage and cross talk.
Is the problem there when stand alone battery equipment
is used?
Your kit is driven from the mains, hence a
capacitive path to ground. Power cubes have quite a
high capacitance to ground, between primary and
secondary, of the transformer.
A dry (rectifying) joint, there are copper oxide rectifiers,
you used to be able to buy them.
A rectifying joint can cause cross modulation between
high and low frequencies. In the old days BT used to
"wet" the line to clear the problem, usually only
for a couple of days, a temporary fix. Wetting the line
in this sense meant sending a 10 to 20 mA current
round the circuit, the voltage used being enough
to break down any oxide film. Hence the temporary
nature of the fix. The chances of this with IDC
connectors seems just as high, if the joint has been
pulled and remade, more than once.
There are plenty of tools (test equipment) designed
specifically to sort these sorts of problems, but BT
is getting fragmented, and the knowledgable hands
few and far between. Any good ones are probably
on the commercial side. If your annual spend on
circuits and services is well into six figures, you get
very good service from the carriers and from BT.
Engineers in suits, with all the right equipment
come out of the woodwork if things stop working.
The rest of us just suffer.
.

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