What does 'unbalanced cable' mean?

[Chris]

Over the weekend we had a fault on our line - lost connections and very
noisy line - which was fixed on Tues. However, since the fix our broadband
speeds dropped from 4.5meg to 3meg, despite having a sync rate of 6.8meg.

I raised this with plusnet suggesting a bras reset, but they've come back
with a new error - an 'unbalanced line' - which OR are due to investigate
on Monday. What is it - google is not very enlightening - and do OR need
access to the house to investigate?

As a side effect the bb is back to its 4.5meg level this evening and
syncing at 8.6meg. Is this the best i can expect with a 6db SNR margin and
46db line attenuation?

[Brian Gregory]

On 22/09/2016 23:40, Chris wrote:
> Over the weekend we had a fault on our line - lost connections and very
> noisy line - which was fixed on Tues. However, since the fix our broadband
> speeds dropped from 4.5meg to 3meg, despite having a sync rate of 6.8meg.
>
> I raised this with plusnet suggesting a bras reset, but they've come back
> with a new error - an 'unbalanced line' - which OR are due to investigate
> on Monday. What is it - google is not very enlightening - and do OR need
> access to the house to investigate?

A good phone line is two identical insulated wires gently twisted
together inside something to physically protect them.

By unbalanced they just mean that they think there is something
significantly different about one of the pair of wires compared to the
other. For instance they might have different resistance due to one
having a poor connection somewhere, be picking up different amounts of
interference for some reason, or one might have some leakage to earth.

>
> As a side effect the bb is back to its 4.5meg level this evening and
> syncing at 8.6meg. Is this the best i can expect with a 6db SNR margin and
> 46db line attenuation?
>

Normally one would hope your bras profile would be something of the
order of 88% of your downstream sync speed.

Why BT can't instantly set it to the correct value each time you connect
with a different sync speed (like many LLU operators do) is a complete
mystery that only BT can explain.

--

Brian Gregory (in the UK).
To email me please remove all the letter vee from my email address.

[Chris]

Brian Gregory <bvdvgvrv...@gmail.com> wrote:
> On 22/09/2016 23:40, Chris wrote:
>> Over the weekend we had a fault on our line - lost connections and very
>> noisy line - which was fixed on Tues. However, since the fix our broadband
>> speeds dropped from 4.5meg to 3meg, despite having a sync rate of 6.8meg.
>>
>> I raised this with plusnet suggesting a bras reset, but they've come back
>> with a new error - an 'unbalanced line' - which OR are due to investigate
>> on Monday. What is it - google is not very enlightening - and do OR need
>> access to the house to investigate?
>
> A good phone line is two identical insulated wires gently twisted
> together inside something to physically protect them.
>
> By unbalanced they just mean that they think there is something
> significantly different about one of the pair of wires compared to the
> other. For instance they might have different resistance due to one
> having a poor connection somewhere, be picking up different amounts of
> interference for some reason, or one might have some leakage to earth.

Thanks for the clear expansion.

This might get interesting. We recently moved into this house and I've no
idea where the phone line comes in. We have an old lozenge under the
stairs, but no overhead wires. It'll be buried somewhere. There is an old
'GPO' marker in amongst some trees at the edge of our property.

If it needs a new cable this might be a big job.

Maybe they can sort our two master sockets as well. One only feeds the
kitchen phone, where the other feeds the rest of the house.

>>
>> As a side effect the bb is back to its 4.5meg level this evening and
>> syncing at 8.6meg. Is this the best i can expect with a 6db SNR margin and
>> 46db line attenuation?
>>
>
> Normally one would hope your bras profile would be something of the
> order of 88% of your downstream sync speed.

The 4-5Mbps is pretty much fine for all our needs, where 3 was a bit touch
and go. If we can get that reliably, I'm ok with that.

[Woody]

"Chris" <ithi...@gmail.com> wrote in message
news:ns1mk6$vfo$1...@dont-email.me...

An unbalanced connection is when one side of that connection is
earthed, such as in a coaxial audio or aerial cable.

Telephone lines are balanced about earth. This is achieved by the line
leaving the exchange going through a transformer the line side of
which has a centre tap which is earthed at the exchange. You can
therefore see the audio across the pair of wires or at a reduced level
from one wire to earth.

The reason it is done this way is that the earth potential may be
(likely will be) different at the point of delivery from that at the
exchange which will result in mains hum. It also means that any
interference induced into the balanced pair en route to its
destination will be induced into both wires identically: at the
receiving end the equipment is looking for a difference across the
pair of wires so the interference being identical in both will be
'rejected.'

The OR response suggests that one leg of the pair of wires coming to
your house is faulty, possibly earthed. As delivery to your premises
is probably overhead then the fault will be between the exchange and
the pole so they should not need access - but they will ask for it
nonetheless to confirm the fault and/or clearance.


--
Woody

harrogate3 at ntlworld dot com

[Graham J]

The cable from the exchange to you is a pair of wires. Each wire of the
pair is supposed to be the same length, same thickness, same resistance,
same capacitance to ground, same everything. The wires should be evenly
twisted together. The signal current flows out along one wire and back
along the other. The receiving device measures the voltage difference
between these signals.

This means that the average magnetic field around the pair due to the
signal is zero. More importantly, any magnetic field - from
interference - surrounding the pair will induce a current in the same
direction in both wires, meaning that the receiving device should see no
signal resulting from this interference.

The sync rate of 6.8Mbits/sec is a general indication of the loss, and
noise margin on the line. The "broadband speed" relates to any number
of things, including the capability of the server sending the test file,
but for ADSL is cannot be more than about 88% of the sync speed. It is
also limited by the WiFi connection between the router and the test
computer - never user WiFi to test this, always use an Ethernet cable.
And switch off all other devices, so only one computer is involved in
the test.

Given that the sync speed has increased to 8.6 Mbits/sec it would appear
that OR have resolved a problem.

--
Graham J

[Graham.]

Chris <ithi...@gmail.com> Wrote in message:

Dial 17070 and select option 2 for quiet line test. Can you hear
any hum on the line, even slightly?

My guess is that OR swapped the pair between the PCP cabinet to
the exchange frame for a spare, but this new pair has a little
leakage to earth on one of the wires.
--

%Profound_observation%


----Android NewsGroup Reader----
http://usenet.sinaapp.com/

[Chris]

No poles here. Line must be buried somewhere.

Annoyingly, OR have already been and fixed 'a corroded connection'. I wish
people would stick to appointments, I would have liked to have been there
to speak with the engineer.

[Chris]

Thanks. Yes, they did, but the unbalanced cable is a new fault. Which my
wife tells me OR have already been and fixed. No immediate change in speed,
though.