Is this line noisy?

I have a friend whose ADSL keeps on dropping and I'm thinking of
trying to pressure his ISP into sending out a BT engineer. His BT
Voyager 105 ADSL modem is plugged into a splitter at the master socket
and there are no other phones connected to the line.

The CTRL-f1 panel of the Voyager 105 utility shows the following figures:

Attenuation is 50dB down, 31.5dB up.
SNR margin 11dB down, 9.5 dB up.
http://stuff.stroller.uk.eu.org/ADSL.gif

are those any good, or am I going to have to fight to get this seen to?

Thanks in advance,

Stroller.

Stroller wrote:
> I have a friend whose ADSL keeps on dropping and I'm thinking of
> trying to pressure his ISP into sending out a BT engineer. His BT
> Voyager 105 ADSL modem is plugged into a splitter at the master socket
> and there are no other phones connected to the line.
>
> The CTRL-f1 panel of the Voyager 105 utility shows the following figures:
>
> Attenuation is 50dB down, 31.5dB up.
> SNR margin 11dB down, 9.5 dB up.
> http://stuff.stroller.uk.eu.org/ADSL.gif
>
> are those any good, or am I going to have to fight to get this seen to?

You'd normally hope to get downstream attenuation+SNR margin to equal at
least 70, so you are about 9 or 10 dB short. These figures will worsen
with extra interference (evening time, greater usage of other ADSL
connections in same cable bundle, mains noise etc), hence the drop-outs.

Is there any extension wiring? Is the master socket an NTE-5? You may
need to filter out the extension wiring or maybe disconnect the
extension ring wire(s) (the ring wire is unbalanced and allows the
injection of local electrical noise into the balanced pair supplying the
signal via the ring capacitor in the master socket).

Note that the attenuation limit for 1Mbps ADSL is currently 60dB, so
this installation should be able to be made to work well even at 1Mbps.

--

Brian Morrison

please observe reply-to address

Brian wrote on Tue, 27 Sep 2005 14:25:19 +0100:

> Stroller wrote:
>> I have a friend whose ADSL keeps on dropping and I'm thinking of trying
>> to pressure his ISP into sending out a BT engineer. His BT Voyager 105
>> ADSL modem is plugged into a splitter at the master socket and there are
>> no other phones connected to the line.
>>
>> The CTRL-f1 panel of the Voyager 105 utility shows the following figures:
>>
>> Attenuation is 50dB down, 31.5dB up.
>> SNR margin 11dB down, 9.5 dB up.
>> http://stuff.stroller.uk.eu.org/ADSL.gif
>>
>> are those any good, or am I going to have to fight to get this seen to?
>
> You'd normally hope to get downstream attenuation+SNR margin to equal at
> least 70, so you are about 9 or 10 dB short. These figures will worsen
> with extra interference (evening time, greater usage of other ADSL
> connections in same cable bundle, mains noise etc), hence the drop-outs.

That makes no sense. By your reply you seem to imply that a 70db
attentuation with 0db SNR would be fine.

Surely you want attenuation as low as possible (higher the attenuation the
longer the signal has travelled), SNR as high as possible (the higher it is,
the less noise you have). Adding the figures together and saying "should be
at least X" just doesn't work. Attentuation 30db and SNR 30db would be a
great line, yet from above you'd be saying it's not.

Dan

Spack wrote:
> Brian wrote on Tue, 27 Sep 2005 14:25:19 +0100:
>
>
>>Stroller wrote:
>>
>>>I have a friend whose ADSL keeps on dropping and I'm thinking of trying
>>>to pressure his ISP into sending out a BT engineer. His BT Voyager 105
>>>ADSL modem is plugged into a splitter at the master socket and there are
>>>no other phones connected to the line.
>>>
>>>The CTRL-f1 panel of the Voyager 105 utility shows the following figures:
>>>
>>> Attenuation is 50dB down, 31.5dB up.
>>> SNR margin 11dB down, 9.5 dB up.
>>>http://stuff.stroller.uk.eu.org/ADSL.gif
>>>
>>>are those any good, or am I going to have to fight to get this seen to?
>>
>>You'd normally hope to get downstream attenuation+SNR margin to equal at
>>least 70, so you are about 9 or 10 dB short. These figures will worsen
>>with extra interference (evening time, greater usage of other ADSL
>>connections in same cable bundle, mains noise etc), hence the drop-outs.
>
>
> That makes no sense. By your reply you seem to imply that a 70db
> attentuation with 0db SNR would be fine.

No, obviously that would not work. You'll note I said "at least" above,
so in the case of a 70dB attenuation, the SNR would have to be 10dB or
higher, giving you a total of 80 which is > 70 the last time I looked.

>
> Surely you want attenuation as low as possible (higher the attenuation the
> longer the signal has travelled), SNR as high as possible (the higher it is,
> the less noise you have). Adding the figures together and saying "should be
> at least X" just doesn't work. Attentuation 30db and SNR 30db would be a
> great line, yet from above you'd be saying it's not.

I see your point, but also note that most routers are simply unable to
measure SNR above about 40dB so often the rule of thumb can't be applied
on short lines. The critical situation is where the attenuation is high,
then the noise level on the line becomes the limiting factor because it
determines where you can no longer detect the signal.

My advice to the OP is correct though; he should be seeing a much better
SNR than he describes on a 50dB loss line, it should be a minimum of
20dB, and more like 25dB. Clearly there is some interference and I
suspect it could be local and coming in through unbalanced ring wiring
on extensions.

--

Brian Morrison

please observe reply-to address

Brian Morrison wrote in
(E-Mail Removed):

> Spack wrote:
>> Brian wrote on Tue, 27 Sep 2005 14:25:19 +0100:
>>
>>
>>> Stroller wrote:
>>>
>>>> I have a friend whose ADSL keeps on dropping and I'm thinking of
>>>> trying to pressure his ISP into sending out a BT engineer. His BT
>>>> Voyager 105 ADSL modem is plugged into a splitter at the master
>>>> socket and there are no other phones connected to the line.
>>>>
>>>> The CTRL-f1 panel of the Voyager 105 utility shows the following
>>>> figures: Attenuation is 50dB down, 31.5dB up.
>>>> SNR margin 11dB down, 9.5 dB up.
>>>> http://stuff.stroller.uk.eu.org/ADSL.gif
>>>>
>>>> are those any good, or am I going to have to fight to get this
>>>> seen to?

> My advice to the OP is correct though; he should be seeing a much
> better SNR than he describes on a 50dB loss line, it should be a
> minimum of 20dB, and more like 25dB. Clearly there is some
> interference and I suspect it could be local and coming in through
> unbalanced ring wiring on extensions.

Yes. I'd suggest the first thing to try is to disconnect any other wiring in
the house, if possible. For example, disconnect anything connected to the
other arm of the splitter between the modem's microfilter.

Presumably the most important figure is not attenuation but noise margin:
the amount by which the signal exceeds the noise. As long as the modem had a
good enough amplifer, it would not matter if the signal was severely
attenuated, *provided* that the SNR was still good.

My equivalent figures (sorry to make the OP jealous!) are

Attenuation 6.5 db (D) 5.5 db (U)
Noise Margin 30.3 db (D) 29.0 db (U)

Mind you, I'm about 100 m from the exchange and I'd be surprised if the
wiring was more than about 300 m in length allowing for it being routed via
the road.

On 2005-09-27 15:52:53 +0100, Brian Morrison <(E-Mail Removed)> said:
>
> My advice to the OP is correct though; he should be seeing a much
> better SNR than he describes on a 50dB loss line, it should be a
> minimum of 20dB, and more like 25dB. Clearly there is some interference
> and I suspect it could be local and coming in through unbalanced ring
> wiring on extensions.

There are no other sockets connected to this line & I tested today with
nothing but a new Voyager 105 connected to a new splitter. The line was
installed two or three months ago after previous support calls failed
to resolve similar problems, so is used only for fax & broadband - I
think there may be extensions on the other line, but not on this one.

When I tested today I think I saw an SNR of 15dB - I wasn't aware of
it's significance, so can't be sure, and can't say how much it varied -
but surely not 20dB or 25dB as you describe.

Stroller.

On Tue, 27 Sep 2005 15:28:53 +0100, "Spack" <(E-Mail Removed)>
wrote:

>Attentuation 30db and SNR 30db would be a
>great line, yet from above you'd be saying it's not.

it wouldn't be a great line, as if it had less noise it would have a
bigger SNR and hence be able to support higher speeds than the above
combination could.

Phil
--
Tiscali - dialup speeds at Broadband prices, see
http://bbs.adslguide.org.uk/postlist...&Board=tiscali

AOL - the unlimited ISP of choice for heavy downloaders.

On Tue, 27 Sep 2005 16:34:49 +0100, "Martin Underwood" <(E-Mail Removed)>
wrote:

>My equivalent figures (sorry to make the OP jealous!) are
>
> Attenuation 6.5 db (D) 5.5 db (U)
> Noise Margin 30.3 db (D) 29.0 db (U)

I get 41 dB of margin with 11 dB of attenuation, so its your turn to
go green ;-)

Phil
--
Tiscali - dialup speeds at Broadband prices, see
http://bbs.adslguide.org.uk/postlist...&Board=tiscali

AOL - the unlimited ISP of choice for heavy downloaders.

Phil Thompson wrote in
(E-Mail Removed):

> On Tue, 27 Sep 2005 16:34:49 +0100, "Martin Underwood" <(E-Mail Removed)>
> wrote:
>
>> My equivalent figures (sorry to make the OP jealous!) are
>>
>> Attenuation 6.5 db (D) 5.5 db (U)
>> Noise Margin 30.3 db (D) 29.0 db (U)
>
> I get 41 dB of margin with 11 dB of attenuation, so its your turn to
> go green ;-)

Maybe if I want to upgrade my line from 2M to 8M in the future, I might
become envious!