Large variations in Noise Margin?

Does a fluctuating variation in downstream Noise Margin, over a period of a
few hours, from 26 db to 14 db suggest a line fault?

Gareth.

Gareth wrote:
> Does a fluctuating variation in downstream Noise Margin, over a period of a
> few hours, from 26 db to 14 db suggest a line fault?

Possibly, but probably not.

My SNR margin is typically between 31 and 36 dB. However, sometimes it
dips somewhat, I've seen values between 7 and 24dB at various times. THe
modem doesn't lose sync, in fact if I didn't monitor the stats I'd
probably not know it happens.

The low SNR periods are quite short, the longest I've seen was somewhere
around 15dB for a few hours but not static during that time.

I think it is probably interference that gets into a phone line pair in
the same cable and is related to a faulty household item somewhere in
the two villages served by the exchange.

--

Brian Morrison

please observe reply-to address

I have been noticing for many months that my attenuation (not so much my
SNR) has been varying. As there is a possibility of a speed enhancement (I
am with Plusnet) in the near future I decided to write some code to monitor
the situation. I had been thinking about this for a long time.

My attenuation has been varying from 53 to 58 db which is uncomfortably
close to the old limit of 60 dB. the SNR however is quite good. When I
developed the code (more later) and have been monitoring the situation the
attenuation suddenly dropped to 52.5 and (apart from one sample) has stayed
there ever since! I have now been running the sampling program since 28
February. I did have some earlier results from a few days before that but I
have discarded them as the format was not quite the same.

My sampling program depends on a Freeware package called Teraterm and is
customised for my SAR110 router. It should be relatively easy to customise
for any other router with a telnet interface. The results are displayed in
Internet Explorer (sorry it does not work for Firefox at the moment). The
data can be generated in CVS and/or XML format by simple configuration. The
IE display uses XML data islands.

For those of you interested here are the results to date sampled two to
three times a day. http://www.soroban.co.uk/routerstats/statistics.htm

A page describing the macro code and how to configure it is
http://www.soroban.co.uk/routerstats. This contains download links for
Teraterm and for the macro code and necessary HTML pages to display the
data.
http://www.soroban.co.uk/routerstats

I had been (possibly still am) interested to see if I could find any
correlation between my varying attenuation and the weather or any other
external factors. I will have to wait until it changes again however to do
that - the jump to 55 db was around the time I needed to reboot my router.

John Steele
jcs AT soroban DOT co DOT uk

"Brian Morrison" <(E-Mail Removed)> wrote in message
news(E-Mail Removed)...
> Gareth wrote:
>> Does a fluctuating variation in downstream Noise Margin, over a period of
>> a few hours, from 26 db to 14 db suggest a line fault?
>
> Possibly, but probably not.
>
> My SNR margin is typically between 31 and 36 dB. However, sometimes it
> dips somewhat, I've seen values between 7 and 24dB at various times. THe
> modem doesn't lose sync, in fact if I didn't monitor the stats I'd
> probably not know it happens.
>
> The low SNR periods are quite short, the longest I've seen was somewhere
> around 15dB for a few hours but not static during that time.
>
> I think it is probably interference that gets into a phone line pair in
> the same cable and is related to a faulty household item somewhere in the
> two villages served by the exchange.
>
> --
>
> Brian Morrison
>
> please observe reply-to address

Brian Morrison <(E-Mail Removed)> wrote on Sat, 5 Mar 2005 at
15:19:57:
>Gareth wrote:
>> Does a fluctuating variation in downstream Noise Margin, over a
>>period of a few hours, from 26 db to 14 db suggest a line fault?
>
>Possibly, but probably not.
>
>My SNR margin is typically between 31 and 36 dB. However, sometimes it
>dips somewhat, I've seen values between 7 and 24dB at various times.
>THe modem doesn't lose sync, in fact if I didn't monitor the stats I'd
>probably not know it happens.
>
>The low SNR periods are quite short, the longest I've seen was
>somewhere around 15dB for a few hours but not static during that time.
>
>I think it is probably interference that gets into a phone line pair in
>the same cable and is related to a faulty household item somewhere in
>the two villages served by the exchange.

Just to add another example of interference, I have an agricultural
electric fence running nearby. When a poor joint causes it to spark for
a while, my ADSL SNR drops from its usual 35 dB to 15 or 20 dB. The
attenuation stays constant, as expected in that scenario, at 42 dB.

--
Tony

"Brian Morrison" <(E-Mail Removed)> wrote in message
news(E-Mail Removed)...
> Gareth wrote:
>> Does a fluctuating variation in downstream Noise Margin, over a period of
>> a few hours, from 26 db to 14 db suggest a line fault?
>
> Possibly, but probably not.
>
> My SNR margin is typically between 31 and 36 dB. However, sometimes it
> dips somewhat, I've seen values between 7 and 24dB at various times. THe
> modem doesn't lose sync, in fact if I didn't monitor the stats I'd
> probably not know it happens.

Well, mine is fluctuating wildly (from anywhere between 12 to 26) polled
every 5 seconds.

I've also been having problems with voice calls as well as ADSL loss of
synch. 3 BT engineers in a few days have given their opinions. The first 2
explained that new cable would have to be laid (because of low insulation on
the existing cable) but as this would be an expensive job another engineer
may be asked to give an opinion. Sure enough he did and found another pair
of copper wires coming in to the house which he duly connected. This seems
to have solved the voice call problem but not the ADSL problem and the line
noise is now fluctuating wildly.

I've been having problems since November and, not seeing a solution, I'm on
the verge of writing ADSL off as a lost cause and moving to NTL instead.

Gareth.

Gareth wrote:
> "Brian Morrison" <(E-Mail Removed)> wrote in message
> news(E-Mail Removed)...
>
>>Gareth wrote:
>>
>>>Does a fluctuating variation in downstream Noise Margin, over a period of
>>>a few hours, from 26 db to 14 db suggest a line fault?
>>
>>Possibly, but probably not.
>>
>>My SNR margin is typically between 31 and 36 dB. However, sometimes it
>>dips somewhat, I've seen values between 7 and 24dB at various times. THe
>>modem doesn't lose sync, in fact if I didn't monitor the stats I'd
>>probably not know it happens.
>
>
> Well, mine is fluctuating wildly (from anywhere between 12 to 26) polled
> every 5 seconds.

OK, that is a significant difference from what you posted previously, it
sounds like there is either a line fault or a continuous source of
impulsive noise.

>
> I've also been having problems with voice calls as well as ADSL loss of
> synch. 3 BT engineers in a few days have given their opinions. The first 2
> explained that new cable would have to be laid (because of low insulation on
> the existing cable) but as this would be an expensive job another engineer
> may be asked to give an opinion. Sure enough he did and found another pair
> of copper wires coming in to the house which he duly connected. This seems
> to have solved the voice call problem but not the ADSL problem and the line
> noise is now fluctuating wildly.

Right, so has the 3rd engineer simply changed the local drop cable over?
If so then the connection to the exchange from the nearest junction
cabinet may be the problem, hence the comments of the first two engineers.

>
> I've been having problems since November and, not seeing a solution, I'm on
> the verge of writing ADSL off as a lost cause and moving to NTL instead.

Depends on what you want and need I suppose, and feel lucky to have the
option, here it's ADSL or whistle.

--

Brian Morrison

please observe reply-to address

Brian Morrison wrote:
> Gareth wrote:
>> "Brian Morrison" <(E-Mail Removed)> wrote in message
>> news(E-Mail Removed)...
>>
>>> Gareth wrote:
>>>
>>>> Does a fluctuating variation in downstream Noise Margin, over a
>>>> period of a few hours, from 26 db to 14 db suggest a line fault?
>>>
>>> Possibly, but probably not.
>>>
>>> My SNR margin is typically between 31 and 36 dB. However, sometimes
>>> it dips somewhat, I've seen values between 7 and 24dB at various
>>> times. THe modem doesn't lose sync, in fact if I didn't monitor the
>>> stats I'd probably not know it happens.
>>
>>
>> Well, mine is fluctuating wildly (from anywhere between 12 to 26)
>> polled every 5 seconds.
>
> OK, that is a significant difference from what you posted previously,
> it sounds like there is either a line fault or a continuous source of
> impulsive noise.
>
>>
>> I've also been having problems with voice calls as well as ADSL loss
>> of synch. 3 BT engineers in a few days have given their opinions.
>> The first 2 explained that new cable would have to be laid (because
>> of low insulation on the existing cable) but as this would be an
>> expensive job another engineer may be asked to give an opinion. Sure
>> enough he did and found another pair of copper wires coming in to
>> the house which he duly connected. This seems to have solved the
>> voice call problem but not the ADSL problem and the line noise is
>> now fluctuating wildly.
>
> Right, so has the 3rd engineer simply changed the local drop cable
> over? If so then the connection to the exchange from the nearest
> junction cabinet may be the problem, hence the comments of the first
> two engineers.

Which is completely the wrong practice as if the cable is going faulty it
_WILL_ affect all pairs, which (if I'm reading between the lines correctly)
is UG anyway (hence the costs in getting it changed).

Keep reporting the fault, it sounds like you've had 2 honest engineers & 1
FRS points chaser, can't help but wonder what the first 2 did about the
problem though...

"kraftee" <kraftee@spamoff& die.com> wrote in message
news:422b6996$0$37813$(E-Mail Removed)...
> Brian Morrison wrote:
>> Gareth wrote:
>>> "Brian Morrison" <(E-Mail Removed)> wrote in message
>>> news(E-Mail Removed)...
>>>
>>>> Gareth wrote:
>>>>
>>>>> Does a fluctuating variation in downstream Noise Margin, over a
>>>>> period of a few hours, from 26 db to 14 db suggest a line fault?
>>>>
>>>> Possibly, but probably not.
>>>>
>>>> My SNR margin is typically between 31 and 36 dB. However, sometimes
>>>> it dips somewhat, I've seen values between 7 and 24dB at various
>>>> times. THe modem doesn't lose sync, in fact if I didn't monitor the
>>>> stats I'd probably not know it happens.
>>>
>>>
>>> Well, mine is fluctuating wildly (from anywhere between 12 to 26)
>>> polled every 5 seconds.
>>
>> OK, that is a significant difference from what you posted previously,
>> it sounds like there is either a line fault or a continuous source of
>> impulsive noise.
>>
>>>
>>> I've also been having problems with voice calls as well as ADSL loss
>>> of synch. 3 BT engineers in a few days have given their opinions.
>>> The first 2 explained that new cable would have to be laid (because
>>> of low insulation on the existing cable) but as this would be an
>>> expensive job another engineer may be asked to give an opinion. Sure
>>> enough he did and found another pair of copper wires coming in to
>>> the house which he duly connected. This seems to have solved the
>>> voice call problem but not the ADSL problem and the line noise is
>>> now fluctuating wildly.
>>
>> Right, so has the 3rd engineer simply changed the local drop cable
>> over? If so then the connection to the exchange from the nearest
>> junction cabinet may be the problem, hence the comments of the first
>> two engineers.
>
> Which is completely the wrong practice as if the cable is going faulty it
> _WILL_ affect all pairs, which (if I'm reading between the lines
> correctly) is UG anyway (hence the costs in getting it changed).
>
> Keep reporting the fault, it sounds like you've had 2 honest engineers & 1
> FRS points chaser, can't help but wonder what the first 2 did about the
> problem though...

Thanks Brian and Kraftee.

Kraftee, you are spot on. Yes the cable is underground and all engineers
explained that the cost of having it replaced (including digging) would lead
to *all* other options being exhausted. The option that was chosen was to
use a spare pair coming in to the home from a box about 40 metres away (and
one that was presumably provided so that an extra line could be provided if
needed)

The second engineer even asked me to sign a form giving permission for
digging on a small area of grass outside the home so that the underground
cable could be replaced. The first engineer explained that there wasn't much
point swapping pairs because the cable itself was faulty. Because it was an
intermittent fault however even the first faulty tested pair wasn't always
showing a fault.

Now I'm buggered though: whilst the downstream attenuation has dropped by
2db the chaotic line noise margin is such that a 2Mbps service will be out
of the question (but it does seem to be supporting a 1Mbps service). Can't
complain too much I suppose.

Gareth.

Gareth wrote:
> "kraftee" <kraftee@spamoff& die.com> wrote in message
> news:422b6996$0$37813$(E-Mail Removed)...
>> Brian Morrison wrote:
>>> Gareth wrote:
>>>> "Brian Morrison" <(E-Mail Removed)> wrote in message
>>>> news(E-Mail Removed)...
>>>>
>>>>> Gareth wrote:
>>>>>
>>>>>> Does a fluctuating variation in downstream Noise Margin, over a
>>>>>> period of a few hours, from 26 db to 14 db suggest a line fault?
>>>>>
>>>>> Possibly, but probably not.
>>>>>
>>>>> My SNR margin is typically between 31 and 36 dB. However,
>>>>> sometimes it dips somewhat, I've seen values between 7 and 24dB
>>>>> at various times. THe modem doesn't lose sync, in fact if I
>>>>> didn't monitor the stats I'd probably not know it happens.
>>>>
>>>>
>>>> Well, mine is fluctuating wildly (from anywhere between 12 to 26)
>>>> polled every 5 seconds.
>>>
>>> OK, that is a significant difference from what you posted
>>> previously, it sounds like there is either a line fault or a
>>> continuous source of impulsive noise.
>>>
>>>>
>>>> I've also been having problems with voice calls as well as ADSL
>>>> loss of synch. 3 BT engineers in a few days have given their
>>>> opinions. The first 2 explained that new cable would have to be
>>>> laid (because of low insulation on the existing cable) but as this
>>>> would be an expensive job another engineer may be asked to give an
>>>> opinion. Sure enough he did and found another pair of copper wires
>>>> coming in to the house which he duly connected. This seems to have
>>>> solved the voice call problem but not the ADSL problem and the
>>>> line noise is now fluctuating wildly.
>>>
>>> Right, so has the 3rd engineer simply changed the local drop cable
>>> over? If so then the connection to the exchange from the nearest
>>> junction cabinet may be the problem, hence the comments of the first
>>> two engineers.
>>
>> Which is completely the wrong practice as if the cable is going
>> faulty it _WILL_ affect all pairs, which (if I'm reading between the
>> lines correctly) is UG anyway (hence the costs in getting it
>> changed). Keep reporting the fault, it sounds like you've had 2 honest
>> engineers & 1 FRS points chaser, can't help but wonder what the
>> first 2 did about the problem though...
>
> Thanks Brian and Kraftee.
>
> Kraftee, you are spot on. Yes the cable is underground and all
> engineers explained that the cost of having it replaced (including
> digging) would lead to *all* other options being exhausted. The
> option that was chosen was to use a spare pair coming in to the home
> from a box about 40 metres away (and one that was presumably provided
> so that an extra line could be provided if needed)
>
> The second engineer even asked me to sign a form giving permission for
> digging on a small area of grass outside the home so that the
> underground cable could be replaced. The first engineer explained
> that there wasn't much point swapping pairs because the cable itself
> was faulty. Because it was an intermittent fault however even the
> first faulty tested pair wasn't always showing a fault.
>
> Now I'm buggered though: whilst the downstream attenuation has
> dropped by 2db the chaotic line noise margin is such that a 2Mbps
> service will be out of the question (but it does seem to be
> supporting a 1Mbps service). Can't complain too much I suppose.
>
> Gareth.

Well you could if it was affecting your voice calls (lirttle hint for you
there)....