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What would cause fast variation in Noise Margin?



 
 
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  #1  
Old January 6th 08, 11:36 AM posted to uk.telecom.broadband
Mike
external usenet poster
 
Posts: 3
Default What would cause fast variation in Noise Margin?

I have been monitoring my noise margin recently and these are some of the
results for this morning.

Time ---- Noise Margin
09:15 = 0dB
09:37 = 3dB
09:45 = 0dB
09:55 = 2dB
10:00 = 11dB
10:05 = 13dB
10:15 = 2dB
10:25 = 0dB

What would cause this type of variation? The router is a Netgear DG834G....
These sort of variations are very common here. As you can see from the time
scale, they are quite fast changing figures.

Thanks
Mike





  #2  
Old January 6th 08, 12:25 PM posted to uk.telecom.broadband
[email protected]
external usenet poster
 
Posts: 529
Default What would cause fast variation in Noise Margin?


On 6-Jan-2008, "Mike" wrote:

I have been monitoring my noise margin recently and these are some of the
results for this morning.

Time ---- Noise Margin
09:15 = 0dB
09:37 = 3dB
09:45 = 0dB
09:55 = 2dB
10:00 = 11dB
10:05 = 13dB
10:15 = 2dB
10:25 = 0dB

What would cause this type of variation? The router is a Netgear
DG834G....
These sort of variations are very common here. As you can see from the
time
scale, they are quite fast changing figures.


Noise from adjacent pairs in the underground plant?
Local interference, something with a dodgy switchmode
PSU.
Dry joint.
Water penetration into street cabling?
Did once put a Tandy battery powered audio amp with speaker
across an unused pair, it's amazing how much racket
gets picked up from adjacent pairs.
  #3  
Old January 6th 08, 12:31 PM posted to uk.telecom.broadband
Mike
external usenet poster
 
Posts: 3
Default What would cause fast variation in Noise Margin?


wrote in message
...
Noise from adjacent pairs in the underground plant?
Local interference, something with a dodgy switchmode
PSU.
Dry joint.
Water penetration into street cabling?
Did once put a Tandy battery powered audio amp with speaker
across an unused pair, it's amazing how much racket
gets picked up from adjacent pairs.


Thanks for that, but what I forgot to add was that if I restart the DG834G,
the noise level comes back to around 15dB. Even when the DG834G was
reporting 0dB just seconds before the reboot.

Why is this?

Mike



  #4  
Old January 6th 08, 01:19 PM posted to uk.telecom.broadband
nospam
external usenet poster
 
Posts: 82
Default What would cause fast variation in Noise Margin?

"Mike" wrote:


wrote in message
.. .
Noise from adjacent pairs in the underground plant?
Local interference, something with a dodgy switchmode
PSU.
Dry joint.
Water penetration into street cabling?
Did once put a Tandy battery powered audio amp with speaker
across an unused pair, it's amazing how much racket
gets picked up from adjacent pairs.


Thanks for that, but what I forgot to add was that if I restart the DG834G,
the noise level comes back to around 15dB. Even when the DG834G was
reporting 0dB just seconds before the reboot.


The lower the connection speed the larger the signal and greater the signal
to noise ratio. The modem negotiates with the exchange to connect at a
speed which gives a minimum SNR margin defined by the exchange.

The normal margin is 6db. If over time the exchange considers your line to
be unstable (because it disconnects and re-trains frequently) it will
increase the required margin in 3db steps. It looks like the exchange
already decided your line is unstable.

--
  #5  
Old January 6th 08, 02:20 PM posted to uk.telecom.broadband
Sean B
external usenet poster
 
Posts: 9
Default What would cause fast variation in Noise Margin?

"Mike" wrote:

I have been monitoring my noise margin recently and these are some of the
results for this morning.

Time ---- Noise Margin
09:15 = 0dB
09:37 = 3dB
09:45 = 0dB
09:55 = 2dB
10:00 = 11dB
10:05 = 13dB
10:15 = 2dB
10:25 = 0dB

What would cause this type of variation? The router is a Netgear DG834G....
These sort of variations are very common here. As you can see from the time
scale, they are quite fast changing figures.

Thanks
Mike



Have you got the latest firmware and what ver. is the router
1, 2 or 3? It might be worth getting the much better GT model
I bought a new (ex SKY) one off ebay (still sealed) for 30

The noise could be anything. If it always goes up at 10:00 it could be
something at the exchange or a timer at your end.

It's worth searching Google for Routerstats (freeware) It shows
a continuous graph of noise etc.

FOUND IT:
http://www.vwlowen.co.uk/internet/files.htm


A typical Noise Margin graph is:

http://img41.imagevenue.com/img.php?...122_1035lo.jpg

or (same)

http://tinyurl.com/2bcqku

These are from my router, but they had been up and down like yours
until my ISP got BT to check my line out. The problems weren't at
my end.

Sean B



  #6  
Old January 6th 08, 02:30 PM posted to uk.telecom.broadband
The Natural Philosopher
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Posts: 1,000
Default What would cause fast variation in Noise Margin?

Sean B wrote:
"Mike" wrote:

I have been monitoring my noise margin recently and these are some of the
results for this morning.

Time ---- Noise Margin
09:15 = 0dB
09:37 = 3dB
09:45 = 0dB
09:55 = 2dB
10:00 = 11dB
10:05 = 13dB
10:15 = 2dB
10:25 = 0dB

What would cause this type of variation? The router is a Netgear DG834G....
These sort of variations are very common here. As you can see from the time
scale, they are quite fast changing figures.

Thanks
Mike



Have you got the latest firmware and what ver. is the router
1, 2 or 3? It might be worth getting the much better GT model
I bought a new (ex SKY) one off ebay (still sealed) for 30

The noise could be anything. If it always goes up at 10:00 it could be
something at the exchange or a timer at your end.

It's worth searching Google for Routerstats (freeware) It shows
a continuous graph of noise etc.

FOUND IT:
http://www.vwlowen.co.uk/internet/files.htm


A typical Noise Margin graph is:

http://img41.imagevenue.com/img.php?...122_1035lo.jpg

or (same)

http://tinyurl.com/2bcqku

These are from my router, but they had been up and down like yours
until my ISP got BT to check my line out. The problems weren't at
my end.

Sean B



Noise?

Well theres MW transmissions., Strongest at night when the ionosphere
does its thing.

Theres line resistance, which increases when warm.

There's an upsurge in all sorts of electrical activity, which happens
when people are doing stuff, or when it gets cold and loads of motors
and valves all click on .

Got someone using an arc welder nearby? that is monumentally noisy in
the MW spectrum.

Then there are thunderstorms..and strange oscillations in te troposphere..

Its a wonder the bloody thing works at all.
  #8  
Old January 6th 08, 04:18 PM posted to uk.telecom.broadband
Steve B
external usenet poster
 
Posts: 25
Default What would cause fast variation in Noise Margin?


"Mike" wrote in message
...

wrote in message
...
Noise from adjacent pairs in the underground plant?
Local interference, something with a dodgy switchmode
PSU.
Dry joint.
Water penetration into street cabling?
Did once put a Tandy battery powered audio amp with speaker
across an unused pair, it's amazing how much racket
gets picked up from adjacent pairs.


Thanks for that, but what I forgot to add was that if I restart the
DG834G,
the noise level comes back to around 15dB. Even when the DG834G was
reporting 0dB just seconds before the reboot.

Why is this?

Mike




Wet cables cause that. I've had the T-shirt on that one. SNR wobbles
around, but if you disconnect the router line for a few minutes the SNR is
good again for some time then it starts playing up again. If you're lucky
there'll be crackles also on your phone and it's best reported as a phone
line fault to BT rather than an ADSL fault. Simpler.


  #9  
Old January 6th 08, 04:36 PM posted to uk.telecom.broadband
dick
external usenet poster
 
Posts: 2
Default What would cause fast variation in Noise Margin?

nospam wrote:
"Mike" wrote:

wrote in message
...
Noise from adjacent pairs in the underground plant?
Local interference, something with a dodgy switchmode
PSU.
Dry joint.
Water penetration into street cabling?
Did once put a Tandy battery powered audio amp with speaker
across an unused pair, it's amazing how much racket
gets picked up from adjacent pairs.

Thanks for that, but what I forgot to add was that if I restart the DG834G,
the noise level comes back to around 15dB. Even when the DG834G was
reporting 0dB just seconds before the reboot.


The lower the connection speed the larger the signal and greater the signal
to noise ratio. The modem negotiates with the exchange to connect at a
speed which gives a minimum SNR margin defined by the exchange.

The normal margin is 6db. If over time the exchange considers your line to
be unstable (because it disconnects and re-trains frequently) it will
increase the required margin in 3db steps. It looks like the exchange
already decided your line is unstable.

My SNR varies exactly the same, however I am on a fixed 0.5M service due
to line length so it is not re-training. I don't even need to restart
the router, disconnecting the line for less than 10 seconds results in
the router re-syncing with 12/13dB of margin. I can understand crosstalk
affecting the margin, but why does it immediately increase following a
line break?

dick
  #10  
Old January 6th 08, 04:55 PM posted to uk.telecom.broadband
Sean B
external usenet poster
 
Posts: 9
Default What would cause fast variation in Noise Margin?

/Tx2 wrote:

On Sun, 06 Jan 2008 13:19:40 +0000 nospam
from the village of lid
felt we might be interested in the following...

[...]


The normal margin is 6db. If over time the exchange considers your line to
be unstable (because it disconnects and re-trains frequently) it will
increase the required margin in 3db steps.


Which doesn't explain why mine is only 7.4db - surely it should be 9db,
the next increment?


I doubt if it ever moves rapidly in 3db steps, probably over days
on the downward side, on the upwards side it shoots up when your line
speed drops suddenly.

Mine seems to drift slowly up and down during the day by about 1.5db
It started off this morning at about 7.3db went up to about 8.8db at
11am and is now moving back down: (log below)

06.01.08 14:21:29 Rx-Noise= 8.4 Tx-Noise= 14 Rx-Sync= 2592
06.01.08 14:22:29 Rx-Noise= 8.4 Tx-Noise= 14 Rx-Sync= 2592
06.01.08 14:23:29 Rx-Noise= 8.4 Tx-Noise= 14 Rx-Sync= 2592
06.01.08 16:27:08 Rx-Noise= 7.8 Tx-Noise= 14 Rx-Sync= 2592
06.01.08 16:28:08 Rx-Noise= 7.8 Tx-Noise= 14 Rx-Sync= 2592
06.01.08 16:29:08 Rx-Noise= 7.8 Tx-Noise= 14 Rx-Sync= 2592
06.01.08 16:30:08 Rx-Noise= 7.7 Tx-Noise= 14 Rx-Sync= 2592
06.01.08 16:31:08 Rx-Noise= 7.8 Tx-Noise= 14 Rx-Sync= 2592
06.01.08 16:32:08 Rx-Noise= 7.8 Tx-Noise= 14 Rx-Sync= 2592
06.01.08 16:33:08 Rx-Noise= 7.8 Tx-Noise= 14 Rx-Sync= 2592
06.01.08 16:34:08 Rx-Noise= 7.6 Tx-Noise= 14 Rx-Sync= 2592

I'm not too bothered about it because I'm on a bad line and
shouldn't be DL at the speed I am i.e. 2000 kbps.... BT only rate
it at 1000 kbps (up from 512k six months ago).

Sean B





 




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