wandering SNR

kinmel · Jan 12, 2009, 09:34:24

Is your SNR stable, mine is wandering all over the place ?

With Attenuation now steady at 58.0 I try to sync at just above the 4meg boundary, ideally 4544. At that sync my SNR varies between 2 and 11 over a 24 hour period and if the router re-syncs at another value it takes me days to catch 4544 again.

What is a sensible SNR range for a line and is there any way of stabilising it ? it doesn't seem to be following a pattern, other that the expected day/night difference.

Rik · Jan 12, 2009, 09:40:13

Using a Netgear, Alan, my SNR would swing through an 11db range throughout the day, with the worst figures coming at night, as you'd expect. Same line and a 2700, I get a 2db swing. Which leads me to question the margins we see reported, are they true figures or a 'feature' of a particular router? Given that BT set the target NM at 6db, I'm guessing that they expected to see 3-4db or so of swing.

The only thing you can do to stabilise noise is to minimise any pickup within the house, and I'm sure you've already done that. For the rest, we are in the hands of BT and wherever their lines run.

g7pkf · Jan 12, 2009, 10:40:25

Look at the attatchemnt now thats a bad snr graph.

[attachment deleted by admin]

Rik · Jan 12, 2009, 10:42:20

Luckily, not everyone enjoys pendolino trains.

g7pkf · Jan 12, 2009, 10:47:02

Everyone in stoke hammond does, the whole village is affected.

and point to note Rik the line was electrified in 1966.

Rik · Jan 12, 2009, 10:51:21

I remember it well, Dean, having lived close to the West Coast line all my life.

kinmel · Jan 12, 2009, 11:11:26

I am using 2700, the SNR varies almost by the minute.

this graph is today at 3 minute intervals

Rik · Jan 12, 2009, 11:18:39

Is that a 1db fluctuation, Alan? If so, it shouldn't be a huge problem.

g7pkf · Jan 12, 2009, 12:18:30

Quote from: Rik on Jan 12, 2009, 11:18:39
Is that a 1db fluctuation, Alan? If so, it shouldn't be a huge problem.

if it is it could just be sitting on the threshold for changeover

Rik · Jan 12, 2009, 12:19:16

True.

kinmel · Jan 12, 2009, 12:32:10

About 3pm it will start to go down and will reach between3 and 2 by midnight, some days by now it is up to 11, all the changes are 1Db at a time. It will usually hang in there on 4544 for weeks at a time.

Rik · Jan 12, 2009, 12:37:11

Going to 11 suggests that there's been an after dark re-sync, Alan, when noise is higher. I'd then expect to see a rise in NM during the day. If you have a 9db swing overall, then your line is noisy. If it's not within the house, you could ask IDNet to test the line, but I suspect it may be something that you have to live with, I doubt BT will want to spend any money on it unless they can identify an exchange fault.

kinmel · Jan 12, 2009, 13:47:09

Quote from: Rik on Jan 12, 2009, 12:37:11
Going to 11 suggests that there's been an after dark re-sync, Alan, when noise is higher. I'd then expect to see a rise in NM during the day. If you have a 9db swing overall, then your line is noisy. If it's not within the house, you could ask IDNet to test the line, but I suspect it may be something that you have to live with, I doubt BT will want to spend any money on it unless they can identify an exchange fault.

I suspect your right Rik and I suppose I have little right to complain when a line with 58 Att. usually gives me 4meg

Sebby · Jan 12, 2009, 13:47:58

To me, it just sounds (no pun intended) like noise, rather than a line issue. The most noise is around at night; it could be a local issue, or something along the line, but there's not a great deal that can be done about it. If you have sorted your internal wiring and are using a 2Wire 2700, I don't think there's a lot else to try.

To be honest, for 58dB attenuation, that's an excellent sync. I could only just get that with 47dB attenuation!

Rik · Jan 12, 2009, 15:16:50

What a difference 1db can make, I'm currently syncing at 3008 on a 57db line.

Sebby · Jan 12, 2009, 18:34:37

Although it's not actually the 1dB that's doing it, it's other line factors (noise along the line, I suspect).

Rik · Jan 12, 2009, 18:38:07

Indeed. Shame about such things. I think we should re-write the words of Jerusalem, "Bring me my fibre, of solid glass..."

Sebby · Jan 12, 2009, 18:39:04

johnny5 · Jan 13, 2009, 19:38:35

Quote from: Rik on Jan 12, 2009, 15:16:50
What a difference 1db can make, I'm currently syncing at 3008 on a 57db line.

Mine is 2976 sync on a 57.7db line,the noise margin has dropped from 12db to 10db over the last week.
Might be something to do with the router not sitting on top of my computer anymore.

As for getting a 4+meg connection on a 58db line,that must be some sort of enchanted holy grail 2700.

kinmel · Jan 13, 2009, 20:02:57

Quote from: johnny5 on Jan 13, 2009, 19:38:35
Mine is 2976 sync on a 57.7db line,the noise margin has dropped from 12db to 10db over the last week.
Might be something to do with the router not sitting on top of my computer anymore.

As for getting a 4+meg connection on a 58db line,that must be some sort of enchanted holy grail 2700.

Any router other than a 2700 sync's me at about 2600, but any of the 2700s that have passed through here got the 4meg without trying, the big problem is stopping them sync'ing at 5000 at mid-day and then crashing to 3800 at night; 4544 seems to be what they are happiest with and so am I