Dropping SNR - How far before BT will fix it?

My SNR is now dropping 6db when it gets dark, used to be about 3db but seems to be getting worse. Question is, how big a drop before BT would do anything about it?, or would they just push up the target margin to compensate?.

Edited by jeff1106uk (Sun 22-Mar-09 15:43:27)

The automatic systems will probably push up the target SNR margin.

It may be useful to know your sync rate, attenuation, and SNR margin.

As John has said, BT's automated systems will probably just push up the target margin to prevent too many resyncs.
Have you tried disconnecting the ring wire (wire number 3) in all sockets? It has a habit of dragging noise into the circuit.

BT probably won't "do" anything about your dropping margin, as it's not usually their fault.
If you did have a 3dB swing, but it's now 6dB, you need to look more local.
Have you recently fitted any low-energy lamps, bought a new TV (or any other electrical item).

Try the steps mentioned here.

If the upstream margin is fairly steady, then you can be more sure that the problem is local to you rather than at the exchange end

Can a variation in the upstream margin signify something amiss at the exchange end? I keep a close eye on my upstream/downstream margins and my upstream, which I had never seen show as anything other than 20, now gives something different each time; I have had 16,18 and 19 all show up recently. Upstream attenuation is 31.5.

Hi jeff1106uk,
As others have said - more info please?
Line stats, Test Socket results, Router, History, etc.

I believe you were changing providers and mentioned getting your Target SNR changed? Has this happened?

It's tricky trying to find out what's happened by reading your previous posts. So best to spell things out

Having tried all sorts of things over the last year or so including different routers, using DMT, rewiring the connections etc. all with no efect.

Here's how things stand at present.

Router - 2Wire 2700HGV connected for 3 weeks, 3 line retrains (2 by me) 1 by BT when they dropped the target margin from 15 to 12db after 18 days solid connection.

Connection - Direct into test socket, router connects to PCs via 15m of Cat5E to a 5 port switch and wireless connection to laptop, PSP or PS3 Also tried direct to only 1 PC with no difference.

Mains block with router is a Belkin filtered unit (has been changed just in case) but still had the same problem when the router was upstairs connected to phone socket by 15m phone extension).

All cables, filters, mains blocks etc. have been changed with no effect at all.

Router holds perfect flat sync (looking at Routerstats) from approx 07:00 to 17:00 then starts a slow drop of 6db over approx: 3 hours then holds there +/- 1db, then around 04:30 starts to climb back until 07:00.

Router stats (at 17:53) are as follows.

DSL Down Up
Current Rate: 6080 kbs 448 kbs
Max Rate: 6080 kbs 1008 kbs
Current Connection:
Current Noise Margin: 11.0 dB 23.0 dB
Current Attenuation: 36.3 dB 20.0 dB
Current Output Power: 19.7 dBm 12.2 dBm

ATM Cells Errors %
Transmit: 46387353 0 0
Receive: 970490132 0 0

IP Bytes Packets Errors %
Transmit: 1278324363 21299504 0 0
Receive: 2534386122 31840871 0 0

I'll do another check in the morning but if I remember correctly the only thing that changes is the downstream SNR.

I'm due to change providers on Wednesday currently using Entanet via UKFSN on BT IPSC, new provider is WebTapestry so still Entanet but via an L2TP reseller which gets me away from the new ALT system and should cure the current sub 2M speeds at weekends. They have said they can get the target magin reset but as the drop is now 6db that would not be a good idea!, the 2Wire will hold sync down to 0db but I'd rather not risk it so will see if BT drop it again by another 3db in 2 weeks time.

Edited by jeff1106uk (Sun 22-Mar-09 18:03:33)

In reply to a post by jeff1106uk:

Router holds perfect flat sync (looking at Routerstats) from approx 07:00 to 17:00 then starts a slow drop of 6db over approx: 3 hours then holds there +/- 1db, then around 04:30 starts to climb back until 07:00.

What is your location?
If you're closer to mainland Europe, you may just be seeing the effects of long distance AM radio stations (only a greater SNR change than most of us get).

It usually means duff filters, or the cause of the noise is more likely to be further from your home, i.e. it need not be in the exchange, but could be the phone line passing next to the railway line, or someone using arc welding equipment

Variations when its a figure of 16 to 20 for noise margin are nothing to worry about, especially if you don't know the power level.

Yeap timing suggests AM radio floor rise is the issue, can occur with UK am stations, and anything else throwing noise out in the AM range.

Only thing to do is to ensure you are using twisted pair cable everywhere you can.