'Normal' SNR evening drop?

[bthompson]

Hi everyone,

Was just wondering what magnitude of decrease in SNR margin most people see due the various factors at play during the evening? My line now has a traget SNR margin of 15db and sits rock solid at that all day long. Once the evening begins it starts to jump all over the place and will always eventually go negative and force a resync. Is a drop of over 15db from optimum daytime performance to be expected or could something be wrong somewhere?

Thanks

[kitz]

Hi and welcome to the forums.

"Normal" range is 6dB,  9dB is not uncommon.  The fact that BT also have 12 and 15dB profiles mean that these ranges do also occur.

However if I was you I would be looking to see if I could identify anything that could be causing this problem.  See if you can see anything that co-incides with the drop such as central heating pumps, street lighting, neighbours external lighting sensors.
The list is practically endless Im afraid. :/

Also try all the suggestions on my Low SNR page.  Quite often some problems can be resolved by fitting and NTE5 adsl filtered faceplate and/or using better cabling.

Have a look through the list and if theres anything you need extra help with or clarification then feel free to ask.

[bthompson]

Thanks for the reply. The problem line already has a filtered faceplate fitted, and even when I physically disconnect the extension wiring at the back of it the large drop still happens.

Now for the confusing bit....I have a second line into the house which comes in via the same physical cable. Also has a filtered faceplate fitted. Target SNR for this line has remained at 6db for over a year since it was activated. When evening starts it only ever shows a 1 or 2 db drop and never resyncs.  If the problem was local to me, wouldn't both lines be affected? I'm thinking something must be 'wrong' somewhere further up the line or at the exchange but I'm not sure how to take this forward.

Brian

[havelock]

Hi Brian,

To clarify, you have 2 separate ADSL Filtered faceplate sockets you can connect to but its the same Broadband line? Or are they two separate broadband lines completely.

If its the former then I would strongly suspect local interference at or near the problem socket or its wiring as Kitz described, as the problem would affect both sockets if it was the exchange or related to external interference. If its two separate ADSL lines completely then it could be anywhere between you and the exchange and you basically need to contact your ISP and report that you are getting intermittent connection and random disconnections after x o'clock - To be honest I would not mention changes in SNR unless they specifically ask or unless you end up speaking to a "Level 2/3 advisor" or a senior tech of some description.


Havelock

[bthompson]

Havelock,

I have two separate broadline lines into the house. Each has its own NTE5 - they are located right next to each other. Even when I swap the equipment around between them, the first line still shows the SNR problem while the second one doesn't.

Brian

[havelock]

It's almost definately a line or exchange issue in this case, and unless you know a local PSTN engineer there's no way of telling if the cables are layed via the same route between you and the exchange.

Your best bet is to phone your ISP, and explain that you are getting intermittent connections and random disconnections on one of your broadband lines but not the other, proving it's not internal interference or your equipment at fault. Request that they raise a BT fault for you to investigate your Intermittent connection issue.

Rgds
Havelock

[bthompson]

Just to let everyone know how this ended up.....

SNR continued to plummet from anytime from 1pm onwards every day.....no pattern to it....sometimes 1pm, sometimes 3pm, quite a few 4pm's but 90% of the time the 'interference' kicked in on the hour and just got worse as the evening went on. Eventually I was dropping through the first 15db of SNR, resyncing, then dropping through another 15db of SNR and resyncing at a very low rate. Even then, it would drop through another 7-10 of the next 15db margin straight away! Finally after all that, my sync rate was lower than fault threshold so I reckon I had a good case.

Contacted my ISP (Nildram - who have been excellent),  who immediately spotted the line was quite 'erratic'. The first guy I spoke to knew all about SNR and instantly knew what I was talking about. Reported to BT as a fault. BT tested line and report nothing wrong. Nildram persist and goes to another team in BT who decide need engineer visit. BT engineer visits, see faceplates etc.....'looks like you have tried everything already', does a few noise tests and leaves to check exchange thinking that a 'lift and shift' may be the best option...broadband will be off for approx 30ins while they do it.

Don't hear anything for a few days......adsl continues....no sign of a lift and shift.... then adsl signal disappears from line and doesn't return. Leave it for 24 hours before contacting them. The 'lift and shift' didn't work?!?!? so a cease and reprovide is needed. A few days later adsl returns. Now a lot more stable than before. SNR falls by 5 or 6db with darkness which is more normal. Line has been syncing at 5728kbps for last 48 hours without any issues - which isn't bad for 47db attenuation. So hopefully, problem solved. Its just a shame BT can't tell you exactly what the issue was! Can't fault the ISP though.

Brian

[kitz]

Hi Brian

Thanks for getting back to us to let us know how you went on.

A lift and shift is changing the port which you connect to the dslam at the exchange on so unless the actual line card was faulty then I wouldnt have expected it to cause the problems you were experiencing.

I dont think they carried out what is known as a full "cease and reprovide is needed", its possible that they found a spare pair (copper wires for your phone line routing) and moved you over to that, as there could have been a fault on the actual line.. or it could have been degeneration/oxidisation of a joint on your line which they fixed.

Like you say they seldom tell the end user what they did to fix the problem... but the main thing is that all is now well