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.

In reply to a post by MrSaffron:

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.

I'm not aware of the European regulatory authorities imposing the same sort of limits the FCC places on AM stations in the US (which forces many of them to either close down, or reduce power, to prevent interference to other stations at night) - Shame really, as this would also help out ADSL .

I've monitored it using the laptop via wireless connection, the only cable connected was the 1.2m line cable from the router into the filter plugged directly into the master socket (and yes, I've tried changing both of those as well!), the results are identical, same pattern day in, day out makes no difference if it's a weekday or weekend. My neighbours line gives a flat 6db 24hrs a day

One thought that occured to me, apart from the actual line from the BT pole the only thing that I haven't changed is the BT socket, I've assumed that being plugged into the internal test socket this would rule it out?.

Edited by jeff1106uk (Sun 22-Mar-09 20:08:37)

In reply to a post by jeff1106uk:

I've assumed that being plugged into the internal test socket this would rule it out?

Indeed; the internal test socket will give the same results as an ADSL filtered face-plate (provided you have just the ADSL router, a micro-filter, and a single telephone with no extension cables plugged in).
This will give the best possible connection (and the best immunity from interference) from your line.
Anything which still shows up, short of actual line faults, will be outside of your control.

Yes, only things connected are the filter, line to the router and the base station of a cordless Dect phone system (3 phones). Phone system was changed about 3 months ago so I've assumed it's not that either, previous phone was a similar 3 phone system.

Check that unplugged base station power supply does not make a difference, Power bricks can be an issue especially if Switched Mode type devices.

I'll unplug it about 4pm and see what happens.

OK, phones unplugged completely (inc PSUs) around 15:45, SNR steady at 12db (as it has been since 7am)

Now 17:50 and dropping as per usual, down 2db since 17:20 so it looks unlikely to be the phones

Edited by jeff1106uk (Mon 23-Mar-09 17:52:09)

You still haven't said where you are.
If you're on the east coast, or south coast (basically anywhere from Land's End to Aberdeen), and are less than 30-40 miles from the coast, you may be suffering more from distant European AM radio stations which propagate further at night, due to atmospheric changes.
I won't go into the technical stuff, but the edge of one atmospheric layer (which reflects AM radio waves) shifts up by some distance at night (basically merging with another layer) meaning the waves bouncing off the layer, are carried further.
This is why local AM stations get swamped by distant ones, and why ADSL is junk at night.
If this is what's happening; especially as you have an overhead wire feed from a telephone pole (long horizontal wires make lovely AM radio aerials), there's little you can do (except move somewhere which is fed by underground cables).

Next to Beamish Museum in County Durham so about 15 miles from the North East Coast.

I'm on the East Coast, literally, and suffer very little variation due to radio station noise effect on my ADSL. In fact I usually see about 0.5db change between night and day. I did used to get German Radio Stations on my poorly shielded speakers which have now been upgraded.

Interesting, I'm also on the east coast, I get battered by dutch radio amongst others, I need an 8dB snrm during the day to survive through the night. Although I have a longish line, 45dB, 3.38KM actual line length.

I'm on a relatively short line with attenuation of 23db, maybe it's Dutch radio and not German, I can't speak either.

How much the Dutch radio stations will affect you all at night probably has a lot to do with length of line, and how much of it (if any) is strung horizontally from telephone poles.
If a line is totally underground, I'd expect the only part of the line (to be affected) would be that which is inside the house.
A long rural (or pre-1970s) line, which has large lengths stung from poles will be more affected.

My line is all underground and it's pre-1970s.

The only overhead length on mine is from the house to the pole over the road, the rest is u/g to the exchange. But probably enough exposed to have a significant effect. I live in quite an elevated position too, excellent radio and tv signals here.

In reply to a post by Banger:

My line is all underground and it's pre-1970s.

You're one of the lucky ones (as were my parents at their old house - estate built between 1967 & 1970, all underground).
Unfortunately, underground lines were all too rare back then.
Also, BT (or the GPO, or Post Office Telecommunications as they were called back then) didn't use cable ducts. You'll find your cable, and the joint are simply buried under a pile of dirt (meaning the road/pathway has to be dug up to fix faults or drain water from the cable joins) .

I don't know where you get your info. from but our estate was built in the 1960s, and it is all ducted. Even the run down our drive is terminated and underground. All the ducts have access points every few metres as I once had a fault and watched the BT Engineer change cabinet pairs in one of these access points. Also inside the access point the terminations were encapsulated in a plastic pod which the Engineer unscrewed to re-terminate my line. I suspect the plastic pod was an upgrade at some point, maybe a BT Engineer can comment?

In reply to a post by Banger:

I don't know where you get your info. from but our estate was built in the 1960s, and it is all ducted.

From the fact BT had to dig a large hole outside my parent's old house to get to the cable joints (no access covers, no boxes, just joints buried under the path).

In reply to a post by jeff1106uk:

My SNR is now dropping 6db when it gets dark, used to be about 3db but seems to be getting worse.

Your margin drops because the sun sets, no other reason.

So it seems, BUT, last time Enta got BT to look at it they did something and when it was reset to 6db it only dropped 3db, 3 months later after the last lot of disconnects which were caused by BT messing about up my telephone pole, and Enta having them do deep diagnostics it jumped to 12 then 15 and that's when the nightly drop increased to 6db.

The target margin was reduced to 12db after 16 days solid connection, still getting a 6db drop. I'm now waiting for the next drop to 9db which hopefully should be at the end of next week.

I'm also still not connected to a business connection, upload sync is still showing at 448, I raised a support ticket with WebTapestry on Wednesday morning after the migration and have phoned them twice, still haven't got an answer as to why or when it will be sorted

Edited by jeff1106uk (Fri 27-Mar-09 14:30:42)

In reply to a post by Alnath:

Your margin drops because the sun sets, no other reason.

We've already established that; what's at issue here, is the unusually large delta (not too many see changes of 6dB just because of AM radio interference, and all the other stuff that comes with darkness - more lights being switched on, etc.).