Quick deterioration of a long and noisy line

I have a relatively long and noisy line which until a week ago had the following characteristics:

Connection 2593 kbps down / 728 kbps up
Attenuation 54.5 dB down / 33.0 dB up
SN margin 6.5 dB down / 9.5 dB up

This is an ADSL2 LLU connection to UKOnline, through a Thomson Speedtouch 585v6 (firmware 7.4.3.2). These characteristics have been more or less constant over more than an year.

Throughout the last week or so the downstream connection speed has been steadily deteriorating. UKOnline techical support tried some adjustments which did not work, and had BT test the line, which was reported to be "free from faults".

As of today, I am observing

Connection 1248 kbps down / 682 kbps up
Attenuation 54.5 dB down / 33.0 dB up
SN margin 7.0 dB down / 12.5 dB up

The deterioration started with a "hole" in bins 96-108, which were not carrying any signal. At the moment, there is no signal above bin 88, and a sharp drop-off above bin 72.

UKOnline technical support are saying that they cannot do anything more, as the line is too long (they estimate it to be 4.4 km, although the straight-line distance to the exchange is 2.4 km), and claim that the more than two-fold deterioration in downstream speed is "normal" for lines of this length. They are refusing to ask BT to send an ADSL trained engineer to check the line.

I have carried out all the usual checks inside the house: Connecting the modem to the test socket does not change anything, my older Netgear DG834G (firmware 3.01.25) achieves another 100-200 kbps, but the SN margins are way lower, switching off everything that I could think of in the house also does not help.

Any advice on what to do next would be much appreciated.

Edited by periv (Sun 16-Nov-08 14:09:37)

Tried tuning an AM radio to the frequency that bins 96 to 108 occupy? It sounds like there may be a noise source locally causing problems.

The line even before this drop was not performing brilliantly it was a little on the slow side, so this may be something that was there before. BT engineer is not likely to see any problems, they don't bring spectrum analysers and the line does not have to support ADSL anyway.

Andrew Ferguson, andrew@thinkbroadband.com
www.thinkbroadband.com - formerly known as ADSLguide.org.uk

I have wondered if ukonline have reduced the output power on their dslam configs, as I also lost some synch speed a while back.

I wouldnt call a halving of synch speed normal, but unfortenatly the excuse oh the line is long nothing we can od is all too common amongst isps as its such an easy thing to blame.

Could be crosstalk.
Could be power reduced on dslam.
Could be more noise due to time of year as things are worse when its darker more.

4.4km at 54.5db attenuation, probably an estimation based on very optimised 12.3db per km loop loss. Loop loss is typically higher than that with only the thickest copper giving 11-12db loss. I think using 14-16db loop loss per km is more accurate with some copper been nearly 20db per km. But it does seem your actual line length is probably over 3.5km.

The supporting evidence for noise or crosstalk is your attenuation hasnt changed.

Thanks for the ideas so far.

I was thinking of the possibility that a neighbour might be using a ham radio and may buy a cheap AM radio to check this, but even if this is the case, is there anything that I can do about it?

It is certainly not street lighting as the situation is very much the same during daytime.

The situation with crosstalk is similar---BT would probably be reluctant to switch the copper pair.

I have been thinking of ordering a second line, switching the ADSL connection to that line and cancelling the original one. This would be costly, and not guaranteed to work, as both radio noise and crosstalk could still be there.

The line was not great before, but has never deteriorated that much, even when everyone had their Christmas lights on.

I'd have thought there's a good chance that the sync rate the OP is now seeing would count as a Fault Threshold Breach and BT would be obliged to investigate?

Line looks to be LLU, so FTR does not exist, it is down to provider to take it up with Openreach

Andrew Ferguson, andrew@thinkbroadband.com
www.thinkbroadband.com - formerly known as ADSLguide.org.uk

The oft overlooked issue of central heating systems and the pumps they have can another issue. It may even be device that was OK before but is now noisy, e.g. electric motor in a treadmill.

The AM radio is the best bet, and then take it from there.

Andrew Ferguson, andrew@thinkbroadband.com
www.thinkbroadband.com - formerly known as ADSLguide.org.uk

Have thought of the central heating system and the pump. Nothing changes when they are off.

Another observation that comes to mind is that at the moment the neighbours in one of the houses at the end of the cul de sac I live in are building an extension and are having electricians around. However, the electricians are not working today, and the situation is worse than ever.

I am puzzled by the fact that if there is a local noise source, it is very much constant, i.e. there are no observable changes. The Speedtouch 585v6 firmware that I am using has SRA, so if the line improves, I should be able to see this without a resync. Before the problem, I was observing a night/daytime difference of about 200 kbps.In fact, the SRA is active even now, but the variations are not more than 20 kbps.

Edited by periv (Sun 16-Nov-08 15:24:16)

Was looking for an AM radio which could be used to investigate the noise. However, the range which I need, 345 kHz - 483 kHz (bins 80-112) is outside the capabilities of normal radios
which cover

FM (MHz) 87.5-108
MW (kHz) 525-1620
LW (kHz) 141-290
SW (MHz) 4.75-21.75

So, back to square one...

An additional piece of information:

Another test that I carried out was to connect to a backup dial-up account with a 56 kbps-capable modem. It managed to connect at only 32 kbps which is rather poor and in the past used to be an indication either of a very poor line, or of a DACS splitter. It is a couple of years since my previous use of a dial-up account on the same line, but I am sure that I was managing to connect at about 48 kbps.

Edited by periv (Sun 16-Nov-08 16:29:10)

Was the ADSL connected at the same time? If so try dialup without it.

Telephone line only needs to support a 28Kbps dial-up so fine as far as BT is concerned.

Andrew Ferguson, andrew@thinkbroadband.com
www.thinkbroadband.com - formerly known as ADSLguide.org.uk