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[seismicboy]

Problem - Every night my SNR drops like a stone and eventually the sync speed drops too. My usual connection speed is 1.8M-2.2M with a 1.5M profile. Attenuation down is ~ 52dB. Good snr is 15-17dB. During the night the snr drops to zero and the sync can drop as low as 160k. Needless to say my download profile is currently very low because of the daily drops in sync. I've had a fault ticket open with BT since 6th May.

BT Broadband
3.5km from exchange
Routers SAR600EW & Thomson TG585 v7

I have attached snapshots of each router on different nights. Router plugged into the BT test socket on master box, no phones, wireless to pc upstairs....

I would imagine these graphs eliminate any source of noise from my internal phones/wiring as they are disconnected when the test socket is in use. I have temporarily powered down my burgler alarm which was the only obvious electrical device near the phone line that is switched on during the night.

Another point of note, when I come into my office first thing in the morning and router stats shows me poor snr, if I take a phone off and back on the hook, the snr will go back to 15dB and the next re-sync will be good (~1800k) See attachement 3 which although is now 07:30 in the morning and the noise is recovering, note the effect on the snr of taking the phone off the hook (3 times) Why does this have such an effect on the snr ? When a phone is taken off hook, doesn't it present a low resistance (~150 ohms) load to the exchange which initiates the dial tone?

I have a adsl face-plate filter from solwise fitted to the master box. But don't pics 1 & 2 (routers in BT test socket) eliminate any phone/filter issues?

Finally attachment 4 is a snapshot of router stats at midday (normality). Errors shown are from very early morning when snr was poor

If anyone can throw any light on this problem I would be most grateful. I have reached the extent of my knowledge of all matters adsl and my patience with BT.

seismicboy.

[attachment deleted by admin]

[roseway]

Hi and welcome.

First, you're right - if you still get the unstable result when plugged into the test socket, then it's not your internal wiring or filters (assuming that someone hasn't improperly connected an extension to the back of the master socket).

The effect you get when picking up the phone is a classic symptom of a high resistance fault. This is a poor wiring connection somewhere along the line, and the extra current taken by the phone temporarily repairs the poor joint. With this type of fault it's quite likely that you will get crackling on the phone as well; if this is the case then the best option is to report it to BT as a voice fault (dial 150) and don't say anything to them about ADSL. Voice faults always get quick attention.

If there's no audible noise, then I'm afraid that it's back to your ISP, making it clear that you're plugged into the test socket so the fault is not inside your house.

[seismicboy]

Hi and thanks for your input.

Yes, I can hear a noise on the line if I'm around while the snr is at its lowest. It's quite subtle but when it's gone the snr returns to normal.

However, in view of this and the nocturnal element, I think it will be hard to get BT to accept there is a line fault.

seismicboy.

[kitz]

Gosh - Thats one hell of a drop!   

12dB down to 0dB - resync 12dB and way back down to 0dB again!  Thats like 24dB fluctuation.


I'd almost say its a REIN issue, but the slope rather than distinct drop is rather unusual for typical REIN faults which dive after something is switched on.
If Im reading the times correct from the upper graphs this decline is over a few hours?

Its like the Noise Builds up over the evening.. but then clears during the late hours.

Those graphs prove that something is interfering with your connection though.

>> if I take a phone off and back on the hook, the snr will go back to 15dB

As already mentioned by roseway that is indicative of a high open (resistance) fault..  therefore needs to be investigated by an engineer.   Its worth showing him the routerstats graphs too as proof that this occurs during the nightime hours.

[Azzaka]

Also ask your ISP to raise it to BTW and ask them to push for a Transmission engineer to check the splittercard. 

[seismicboy]

Thanks for your posts guys.

I've come across the term "sealing current" in my googling. Its a small dc current applied to circuits to maintain connectivity of joints in cables etc. especially and historically telephone lines (I'm not sure if telecom companies still use the technique)

My adsl link works best (lowest noise) when any of my phones is off the hook (current flowing down the phone lines). I'm rapidly coming to the conclusion that, as suggested, I have a marginal connection somewhere between my house and the exchange which is temporarily repaired when current flows down the line and "seals" the connection. Isn't technology wonderful?

I'm in Paris airport right now on my way to Gabon for a week to earn some money to pay my bills. I will be on to BT (again) when I get back.

seismicboy.

[kitz]

I've come across the term "sealing current" in my googling. Its a small dc current applied to circuits to maintain connectivity of joints in cables etc. especially and historically telephone lines (I'm not sure if telecom companies still use the technique).

Yes thats what we commonly call a "High open" or "High Resistance" Fault in the UK
 - see ~ adsl only works when the phone is being used...  and  its still very applicable today.

[The Wolf]

Interesting stuff.  I started to suffer an identical problem with BTBroadband about a month ago after nearly a year of fairly reliable sync speeds (I am 5.2 km from the exchange and the best I ever get is around 1440kbps).  The first signs were identical to those described with adsl working fine after the router was rebooted.  Sometime during the night, the sync speed would drop as low as 135kbps.

BTW have been working on the fault and did at least switch lines from an older one with aluminium connectors to an all copper one - this increased speeds marginally, but seems to have done little for the overnight drop.

The high resistance fault/splittercard ideas are interesting ones - in fact BT Openreach rang as I was writing this email and I mentioned it to the engineer, it seems as if they are coming to similar conclusions.  Of course knowing what the problem is, is one thing.  Getting it sorted is something else entirely.

Just in case the problem persists, how did seismicboy produce the router stats graphs and would it be possible to do the same with a BTHomehub?

[roseway]

Hi and welcome.

You can get Routerstats here. It can be made to work with quite a lot of routers, but you may have to do a bit of messing around if it's not one of the directly supported ones; I don't know if it will work with the HomeHub.

[The Wolf]

Many thanks for the info.  RouterStats works just fine with a BT Homehub v1.5 (the black one), the only tip being to reboot the router after setting up the software as it fails to register the correct Rx Sync before a reboot.

Surprise, surprise, my connection failed during the night, unfortunately before I had seen the advice from roseway:

DSL Connection 

Link Information
   
 
Uptime: 0 days, 7:04:36
 
Modulation: G.992.1 annex A
 
Bandwidth (Up/Down) [kbps/kbps]: 448 / 320
 
Data Transferred (Sent/Received) [KB/KB]: 448.00 / 590.00
 
Output Power (Up/Down) [dBm]: 12.0 / 12.5
 
Line Attenuation (Up/Down) [dB]: 31.5 / 63.5
 
SN Margin (Up/Down) [dB]: 10.0 / 20.0
 
Vendor ID (Local/Remote): TMMB / TSTC
 
Loss of Framing (Local/Remote): 0 / 0
 
Loss of Signal (Local/Remote): 1 / 0
 
Loss of Power (Local/Remote): 0 / 0
 
Loss of Link (Remote): 0
 
Error Seconds (Local/Remote): 8 / 0
 
FEC Errors (Up/Down): 0 / 766
 
CRC Errors (Up/Down): 0 / 3
 
HEC Errors (Up/Down): 0 / 3
 
Line Profile: Interleaved
 
 
Since re-booting downstream CRC and HEC errors have been increasing at about 1/min. 

BT Openreach, to their credit, are starting to take this seriously and are calling in another engineer to look at the line between me and the exchange.  Time will tell!

[roseway]

Hopefully BT will find a corroded connection or something like that. With such a long line any fault is likely to have a big effect on ADSL performance. Routerstats might show up some useful information to help diagnosis, so I think the best we can do is cross our fingers for you.

[Ezzer]

Sealing current...... the typical term I've come across for the same thing is "whetting" or "wetting" the fact you have a pstn running on the line at 50v dc all the time provides the whetting

[Azzaka]

Interesting name to give a common fault. I guess 'Sealing fault' is something alot more people will be able to understand.

[4candles]

That brings back memories. When I was on transmission engineering with BT, it was standard practice to apply 'DC wetting' to the local copper loop section of a private circuit.

This was to achieve the previously mentioned 'sealing' effect, and also indicated to field engineers that here was a working circuit, even if it had no dial tone!

[Ezzer]

Hadn't been working solo for long when I was providing 2 lines, pushed 2 pairs throught to the customer but one of them was a private wire which I inadvertently pinched as there was no dial tone  Never did that again  straight to the naughty corner