SNR problem - Evenings

I have a rather strange one. To summarise my setup:

Have a fixed DSL circuit at 1MB, att of 57dB and normally (by day) SNR sits stable at around 15-16dB.

Cisco 1721 (with WIC-1ADSL), plugged into master socket (ADSL Nation pre-filtered), no extensions patched in on the back of this socket, so it's stand alone. using a shielded RJ11 UTP cable between master socket and port on back of router.

Between the hours of (in the region) 6pm and 11:30pm, my DSL circuit bounces like crazy (around 60 carrier transitions on average), SNR drops right out. Cisco router reporting minus (-9.0)dB with LOS, LOF, LOM flags, so basically the circuit is picking so much noise no signal can get through. Voice line is 100% clear however.

I have used a different RJ11 cable, router (Zyxel) and get the same results (between 6pm and 11pm - roughly)...

BT Engineer visited yesterday (12pm), circuit fully stable, ran woosh tests, etc. Even changed the face plate to a BT NTE 5 (actually made the SNR worse - so changed back to ADSL nation one).....

BT engineer couldn't see any problem at all. SNR sat at 15dB. Come last night after 7pm line started bouncing again.

This problem started over a week ago (Wednesday 17th), DSL line wouldnt sync at all from Wednesday 17th Oct and then started to sync up again on Monday 23rd (bouncing like mad again)...... Line hasn't been fully stable since prior to Wednesday 17th.

I turned off all electrical equipment bar the router, even flicked the fuses out of the main fuse box (bar the mains circuit for the router).... Made no difference.

I suspect that it's emissions coming off (faulty street lamps), someone operating a CB radio unit or something being picked up on the local loop back to the exchange?

Do you think it would be worth getting BT to jumper me onto a different copper pair. I'm suprised no one else reporting any problems in close proximity to my house either. Surely if, I'm experiencing this, others close-by will?

Any experts here give any indications?

From my days working in electricity supply, I recall that when electronic timers became the norm as opposed to motor driven time clocks, faulty ones could and did give us many problems. Even "Magic Eyes" and timers on street lights.
If you get no joy from BT suggest you try a complaint to local Power Co.

ADSL gets worse after dark because it uses the same frequencies as MW radio, and (due to a layer in the ionosphere which is destroyed by sunlight) the radio signals get stronger at night.

Any telephone wiring above ground will act as an aerial. You can't do much about the wirng leading up to the master socket (although BT will bury cable if you dig the trench and lay the duct), but you can do something about your internal wiring. Best plan of action is to fit a filtered master socket, run the ADSL modem from a short cable off that, and then run ethernet cables if a longer route back to the PC is required. A less drastic (but not quite so effective) option is to remove the ringer wire (wire #3) from the extension wiring.

If you want to prove that the internal wiring is at fault, connect the modem directly to the socket behind the NTE-5 faceplate (if you have one of those), or disconnect the extension wiring manually if you have not got an NTE-5.

Edited by deleted (Fri 27-Oct-06 14:54:32)

Hey thanks for that, but please read my posting carefully you will notice that I have done exactly that 2 years ago. Even the RJ11 cable between master socket and router is shielded.

I fully appreciate the physics behind the MW frequency band.

My 1MB DSL line has worked 100% clean for 2 years until now. The problems occur after 19:00 hours and continue until about midnight.

Everything on the E-side (customer premise side is in A1 condition). The problem I suspect is backhaul on the copper spine cables back up to the exchange or on the frame in the exchange room up to the DSLAM.

Thanks mate. Surely other people must be experiencing their line bouncing in similar circumstances? But the BT engineer who cam out yesterday didn't state that their where any in close proximity to me.

He did say a lot of LLU work has going on in the exchange room during the last week or so. I suspect something to do with that? disturbed connections/jumpers, etc

I see a similar thing (a rise in noise margin fluctuations between 6pm - midnight), although nowhere near as bad (mine only vary by around 1-2db).
The period between 6pm - midnight is always worse for me.
I'd put it down to increased levels of interference caused by plasma TVs, heating boilers, microwave ovens, and everything else that gets used more in the evening (when people are at home, and awake), than any other time of the day.
Add this to RF interference and you've got yourself one hell of a problem, that may not be fixable.
Try getting some ferrite cores from your local Maplin store (I've got one on every cable going into my router) - may help if the problem, may not, but at a few pounds each it'll be worth the try.

Ah cheers for that. Worth a try....

The puzzling thing is though, after 2 years of operating a DSL circuit on 58dB (att) and a stable SNR of between (with fluctuations) in the region of 10-15dB and then suddenly after all this this JUST one night (from Wednesday 17th) it drops out to -9.0dB and stuggles up/down until about mid night.

Just out of the blue like that, really puzzles me without any degradation occuring gradually over time that would support the arguments for human habits contributing to this.

I strong think BT have *done* something that has influenced this or someone is operating a CB radio ham in the evening close by.

I wonder if a near neighbour has just purchased a plasma TV?
They are notorious for generating widespread interference.
Some friends of mine have a Panasonic 42" plasma TV (one of the UK market domestic types - i.e. not a "display" plasma). If I visit when they have the TV on, the RF based "blipper" remote key for my car will not work. If they turn the TV off, the key works again (turns out their neighbours have the same problem - TV has to be turned off so they can lock their cars at night).

In reply to:

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Everything on the E-side (customer premise side is in A1 condition). The problem I suspect is backhaul on the copper spine cables back up to the exchange or on the frame in the exchange room up to the DSLAM.

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Strange use of terminology, the E-side in 'telephone speak' is the pair between the exchange and the cabinet.

Reading on, it sounds like you *may* be experiencing an RFI issue. Time to go wandering with an MW radio and see what you can pick up, and before all that, try turning off and unplugging everything electric in the house, another top tip would be to ask nieghbour to unplug thier Sky boxes (always a good culprit). I would have suggested looking at the streetlights coming on, but you say it stops at 12:00 ?

Happy hunting.

If you understand the physics as well as you claim, you will understand that CB radio and ham radio don't operate on frequencies anywhere near ADSL.