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.

Agreed, never seen one be the cause of an RFI fault.

Hmmm... sound like it could be a physical fault with some wiring. My connection was unable to sync during my worst time (1600hrs-1900hrs). Other times during the day it did sync but at pretty poor speeds. If a lot of work has been done in & around your exchange it is possible that something might have been disturbed.

As it turns out my issues was a bu55ered connection in the distribution point at the end of the road. The state of the connection made it particularly susceptible to interference. The BT engineer brought back the offending wire, which looked to have been pinched a couple of times along its length. Maybe a case of someone going to cut & then deciding they had the wrong connection? Who knows? Suffice to say all is better now although I do see +/- 6db - easily tuned with DMT tool & a Speedtouch 546 :-)

Well that's the theory of time being a factor in seeing line bounces. My line has been dropping all weekend on and off now.

Saturday around 3pm, up and down until about 10pm. Dropped again several times during the early hours (2am) then up/down like crazy at 5am until about 10am.

It's currently down now, bouncing every 10 secs barely enough time for LCP/NCP (PPP) negotation :-( . (using a neighbor's wireless AP now to report this).

When it's syncs during unstable periods, att. sits at 57-58dB, SNR around 8dB (1MB by the way).... then drops out to -9.0 SNR with complete loss, (LOS LOF, LOM, LCDf) comes back in the region of 10 seconds later SNR 10dB then drops again regularly.

I suspect fault of the copper pair somewhere on the loop back to the exchange (though my voice line is 100% clean.) Puzzling.

It maybe that even the DSLAM port could be faulty, who knows.

Can't see what I'm gonna do to get this sorted now, already had BT out. :-(

I think I have eliminated street lamps and Plasma TVs..... As the line is now bouncing constantly during the day (saturday and sunday), looking through the logs on my SYSLOG server, I am seeing the ATM port bouncing constantly between 2am-4am then again between 5am to 10am....stable until around 12.30pm and constantly bouncing all afternoon - including now.

I suspect faulty connection (on copper pair) or DSLAM port perhaps? I very much doubt it's RFI picked up on the street now..... very puzzling!

Tried absolutely everything.... Dunno how I'm gonna get BT to tackle this one.

Can only think of them putting me on another pair at the DP/Cab etc or moving me to another DSLAM port ( i know that means some provisioning work because I'm on an Datastream service NOT - IP Stream....)

136kHz (but limited use), and 1.8MHz (just about touching the upper ADSL2+ frequencies), although the RSGB have applied to Ofcom for use of 500kHz (hope it's not too widespread, as that's slap-bang in the middle of ADSLmax).

I don't think 1W ERP on a very narrow band which occupies one ADSL cell is going to cause too many problems somehow, and neither is 500kHz (if it ever happens). Since amateur radio is all but dead in this country, I'm far more concerned with wide-band AM broadcasters screwing up my ADSL.

After 27 hours of outage. My line has just kicked in again (for how long I don't know):

SNR at 13.5dB......bit lower than normal when it was healthy for the past 2 years of 15-16dB

Kicked in at 4:20pm. Street lamps are on outside too. Neighbours not at home (hence no Plasma TVs on nearby...)


DSL-FW1#sh dsl int atm0
ATM0
Alcatel 20150 chipset information
ATU-R (DS) ATU-C (US)
Modem Status: Showtime (DMTDSL_SHOWTIME)
DSL Mode: ITU G.992.1 (G.DMT) Annex A
ITU STD NUM: 0x01 0x1
Vendor ID: ' ' 'TSTC'
Vendor Specific: 0xDBB0 0x0000
Vendor Country: 0x04 0xB5
Capacity Used: 47% 40%
Noise Margin: 13.5 dB 22.0 dB
Output Power: 18.0 dBm 11.5 dBm
Attenuation: 58.5 dB 31.5 dB
Defect Status: None None
Last Fail Code: None
Watchdog Counter: 0x8A
Watchdog Resets: 0
Selftest Result: 0x00
Subfunction: 0x15
Interrupts: 2650 (0 spurious)
PHY Access Err: 0
Activations: 1
LED Status: ON
LED On Time: 100
LED Off Time: 100
Init FW: embedded
Operation FW: embedded
FW Version: 3.8.131

Interleave Fast Interleave Fast
Speed (kbps): 0 1152 0 288
Cells: 0 1421 0 256286
Reed-Solomon EC: 0 0 0 0
CRC Errors: 0 501 1 0
Header Errors: 0 311 0 0
Bit Errors: 0 0
BER Valid sec: 0 0
BER Invalid sec: 0 0

Correction both neighbours at home. TVs are on (one plasma) one flat screen...