Noise on line when ADSL modem connected

Have had problems with noise on line for a while but have now refinded the exact problem and need some advice before BT engineer visits.

- Sky B/B unlimited
- DG934 modem connected directly to test socket via filter via two different cables (one supplied with router, one a third party super shielded one)
- have tried two different filters (both supplied with sky router) and a filtering faceplate from ADSLnation (is it xte2005??)
- NO extensions connected
- also tried old sky DG834 flashed with DGteam firmware
- tried a wired and a cordless telephone

(below tested with BT quiet line test, 17070 option 2)
With no ADSL modem connected there is NO noise on the line.

When I initially connect modem (tried both the above modems with different leads listed above) there is a quiet high pitched noise quickly followed by background hiss and loads of crackles. The crackles then become intermittent but the hissing/quiet crackling noise is constant.

If I then disconnect the ADSL modem the noise CONTINUES for 5 seconds then the line is quiet as if the DSLAM at the exchange disconnects as no ADSL modem is present at my end.
I would blame my modem for the fault but it clearly continues for several seconds after disconnecting the ADSL modem.

When I make a phone call and monitor the noise margin with "routerstats" the downstream and upstream noise margin become unstable dropping the noisemargin by 3-7dB in spikes. This often leads to ADSL disconnections when I make a telephone call. This especially affects the upstream noise margin.

Could this be a DSLAM problem?
Could it be a problem with the 'splitter' which splits the voice and DSL signal at the exchange end? akin. to a filter at the exchange if there is such an entity??
Could this be a 'high resistance' line fault - the ADSL signal inducing noise in the voice spectrum as a result of dodgy insulation/connector??

I previously had a problem with noise on the line which was present even with the phone connected directly to the test socket..... this started after two weeks of rain/wind in November. But this was very intermittent and was never present when BT came out so they haven't done anything to fix it!

Any ideas anyone??

Stable line stats below (during a phone call Noise margin upstream drops to 2-3db, and resync is often at around 600-800kbps upstream). A reset after the phone call has finished results in the following:
ADSL Link Downstream Upstream
Connection Speed 11260 kbps 1024 kbps
Line Attenuation 33 db 18 db
Noise Margin 12 db 8 db

(cross posted from sky user)

I had a similar problem,im with ukonline ,so on easynet llu, my problems started in December 2009 when my downstream snr dropped by 1-2db, shortly afterwards i got the dropouts,which became more frequent, from one per every 7-10days to 1-2 times in 24 hrs at one point, also i too was able to hear noise during the bt quiet line test 17070 option 2 ,also noise would sometimes continue for a few secs after unplugging router, and i was able to hear it sync too,

have you got another router that you could try that has a different chipset than broadcom,?
There is a app you can download "Routerstats or routerstats lite, "once set up it will monitor your sync speeds Snr values and one some routers all other stats too,
what router are you using the sky netgear or sagem. or your own?
As some routers are more compatable with the easynet exchange kit than others, if you are on LLU you may benefit from a router with a conexant chipset in it,

I swapped my eddimax ar7084a to a netgear dg834g v5, my snr now hardly fluctuates it was constantly with the other router and my attenuation was lowered by a couple of db,(IEdimax router used without any probs for 18mths)It maybe something to do with the equipment in the exchange, maybe it's been changed in some way,
The problem of logging this as a PSTN(voice) fault is that the problem of noise is only present when the router is connected, a bt engineer will 1, only check your line for a PSTN fault, so if none found,as may well be the case you get charged, or he may turn around and try and blame the router for causing it,
so the more things you try ,that demonstrate that your equipment is not behind the fault the better ,
what has sky tech said or done,presumably they may of increased your noise margins, or if you are interleaved maybe put the noise pulse protection on,or lowered your line speed sync rate, as they most probably will try those sort of things before calling out bt for a sfi visit, the problem may just go, like mine appears to of done,but im still monitoring things to confirm it has,
at the end of the day there is a chance that this problem like mine were caused by a bt engineer fixing another fault or doing other work in a street cab that our lines run through, as most bt cabling is old and rotting away, plus you also have the wet weather winter delivers,

Edited by tommy45 (Tue 23-Feb-10 00:43:39)

Could this be a DSLAM problem?
Could it be a problem with the 'splitter' which splits the voice and DSL signal at the exchange end? akin. to a filter at the exchange if there is such an entity??
Could this be a 'high resistance' line fault - the ADSL signal inducing noise in the voice spectrum as a result of dodgy insulation/connector??

Could be any any of those, though I think the filter sits with the line card except maybe for any of the old DSLAM's that may still be in use.

Sounds very much like an HR fault. To ensure that the engineer who comes is aware of what these symptoms indicate, raise the fault via your ISP.

BT engineer agreed likely HR fault but was on a voice fault job and reccomended a line pair quality test.
Sky then sent out an SFI engineer on a 1 hour job without line pair quality test equipment.

Sky now going to organise line pair quality test next week some time to suit my availability.

But they said they were going to change which equipment I change to at the exchange. The following day (Friday just gone) the B/B went down for 1/2 an hour and came back up for a short period and then stayed down until the small hours of the morning when the router seemed to reset itself (I was away from the house and could only monitor remotely).

Now I have the following line stats

upstream/downstream
Sync 6140 / 412
Attenuation 22 / 18
Noise amrgin 18 / 2147483647db

I assume the absurdly high noise margin for upstream is actually a negative noise margin misreported???
I assume that either the equipment change at the exchange has created loads of noise on the line or the pre-existing fault has coincidentally got a lot worse??
I don't quite understand why the downstream sync rate is so slow though..... unless they have increased my target noise margin to 'solve' my problem rather than fix my line. Does a really poor upstream noise margin limit how fast the modem wants to connect downstream?

I think I will be having a long irate phone call to Sky once I get back to the house after the w/e

Any suggestions anyone?

2147483647 - 2147483648 = -1 dB

Something is definitely amiss to get a negative upstream noise margin.


John.

Edited by deleted (Sun 28-Feb-10 11:33:37)

In reply to a post by John_ON:

2147483647 - 2147483648 = -1 dB

Something is definitely amiss to get a negative upstream noise margin.

Edit: It's actually the downstream figure but there's obviously still something wrong.

John.

What is "2147483648"?

I mean, 2-3=-1 too....

In reply to a post by BatBoy:

In reply to a post by John_ON:

2147483647 - 2147483648 = -1 dB

Something is definitely amiss to get a negative upstream noise margin.

Edit: It's actually the downstream figure but there's obviously still something wrong.

John.

What is "2147483648"?

I mean, 2-3=-1 too....

It's the "twos complement" http://en.wikipedia.org/wiki/Two%27s_complement

There are better explanations if you google a bit.

John.

Edited by deleted (Sun 28-Feb-10 11:39:15)

This looks more likely

For 32-bit signed integers, the minimum value is 0x80000000 (-2147483648) and the maximum value is 0x7fffffff (2147483647). Note that there is no value than can hold 2147483648, so if you negate (int)0x80000000, you get (int)0x80000000 again. That is something to look out for, because it means abs() returns a negative value when fed -2147483648.

It seems it's the largest value of a 32 bit Int.

Yeah, I think it comes down to the same thing. The top (left-most) bit is used as the sign bit.

John.