Line noise problems

Hi all. I'm having what appears to be intermittent line noise problems which are screwing up my ADSL and driving me crazy. I work from home so it's important to me to get this sorted.

Problems started on a specific day - last Monday. All fine before then and no kit changes at home at that point. Symptoms are that the connection drops or dramatically slows down at frequent but irregular intervals. Ran a speed test on this site last Monday, getting 500k. Previous months was getting 4.5 to 5.5 Mb. Zen have confirmed nothing changed and agree with my drop-out observations. If I listen to the phone line while the connection is poor I can hear audible noise on the line - sort of like faint hissing interspersed with fax/modem like noises, but faint. Sometimes it happens every minute or so, other times it goes for an hour without dropping.

I've called the BT engineers in, but I want to make sure I've eliminated everything at my end first. I've disconnected everything except a plain phone and haven't heard the noise, but then it's intermittent as I've mentioned. I've tried 2 different routers and 3 different microfilters.

It feels to me like they've connected something up at the exchange which is interfering with my line. my worry is the engineer is going to turn up, listen for 30 minutes and not hear anything then charge me

If you have an NTE5 then read this
http://www.kitz.co.uk/adsl/troubleshooting.htm

Probably a high resistance joint (HR) or water ingress in your line to the exchange. I had similar a while back. Fairly common problem but a nightmare to solve, and the online testers normally fail to show anything. If you can hear noises on your normal phone best to do it via BT phone faults (151) rather than through your ISP.

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If you can hear noises on your normal phone best to do it via BT phone faults (151) rather than through your ISP.

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Agree, but make sure you can still hear them with your router or modem disconnected from the line first

Thanks all - lots of help as usual on these forums.

I currently have the front plate off my NTE5 socket and the router is connected directly to it without a filter. I'm monitoring the line and will run it all day without anything else connected (with the front plat off the extensions are disconnected if I have it right).

For interest, the router is showing downstream line attentuation of 23.0 db and Noise Margin of 4.8 db with a connection speed of 6784 kbps. Upstream is 26.0, 15.0 and 448 kbps respectively. The router is a Netgear DG834PN RangeMax.

The speed test on here shows 5.9 Mb (!!!) downstream and normal upstream (450 ish). yesterday afternoon I checked it and got similar results. I was on the verge of cancelling the engineer visit, when it dropped out on me and I couldn't reconnect for 10 minutes. I picked up the phone line and there were the noises again. I'm going to try to catch the noises, rush over to the master plate and plug a phone in place of the router to see if I can catch them on a normal phone and nothing else connected.

I've also ordered a filtered NTE5 faceplate from ADSLnation - just seems to make sense.

Those figures are not great. The majority of lines with ~24dB downstream attenuation will easily manage the full 8mbits, but yours is abit short wth a very low noise margin.
Dosnt in itself indicate a line fault , could just be a `noisy' environment.

Thanks - was about to ask how that compares.

Will sort out the faceplate and continue to monitor. Figures are remaining constant, with noise hovering between 4.9 and 5.1

Sorry to be dumb, but the term "Noise Margin" is a bit ambigous. Am I better off with a higher or lower figure here ? Does it mean the amount of noise on the line or (as I assume) the headroom between signal level and noise level ?

You want a higher noise margin figure, it is, as you surmise the headroom between signal and noise (albeit in a slightly simplified way).

It just changed to the following

System Up Time 03:53:52
Port Status TxPkts RxPkts Collisions Tx B/s Rx B/s Up Time
WAN PPPoA 21159 29045 0 589 4468 01:50:41
LAN 10M/100M 60138 46957 0 3859 636 03:53:50
WLAN 11M/54M 1191 0 0 27 0 03:53:47


ADSL Link Downstream Upstream
Connection Speed 8128 kbps 448 kbps
Line Attenuation 11.0 db 6.0 db
Noise Margin 7.4 db 23.0 db

Speed test, however, shows lower throughput downstream at 4.8.

Theres something amiss with your line as your downstream attenuation has dropped significantly, your line rate has increased to the maximum with an improved noise margin. You must have lost sync .

Not lost sync - the router confirms it's been up for over 2 hours.

No noticeable change as far as perceived speed goes.

Can't understand why the noise margin has gone up when the attenuation (= volume ?) went down ?

Also - what are "normal" noise margin figures ?

Lost sync since your earlier post , connection speed of 6784 kbps.
Attenuation isnt the the power of the signal but the loss over the line.
Less loss equals more signal received for a given power output.

OK - thanks. My amateur audio engineering getting in the way of my understanding (not for the first time).

All runnign ok until 13:30. Connection dropped completely. Came back up with the following ...

System Up Time 05:14:04
Port Status TxPkts RxPkts Collisions Tx B/s Rx B/s Up Time
WAN PPPoA 7463 12726 0 4933 55946 00:05:12
LAN 10M/100M 93483 72860 0 4397 689 05:14:02
WLAN 11M/54M 1568 0 0 27 0 05:13:59


ADSL Link Downstream Upstream
Connection Speed 7168 kbps 448 kbps
Line Attenuation 15.5 db 27.0 db
Noise Margin 4.9 db 17.0 db

So, attenuation is back up and noise margin is down. Coudln't get to the line in time to listen with a phone.

Its worse than that as your line rate has dropped also.
I expect all this up and down rate change is playing havoc with your IP profile

Just after posting that (with line noise margin still down at 4.9) I took the router out of the phone test socket and put the phone in - clear noise on the line when I picked up, which went after a couple of seconds. Nothing else on the line except single phone.

Swapped back, router came back up with ...

System Up Time 05:17:56
Port Status TxPkts RxPkts Collisions Tx B/s Rx B/s Up Time
WAN PPPoA 86 83 0 280 484 00:01:32
LAN 10M/100M 94254 73577 0 4364 687 05:17:54
WLAN 11M/54M 1574 0 0 27 0 05:17:51


ADSL Link Downstream Upstream
Connection Speed 8128 kbps 448 kbps
Line Attenuation 10.0 db 6.0 db
Noise Margin 6.9 db 24.0 db

So - back up to 8128, with attentuation down to 10 and noise margin back to 7.

Anyone think I'll get charged by BT ?

Oh - and speed test now shows 3.3.

What's an IP Profile ?

Noise margin just dropped to 2.5, then steadied at 3.7. Speed test showed 0.7 !!!

After a smooth morning I was thinking of cancelling BT, but will let him come and see what happens on Thursday. With this evidence it seems clear there is a line noise problem.

Are you running Routserstats? That will log the noise/attenuation for you (and graph it), which, together with copies of your router log, should help you demonstrate the issue to the BT engineer.

Thanks - was just thinking of writing one

So - just to make sure I have this right. Ideally you want a low attenuation figure (loss over line) but a high Noise Margin figure (headroom between noise and signal levels).
Right ?

Over the day, and using routestat program, I'm averaging 12 or 24 or 15 for RX Attenuation. I phrase it like that because I'm getting a lot of short "noise-bursts" which cause disconnects (and in most cases I by taking the router out of the test socket and replacing with a phone I can hear significant noise which then stops after a while). After each disconnect the router can reconnect but may give a different RX Attenuation figure.

I'm getting 6k to 8k RX Sync, again interrupted by the disconnects.

RX Noise Margin is ALWAYS less than 10, usually less than 6.

So, if I have understood it correctly, the above means that my line is basically ok (based on Sync and Attenuation) but there is a high background noise level and the "noise-bursts" kill the connection on a frequent but irregular basis.

Any comments ?

I'll keep you posted as to what BT say on Thursday and thanks for your help.

Just installed filtered NTE5 faceplate from ADSLNation. No change I'm afraid, well I guess the downstream Noise Margin is a little higher, hovering around 6.5 to 7. Speed test on here shows only 3.3 Mbps.

I think I have enough evidence of line noise to let the BT guy come on Thursday. Will post update then.

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So - just to make sure I have this right. Ideally you want a low attenuation figure (loss over line) but a high Noise Margin figure (headroom between noise and signal levels).
Right ?

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Thats basically it.

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if I have understood it correctly, the above means that my line is basically ok (based on Sync and Attenuation) but there is a high background noise level and the "noise-bursts" kill the connection on a frequent but irregular basis.

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Not in my opinion. The attenuation should not be jumping around so wildy as that.
Is susspect the reason the noise margin stays around the same is because Broadband MAX is allways trying to connect at the best speed, and in order to attain that it tries to connect at around the same target noise margin, which AFAIK is set to 6,9,12 or 15dB.
I am guessing there is an intermittent line fault somewhere, possibly an HR but there maybe other possibilities.

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I am guessing there is an intermittent line fault somewhere, possibly an HR but there maybe other possibilities.

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The fault is probably at (or very close to) the exchange. The stats show that the underlying SNR is rising and falling almost exactly in line with the attenuation, which is only going to happen if the fault is before most of the noise being picked up.

I have a similar problem thats driving me made.

My connection can stay synced solid for weeks then all of a sudden a get strange blips that drop my sync rate down to 500 - 700k (from about 3.5M). add to this that occassionally everytime a use the phone the sync is lost (and i've tried dozens of filters to rule out a fauly one + my filtered faceplate) then suddenly it will go back to normal.

Done all the standard BT tests to no avail. this is driving me nuts.

any thoughts

First - update on my problems. All seems to have settled down over the last two days, which is actually NOT reassuring. That's the problem with intermittent faults - they never show up when the engineer is here. Actually he did a lot of checking around and did find a couple of things. The box where the line comes into the house had a couple of corroded wires which he replaced. He noticed that the overhead line from the house was rubbing a couple of branches, which I'll take off tomorrow. He's also said that there has been a lot of work going on at the exchange and he's going to ask them to check my circuit out for dry joints. All in all - he was pretty good. There was never a hint of charging me a call out fee, even though he couldn't find a fault on the day. In his view, I had done more than enough to prove that it wasn't my equipment. The key was hearing the audible line noises through a standard phone into the test socket with no extensions connected. Pretty satisfied overall.

Your fault is a tricky one and I wouldn't be surprised if it's also intermittent noise. Read the various posts in this thread. Prove to yourself that it is the line and not equipment or wiring inside the house. Use the routerstats program (it's free - plus it has an alarm when the sync drops) to keep logs of when it drops out. When it drops, rush over to the test socket, plug a phone in and see if you can hear anything.

All in all - hat's off to BT. I wouldn't be afraid to call them.

Your sync rate - presumably you mean you get just over 8kbps ? If you're talking about 3.5M you must mean the speed test, right ?

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Your sync rate - presumably you mean you get just over 8kbps ? If you're talking about 3.5M you must mean the speed test, right ?

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No. My line length is very long so the max I can normally sync at is about 3.5 - 4Mbps.

I'm pretty sure my problem is also intermittant, its just a case of catching it and ruling out everything else at the same time.

Good to hear the engineer seems to have no intention of charging you, thats the one part the worries me.

OK. Good luck. As I say as long as you've taken reasonable precautions to identify that the problem isn't caused by your equipment I don't think they will cause a problem.