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Standard User mixt
(experienced) Sat 09-Apr-11 13:14:20
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BT Quite Line Test / Bad Earth?


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Hi all,

Brand new line, installed middle of last month. Couple of days ago the BT's DLM decided to change my target SNR from 6db to 9db, thus decreasing my sync speed by an entire 1Mbit. I've had A&A put it back to 6db for the moment, but it may flip again.

A&A support have said it is due to the modem clocking errors on the line. I had a look at my modem stats and the FEC count is always increasing fairly uniformly - 12,253 FEC errors in half an hour. This doesn't seem to affect line throughput or stability.

I've swapped filters around etc etc and there's no real improvement, so I finally decided to dial 17070 option 2 to do a quiet line test. I did this and clocked a noticeable mains 50Hz hum on the line. Same result whilst having the phone directly plugged into the master socket.

But there is more. The master socket is in a small storage cupboard, so I've placed all my internet and broadband related hardware in this cupboard so its out of site. I've also put my NAS in there. There are couple of devices I know that are not earthed. The NAS is one of them, and I suspect the 3com wireless access point/router might be too. Why do I suspect this? If I perform the quite line test, and touch the casing of the NAS unit (which even has black paint on it) or the underside of the 3com unit (which is just bare metal), I get a really noticeable amplification in mains hum - not just a bit, fairly substantial! Is this normal?!

I don't have another phone to try the quiet line test with. I guess it could be the phone (it's a very cheap one), but if its not the phone, could there be something wrong with the line install that warrants opening this issue as a line fault?

Thanks.

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Standard User RobertoS
(sensei) Sat 09-Apr-11 13:24:44
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Re: BT Quite Line Test / Bad Earth?


[re: mixt] [link to this post]
 
Just a thought, did you use the test socket inside the master for the second quiet line test, or just the normal external socket? If there are any extensions connected to this line you need to use the test socket for the test, to eliminate any noise picked up by the extension wiring.

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Standard User mixt
(experienced) Sat 09-Apr-11 13:37:53
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Re: BT Quite Line Test / Bad Earth?


[re: RobertoS] [link to this post]
 
I hadn't done this, but I have now.

Same result.

There are only two extension points in the flat. One in the kitchen (which I don't use, has nothing attached, not even a filter) and the other in my room which only has a phone attached (with filter).

What do you reckon?

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Administrator MrSaffron
(staff) Sat 09-Apr-11 13:42:24
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Re: BT Quite Line Test / Bad Earth?


[re: mixt] [link to this post]
 
Having the master sat amidst the computer kit is asking for trouble.

What you need to do is experiment with turning off kit and determining which if any are affecting the number of FEC.

FEC errors are errors that have been caught and corrected by the interleaving.

Andrew Ferguson, andrew@thinkbroadband.com
www.thinkbroadband.com - formerly known as ADSLguide.org.uk
The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Standard User RandomJointer
(eat-sleep-adslguide) Sat 09-Apr-11 17:36:40
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Re: BT Quite Line Test / Bad Earth?


[re: mixt] [link to this post]
 
likely to be unbalanced circuit making it hum. Disconnect extension wiring and try again.

Standard User mixt
(experienced) Thu 21-Apr-11 22:55:08
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Re: BT Quite Line Test / Bad Earth?


[re: MrSaffron] [link to this post]
 
I appreciate your comment. There's been no improvement of the line since I opened this thread. But with interleaving on, it holds a stable sync, with minimal (nearly 0) errored seconds. So I'll just put this down to yet another poor(er) quality line, supplied by BT OpenReach.

As I plan to move to FTTC when it arrives, the master socket ain't moving anywhere. So all the kit I've put next to it will stay precisely where it is. At least on FTTC, it will be a shorter line running VDSL, so less prone to line noise. That's the one thing that's always grated me about ADSL and long lines - more potential for things to go wrong with the signal on the wire, issues which, sometimes, just can't be resolved - or maybe they can, but diagnosing what's causing them is nearly impossible, and extremely time consuming.

Like ADSL is to dialup, VDSL/Fibre/Cable is to ADSL. In my eyes, it will always be a technological fudge to provide broadband to most of the population of the UK, in the cheapest possible way. I'll give BT credit for that; they've done a pretty good job of it. If I had my way though, I would go cable/fibre every time, but no joy in this new build I've just moved into.

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Standard User polemonkey
(newbie) Fri 22-Apr-11 21:56:53
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Re: BT Quite Line Test / Bad Earth?


[re: mixt] [link to this post]
 
In reply to a post by mixt:
I appreciate your comment. There's been no improvement of the line since I opened this thread. But with interleaving on, it holds a stable sync, with minimal (nearly 0) errored seconds. So I'll just put this down to yet another poor(er) quality line, supplied by BT OpenReach.


Hi mixt, I'm curious, did you follow the advice from the randomjointer and mr saffron to fix your line or was it something else?

Is your test phone corded or cordless, the reason I ask is that the power supplies from some (mainly cheaper) cordless phones are electrically very noisey.

Mains hum is very rarely caused by the Openreach side of the line, regardless of installation qaulity, but like rj says extensions using unbalance cables (non-twisted alarm wiring) can be culprits.

Also severe earth contact faults on the line (Openrach side) can sound very much like mains hum, so if you were to report it, this would be discovered when they run a remote line test.

Good luck fault finding, it sounds like a tricky one smile
Standard User RandomJointer
(eat-sleep-adslguide) Fri 22-Apr-11 22:12:27
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Re: BT Quite Line Test / Bad Earth?


[re: polemonkey] [link to this post]
 
>>Also severe earth contact faults on the line (Openrach side) can sound very much like mains hum, so if you were to report it, this would be discovered when they run a remote line test.

Severe earth contact faults would also cause bell problems. Ring Trip, Continuous ring etc. Far more likely to be unbalanced internal wiring IMHO.

Standard User burakkucat
(newbie) Fri 22-Apr-11 22:24:06
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Re: BT Quite Line Test / Bad Earth?


[re: polemonkey] [link to this post]
 
Like, I suspect, both RJ & PM I would really like to know the result of:

(1) tuning off and isolating all mains-powered electronics in the cupboard
(2) connecting a basic wired telephone to the NTE5A test socket
(3) performing a quiet line test

If mains hum is still noticeable, it really should be reported as a voice line fault -- without any mention of broadband.

100% Linux and, previously, Unix.

Edited by burakkucat (Fri 22-Apr-11 22:28:13)

Standard User polemonkey
(newbie) Fri 22-Apr-11 23:15:21
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Re: BT Quite Line Test / Bad Earth?


[re: RandomJointer] [link to this post]
 
In reply to a post by RandomJointer:
>>Also severe earth contact faults on the line (Openrach side) can sound very much like mains hum, so if you were to report it, this would be discovered when they run a remote line test.

Severe earth contact faults would also cause bell problems. Ring Trip, Continuous ring etc. Far more likely to be unbalanced internal wiring IMHO.


Yeah agreed, good point. Maybe 1 leg contact, earth leg to earth? They don't always ring trip, it's those ******* rectified loops that generally come with earths on both legs that are killers for ring trip.

Either way if mixt is unhappy then it's definately worthwhile doing some basic checks with a known good corded phone in the test socket, before reporting it faulty.
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