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Aspiring Expert
Message 1 of 58

How to get noise margin raised slightly?

Having moved and had our phone line take 4.3KM to travel 700 meters we've got pretty poor connection speeds and a rather unstable internet. This has caused our speed to drop to ~2.3Mbps, the problem is our noise margin isn't increasing with it so again, when a phone rings or theres a little interferance we drop, speeds drop again.... we've lost just over 1Mbps in a week because of this...


Line stateConnected
Connection time1 day, 8:30:49
Downstream2,297 Kbps
Upstream487 Kbps
ModulationITU-T G.992.3
Latency typeInterleaved
Noise margin (Down/Up)5.3 dB / 5.0 dB
Line attenuation (Down/Up)58.5 dB / 37.3 dB
Output power (Down/Up)0.0 dBm / 13.0 dBm


As far as im aware we shouldnt have less than 6dB noise margin especially on our line, is there any way to increase our noise margin by a couple of dB 8-9 or so and will this have any huge impact on our line speed (taking into account our failure, cost cutting distance of a phone line)


Another question, why is line attenuation down different to up? They two different measurements?

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Message 2 of 58

Re: How to get noise margin raised slightly?

Check internal setup (ext cables, sockets etc)
Not gonna spend too much time on this as I can see you've quite a few more posts than me 😄

DS Attenuation, as a rule of thumb, should be between 30-45dB dependant on your line length. Shorter the line, the lower it should be.

If your DS SNR is low and DS Atten is high, it points towards internal setup, in my humble experience. Can't rule out a line issue though. If you've no NTE5 socket they it may be poor internal wiring.

In answer to your question, the line is divided into two parts, US and DS. Attenuation is basically a measurement of signal loss. The figures should be similar but probably never exactly the same. Someone with a bit more know-how might give a better response.

Hope this helps a little

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Aspiring Expert
Message 3 of 58

Re: How to get noise margin raised slightly?

question is, how do I bypass internal wiring? dont have a test socket, need to pay BT ££££ to sort it out I bet? Smiley Tongue

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Message 4 of 58

Re: How to get noise margin raised slightly?

Dis all other equipment and just have filter, rj11 and router connected.

Might wanna try a different adsl mode if you can change it. Depending on how far you are away, you might want to try G.DMT

Tech Support should be able to run line diagnostics before a Openreach engineer is sent out.
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Recognised Expert
Message 5 of 58

Re: How to get noise margin raised slightly?

@Sweeney47 wrote:

Another question, why is line attenuation down different to up? They two different measurements?

Upstream uses the lower of the available frequencies - downstream uses the higher frequencies.  Attenuation on a pair of wires is different at different frequencies.

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Message 6 of 58

Re: How to get noise margin raised slightly?

Hi Sweeney


Thought I'd educated you already ....   🙂


Attenuation is loop loss on the line for a pre-requisite throughput signal. (different in either direction) TX and RX


Line length increases attenuation .... as you already know.


Low SNRm at high attenuation doesn't mean noise at home ... it means the opposite, line is stable.... BUT you may be getting occasional burst noise causing LOS and reset, if your losing connection .... or ... you may have a high resistance joint somewhere on the line, in which case the occasional phone call will drop the connection.


Sometimes you can get increased SNRm by using another router .... Netgear for example, and if you choose the right one with a broadcom chipset, and load DMT or DG Teamware firmware, you can negotiate your own SNRm within 6 - 9db.

An increase of 3db in SNRm terms might snatch about 600kbps from sync, depending on your bitloading.


Get BT to fit an NTE when you have the pennies .. 😉  or better still, a splitter socket, RJ11 & RJ45.

Aspiring Expert
Message 7 of 58

Re: How to get noise margin raised slightly?

So if I disconnect everything, plug the router into the master socket (one by front door) and nothing else and the line attenuation is the same, then that rules out internal wiring? Or rules in internal wiring? Smiley Indifferent


Thought it would be something along those lines Ian, thanks.


Thanks roger, any idea what sort of cost it will be for BT to fit one? Is it something I can do myself or is that kind of breaching contracts/ToS territory?


Just as an added thing, im suprised the new house didnt come with the new socket type and is installed with the old type, is this 'normal' or is it something we might be able to call our builders on?

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Message 8 of 58

Re: How to get noise margin raised slightly?

Which socket you connect to has no effect to attenuation as such ..... extension or master, unless you live in a huge mansion ...

What affects socket choice is SNRm ... as you may get induced noise from extensions, whereas the main socket, if it was an NTE especially .... would give the true line noise margin, and not indication of increased margin due to extensions picking up impulse noise in the home.


It's illegal to change BT master phone sockets your self, BT would tell you the cost.


I doubt builders would be under any obligation to fit Network Terminal Equipment  NTE sockets ... for the purpose of broadband communications ....  but they might be under obligation to fit you a phone socket, that's what you've got.


Broadband is transmitted down copper wires by loading atm packets with data and transmitting down the wire by using multiple bit bucket frequencies, modulated and demodulated between the dslam and your router/modem (modulate/demodulate).

It's known as discrete multitone technology .... DMT.

Error correction is done between the two using interleave, and forward error correction.

On long lines the higher frequencies can be difficult to receive because of noise levels and poor bitloading happens, where bit swapping and retransmission of data has to take place ... it all slows the process of communication. These are CRCs and FECs .....

That's why a good stable quiet line is paramount, especially on a long line.

What you don't need on a long line is poor noise margin and high resistance faults ....  both broadband killers.

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Distinguished Sage
Distinguished Sage
Message 9 of 58

Re: How to get noise margin raised slightly?

An NTE5 socket would help identify problems easier especially noise caused by any internal extensions just as has been suggested. Pity you are not permitted to replace the master socket - however you might find some usefull help and illustrations here Smiley Wink


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Aspiring Expert
Message 10 of 58

Re: How to get noise margin raised slightly?

From what ive looked up on, our 'test socket' would be inside a box outside the house, am I permitted to test the connection here? Info below...


With effect from Dec 2008, BT have started installing External NTEs on new build properties. These new NTE housing boxes can terminate up to 2 x copper pairs.

The box will be located on the exterior of the premises allowing BT Openreach Engineers easy access for testing etc and are clearly marked "Wiring and equipment from this point belongs to the property owner. Where Openreach attend for a reported fault and determine that the fault is beyond this point the visit and any work will be chargeable."

BT External NTE
External NTE

Inside the grey NTE is a red tamper proof unit where the copper pair terminates and are connected to the box by an IDC labeled A and B.

The box is also said to contain a filter to help prevent electrical interference.

Entry point to the customer premises is via a cable that passes through the rear of the box which connects to IDC terminals labeled 2, 3 & 5. The orange ringwire is not connected in order to reduce interference on adsl enabled lines.

External NTE - inside the box
Inside the External NTE box

The External NTE unit contains a yellow plug which can be removed to disconnect the customer owned wiring, when testing by an Openreach Engineer.

BT appear to be connecting these new units internally to LJU's (non NTE5 sockets) which unfortunately means that there is no internal test socket for the customer.

External NTE yellow plug       external NTE yellow plug removed
BT yellow plug & test socket
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