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Noise margin confusion

Rising Star
Posts: 70
Thanks: 10
Registered: ‎04-11-2017

Noise margin confusion


I am a little confused by my Home Hub 6 stats, not in a big way, but just wanting some clarity.

Specifically the very low "down" noise margin. It has consistently fallen to 1.7 since the router reset over two weeks ago. Is that good or bad? I thought 3 db was the furthest it should go.  My line is very stable so no complaints there.

DSL uptime:


17 Days, 23 Hours 17 Minutes 9 Seconds

6.21 Mbps / 30.84 Mbps

6349 / 30849

6.2 dB / 1.7 dB

42.8 dB

25.5 dB / 42.8 dB


Any thoughts and info appreciated.




All Star
Posts: 747
Thanks: 232
Fixes: 24
Registered: ‎19-11-2008

Re: Noise margin confusion


Hi @fred77

Your modem would target a noise margin of 3 dB or higher (depending on cabinet make and line stability) at initial synchronisation.

After your modem synchronised the ambient noise or a crosstalk noise from other lines has risen.

This had reduced the noise margin to 1.7 dB.

If you re-synch the modem will restore the target noise margin by reducing the synch speed.

DSL exchanges noise margin & stability for speed and vice versa.

A reduction in noise margin can occur after a local power cut, for the modems that are fastest to re-synch say at 3dB.

Once the slower modems in the neighbourhood re-synch the crosstalk increases and the noise margin is eroded.

That happens to my modem and the noise margin drops from 3 dB to 2.1 dB.





Rising Star
Posts: 70
Thanks: 10
Registered: ‎04-11-2017

Re: Noise margin confusion

Many thanks.