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What is a good line for 2Mb?


What is a good line for 2Mb?

I used to suffer irregular disconnect problems which have recently come back and so have been trouble shooting this.

Plugging just the modem into main socket, as suggested by the fault reporting tool, my modem reports what are apparently good figures:

Downstream :
Noise Margin : 30.0 dB
Attenuation : 26.5 dB
Output Power : 21
Upstream :
Noise Margin : 12.0 dB
Attenuation : 19.0 dB
Output Power : 9

Adding the telephone back takes off only 1dB downstream, then including the extension to the room where the modem used to be placed reduces it to 26.5 dB. But having the Sky+ box results in around 15 dB downstream noise margin (irrespective of the extension).

I have two questions:

What is the minimum downstream noise margin I should be requiring for 2Mb ADSL?

Why would the Sky+ box be causing such a difference? Could it just be a cable problem?

Thank you to anyone who can help.

Community Veteran
Posts: 38,305
Thanks: 971
Fixes: 57
Registered: 15-06-2007

What is a good line for 2Mb?

Did you have a filter on the sky box

What is a good line for 2Mb?

Normally the master socket has an extension plugged into it, which has a socket and runs a cable into a socket in the other room. There is a micro-filter attached to the socket directly on the splitter, and then a two-in-one splitter in the phone side for the phone and the Sky+ box.

To make sure none of those were the problem I tried plugging just the Sky+ connection and modem into the micro filter, and plugging that directly into the master socket. This still gave the same problem though, so I have ruled out the splitters as I only lose 3.5 Db with everything except Sky+.

Plusnet Staff
Plusnet Staff
Posts: 12,169
Thanks: 18
Fixes: 1
Registered: 04-04-2007

What is a good line for 2Mb?


For 2Mbps the line loss needs to be below 43dB and the SNR or noise margin I would say ideally above about 10dB (lower may be OK for some people).

If the Sky box is dropping the SNR that much then there's definately something either in the wiring or the way the filters are connected.

Take a look at


to see if they help. Otherwise it probably is looking like a damaged cable going to the Sky box.