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Author Topic: 4db drop in margin  (Read 1563 times)

Sheepie

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4db drop in margin
« on: January 08, 2017, 09:38:48 AM »
A few months ago I had a sudden drop of both US & DS SNR margin by about 4db each, and this has never recovered. The drop happened without a resync.
I have seen other drops before, usually when the openreach van is around installing FTTC at a neighbours house, and then the drop is about 0.4db.

Does anyone know what would cause a 4db loss of margin? Quiet line stats before and after the 4db loss look exactly the same.

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S.Stephenson

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Re: 4db drop in margin
« Reply #1 on: January 08, 2017, 01:54:40 PM »
Crosstalk I'd say I have at least 2 that knock off 3db.
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Sheepie

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Re: 4db drop in margin
« Reply #2 on: January 08, 2017, 01:59:21 PM »
Oh I didn't realise a single crosstalker would affect margin by as much as 3dB  :'(
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j0hn

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Re: 4db drop in margin
« Reply #3 on: January 08, 2017, 02:02:16 PM »
That was back in November. Your snrm has been up and down quite a bit since then. As said above though, it's crosstalk. A 4dB drop is quite a big crosstalker. The fact it never recovered just means they always leave their modem on.
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Talktalk FTTP 550/75 - Speedtest - BQM

ktz392837

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Re: 4db drop in margin
« Reply #4 on: January 08, 2017, 08:31:10 PM »
My worse cross talker takes out 6-7db.  I may get once or twice a year where they must go away on holiday and get 20Mb back for a month or so before DLM intervenes.  This also assumes it does not band me and then I have 12db free but can do nothing with it.
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