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Standard User MrDeeJay
(regular) Fri 26-Dec-14 15:30:26
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Preparing for FTTC install

[link to this post]
I am currently planning for my FFTC installation.

By looking around the web it is saying anything connected before the master socket is illegal. I notice there is an extension connected at the junction box where the line enters the building. As openreach put a new filtered faceplate on the master socket will this extension cause interference to the VDSL signal?

I also see that you can use an ethernet cable from new filtered master socket to the router as long as it's under 100 meters.

I am not fussed about this extension that's from the junction box as I don't use it - however if it would be an issue it will have to be removed.

Thanks in advance.

Liberty Surf, freeserve, Wonadoo, Freedom2Surf, BT Broadband, O2 Broadband, Xilo
Standard User AndyPandy
(fountain of knowledge) Fri 26-Dec-14 16:31:36
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Re: Preparing for FTTC install

[re: MrDeeJay] [link to this post]
The extension sounds like "star wiring", where there is no master socket, from which all other extensions branch out.

Personally, if I weren't using it, I'd remove it just to be safe. That, or wire it correctly back to the NTE5 master.

ZeN Office
Fritz!Box 3390
Standard User TheEulerID
(member) Fri 26-Dec-14 17:25:41
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Re: Preparing for FTTC install

[re: MrDeeJay] [link to this post]
The simple answer is that it will degrade the VDSL signal (although just how much it matters will depend on the length of the line, package chosen and so on). However, as a basic principle it's bad.

The configuration would also have degraded ADSL signals as well, but VDSL is even more sensitive to non-optimal wiring.

As a basic matter of principle, it's best to run all phone extensions from filtered outputs from a filtered faceplate with, if required, one unfiltered extension using twisted-pair cable for a modem.

nb. if the extension was installed by BT (or more likely the Post Office), then it's not illegal as such. Technically it would be illegal to interfere with it in any way, but if it's done carefully, nobody will be any the wiser if it's removed.

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Standard User WWWombat
(knowledge is power) Sat 27-Dec-14 13:50:55
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Re: Preparing for FTTC install

[re: MrDeeJay] [link to this post]
Yes, it will cause interference.

In the usual terminology of telecoms, this is known as a bridged tap.

At the point it connects to the main line, it would cause a split in the signal (so a loss of some of the signal strength). Any signal passing along the extension line will get to the end and (as it is unterminated) reflect back. The reflected signal would arrive at the joint again, and split - some going back in the direction the original signal came from (relatively harmlessly), some following the original signal with something of a time lag.

The delayed signal acts like ghosting used to on analogue TV screens - and has the same impact on DSL - it causes interference to the signal, potentially making the bit of signal it now overlays unreadable at the receiver.

According to this document:
a bridged tap of 10m length affects frequencies around tone 1200 or so, so would never have been seen within the ADSL or ADSL2+ signals. But it does affect VDSL2.

The JDSU document shows how it will been seen as spikes in the Hlog and QLN graphs.
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