What might Kill Upstream SNR when Downstream is Good.

TalkTalk. ADSL2+, iPlate isolated BT socket.
Only few houses down our road and nearest 100M away.
Nothing different in house or electrical equipment I am aware of that might do this.
Tried 2 different modems, TT's OEM Technicolour 582, & Linksys Wag160n.

Usually stable sync 9000kbps Down & 980kbps Up on SNR of 6dB for both which varys 7-5 day to night etc. Has been for a good year or so since ADSL2+ enabled at my exchange.

Last few days Downstream is steady at 6dB with min of 5dB but little variation.

Upstream however is all over the place, Jumping from 13 to 6 to 2 & dropping out completely. (When it come back on it might sync slow at 500kbps so SNR can start at 13dB)

Can change every few minutes or remain steady for an hour or two.
Did seem to start high, slowly go down over a few hours then drop out & start again.
but also can go from 12 to 6 to 3 to 12 all in the space of 10 minutes.

Generally when sync'd at 600kbps I do keep connection without drop outs but SNR is still all over the place & threatening to go below 2dB.

Have emailed talk talk but no response yet & would like to be prepared for there reply's.

Usual response is to reduce profile but there must be more to it than that & I was enjoying faster upload speeds, I use Vodafone suresignal for my mobile & need a decent upload.

If Downstrem SNR & sync if fine is it likely that nothing electrical in my house or down the road would have an effect. I know they work on different frequencys.

My instinct says something at the exchange in not right.

Could it be the modems whilst I have tried both, I did once suspect the Linksys was being flacky & moved to the Technicolor, Big coincidence but could have been damaged in the same way. Does feel a bit like a modem thing.

Whilst I do have iPlate isolated (BT installed) I do have 20feet of Cat5e cable to a single BT box, Will try to plug direct but not sure of wiring into a BT socket, Comes out of from with rj45 network plug.

Any advise
Thanks I/A

Edited by bignose2 (Sat 21-Sep-13 16:02:21)

Could be a filter issue or some noise confined to to upto 100 KHz band

Don't understand the rj45 comment. The test socket which you access by removing the iplate is a bt plug socket

Thanks for your reply,

I think it is called a filtered faceplate as opposed to the BT iPlate.
So no individual phone filters are required around house, ADSL does not go any further than this master socket that BT fitted many years ago and immediately made a huge difference to speed & stability & been pretty reliable ever since.

The broadband signal comes from the front of the faceplate via Cat5e cable, it is a standard network plug RJ45 and on the other end of the cable a standard BT master socket that the modem plugs into as normal.

I am just surprised, even with the different frequencies, that it only effects the Upstream.

Components in filters can fail so worth testing at the real test socket. Isp should have got you to do that

Presume its this socket
http://www.coolwebhome.co.uk/faceplate

I had the same problem for many years after numerous engineer visits it was finally fixed by switching me to the best pair from the exchange which had the lowest upstream errors
The one thing I found was that when there was an incoming call and it was left to ring for a while the broadband dropped out and the upstream resync could be as low as 192kbps with a 6dB noise margin while the downstream speed was hardly affected
Until it was fixed I had to stay with a fixed upstream of 448kbps and 20dB noise margin as having it uncapped made the problem impossible

Edited by Oldjim (Sat 21-Sep-13 18:54:45)