snr drop when plugging phone in

Hi, I'm new.

Using Adsl2+ on Plusnet. Long ways away from the exchange where low snr and high attenuation are simply the norm.

I am using a TD-W8970 as a modem plugged in to a ADSL faceplate on an NTE5 mastersocket (BT logo but not openreach logo) There is one phone plugged in to the phone socket on the faceplate, a panasonic kx-tg8521

I have been looking at some connection issues as of late. I've noticed that I become disconnected when I make or receive phonecalls, after which it is difficult to resync. I have noticed the modem finds it easier to resync if the phone is unplugged from the faceplate. I then noticed that even plugging it back in (without making or receiving calls) lowered the snr margin.

Any ideas as to why this could be happening? Is there anything I can do about it?

I get an snr margin of 6dB with the phone unplugged
This drops to 5-5.2dB with the phone plugged in
If I "pick up" the phone to get a dial tone, this drops further to a minimum of 4dB
I dare not make a call

Try plugging a microfilter into the BT test socket and plugging the phone and router into that, check again if issue cleared.
Try swapping the telephone, check again if issue cleared.

You should be OK with most routers to much lower than 4dB SNR, as it isn't SNR anyway, it is SNRM despite its labelling by some kit. The M meaning "Margin", which is how much you have spare.

The whole point of it being set at 6dB (for most ISPs) at sync time is precisely to allow for such changes. On my line I used to get a 3.5dB drop when using the phone. Speedtouch routers (585s) didn't like that, but Netgear 834 series were perfectly happy.

The Plusnet 582n is a Technicolor = Speedtouch. Hmmm.

Having said all that, as you seem to have been OK until recently, it is possible the filter in your ADSL faceplate has failed. If the suggested check using the test socket is fine I suggest the next step is to replace the faceplate.

My line dropped 0.5db of margin when the phone was in use, until one day it went and started dropping 5.5db. This was when I was on ADSL2 with Be.

Much research and talking on forums with BT SFI engineers determined it was most likely an HR (High Resistance) fault. Good luck finding it! Took me years.

You'll probably have to do what I did ... what until it breaks down completely then report it as crackling on the voice side.

In my case, it turned out that a link wire in the PCP cabinet wasn't screwed down properly - so every time BT worked in there it was wiggling my cable against the connectors causing all sorts of intermittent fun.

Make a call, log all the stats before, during and after it. Send them to plusnet - the more data they have, the more they can help you.

J