SNR margin drop - possible electrical interference

Hi

I've got FTTC broadband with BT. Download sync speed is around 42 to 48Mb. SNR margin usually around 5db, but this fluctuates quickly (e.g. it could be 5 one second and then 5.8 just a second or two later).

An extension lead is wired into the original master socket (which itself is disconnected) and the lead runs around the edge of the living room into a new BT master socket on the wall, which the Billion router's connected to. (This setup was done by the previous homeowner!)

Since I moved in in 2018, I've had the occasional dropout but nothing too bad, with syncs often lasting for several weeks. At the end of November, after being synced for a month, the router resynced with a lower SNR margin (around 2 or 3db) and the sync speed was much higher than usual (52Mb). I assume this was DLM intervention.

This caused a lot of errored seconds and I assume the DLM intervened again as it resynced again at a higher SNR margin, lower speed and then the errors went. Since then there have been random resyncs once a week or so at random times of day. I have a Raspberry Pi and set it up to record the SNR margin each second.

I've found that every few days the SNR margin drops to below 2 for about 5-10 seconds but it doesn't cause a resync. Last night though it twice dropped down like this and went so low it caused two resyncs (I went into the router stats and it registered -4 db just before dropping). I listened to the phone line when the SNR margin dropped and there was no noise at all.

I've checked against when my heating kicks in and I don't think there's a link. I can't think of anything else that could cause it.

However, I've noticed the router can be sensitive to what I assume is electrical noise. For example I once switched a fan on upstairs and it caused a resync. I tried turning the fan off/on again and it caused another resync so it was definitely the fan. I rebooted the router, tried the fan again and it was then fine.

The router's near my Raspberry Pi and a couple of other power adapters for the TV etc., which I know isn't ideal, and neither is the odd master socket setup. However I've had it like this for years and it's not been a problem.

Is it possible that something like the fridge or freezer (in the next room) has started to cause interference on the mains? Or perhaps a nearby power adapter has started doing it?

I'm considering buying a Tacima mains conditioner to see if this will help, but I'd appreciate any advice as I'd like to ensure this problem doesn't worsen.

Thanks.

Are there heavy errored seconds (CRC’s) showing in the router stats ?

In reply to a post by davidw87:

I'm considering buying a Tacima mains conditioner to see if this will help,

It won't, save your money.

In reply to a post by davidw87:

I'm considering buying a Tacima mains conditioner to see if this will help, but I'd appreciate any advice as I'd like to ensure this problem doesn't worsen.

Just because mains events may be causing interference, it is not necessarily the case that the interference is getting into your router via the mains. Still less likely it is getting from the power supply into the signal from the cabinet - unless there is some hardware failure. Most likely it is airborne noise. In neither case will a mains conditioner assist. Of course, if you can borrow one to try, then why not - but it's not worth spending money

Fluctuations of 0.8dB in S to N are more or less to be expected. A drop of 4dB is significant and a drop of 10dB is serious stuff. Are you still on analog phones or still have the wiring in place? If you are that might suggest an avenue of investigation

In reply to a post by davidw87:

An extension lead is wired into the original master socket (which itself is disconnected) and the lead runs around the edge of the living room into a new BT master socket on the wall, which the Billion router's connected to. (This setup was done by the previous homeowner!)

i think this is now starting cause problems. Can you take some photos inside where the extension starts in the original master socket. Some of the other forum members then can have a look.

In reply to a post by Taras:

i think this is now starting cause problems. Can you take some photos inside where the extension starts in the original master socket. Some of the other forum members then can have a look.

Missed that. I agree, a phot or2 would be useful and definitely of the inside wiring. Who knows, it might be our old friend burglar alarm cable.

In reply to a post by DFScale:

In reply to a post by Taras:

i think this is now starting cause problems. Can you take some photos inside where the extension starts in the original master socket. Some of the other forum members then can have a look.

Missed that. I agree, a phot or2 would be useful and definitely of the inside wiring. Who knows, it might be our old friend burglar alarm cable.

from what the OP has suggested means, from my understanding is that he can't do a test behind the master socket which is worrysome when you have this type of fault. I don't understand what typing of extension cabling can induce issues which is why i suggested others to have a look at the wiring !

In reply to a post by Zarjaz:

Are there heavy errored seconds (CRC’s) showing in the router stats ?

It doesn't show CRCs but it shows errored seconds and severely errored seconds. In 20 hours of connection there's been one of each.

In reply to a post by DFScale:

In reply to a post by davidw87:

I'm considering buying a Tacima mains conditioner to see if this will help, but I'd appreciate any advice as I'd like to ensure this problem doesn't worsen.

Just because mains events may be causing interference, it is not necessarily the case that the interference is getting into your router via the mains. Still less likely it is getting from the power supply into the signal from the cabinet - unless there is some hardware failure. Most likely it is airborne noise. In neither case will a mains conditioner assist. Of course, if you can borrow one to try, then why not - but it's not worth spending money

Fluctuations of 0.8dB in S to N are more or less to be expected. A drop of 4dB is significant and a drop of 10dB is serious stuff. Are you still on analog phones or still have the wiring in place? If you are that might suggest an avenue of investigation

Is it likely then that the SNR margin dropping is due to interference on the internal wiring, rather than on the line coming into the house? I have an analogue phone plugged in but rarely use it. There's no noise on it though, even when I listened while the SNR had dropped.

In reply to a post by Taras:

In reply to a post by davidw87:

An extension lead is wired into the original master socket (which itself is disconnected) and the lead runs around the edge of the living room into a new BT master socket on the wall, which the Billion router's connected to. (This setup was done by the previous homeowner!)

i think this is now starting cause problems. Can you take some photos inside where the extension starts in the original master socket. Some of the other forum members then can have a look.

Is there any reason why it would suddenly start to cause problems?

Here are two photos:

https://i.ibb.co/ckTyWgM/IMG-20250114-151403944.jpg
https://i.ibb.co/xLfghKL/IMG-20250114-151536625.jpg

The top plate covers where the (underground) phone line comes into the house. Behind this is where the extension lead (off to the left) is connected and runs about 10 metres around the room to a socket on a wall which looks like a BT master socket.

Also connected is a short cable going to the bottom socket, but it terminates in the socket and isn't connected, so the socket is dead.

The connections behind the top plate seem to be made using some sort of transparent connector. None of it looks good to me!

Thanks all for your help.

It doesn't show CRCs but it shows errored seconds and severely errored seconds. In 20 hours of connection there's been one of each.

For me that rules out REIN being the cause.

I don't understand what typing of extension cabling can induce issues

The ‘alarm cable’ referred to is hideous stuff. All non twisted, multi strand.