Just over a year ago we had a fibre cabinet installed approximately 0.5 miles outside of the main village. Uptake has been good and it appears most people have now transitioned across to FTTC broadband.
A couple of weeks ago I was asked by a fellow resident which ISP I use, because he was looking to switch provider, mainly because he wasn't happy with the speed he was getting. When I asked a bit more, it began to sound like he was having issues with this line so I suggested we should monitor it for a while and see if that reveals anything.
He already had a Zyxel VMG8924-B10A router, so it was easy to hook up my Pi with DSLstats on it. While plugged in to the 5C master socket, testing to date has revealed three things:
1) The HLog plot has a big dip around tone 1670, see here
2) The U2 band is not utilised (possibly related to item 1?).
3) Every so often the downstream SNRM would fluctuate severely, causing the broadband connection to drop.
I'll start with item 3. Following some troubleshooting, we think we have narrowed this down to Powerline adapters, but this is still to be confirmed. Essentially, each time he would stream content to a TV connected to one of these adapters, the fluctuations would start (mainly affecting the D3 band). We have now removed the adapters from the mains and all is good so far. These are the newer TP-Link adapters, so I'm planning to enable VDSL compatibility mode and see if that cures the issue. Unfortunately, in his property, the phone line comes in at the back of the house, and we don't know the cable routing to the master socket at the front of the house, so it could well be that the mains power cables run close to the phone cable, causing the interference. I'm hoping that with item 3 resolved, the DLM will soon start reducing the SNRM to get the download speed up (it's currently sitting at 8.9db 35Mbps, with an IP profile capped at 32Mbps, and interleaving is also high).
With regards to item 1, the HLog plot, from my limited research this seems to point to a bridge tap. Is that correct and is that the only thing it could be? Is it recognised by Openreach as a fault? If so, I guess it could be reported as such? The bitloading plot can be found here
Thank you in advance for any informative feedback you are able to provide.