ADSL Noise Margin weirdness

[scottyman]

Hi guys
I've been chasing a really annoying issue in my rental for well over a year now, and here in Sydney they kind of don't like POTS and ADSL but it's the only option until 2019 when Fibre is planned for my area.
I've been getting more and more frustrated, as I'm getting 6-8 connection drops a day, and they are usually about a minute or two long - but at least 2-3 times a week the router doesn't recover.

Telstra have replaced the pair to the exchange twice now, and when they do their checks after changing the pair, the connection is good and stable, but will start to drop 3/4 hours later.
Where it gets weird is when you look at the stats - when I reboot the router (Netgear D7800) the noise margin initially syncs at 6.5dB, but over the next few hours drops gradually all the way down to 4.4/4.5 and we start getting frequent drops and resyncs

Has anyone seen anything like this before?
It's bloody annoying, but if they turn on the maximum stability profile, the internet speed drops to about 3meg, which is hopeless (given that I'm getting 12.5 at the moment, just multiple drops)
Any thoughts?
Cheers

[Dashers]

I'm not sure how the telephone systems work down under, but if it's anything like BT:

Do you have microfilters on each extension in the property, or is ADSL provided by a faceplate on the master socket? Microfilters don't tend to be that good, and replacing with a faceplate is always a winner.

Noise from inside your property is a common problem. Remove this by opening up your master socket and pulling out the extension lines going into the rest of your property (being careful not to tamper with the telco side of the wiring). This will rule out internal wiring as being a problem.

Ruling out the filters and the wiring means the problem doesn't lay on your side. But that just means you've got to spend a lot of time on the phone complaining to your provider.

[scottyman]

Hey Dashers - I've only got a two wire connection, and the wiring is on a loop - we've isolated all the points internally and tested each in turn, and there's nothing that would indicate what is adding noise. I've never seen anything that causes a gradual drop of signal before- so that really suggests a software bug in the router or an external factor.
It's just bloody baffling!

[Dashers]

Two wires is normal, it's twisted pair. But it's very sensitive, even if the twist is off you'll get problems. There will be a point where your internal wiring joins the external wiring. This is where you need to disconnect your internal stuff - the interference only needs to be intermittent to cause noise on the line.

You are of course correct, it could be a software bug or something external. Software bugs can be ruled out by using a different ADSL modem for a while, see what that does. External factors can be identified only through deduction of everything else internal.

[scottyman]

So have now run for 3 days with our emergency spare ADSL router from the office... which has been perfectly stable. What's annoying is that it's basically the previous model of what I've got - so the surfboard modem should be basically the same!
I'm going to switch it back tonight, but that's incredibly frustrating. Now I've got to get in a pissing match with netgear over a $290 ADSL router not being fit for purpose.

Interestingly, in NZ I had two pairs run into the older house, and seem to recall that I did in the UK as well

[Dashers]

Yep, BT tend to use four core, but only two are active. I guess they can use the other two for a second line without having to run new cable or something.

Sounds like you've narrowed down the fault though. Have you tried reflashing the firmware on your router with the latest firmware? It's also worth having a hunt online to see if anybody else is reporting this issue with the same model (and hardware revision).