can someone explain SNR to me ? G.DMT/ ADSL2+

Hi my SNR is all over the place and its doing my head in.
i have installed routerstats and shows snr was 14 from 8am till 10 pm today

router resynced to 4000 and snr dropped to 7.8

this has lasted an hr and is now at 2.8

im still getting 3500 in speed tests and i am on sky max

i am on G.DMT instead of ADSL2+ , i phoned up to ask why and they said all sky max custs are put on G.DMT by default, I asked for a change as I thought line stats might improve as line is poor at 58db and noise was always hanging around 5.8 -7 when i was with zen, virgin, bt. But they said no as exchange couldnt do it.... a lie i think !

Is poor snr a sign of a line fault, ?

Can i ask for a BT eng to look at my line SNR at a cost to myself just in case water is getting in somewhere etc ?

thanks in advance

SNR is a measure of how much louder the ADSL signal is compared to the electrical noise on your phone line. The louder the signal is compared to the noise, the better your modem can hear the signal and therefore the better the speed it can communicate.

Falling SNR is caused either by the noise level increasing or the signal reducing. This may be due to increase in electrical noise in the environment (eg: electrical equipment being switched on, or AM radio interference increasing at night), or from the signal reducing due to attenuation (eg: faulty joint, water in conduits), or from the line being more prone to picking up noise (eg: a ring wire in your extension cabling or a missing or faulty micro filter).

If your SNR is getting worse at night, then the problem is almost certainly that your line is picking up interference from MW radio stations, which get much stronger at night. The problem can be reduced by keeping unfiltered extension wiring as short as possible. The best thing to do is to fit a filtered faceplate to the master socket (assuming you have the type of sockets with removable faceplates), and connect your ADSL modem/router to that, and then run a Cat5 network cable back to your PC('s). Then connect all your extensions for phones (etc) to the filtered output on the faceplate.

If you can't do that, then the next best thing is to remove all the ring wires from the phone sockets (the ring wire is on terminal #3).