Can anyone help? High noise margin and low sync sp...

Question

Hi all,
just registered on the forum so this is my first post. Hopefully someone out there can help.
I transferred my broadband to BT from Sky. With Sky my sync speed was around 4000kbps and download of about 3500kbps. I had a Netgear router with Sky but for some reason every day or so  my sync speed dropped to 2500kbps and download down to 1800kbps. I had to reboot the router to get the speeds back up again, very frustrating.
I got BT broadband on 20/1/2010, set everything up and also fitted an I-plate. I noticed that line attenuation was 46db, this was previously 50.5 with sky and prior to I plate. The home hub sync was at 7200kbps at the start which i was very pleased with. I know this DLM thing is active for the first 10 days or so and speedtests during this time are not exactly accurate but still I was happy. after 3 days i did a speed test and got download of 5800kbps, chuffed to bits!
But, after 2 days at that speed the sync dropped to 2176kbps, gutted. I have only rebooted the router 3 times since the service started and each time the sync goes back to 7000kbps ish but drops again a day later. The thing I dont understand is the noise margin. Its currently at 24.5db, isnt that awfully high? Why is this? when I reboot it drops to 8-9db ish but then goes up again with the speed dropping.
currently connected to test socket, no other telephone equipment connected to any extensions
Can anyone please help/advise whats going on or how to rectify it? I'm wondering if theres a line fault somewhere.
And with attenuation at 46db I would have thought the speed could well be much higher than 2200kbps.
I'll stop babbling now,
Thanks

Answer 1

whitesp wrote:
Thanks for your reply Somerled,
ok so something is causing noise at a particular time, i had wondered about the quality of the home wiring, there are 4 extension sockets in the property, but again i am currently only connected to the test socket.
I dont have the old netgear router unfortunately so can't follow up on the suggestion you made.
God this is gonna be a nighmare to track down, although come to think of it I do have a dimmer on quite close to where the master socket is.
Can we say for sure that there definitely IS a source of noise/interference??
Many thanks
SOMETHING is forcing a resync, and at a low speed. The only thing that would cause that is a prolonged burst of noise.This is known to BT technicians as "REIN" (Repetitive Electrical Impulsive Noise). No point trying to get BT to investigate at this stage though, as it sounds very intermittent.
The way to spot radio interference noise is to use a suitable receiver - and the most convenient is a portable medium wave transistor radio. Tune to a quiet spot at the lowest end of the scale, and turn up the volume. All you'll hear is white noise and the occasional quiet crackle. A burst of noise strong enough to affect the DSL signal will be unmistakeable - a LOUD crackling/buzzing/rasping noise.  If that coincides with a resync, you've found it. You then have to figure out what electrical device caused the noise.....
Another possible source of DSL noise problems is less obvious -  noise caused by a line fault. This causes an unwanted mixing of the phone and DSL signal in a way that can't be corrected by the filters. This will have much the same effect as external interference noise.
Check this : does the router resync when the phone rings, or when the phone is in use ?  If it does, then we're on to something - a fault known as an "HR" (High Resistance). If that doesn't happen, then we are back to external radio interference as the cause.
I suppose the HV lines you mention might have some effect, but it's a bit of a long shot. I'd expect noise from them would be a bit more constant, and would cause problems all the time, rather than intermittently.