58 dB attn <500k sync 6 dB SNRM

Here's an odd one, voice works fine, attenuation about right for location but speed about 1/10 - 1/4 what it should be. Noise margin up/down at 6 dB. Test socket gives same sync n& stats. BT 21CN line.

Things to try (apart from suggesting they nag BT who are the ISP)

Run up DMT using a DG834, preferably a V4 and you'll most likely see a large notch in the spectrum due to (probably local) RFI... Tune a scanner or MW radio to the frequency indicated to hear it and simply follow the noise souce to the troublesome device.

Possible causes (I have found this way) include:
PC PSU in standby mode
Low energy lamps
Old CRT Monitor
Netgear ProSafe Switch (NOT the PSU)
Various plug-top PSUs
etc...

Unless of course there's an RFI Filter in the ADSL path... That'll do the same...

Edited by TechGuyUK (Sun 17-Feb-13 17:14:51)

As I think you probably know full router stats will help people see the state of the line!

I take it you've also checked to see that the test socket hasn't been compromised by dodgy wiring?

Edit:
Are you able to check with neighbours to see if they have similar issues?


[Has yarwell's userid been hacked? :P ]

Edited by b4dger (Sun 17-Feb-13 17:32:22)

Post deleted by RobertoS

Here's an odd one, voice works fine

Bah!

Replaced the ADSL cable? And the dangly filter if one is in use?

the upstairs phone (DECT base station, filtered) went dead when I used the test socket and the stats were the same (I thought it was going to be a quick win with a filtered faceplate). Wiring is in the wall so I don't think anyone's filtered the line ahead of the master.

House opposite was offline for 3 weeks with an exchange issue (flashing DSL light) and another in the same village with a fixed speed 512k was very unstable but now its on 21CN runs fine at 4M. So I don't think there's a generic issue in the area.

Looks like I'll be going back with a router that shows the bin plots, and an AM radio.

Replaced the ADSL cable? And the dangly filter if one is in use?

not yet, dedicated RJ11-BT lead for next time. Not sure that fits the symptoms though as the attenuation is ok so we're not losing the signal, it's just arriving with a lot of noise.

Full router stats might still help people...

I take it you've also swapped the router?

Is there any ADSL history with this line?

I was thinking more in terms of a cable having been tugged hard - for example by a vacuum cleaner - thereby loosening the connection between the cable and its plug. Or damaged internally.

That can give background noise without affecting the attenuation. Probably a red herring, but you've eliminated the normal causes.

I don't have the full stats - I was there doing something else and took an interest in why a download was taking forever. Mind as it didn't stay up for long and we replugged it the error counters etc wouldn't tell us much. Upstream sync was faster than downstream by a factor of at least 2.

The homehub in use was a replacement in an attempt to fix it, I'll go back with another router. The people concerned worked shifts so it's not simple to get in.

will have a listen in. Another thought that just came to me is that if there's been a line repair it may have a split pair - this ties in with previous observation on another line where speed went from >4M to <1M and it was due to "something" between the cab and the house - switching to the second pair fixed it as helpfully the house had two lines in service.

So SFI maybe the only answer.

I'd suggest it was capped, but would have thought the SNR would be higher.

Try it will ALL power turned off running the modem from a battery and use a laptop.

Have drive back down the line route - or where you thing, look for potential noise sources.