Unresolved support ticket open for more than six months - is this a record?

[#1]

As OldJim has pointed out that is a very odd graph. Totally abnormal shape.
Could there be some sort of crosstalk on lower frequencies from, say, a fixed-rate line or similar?
What we need to see is the same graph at a quiet (high SNRM) time. If necessary after a forced resync.
Edit: The interference is over a wide range; it actually starts in the upstream range which drops in the middle - normally it's a peak!

[#2]

For comparison, here's a graph from my DG834GT on a line which doesn't suffer any problems.
Because of the model#, it only gets the SNR per tone graph, and only for downstream.
From what I gather, that's a pretty standard shape.
It has an attenuation level of 30db, which (on the speed prediction tools)  seems to be the border for the full-speed downlink. I think the 7616 is top-speed when interleaved.

[#3]

Ok, thanks for the advice and DMT graphs - it's good to see what other people are getting. I've just rebooted the router and taken another DMT Tools snapshot - this is quite different from last night's snapshot. And the sync rate's back to a pretty reasonable level.

[#4]

That's more like it (but things still not right). I'll just revise the post I was doing.
@WWW - I don't have a green smiley 

[#5]

Hi Catweazle,

Quote from: Catweazle

Quote from: Anotherone Don't they understand that untwisted cable pairs can be a source of interference pickup, never mind the potential impedance changes and possibly higher capacitance of this bit of cable. I did try to explain but they were adamant that the RF filter would sort out any problems with the cable or any other sources of local interference (which they couldn't find anyway, using the portable radio).

That's a load of Bull! Any  "in-band" interference that is picked up by that bit of cable CANNOT be filtered out without filtering out the BB signal
Could you have a closer look at that filter, see if it's got any identifying marks on it, also take the cover off and take a pic, have a look for identifying marks inside if none outside.
Those previous DMT graphs are definitely showing a / the problem.
Can you find out if that Lift & Shift was done?
Re:the electrics. Can you take some pics of the earth bonding at your boiler and at meter, dis-board, elec co's cut-outs.
Back to the previous DMT graph's - something (electrical or electronic) is either producing wideband noise or breaking down or there could be a dicky connection somewhere. Next time the sync /snrm changes dramatically,take another snapshot.
Edit: TalkSport Radio transmitter not far away?

[#6]

OK, great - thanks for that. I'll see what I can do tonight or over the weekend.

[#7]

More thoughts, do you have any Dusk to Dawn lighting? Do you have any 12v Halogen lighting using electronic transformers?

[#8]

Quote from: Anotherone

Quote from: Catweazle I did try to explain but they were adamant that the RF filter would sort out any problems with the cable or any other sources of local interference (which they couldn't find anyway, using the portable radio). That's a load of Bull! Any  "in-band" interference that is picked up by that bit of cable CANNOT be filtered out without filtering out the BB signal

@Catweazle - If they didn't find any interference, how did they work out what frequencies an RFI filter should be filtering? I see from DMT that your line attenuation is 25dB. Didn't it used to be 22? I wonder if the filter is causing that?
It is very strange to see the two graphs together, but they show that when you do get interference, it seems to cover the band from 50kHz through to 700kHz. Maybe it isn't surprising that you don't hear anything on the line.
@Anotherone - Yes, luckily my line is OK. Unfortunately, I'm trying to sort out a similar noise/interference problem on my Mum's line, that causes the connection to drop many times between 6pm and 9pm. Trying to do analysis remotely, on an unstable line with dynamic IP is, err, fun I'm just weighing up the risks of doing a remote firmware upgrade to get better DMT graphs from that one.

[#9]

http://en.wikipedia.org/wiki/Low_frequency
Does any of the above apply?

[#10]

Nice link axis. But I suspect that whatever is causing Catweazle's problem is more wide spectrum rather than spot frequencies, but out of curiosity I have asked about one.
@Catweazle
Another thought - does your neighbour keep his router on 24/7 or only switch it on when needed?
@WWW
I'd spotted the attenuation, but put it down to the slight differences from different routers as the Draytek was still giving 22dB after the filter (reply#75 & #85). The filters that they can fit are usually low pass types, but there are 3 different ones IIRC.

[#11]

PN support have confirmed that this problem is now with BT's Complex Faults Team - they also said that BT didn't do the Lift and Shift as tests at the exchange didn't justify this (they got an "OK test", apparently). I thought BT were going to do the L&S to see if this made any difference, so I don't know what prompted the change of tack. I'll investigate the RF filter and earthing scenarios tomorrow - it's been a very long week at work...

Quote from: Anotherone

More thoughts, do you have any Dusk to Dawn lighting? Do you have any 12v Halogen lighting using electronic transformers?

Yes, but not switched on - the house had a couple of outside lights (front and back) that used dusk-to-dawn fittings, but I disabled those a while back as possible culprits. No halogen lighting, but I do use a lot of low energy bulbs (not at the same time, though!) - I checked these as part of the REIN tests but couldn't find any bad ones.And I wouldn't have any lights on while I'm away at work, so that wouldn't explain synch rate drops or noise margin changes during the day.

Quote from: WWWombat

@Catweazle - If they didn't find any interference, how did they work out what frequencies an RFI filter should be filtering? I see from DMT that your line attenuation is 25dB. Didn't it used to be 22? I wonder if the filter is causing that?

@anotherone is right - this is due to the change of router. The Draytek used to show 22DB consistently, but the Netgear shows anything from 24-26Db. I suspect the RF filter was inspired by guesswork and the box might be empty for all I know - more will be revealed tomorrow, no doubt...

Quote from: Anotherone

Another thought - does your neighbour keep his router on 24/7 or only switch it on when needed?

Yes, it's on 24/7 now that he's with a new ISP (Sky - switched in early December) as that's what he's been advised by Sky. He used to be with BT and had poorer synch rates (about 4000kbps), but that might have been because he switched the router off overnight.

Quote from: axisofevil

http://en.wikipedia.org/wiki/Low_frequency Does any of the above apply?

Thanks for that - I'll check this in more detail later, but at first glance I can't see anything that might be causing the problem. And I suppose any such sources would affect my neighbour's broadband as well - hence @anotherone's comment, I guess.

[#12]

Just an interim comment as I'll post some pics later, but here's a couple of things to get you thinking...
I opened up the RF box and found the following numbers printed inside:-
UYZL2951 / 1
BT80B-RF3
But the worst find so far, is that EDF Energy managed to disconnect the main earth cable when they replaced my Economy 7 meter with a standard meter on 26th August last year. It was only when I started tracing the earth cables that I realised that the one bonded to the mains water pipe isn't actually connected to anything anymore! I've just phoned EDF and they told me not to worry too much about this as overhead power supply cables have multiple earthing points anyway, but I must admit that I'll be a little nervous about touching the bath until this is sorted out.... EDF said this doesn't need to be treated as an emergency, especially as I haven't experienced any electric shocks (yet!), so they've suggested I arrange for an engineer to come out next week to fix the earthing. I suppose I shouldn't be too worried as this has not caused any problems (apart from the potential broadband interference) since August, but it does make you wonder about how competent these people are. I may get an independent electrician to visit instead, though, as it's probably about time I had the electrics checked i.e. they're probably 25+ years old (as you'll see from the pics!) and I've been putting this off for the last 18 months since I moved in...
Now, this does look very suspect from the broadband perspective, but I'd like to reserve judgment until the earthing is repaired as I've had significant broadband faults since June last year i.e. incomplete earthing probably didn't help since the end of August but what about the two months before?

[#13]

A point to note - earthing to the water pipe is no longer legal - you must have a proper earth connection
Also when a new meter is fitted they should check the earth system in the property

[#14]

When I had a new gas boiler fitted they insisted that the gas pipes had to be bonded.
Even though I had a properly earthed (and recent) electrical installation.

[#15]

Quote from: Catweazle

BT80B-RF3

standard RF3 filter, don't worry about it.

Quote from: Catweazle

overhead power supply cables have multiple earthing points anyway

True, ours do at every other pole and (I believe this is standard) the earth is the Neutral.
Our earth is bonded to the incoming neutral, done by Southern Electric engineers after problems were found with the old water pipe connection.