Why are two lines which are next to each other so different?

[#1]

Hi,
I have two BT lines in my (quite rural) house.  Both have plusnet DSL.
One line belongs to my brother (who has aluminium phone lines and cannot get DSL at his house.)   This broadband connection is sent over to his house via an 802.11 link.
I have the other line for my own broadband.
His sync rate is pretty stable, whereas mine goes up and down like a yo-yo.   See my charts below:


The master sockets are *right* next to each other - so why are the two so different?  And is there anything I can do to get my line more stable?
Thanks in advance for any advice.

[#2]

Have you got other sockets on your line? If so do all of them that are in use have filters fitted?
(My guess is that the blips correspond to when the phone is in use - your brothers line I suspect won't have a phone attached)

[#3]

Each change of speed implies a new synchronisation has been done, and almost certainly indicates that the modem encountered different line conditions during that synchronisation.
The usual causes for a new synchronisation are
- Turning router on;
- Errors on line causing modem to spontaneously resync;
- DLM or Manual admin at BT performing action that triggers resync;
The latter is probably the least likely.
The obvious first question - are both modems left plugged-in and powered up 24/7?
If they are both treated the same, then the likely difference is how they perceive the line conditions. Some factors:
- What extensions are wired to each socket, the state of the connections, and whether the bell wire is connected
- What phones are connected to the line, and whether they are wired or cordless
- What filters are connected to the line, and whether they are faulty
- What Make/Model/Version of router (some routers are better at longer lines)
- The state of the line (including all the connections) on its route back to BT
As jelv points out, it's more likely that the *only* bit of equipment on your Brother's line is the router, while yours, in your own house, is likely to have other sockets & phones attached.
Line problems are frequently down to the internal wiring or equipment, so this is the first area to check. See http://www.plus.net/support/broadband/bbfaults/droppingconnection.shtml and http://www.plus.net/support/broadband/bbfaults/slowspeed.shtml
It could be a fault on your line back to the exchange, that your brother doesn't suffer from. However, you need to eliminate all the internal stuff first...

[#4]

Thanks for the replies:  For brevity I shall refer to my line as line 1 and my brother's as line 2.
Both modems are left on 24/7.
Line 1 has one extension to a sky box - I leave the sky box (and its micro-filter) unplugged from the socket, except for the ten seconds or so when I order a pay-per-view film.  Which is pretty infrequently.  
Line 2 has no extensions and no phones  - the only connection is the modem attached to the DSL socket of the faceplate.
Line 1 has a micro-filter attached to the test socket of the master socket (I leave the faceplate off.)  That micro-filter has the modem attached to the DSL port and a cordless phone base-station attached to the phone port (Siemens Gigaset S685IP)
Line 1's Router is a Linksys WAG120N
Line 2's Router is a Draytek Vigor 2600 plus
If I have my router attached to the test socket does that mean that the extension shouldn't affect it?

[#5]

If you are using the test socket the extension socket should be dead. Are there wires attached to the back of the removable lower half of the faceplate?
Can you confirm that the Sky box is attached via a proper ADSL filter and not just a simple splitter that may have come with the box?

[#6]

Yes - the sky box micro-filter is a proper filter.
I'm not sure what you mean by the other question - there aren't any wires attached to the removable part of the faceplate. 
You can see the master sockets here:

[#7]

Have you tried swapping the routers to each other's lines and re-running tests on each line to see if the speeds stay the same?

[#8]

Hmm - no.  That's a good idea.
I'll give it a go.

[#9]

When you said an extension to the Sky box did you mean a loose cable fitted in to a doubler beside where the phone base unit plugs in or an extension socket?

[#10]

Quote from: Diggory

Hmm - no.  That's a good idea. I'll give it a go.

Another swap that you could try is to put the ADSL-Nation faceplate on your master socket, and put the rat-tail filter on your brother's socket. The relative quality of those 2 filters can make a difference too.
I'll add the usual cautionary note that if you make too many disconnections within a short period, then BT will increase your noise margin as it thinks your line is unstable, and you'll lose some speed. In any testing, do single swaps and wait a long time to watch the results! Using the controls within the router's admin page to disconnect will be better than just powering down, but I don't know iff that is possible with either of your router models.

Quote from: Diggory

I'm not sure what you mean by the other question - there aren't any wires attached to the removable part of the faceplate.

If the extension for the sky-box is a full permanent installation, then the wires from that ought to end up connected to the front faceplate of your master socket (ie the half-height faceplate that is not plugged in at the moment). Or, if it is wrongly wired, then it could be wired into the back of the master socket, so can never be unplugged from the line.
If it is more of a temporary installation, then it will end as jelv describes - a loose cable, with a standard BT-style plug, that you then plug into where the phone base plugs in.

[#11]

Quote from: jelv

When you said an extension to the Sky box did you mean a loose cable fitted in to a doubler beside where the phone base unit plugs in or an extension socket?

It's a proper extension socket.

[#12]

Well that could be a cause of your problem as it looks like it's not properly wired up. Extensions should be wired to the back of the removable lower half so that when it is removed to enable use of the test socket all the internal wiring is disabled. That is the whole point of the customer removable faceplate and test socket.
With it in it's current state don't bother trying the ADSL Nation faceplate!

[#13]

Quote from: Diggory

Quote from: jelv When you said an extension to the Sky box did you mean a loose cable fitted in to a doubler beside where the phone base unit plugs in or an extension socket? It's a proper extension socket.

How does that wire back to the master socket?
It should be isolated when the face plate is taken off.

[#14]

It appears not to be properly wired - the lower (removable) half of the master faceplate has no wiring attached and the extension works when the faceplate is removed.
I have removed the top half of the faceplate to expose the box behind - this is how it looks:

I have now managed to connect my Sky box to a VoIP line, so don't even want the extension connected any more - I want the line as clean as possible. 
Any ideas what I need to do to disconnect it?
Thanks.

[#15]

You need to find where the "old" sky box extension connects to the outside world, it should have been on the removable part of the face plate looks like it's elsewhere...naughty BT