Noise margin change

After reading the news item yesterday I notice that my noise margin changes quite alot, from the normal sort of 15-19 to as low as 1. The thing is that the connection is stable and is always solid 2MB which is what I have. I dont know if its just the Netgear router reporting it wrong.

Is there anything particular about Evenings? As the news item specifically mentioned it. Should I be worried? As if downloads and connection are fine.

I assume you're on a fixed 2mb product, yes ?

Yes fixed 2mb with Pipex.

ADSL uses the same frequencies as AM/MW radio, and interference is worse at night, because AM radio is stronger at night because the signals are bounced around by a layer in the atmosphere which is much weaker during the day.

In which case, as you're dropping as low as 1db, don't think of moving to a Max product, as you start with a target 6db noise margin, which means your line is likely to become very unstable.

It might be worth your while checking your internal wiring to see if there's a reason for such a large drop. If you have an NTE5 master socket, where the bottom part of the face plate is detachable, remove it and plug into the test socket behind. If your margin becomes more stable there, it's probably an issue with your internal wiring.

Last night I did see it drop to 0db. The internal wiring I would have thought is ok as we had BT come in and sort out the section between the PC and the main socket as my dad had screwed it up doing some DIY. I dont know if they changed the wires at all but it was all fitted by BT. Would other sections of the phone line cause this?

From resetting the router this normally brings the DB up quite abit so maybe its the router reporting incorrectly? As I think it may have even gone into minus DB last night as on the Netgear router it reports it as a massive big number.

I would have thought a true low noise margin would cause line instabalities and speed issues, but as I said mines always rock solid and perfect 2Mb speed and the router only occassionally drops connection.

It's always possible that the Netgear number is sloping off, but that tends to be gradual, not recovering during the day. The fact the number drops at night suggests it is an interference (noise) issue. Doing the test as suggested will eliminate your internal wiring, which may be the cause, especially if the ring wire is connected, terminal 3, often orange/white. Bear in mind that, if you had a 'normal' BT voice engineer do the work, it would not necessarily resolve any ADSL issues.

You need to keep the unfiltered wiring as short as possible, because it acts like an aerial for MW radio. Best case scenario is to use a filtered faceplate in the master socket, and plug the ADSL modem directly into that, which may require a long ethernet cable back to the PC(s). Ethernet wiring can be as long as you like, and doesn't have big noise issues. If you can't do that, removing the ring wire (wire #3) on the extension socket wiring at the master socket can pay dividends.

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Ethernet wiring can be as long as you like, and doesn't have big noise issues.

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I thought the limit was 100m/segment?

Yes it is, but if your house is so big that it needs more than 100m of wire between the ADSL modem and PC, I think you can afford a leased line

Not if I'm a tightwad!

Will try that.

We have the master socket in the kitchen so I can plug my router into that. How my current connection is done, is a phone cable coming from the master socket (wired in not an adaptor) that runs upstairs, then theres a connector(1) box outside the room that takes a line to my parents room and another to the PC room which ends with the normal phone socket on the wall.

This ring wire where would it be? Main socket of the house? I'll get my dad to have a look and see what we can do. Would be good to solve this for the future when I do get switched onto Max.

I will reboot the router tonight and see if that makes the margin increase, as if its say 3db and after a reboot it turns out to be 13db, there cant be that much change in only a few seconds.

The BT engineer was a phone one, but at the time we did say it was particular for ADSL. I just remember we did have to have a 2nd guy out as we had a new boiler that British Gas fitted and they had to pull up the floor boards and they actually ripped out the wire from the connector box(1).

The ring wire will be connected at the master socket (wire #3), and it's fed to all the other sockets. You need to disconnect it at the master socket.

Edited by deleted (Sat 21-Oct-06 23:52:14)

Thanks, i'll have a look at mine and see how it is. So no need to mess with any other socket for the ring wire? Just the master? Might just wait and see what happens and if I do get Max and I run into instabalities I know to have a good test of internal wiring as one of the main areas.

Well I just rebooted the router and within the 20-30 seconds it takes for a reboot it the noise margin went from 0db to 18db. So I think something is up with the router reporting it incorrectly. I suppose it could have a . As from what I have read a low noise margin should give you and unstable connection and also slower, but mines always solid and speeds never drop.

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The ring wire will be connected at the master socket (wire #3), and it's fed to all the other sockets. You need to disconnect it at the master socket.

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It's best to disconnect it on all the sockets.

The whole purpose of the ring wire is to allow a short circuit to be placed across the ring wire and one leg of the line when any of the phones are lifted.

If you leave the ring wire linking all the extension sockets then when a phone inserted in any of those sockets is lifted you will be back to having the ring wire connected to the line and acting as an aerial.

Ian

Sorry, but you are wrong. The ring wire was solely there to feed the 75V AC ring signal to old phones which required it to drive old-fashioned bells in the old style phones. The ring wire (#3) is fed from the A wire (#2) via a 2mF capacitor in the master socket - this capacitor passes the ring signal, but blocks the 50V DC. Unfortunately the ring capacitor also passes any HF signals floating around, including strong MW radio signals picked up by the relatively high-impedance ring wire, which are passed back through to the A wire via the ring capacitor. Placing a short across the ring wire would have no effect because it would be blocked by the ring capacitor.

If your theory was correct, then phones would not work at all if the ring wire was didconnected, and they all do. Even the old ones will still work - they just don't ring. Fortunately most modern phones don't need the 75V AC signal, but it's wise to check after you've disconnected the ring wire. There's nothing to stop you cutting the ring wire at each socket - you're just giving yourself more work to do, with little or nothing to gain.

Edited by deleted (Sun 22-Oct-06 10:42:25)

Well, it's not worth getting into a big debate about it but I have always known it to be provided for anti bell tinkle purposes.

Originally multiple phone installations were provided serially and one phone being picked up would interrupt the ringing circuit for the other phones (the good old plan 1A).

With the advent of the plug and socket system and it's parallell wiring this could not work and, as pulse dial phones were the norm, dialling on one phone would cause the bell in all the other phones to tinkle.

The third wire was the way to get around this by allowing the bells to be short circuited when any phone was picked up.

Ian

Oh come on ! Are you seriously suggesting that any phone made in the last 20 years is going to have a "bell tinkle switch" ? If any phone in the house was old enough to have one of those, then you wouldn't be cutting the ring wire anyway.

Any chance you can borrow a modem or router? That would enable to to eliminate your current router as the cause of the drop, or confirm it is the router. That said, the sort of drop and recovery you have described is more likely to be down to noise, imo. When you re-synch, the modem negotiates a whole bundle of new frequencies, so an improvement in noise margin is quite normal.

There's no point in disconnecting the ring wire on extension sockets with plug-in filters, because that terminal isn't connected to anything. Plug-in filters only connect to pins 2 and 5, and contain their own ring capacitor for the benefit of old phones which need it.

If on the other hand you use a filtered faceplate you should keep the ring wiring connected throughout. It won't interfere with the ADSL signal because it's on the filtered side of the connection.

Eric

I have another modem, but this has been fine for the last 24 hours. I will keep checking and see how many days it takes to change but at the moment the noise margin is stable.

The other modem is USB and as I turn off my PC at night it wouldnt really be much use especially if the router only shows signs of drop off after a few days.

I'll keep an eye on it and if it means with Max I need to resync the router every 7 days or whatever then its not much of a problem.

Thanks for all the advice so far. Really interesting discussion, always like finding out new bits of info.

Edited by mossmanfly (Sun 22-Oct-06 23:27:10)

I would suggest you leave the computer on for a few days, but turn the monitor off at night. See if you get any clues from that. Ultimately, you have to try and trouble-shoot as much as possible yourself, or risk having a BT callout which will cost you upwards of