In reply to a post by billford:

It doesn't. It only removes any frequencies coming from the "voice" side which are high enough to potentially interfere with xDSL operation.

Yeah, that makes much more sense.

In reply to a post by RobertoS:

It's badly put, that's all. (He does say it's a simplified guide).

Cheers, it was reading that guide some time ago that lead me to believe that the voice frequencies should not reach the modem, hence they should be filtered off (blocked) even if only a modem is connected to the test socket.

In reply to a post by billford:

In reply to a post by Oliver341:

Odd. If the filter removes voice frequencies from the line entirely...

It doesn't. It only removes any frequencies coming from the "voice" side which are high enough to potentially interfere with xDSL operation.

So any devices connected to the "phone" socket of a filter producing frequencies which could interfere with the xDSL signal would have that range of frequencies blocked by the filter. All downstream frequencies would be allowed to reach the modem and the normal range of voice frequencies would be ignored. Upstream frequencies post filter would be combined and then filtered at the exchange.

So noise picked up on the line between the filter and the exchange would obviously reach the modem because it's not filtered and that could include the bell wire.

Is that about right?

In reply to a post by 4M2:

So noise picked up on the line between the filter and the exchange would obviously reach the modem because it's not filtered and that could include the bell wire.

Is that about right?

The rest of it was, I think, but this bit isn't.

The bell wire is purely a feature of extension wiring within the premises. Nothing to do with the line from the filter to the exchange. The bell wire can pick up electromagnetic noise at all sorts of frequencies because it acts as a simple aerial.

It is also connected into the circuit in a different way, via a capacitor in the master socket that creates the voltage on it to ring the extension bells. It can feed the noise back onto the line in some way. I'm a bit hazy about how, and will probably find someone with full knowledge of it steps in .

Most decent dangly filters contain that same capacitor so the bell wire is not needed when they are in use, and most modern phones also have one so it isn't an issue for them even if the user disconnects it then later moves house and leaves it disconnected. Better to reconnect it though as the new owner may have a phone that needs it, and doesn't get broadband. Or gets FTTC where again he might need the bell wire.

The Openreach normal NTE5 faceplate contains a ring wire filter, which caters for all the extensions. Older "BT" ones didn't, and it's those that the iPlate was designed for. All that does is filter the bell wire.

In reply to a post by RobertoS:

The bell wire is purely a feature of extension wiring within the premises. Nothing to do with the line from the filter to the exchange. The bell wire can pick up electromagnetic noise at all sorts of frequencies because it acts as a simple aerial.

It is also connected into the circuit in a different way, via a capacitor in the master socket that creates the voltage on it to ring the extension bells. It can feed the noise back onto the line in some way. I'm a bit hazy about how, and will probably find someone with full knowledge of it steps in .

To the layman, it is does seem odd that the bell wire should cause problems and feed interference into the circuit since it's only function is to carry voltage and is linked to the unfiltered line via a capacitor that creates that voltage. Hence any noise that it picks up, acting as an aerial, would have to travel through the capacitor in order to disrupt the adsl frequencies - I guess one would just have to conclude that the capacitor is not a filter

Edit: if I were to connect an extension to the A&B connectors on the back of a filtered faceplate (at the master NTE5) then use my own additional NTE5, complete with filtered faceplate, as an extension socket then presumably a phone that requires a bell wire would ring if connected to it. That would mean that I could have an extension that would be suitable for both a router and a phone that requires a bell wire although, of course, the length + quality of the extension between the NTE5's and the fact that I'm using two NTE5's could perhaps be detrimental to the ADSL signal?

Edited by 4M2 (Fri 24-Aug-12 04:25:32)

In fact the true reason will be even more mysterious to the 'layman'.

The reason that the ring wire causes problems is that it upsets the balance of the twisted pair carrying the broadband signal. For good transmission of the rf broadband signal and to minimise pick up of interference it is important to maintain it as balanced throughout its length. Adding a third wire via the ring capacitor means the part within the house extension wiring is no longer balanced - and as such it will pick up any common mode interference present in the house. Note that it is the main twisted pair that picks up the interference, NOT the ring wire.

(and is the reason why homeplug/powerline is notorious for radiating interference, the house mains wiring is far from being a balanced system, made totally unbalanced by wiring to lighting switches and other things. But it seems the layman doesn't understand that either...).

Post deleted by GeeTee

Edited by deleted (Fri 24-Aug-12 07:42:33)

In reply to a post by 4M2:

Edit: if I were to connect an extension to the A&B connectors on the back of a filtered faceplate (at the master NTE5) then use my own additional NTE5, complete with filtered faceplate, as an extension socket then presumably a phone that requires a bell wire would ring if connected to it. That would mean that I could have an extension that would be suitable for both a router and a phone that requires a bell wire although, of course, the length + quality of the extension between the NTE5's and the fact that I'm using two NTE5's could perhaps be detrimental to the ADSL signal?

Not a good idea. Having two master sockets in the circuit is not recommended, as it does more than just provide the bellwire connection.

Your example requires a filtered extension, such as the XTF-68/85, or other manufacturer's passive equivalent.

In reply to a post by dsergeant:

In fact the true reason will be even more mysterious to the 'layman'.

The reason that the ring wire causes problems is that it upsets the balance of the twisted pair carrying the broadband signal. For good transmission of the rf broadband signal and to minimise pick up of interference it is important to maintain it as balanced throughout its length. Adding a third wire via the ring capacitor means the part within the house extension wiring is no longer balanced - and as such it will pick up any common mode interference present in the house. Note that it is the main twisted pair that picks up the interference, NOT the ring wire.

(and is the reason why homeplug/powerline is notorious for radiating interference, the house mains wiring is far from being a balanced system, made totally unbalanced by wiring to lighting switches and other things. But it seems the layman doesn't understand that either...).

As a "layman" that would suggest to me that filtering a bell wire would not totally remove it's detrimental effect: I use a filtered faceplate (pressac) that I believe filters the bell wire but I don't connect the bell wire only the twisted pair; if the bell wire was connected then the extension wiring would perhaps no longer be balanced? Even though all three extension wires are filtered, i.e. frequencies that are detrimental to the adsl signal would be blocked from entering the circuit by the filter, that may not be totally effective in removing the bell wire's effect since it is still present?

In reply to a post by RobertoS:

In reply to a post by 4M2:

Edit: if I were to connect an extension to the A&B connectors on the back of a filtered faceplate (at the master NTE5) then use my own additional NTE5, complete with filtered faceplate, as an extension socket then presumably a phone that requires a bell wire would ring if connected to it. That would mean that I could have an extension that would be suitable for both a router and a phone that requires a bell wire although, of course, the length + quality of the extension between the NTE5's and the fact that I'm using two NTE5's could perhaps be detrimental to the ADSL signal?

Not a good idea. Having two master sockets in the circuit is not recommended, as it does more than just provide the bellwire connection.

Your example requires a filtered extension, such as the XTF-68/85, or other manufacturer's passive equivalent.

Yes it would be passive - the result though would be two locations in a premises where a phone and router could be connected to a filtered faceplate (obviously only one router would be used and not two routers at the same time.)

However you suggest that such a setup would be inadvisable since one would be using two NTE5's