Kitz Forum

Broadband Related => Telephony Wiring + Equipment => Topic started by: soms on January 10, 2008, 11:04:40 AM

Title: New BT Bell Wire Filter
Post by: soms on January 10, 2008, 11:04:40 AM
Hi all,

Just a little heads up on a development you may or may not be aware of.

All new BT NTE5 units (which are now Openreach branded) include a bell wire filter in the standard faceplate to help reduce interference being induced onto the line and causing problems with ADSL. Of course it is still a great idea to use an ADSL adaptor faceplate if it suites you.

This development appears to aimed at reducing the number of ADSL faults reported as a result of noise on the line. As you can imagine the majority of home ADSL installations are simply plugged into existing wiring with no thought for how it works.

In theory all field engineers who deal with line work or stuff like Vision should have them and use them when required. In the case of openreach this will  be for any new analogue exchange lines or replacement lineboxes.

If you can't fit an ADSL adaptor to your master socket and you have an engineer out faulting your broadband problems, you might want to ask him/her to replace the master socket with a new one including the new front plate.

I have known about this for a good few weeks but didn't know if it was in the public domain or not. It clearly is now as I typed it into google and found relevant results.

The faceplate is also available to engineers as a separate item. I have attached a pic which shows how to tell the difference.
Title: Re: New BT Bell Wire Filter
Post by: jaydog on January 10, 2008, 11:38:28 AM
isnt it much easier to just snip the bell ring wire like i did?!
Title: Re: New BT Bell Wire Filter
Post by: soms on January 10, 2008, 11:43:18 AM
Yes perhaps but this saves having to do that. You won't have to worry about reconnecting anything if you move house and the new occupiers won't be puzzled at why their old phones won't ring (most new phones being 2-wire and all that).
Title: Re: New BT Bell Wire Filter
Post by: jaydog on January 10, 2008, 11:49:41 AM
one of those new plates measns you have to rewire everything behind the socket though, as all wires are attatched to the back of the faceplate!
if i move, il just claim i know nothing about the bell wire, new installations dont install the wire anyway.
Title: Re: New BT Bell Wire Filter
Post by: soms on January 10, 2008, 02:55:26 PM
Quote
one of those new plates measns you have to rewire everything behind the socket though, as all wires are attatched to the back of the faceplate

In a standard daisy-chain installation you would only have four wires from one cable attached to it and to guarantee a proper termination you should avoid having more than two wires connected to each of the terminals. I'm not sure how removing and replacing these few connections qualifies as a rewire?
Title: Re: New BT Bell Wire Filter
Post by: jaydog on January 10, 2008, 06:32:25 PM
just snip the bell wire, 60 second job
Title: Re: New BT Bell Wire Filter
Post by: Astral on January 10, 2008, 06:39:17 PM
Quote
just snip the bell wire, 60 second job

It's the persuading someone to do it that takes the time. ;)
Title: Re: New BT Bell Wire Filter
Post by: jaydog on January 10, 2008, 06:42:37 PM
lol i know, but its not a case of "oh snip it, itl be good!" id rather snip than replace the faceplate.

lets face it, a new faceplate wont have an effect if the ringwire is already snipped.
Title: Re: New BT Bell Wire Filter
Post by: roseway on January 10, 2008, 07:29:28 PM
>> lets face it, a new faceplate wont have an effect if the ringwire is already snipped.

Well yes, it probably will. Snipping the ring wire removes that possible source of interference pickup, but the remaining extension wiring can pick up interference itself. Ideally the extension wiring would be proper twisted-pair cable, which would minimise interference pickup, but this is rarely the case - extension wiring is usually done with untwisted cable (which is cheaper). A filtered faceplate completely isolates the extension wiring from the ADSL signal, and gives a result which is effectively the same as plugging into the test socket.
Title: Re: New BT Bell Wire Filter
Post by: soms on January 10, 2008, 07:54:06 PM
Quote
Snipping the ring wire removes that possible source of interference pickup, but the remaining extension wiring can pick up interference itself. Ideally the extension wiring would be proper twisted-pair cable, which would minimise interference pickup, but this is rarely the case - extension wiring is usually done with untwisted cable (which is cheaper). A filtered faceplate completely isolates the extension wiring from the ADSL signal, and gives a result which is effectively the same as plugging into the test socket.

I agree with roseway, an ADSL adaptor which seperates the ADSL before any extension wiring is involved is certainly this is the best possible way of doing things.

My point was that this modification has been designed for the average premises where people are not aware of what makes broadband work and not work and where the customer uses their ADSL equipment at an extension point. Being included with the NTE5 it will be fitted by default in the future with the hope of reducing ADSL fault reports the likes of which can be cured by disconnecting the ring wire.

With regards to twisted pair extension cable, all the proper telephone cable I have ever seen and used for hardwired extensions has been twisted,  I reckon it must be part of the CW1308 specification. It is often commented how similar CW1308 is to category 3 ethernet cable.

Of course use cat 5 or cat 6 if you can be it is most unsightly if surface mounting is the only way to run it in. Another choice to make for cat 5/6 is whether to use plain UTP or FTP/STP screened cable for maximum resilience to sources of interference.

The classic example of un-twisted cable is I see quite a lot of friends who use flat extension leads/kits to get their router to go where they want it.
Title: Re: New BT Bell Wire Filter
Post by: setecio on January 10, 2008, 11:11:33 PM
Quote
Another choice to make for cat 5/6 is whether to use plain UTP or FTP/STP screened cable for maximum resilience to sources of interference.


Last time I looked into STP cable, I got the impression it was more likely to cause more problems than cure things .... it had to be grounded correctly and there were other issues .... forgive me if this isn't correct but I got the impression it was too complicated.

These links were in another thread to new adsl filtered faceplates with the ability to punch down adsl extensions as well as telephone extension
http://www.clarity.it/xcart/product.php?productid=16134&cat=262&page=1
http://www.clarity.it/telecoms/adsl_faceplate_mod.htm
http://www.adslnation.com/phpapps/catalog/product_info.php?cPath=24&products_id=90

I've read you get poor and good quality adsl filters, but adsl filtered face plates only seem to be supplied by a few companies and are £10-£15, is is safe to say they will all be good quality, well espc from the companies above?
Title: Re: New BT Bell Wire Filter
Post by: roseway on January 11, 2008, 07:13:06 AM
I think it's generally accepted that the Clarity and ADSLNation products are good quality. I use a Clarity one myself, and it certainly made a difference when I installed it.
Title: Re: New BT Bell Wire Filter
Post by: soms on January 11, 2008, 07:20:59 AM
Quote
've read you get poor and good quality adsl filters, but adsl filtered face plates only seem to be supplied by a few companies and are £10-£15, is is safe to say they will all be good quality, well espc from the companies above?

The one sold by Clarity is based on the design used by BT, it is identical but features a different terminal arrangement on the back, notably this allows you the option to "pass through" the ADSL if you please on a dedicated set pair of wires.

 ADSL nation claim their ADSL faceplate to be of a very high standard, better than all the available plug in ADSL filters.

I am not a fan of the sockets for extension points with built in splitters though. One of the main reasons being the sturdiness - try and fit one in a flush wall box without it bending horribly. I one of these people who doesn't over tighten things but it just can't be avoided with products like those. Crabtree secondary sockets all the way.

Also I didn't know STP cable ought to be grounded but you might well be right.
Title: Re: New BT Bell Wire Filter
Post by: setecio on January 11, 2008, 11:36:24 AM
People who have house alarms fitted to the telephone wire have to get the alarm company in to install a broadband filter. How would they ever know if those were cheap or expensive filters .... I could see situations where a poor quality filter fitted on the alarm system could cause adsl connection problems and never be detected as the problem.

Does anyone know if alarm adsl filters are usually specialist high quality devices ?

I presume that adsl filters on these sort of alarms are necessary, in the same way that every telephone needs to be filtered ?
Title: Re: New BT Bell Wire Filter
Post by: mr_chris on January 11, 2008, 04:38:03 PM
I presume that adsl filters on these sort of alarms are necessary, in the same way that every telephone needs to be filtered ?

Yes, they are necessary - and a good question actually. You might be onto something there...
Title: Re: New BT Bell Wire Filter
Post by: setecio on January 12, 2008, 01:20:54 PM
Interesting test of these new Bellwire filter faceplates back in May07 ... 6th post on this page >
http://yarwell.blogspot.com/

So these bellwire filters stop interference of the same frequency as adsl (picked up by the bellwire running around the house like an antenna)  passing back through the mastersocket and onto the 2 wire line.

Whereas the adsl faceplate filter stop the same happening with the bellwire and the other 2 wires, but the other 2 wires should be twisted pair and should thus be minimum.
Title: Re: New BT Bell Wire Filter
Post by: kitz on January 13, 2008, 02:22:47 PM
>> nteresting test of these new Bellwire filter faceplates back in May07

Good linky - :)
Title: Re: New BT Bell Wire Filter
Post by: Ezzer on January 21, 2008, 01:03:46 AM
Typicaly a broadband fault is caused by some of the internal wiring after the master socket / nte. and usualy this is caused by the bell wire (no. 3 on the socket/face plate). When on a broadband fault I would test to the wiring as is, then to the test socket behind the faceplate. If i get a significant difference in the test result between the two the first step is to dis (disconnect) the bell wires.
If this does the trick then the end user gets the option of either leaving the bell wire disconnected, so unless microfilters were in each socket with equipment plugged in then nothing would ring beyond the master socket on an incomming call. or the full adsl ssfp (service specific front plate)
Recently we have the choked bell face plate. If fitted as a retro fit the flap at the front is a slightly off white, marginaly grey colour, otherwise ant nte5 with the "openreach" logo has the choked plate. Thery're quite new so not many have been fitted so far. the main way if id'ing them is a smell cylindrical lug on the inside of the face plate about 5mm across, 10mm high.

If you have an issue with the quality of dsl service, then find the master socket/nte. if it is an nte5 ( a seam running about halfway down, across the socket) take the face plate off & either plug your router/modem in the test socket underneath or disconnect the wires in no.3 (usualy thie wires here should be orange with white hoops but note what wires are already connected here just in case the're different). If you get a good result then leave the bellwires disconnected (although as I stated earlyer you'll need microfilters in any socket with equipment plugged in in order for them to ring on an incomming call.
Title: Re: New BT Bell Wire Filter
Post by: soms on January 22, 2008, 07:23:53 PM
The sockets seem to have been a different colour noticable since they have been RoHS compliant but perhaps longer...
Certainly the RoHS Openreach branded ones and the former BT ones are more of a beigh colour that the older white ones.

I am guessing your a CSE ezzer?
Title: Re: New BT Bell Wire Filter
Post by: setecio on January 28, 2008, 02:59:10 PM
If you get a good result then leave the bellwires disconnected (although as I stated earlyer you'll need microfilters in any socket with equipment plugged in in order for them to ring on an incomming call.

I thought I read that all modern phones can ring without needing a microfilter, so if your telephones are reasonably new they will still ring anyway? is this true or do they all still need a microfilter if the bellwire is disconnected ?


I have read cat5e is a good way to wire telephone extensions but reading this http://www.diynot.com/forums/viewtopic.php?t=69574 it was pointed out :
A:cable type wise its best to use BT spec CW1308 cable.
B:Or even cat5 cable
A:i'd disagree, the aim for best broadband performance should be to use the same cable that BT use so that the characteristic impedance will be the same.

Now this would say 'don't use cat5 or cat5e but use CW1308 to keep impedance the same'
Is this true ?

The main argument for a filtered NTE5 faceplate on the mastersocket seems to be to isolate additional interference induced on the speech and ringing pair (2&5).
If cat5e is used for the telephone wiring, is this an alternative way to almost rid this interference ? or is the argument above about impedance important ?

Is 1 pair (yes 1 twisted pair) cat5e available.
Title: Re: New BT Bell Wire Filter
Post by: roseway on January 28, 2008, 03:31:34 PM
Quote
I thought I read that all modern phones can ring without needing a microfilter, so if your telephones are reasonably new they will still ring anyway? is this true or do they all still need a microfilter if the bellwire is disconnected ?

All POTS equipment (phones, faxes, Sky boxes, etc.) have to have a filter between them and the incoming line pair. So if you haven't got a filtered master socket faceplate then you have to use a filter on any socket which has POTS equipment connected.

Concerning the type of cable to use for extensions, I don't know the answer for certain, but I doubt if there would be much if any discernible difference between CAT5, CAT5e and CW1308. My reason is that ADSL frequencies are pretty low in RF terms so the characteristic impedance is not a big factor.
Title: Re: New BT Bell Wire Filter
Post by: soms on January 28, 2008, 04:04:50 PM
Quote
i thought I read that all modern phones can ring without needing a microfilter, so if your telephones are reasonably new they will still ring anyway? is this true or do they all still need a microfilter if the bellwire is disconnected ?

A microfilter is required to keep the ADSL frequencies from reaching the telephone equipment. A microfilter is not required in a socket which is not carrying broadband.

In non-broadband installations the ring wire should be connected and since the release of the bell-wire filtered NTE5 front plates there is really no need to disconnect it.

With regards to ringing...

Most, nearly all new telephones are two-wire phones. This means that they do NOT need the ring wire to ring.

Even with the ring wire connected at the socket, most phones use a 2-wire cord which doesn't carry the ring current.

These modern phones incorporate an internal ring capacitor in the same way as an ADSL microfilter does.

Old telephones definitely do use the ring wire. Examples are all the old GPO telephones and older BT telephones.

In these cases, where the ring wire has been disconnected, if the phone is plugged in to an extension socket directly, it will not ring.

Plugged into a microfilter it will work fine. Plugged directly into the master socket front plate or the test socket, it will work fine as the ring wire is connected internally at this point.
Title: Re: New BT Bell Wire Filter
Post by: setecio on January 28, 2008, 05:59:36 PM
Thanks for that. Yes, I was thinking in terms of cutting the ring wire and then moving house in the future, but forgetting to reconnect it. The new owners would probably have new enough phones that would just work, and if not they would probably think the phone is broken and try a newer one, thus fixing the problem quickly without BT being involved. So cutting the ring wire shouldn't really be much of an issue.

If cat5e was used for the telephone extension cable, would it still act like a big antennae for noise in the same way that CW1308 does ?
Title: Re: New BT Bell Wire Filter
Post by: roseway on January 28, 2008, 06:49:03 PM
Quote
If cat5e was used for the telephone extension cable, would it still act like a big antennae for noise in the same way that CW1308 does ?

Both CAT5e and CW1308 are twisted pair cables, i.e. each data pair is twisted together. This substantially reduces interference pickup because most of the interference is picked up equally on both wires, so there's no voltage difference between the pair of wires. It's not perfect of course, so even twisted pair cables will pick up a little interference, but it's quite a small amount. Without looking at the specs I suspect that CAT5e is the better spec, but as I said, I doubt if it makes much practical difference.
Title: Re: New BT Bell Wire Filter
Post by: setecio on January 29, 2008, 10:18:50 AM
Since new phones can now ring without the presence of a ringwire, and householders desire for wires to be 'hidden' I'm surprised that single pair CW1308 (and cat5e) has not appeared in mass on the market. I would imagine it would be a thin cable which is easy to hide.

The filters that are used in this new Bellwire filter and those used for adsl filtered NTE5 faceplates are two way filters, aren't they ? In the adsl filtered NTE5 faceplate, the idea is that the broadband signal does not get through the filter, AND also that any interference induced into the telephone extension wiring, which is the same frequencies as broadband, does not pass back through the filter. ?

Thanks.
Title: Re: New BT Bell Wire Filter
Post by: roseway on January 29, 2008, 12:57:43 PM
The filters aren't two way exactly. They do two things: they stop ADSL signals from interfering with the telephones, and they stop the phones from loading the ADSL signal (which would have a big impact on the quality of the ADSL signal).
Title: Re: New BT Bell Wire Filter
Post by: setecio on January 29, 2008, 08:01:29 PM
If they aren't 2 way, how do they stop the mush feeding back into the line and degrading the adsl signal as described below. I thought an adsl filtered faceplate was more effective than disconnecting the bellwire, but surely it must be a 2 way filter to do this effectively and stop the mush coming back onto the main line and degrading the adsl signal ?

Taken from 'adsl tweaking' here http://yarwell.blogspot.com/2005_08_01_yarwell_archive.html

Quote
In my case, the ring wire runs around my house as part of the feed to at least 6 extension phone points, in doing so it acts as a nice big aerial (antenna) to collect any radio transmissions and random electrical noise that may be passing through. It then feeds this mush back into one side of the twisted pair through the capacitor that is there to provide the ring signal and consequently degrades the ADSL signal.
Title: Re: New BT Bell Wire Filter
Post by: kitz on January 30, 2008, 10:36:55 PM
heh - dunno if its me speed reading  and I may have lost the plot...  but everything everyone has said seems to be correct  :D
Title: Re: New BT Bell Wire Filter
Post by: roseway on January 30, 2008, 10:54:55 PM
Quote
If they aren't 2 way, how do they stop the mush feeding back into the line and degrading the adsl signal as described below. I thought an adsl filtered faceplate was more effective than disconnecting the bellwire, but surely it must be a 2 way filter to do this effectively and stop the mush coming back onto the main line and degrading the adsl signal ?

Sorry, I missed this question earlier.
The point is that the ADSL side isn't filtered at all. There is a direct connection with no filtering from the incoming line pair to the ADSL modem or router. The 'mush' which comes from the ring wire is (or was) connected directly to the input of the modem. In fact, BT are now supplying faceplates with filtered ring wires to overcome this problem. But there is no requirement for POTS signals to be filtered out from the ADSL side because ADSL modems and routers are designed to respond only to the defined ADSL frequencies.
Title: Re: New BT Bell Wire Filter
Post by: soms on January 30, 2008, 11:12:20 PM
Quote
Since new phones can now ring without the presence of a ringwire, and householders desire for wires to be 'hidden' I'm surprised that single pair CW1308 (and cat5e) has not appeared in mass on the market. I would imagine it would be a thin cable which is easy to hide.

Just a quick reply to this...

I recon two-wire would be acceptable on the basis that PBX master sockets were used, phones using ring wires are still out there, and much used, and anyone who put in such an installation would create a fair bit of confusing on that point.

Also, BT is now using 4-wire again (seems to the old colour scheme as well) which is pretty tiny stuff.

Mind you, cable from different manufacturers alone, regardless of the no of pairs can make a big difference. I have a reel I bought which is decent 3-pair with a nice finish sheath which is the size of BT's 4-wire.

Then again, well manufactured 2-wire would be even smaller.

Standard cat5e being unshielded will still act as a ring wire antenna the same as CW1308. The reason being the "imbalance" caused by the utilisation of only one wire in the pair, even though the cat5 has more twists it will behave in a similar way.

As long as it is twisted pair and solid core (not that nasty alarm wire or mutli-core stuff) it should be fine.

The 4-wire colour code is like so:

Pair 1 - solid blue and solid orange wires
Pair 2- solid green and solid brown wires

Blue - same as blue/white - terminal 2 (Line B leg) on LJU
Orange - same as white/blue - terminal 5 (Line A leg) on LJU
Brown - same as Orange/white - terminal 3 (ring) on LJU
green - same as white/orange - terminal 4 (spare/earth) on LJU

Title: Re: New BT Bell Wire Filter
Post by: setecio on January 31, 2008, 07:21:43 PM
Thanks, sorry for the confusion, I was meaning 2 way filtering in both directions of the telephone side of things as opposed to the 2 seperate sides of adsl and telephone. So the filters on the NTE5 telephone side filter out the adsl signal going onwards, and also filters out the adsl interference coming back.



                                                 >>>>>>>> filtered telephone signal >>> telephone
1) Telephone line >>>>>NTE5 filter     
                                                 >>>>>>>> unfiltered adsl side >> adsl modem


                                                                       blocked <<<< intereference on extensions on same frequency as adsl <<< telephone
2) Telephone line <<<<< NTE5  filtered faceplate
                                                                       <<<<<<<<  adsl modem


 :)
Title: Re: New BT Bell Wire Filter
Post by: soms on February 01, 2008, 12:01:02 AM
This is a very good question and I certainly do not know the answer.

Given the component is a choke so to speak, one would think the component itself would work the same in either direction. Unfortunately I do not know myself exactly how it all works in practice.

I get rather confused as for example I originally thought the ring wire only carried current when the line was rung and the voltage increased and so the capacitor generated the ring signal??

Then again the I guess the ring wire would have to be somehow "powered" to act as an antenna?

If I can I will endeavour to ask someone who knows something about electronics (unlike myself)  ::)
Title: Re: New BT Bell Wire Filter
Post by: roseway on February 01, 2008, 07:16:33 AM
The point about the ring wire is that the 2-wire input is essentially balanced as far as the ADSL signal is concerned. The two wires are also twisted together. So any interference which is present is picked up equally by both wires, so there's no noise voltage difference across the pair, and therefore the interference has no effect on the signal.

But the ring wire is a single wire connected via a capacitor to one side of the signal pair. So any interference which is picked up by the ring wire is fed via the capacitor to one side only of the pair, and therefore causes a noise voltage difference across the pair. In some situations this can have a considerable effect on the quality of the ADSL signal.
Title: Re: New BT Bell Wire Filter
Post by: Ezzer on February 02, 2008, 10:26:21 AM
Hi Soms, yes I am a CSE, been on the broadband side (on top of "proper" faults )for 3 1/2 years now

If there's an issue with the internal wiring from the NTE about half the time it's due to the bell wire on it's own. When you look at the basic circuit diagram for a radio, it has a good resemblance in part to an nte, particuarly with the bell wire.

The choked plate tries to get around this problem, as I mentioned before you can reconise one either by the flap at the front being a slightly off white-grey tint. unless it already came with an nte with the openreach logo. other wise look for a small (I think I mistyped it as smell before, soz) cylinder behind the plate.

If the problem is caused by the other pair of wires (terminated in ports 2 & 5) then you would look at the dsl/ssfp front plate. The one with both a telephone & dsl socket on the front much like a micro filter.

The micro filters let the dsl signal go straight through them, the filters are there in case any equipment such as phones faxes, sky boxes,etc act like a radio reciver (by radio I mean any electrical noise, not bbc broadcasts & the like) & throw some of this noise on the phone line. If it's some thing the broadband can hear then it affects the quality of your connection to the net.
Also some times your equipment might hear the dsl signal & convert it to something you can hear so the microfilter prevents you trying to have a normal phone conversation over some horrible squealing & shushing noises.
This can come through either the bell or voice (other 2) wires.

As Roseway has said, some phones will respond to the ringing down the line without a bell wire. if you have the bell wire disconnected for any reason then microfilters have a capacitor within them which will still allow any bit of equipment to ring on an incomming call regardless if the equipment needs a bell wire or not.

Using CAT3,5,or 6 cable means you're less likely to pick up interference via the cable, it's really intended for digital data signals, the extra twists on each pair of wires mean one cable is less likely to overhear a nearby similar digital signal. Hence the're common in commercial networks where there are lots of data cables in close proximity.

As to wether old internal wiring or pristine new wiring would give you a better result for broadband, It's mainly luck. If the wiring is in tune/harmony with some noise source. You'll have an issue.

Don't know if this makes things clearer, ho hum..........
Title: Re: New BT Bell Wire Filter
Post by: setecio on February 02, 2008, 05:19:49 PM
...... Don't know if this makes things clearer, ho hum..........

Thanks for that excellent explanation ...  certainly makes things clearer as to how it all works.  :)