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Standard User machadon
(newbie) Fri 23-Mar-12 15:27:18
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RFI filters on BT Lines

[link to this post]
First time on here. I thought i would share the following with you.

Just recently went live with a Phone and Broadband package from a well known Communications Provider. The phone side no problem, clear as a bell.

The ADSL side mainly non existent or when the router manage to find the sync signal managed around 300kbs tops. My house is around 1.5 miles from the exchange but got down stream attenuations of 80db. S/N ratios were pretty low too.
Being reasonably clued up technically i carried out all my investigations within the house right up to the test socket on the NTE5A box with still the same results.

Having to run the gauntlet of the 1st and 2nd line technical departments (Indian call centres) and a visit of the CP's own engineer, the problem was no nearer being resolved. Next stage was to actually be able to speak to a 3rd level engineer in the UK, what a welcoming experience. He arranged to have a BT Open reach engineer visit the house hoping that the ball lay squarely in their court and not being hit for £130.

BT Openreach engineer arrived and within two minutes found the problem, luckily on their side. This was an illusive one. The drop wire was terminated (Screw terminal block) in a white BT junction box which also had two encupsulated towers which appeared to me to be anchoring posts of some sort as the orange and white wires were wrapped around them. From the junction box (IDCs) another wire was connected to a BT Openreach NTE5A box.

The two so called anchoring towers in the BT junction box turned out to be RFI chokes (Inductors to suppress radio interference) one in each of the A and B wire circuits. Living in North London, there was time that Capital Radio was being picked up on telephone circuits amongst other audio devices, as their AM transmitter was very powerful and was sited a few miles away. It was these RFI chokes that was attenuating the ADSL signal.

Following their removal and a straight through connection made, the engineer measured an increased ADSL speed of around 5Mbs. These components were not detectable by the various diagnostic tests carried out by my CP or from the exchange. The telephone line also had a DACS (Digital Access Carrier System) unit fitted at one time which i had to get BT to remove some years ago when i had dial up internet. I had initially thought BT had put it back on again, due to lack of spare twisted pairs in the area, which was killing my ADSL signal.

These BT junction boxes fitted with RFI chokes/devices may well be still existing in various locations in many properties including roof spaces out of sight out of mind.
Just another factor to consider amongst all the others when dealing with ADSL speeds.

Legally it is up to BT Openreach to remove these and effect a straight through connection to the NTE5A box but even if one is aware of these try explaining this situation to a call center operative 5000 miles away.
Standard User huwwatkins
(member) Fri 23-Mar-12 15:46:24
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Re: RFI filters on BT Lines

[re: machadon] [link to this post]
Was it one of these?

They also made an RF3 which was ADSL compatable.
Standard User Zarjaz
(knowledge is power) Fri 23-Mar-12 17:16:55
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Re: RFI filters on BT Lines

[re: machadon] [link to this post]
The engineer should have replaced it with an RF3 filter, this would be ADSL compatible, and would still have filtered any stray radio signals, also helpful for REIN issues.

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Standard User b4dger
(knowledge is power) Fri 23-Mar-12 18:19:53
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Re: RFI filters on BT Lines

[re: machadon] [link to this post]
Interesting story and glad to hear you had a result! smile

It's a shame everyone has to "run the gauntlet" frown

Standard User machadon
(newbie) Fri 23-Mar-12 19:32:31
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Re: RFI filters on BT Lines

[re: huwwatkins] [link to this post]
Hi huwwatkins yes it was one of those boxes which was fitted, thanks.
The engineer just ripped out the inductors and joined the wires together with those transparent joints. I have not noticed any RFI on my phone system. If i do then i will have get my communications provider to arrange for BT Openreach to fit an ADSL compatable RFI filter.
Standard User machadon
(newbie) Fri 23-Mar-12 19:36:00
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Re: RFI filters on BT Lines

[re: Zarjaz] [link to this post]
Thanks for the info Zarjaz, i will keep the RF3 in mind.
Standard User machadon
(newbie) Tue 27-Mar-12 16:05:31
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Re: RFI filters on BT Lines

[re: machadon] [link to this post]
Hi all

Further to the use of a BT 80B RF3 junction box

Since the BTO engineer removed the RF2 which was killing my ADSL i have not experienced any RFI on my telephone system to date. I have also fitted an ADSL Nation XTE-2005 filtered faceplate to my NTE5A box. The whole phone system is now filtered at source. I have installed a separate ADSL feed from the AB terminations on the XTE-2005 to another room and terminated this with an ADSL Nation XT-68 filtered faceplate. My router is connected into this.

I am seeking clarification regarding the following points.

1 Do the XTE-2005 and XT-68 have any common mode filtering in the AB
lines (unfiltered ADSL) performing what the RF3 would do?

2. Do the XTE-2005 and XT-68 have an filtering in the bell wire circuit
feeding the phones.

3. Reading the blurb on ADSL Nationís website, under XTE-2005 it
mentions the including of a ringing capacitor but under XT-68 this is not
mentioned. Are the circuits in the both products the same?

4. Does anyone know if any circuit diagrams of these products, for my own
interest, are available any where. May be someone may have a drawn
schematic from retracing the tracks to/from components and connectors.

5. If there is no RFI detectable and as i do not have specialist equipment to
detect the existence of any localised REIN, is there any benefit to
installing a RF3 box or could the insertion of a RF3 box actually hinder my
BB performance due to some top end filtering/and or insertion losses.

6. If one possible answer to item 5 above is try it and see, can i insert the
RF3, in the AB line before my ADSL extension socket to which my router
is connected. I understand the RF3 should be installed before the
NTE5A box but strictly thatís BTOís domain, but i am only curious with
any possible improvement the RF3 may have on the BB speed.

I may be looking too deep into all of this as have not checked my speed since after BTO engineers visit last week, which was 5Mb/s. Thanking you in anticipation for any information provided.
Standard User yarwell
(sensei) Wed 28-Mar-12 12:57:47
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Re: RFI filters on BT Lines

[re: machadon] [link to this post]
1. I believe not, the iPlate does have a common mode filter.

On point 2 all filters that meet the BT SIN spec have either a filtered ring wire or more commonly a re-created ring wire using a capacitor on the filtered side phone connection.


MaxDSL - goes as fast as it can and doesn't read the line checker first.

MaxDSL diagnostics
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