question about those broadband filter thingies

  mco 19:59 10 Aug 05

Can someone confirm (or deny) this for me? Do you only need those broadband filter things for your phone line if you are actually going to use the line concerned for the phone AND internet? I want to use an extension line merely for the internet, so do I not need one? Also, does the REN number matter with internet? I currently have 4 REN (3 phones/internet and a caller display machine )- will adding another one b** up my phone ringing? thanks! (Before you query my system it's BT home pna and I know what I'm doing, just not sure of the filter/REN issues!)

  stalion 20:04 10 Aug 05

the filter is to stop interference on your phone line when connected to broadband.If you have no phone line connected you don't need a filter

  woodchip 20:04 10 Aug 05

Yes..... it stops noise on the phone, but you need one in for the RJ11 plug to connect modem

  mco 20:06 10 Aug 05

thanks - what I thought; will save a couple of pounds. Any ideas on the REN issue?

  Forum Editor 20:08 10 Aug 05

even if you only intend to make voice calls on the line.

An ADSL line is separated into two 'pipes' (for want of a better word), each one working independent of the other. The filter enables traffic to be routed into the correct pipe, and you need the phone to be plugged into it - even though you may not be connecting a computer to that socket. If you don't do this, and the line is being used for data transfer, you'll experience excruciating noise on the phone line.

The total REN on a BT UK Telcoms line must not exceed 4 - you can ignore ADSL devices when calculating the total.

  Forum Editor 20:14 10 Aug 05

that With the advent of 'wires-only' or 'self-install' ADSL, you do not get a modified linebox, so the combined Data/Voice signal is carried to all extension sockets on your line. This means that you can install your ADSL modem or router anywhere where you have a phone extension. However, as this combined signal will interfere with your regular telephones/faxes/answerphones or whatever, you need to fit each extension socket with an individual microfilter to strip out the data signal.

  mco 20:18 10 Aug 05

your second posting made it clear, Forum Editor. So I will need a filter after all. However, since this particular extension line is only going to be used for internet (via bt home pna adaptor) it doesn't count for REN, so I'll still be ok on four, right?

  Technotiger 21:36 10 Aug 05

Right!! I have similar set-up with four phones and btbb.


  Mino 21:56 10 Aug 05

BT would like residential users to NOT have more devices on the line than is necessary, so recommend a limit of 4 for the REN (Ringer Equivalent Number) value. A few years ago, I complained that my signal was weak - on the old analogue line - and I was having difficulty with background noise. A BT engineer I spoke to in the road, advised me to contact BT and ask for the 'Gain' to be increased. This upped the voltage pushed through my line by a fraction, but at the same time, allowed my line to use equipment up to a REN of 7 - without affecting the quality.

Apparently, it is the 'Gain' limit that dictates the REN number. Obviously, lifting the 'Gain' too high could cause damage to equipment connected, as the voltage increase could potentially fry connected phones, faxes, etc. It was explained to me that this is why BT likes a REN of 4 in residential homes - so we don't unnecessarily overload the network.

How this works with Broadband I do not know, but it must be similar, as BT have increased the distance from exchange for users from 6.5km, to around about 9km. This must have been achieved by increasing the 'Gain' on lines that are further away from the exchange. As it gets further, it gets weaker, thereby limiting the potential for frying connected equipment.

  mco 22:13 10 Aug 05

interesting stuff that Gain business, Mino.

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