BT are allowing their 512k ADSL broadband service to be connected up on lines of any length, some of which will be too long or of a quality that means getting it to work will be difficult or perhaps impossible. This page is to help you get the best chance of making it work reliably. Always remember that you order and pay for ADSL from an Internet Service Provider or ISP and they should do their best to help you including arranging for a BT engineer to visit.
You can help yourself by buying a modem or router that gives line statistics to help you understand the problem. The BT Voyager 105, Fujitsu FDX310 and SAR-100 do this, as does the Sagem 800, but not the Speedtouch 330, see ADSLguide reviews for info. The BT Voyager 105 is used by BT and AOL and they can be picked up for less than £20 off Ebay. The stats are viewable by accessing extra features – either Ctrl/F1 when in the modem's control panel software or a series of 3 right and 3 left clicks with the mouse. The Sagem requires you to press Alt/P. Most routers include line statistics pages, you need to know the Noise Margin, also called SNR or SNR Margin, and the Line Loss or Attenuation is also handy – all these are measured in decibels or dB.
You may also stand a better chance with a “Home 250” product such as that from Zen which uses a slower speed BT connection that needs a bit less signal to work. A router plot from a Home250 connection on a high loss line is here. Avoid so called 150 or 250 products from AOL and others that actually use 512k connections (or faster) and are throttled elsewhere. I would recommend trying 250 if the BT line checker says you are “VERY UNLIKELY” to be able to receive a service. If it works well and has a noise margin over 12 you can upgrade to a Home 500 service, this may be a better approach than trying for 512k and failing. Send us an email if Home 250 works for you.
If you are having problems the first thing to do is unplug everything else from your phone extensions – faxes, phones, TiVo, Sky digiboxes etc etc. If you have a burglar alarm that is hard wired talk to the supplier about filtering for ADSL / Broadband lines. With everything unplugged you have the best chance of it working, if the modem doesn't synchronise with the exchange (flashing LED) then you have more work to do. Look at the statistics from the modem, you want to see a Noise Margin of 6 dB or higher and ideally the upstream speed should be 288 kbps. If the noise margin is less than 6 or if the upstream speed has backed off to perhaps as low as 64 kbps then there's more work to do.
If everything works well with the modem on its own, add the phones etc, each fed through a microfilter, and see if it works with everything plugged in. Microfilters can be faulty and there are some cheap and nasty ones around. There is one high quality microfilter that has a money back guarantee if it doesn't solve your filtering issues. You can feed more than one phone-type device through a microfilter, but each and every one must be fed through at least one filter.
If the modem doesn't work reliably or at all on its own then your line may have a very high loss or you may have an interference problem. To work out what is happening you need to disconnect all the internal wiring in your house and get to the signal as it enters. This is achieved by taking the bottom half of the NTE5 Linebox or master socket off, to reveal a test socket behind. See Clarity or here for background info on phone wiring and the NTE5 line box.
With the bottom off, plug in your modem or router to the test socket and try again. The extensions are disconnected at this time. If you don't have a linebox then you'll need to get on to the ISP to get BT out to fit one and diagnose your ADSL.
If the modem/router will work happily in the test socket, but not in the faceplate of the same socket, then you have an interference problem. This is caused by the wiring in your house picking up signals that interfere with ADSL (in the 200 – 1000 kHz range so you may hear it on an AM radio not tuned to a station) and feeding it into the modem. The solution is to have a filter between all the internal wiring and the ADSL connection. To test this out plug a microfilter into the NTE5 test socket, plug your modem into that, then plug the faceplate into the BT socket of the microfilter (may need a short extension) – if the modem/router will work in the faceplate with the filter interposed in this way then you need a faceplate filter/splitter installing by BT (ask your ISP) or you can buy your own from from Clarity ADSLnation or Solwise and DIY.
The faceplate splitter puts the unfiltered connection from the modem at the master socket. If this isn't convenient you can run an extension cable from the front socket or from connectors on the back of the filtered faceplate – it is wise to use Cat5 network cable for this to avoid re-creating the interference pickup problem. The Clarity site explains this and they offer extension kits.
It is worth remembering that ADSL modems don't need to be filtered, you can use an RJ11 to BT adapter to plug them in equally well, though avoid using an old 56k modem lead unless you are certain it is wired so that middle 2 pins of the RJ11 connect through to the next pair out on the BT plug. Note also that if you have a 56k modem or fax modem it needs to be connected to the phone port of a microfilter and not the one marked ADSL or (confusingly) “modem”.
If you've got to the bottom of the page and it still isn't working then badger your ISP and insist they get a BT engineer out – this brings a fresh mind and different kit into the equation, in the hands of someone who can also try different pairs of wires and investigate other faults on the line not covered above. The forums on ADSLguide are helpful, if you have a problem try your ISP forum or the General Chatter forum – take time to read and search the old posts before asking a new question. On Usenet uk.telecom.broadband is useful, can be accessed through Google Groups . Good luck and happy surfing !