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Isolation Tests & Filtering

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Isolation Test

If you are having problems with your Line you and you call your ISP about this, you will be asked by your ISP to conduct an Isolation Test.

basically it means you need to disconnect ALL the devices from the Telephone line and Outlets and then reconnect the Modem and then after succesfull connection you then start plugging in each device one at a time to see which outlet/ device is causing the problem

And they Might ask you about what Filters you have in Place.

Many Modems come with filters they are generlaly ok...

the Best type are either ACS [1] or C10 [2]


You need to have every device Filtered.. Extra Handsets (base stations for cordless phones), Fax Machines, Dial up Modems and Dialer devices Like Alarms and Medic alert devices you can only have 3 devices filtered via inline filters any more than that, you will need a Central Filter installed for you.

Isolation test

One of the fastest ways to find a line or filtering problem is performing what's called an "isolation test". If you call us and you're having problems with the ADSL light flashing or not coming on (see above), chances are we'll ask you to do one of these.

An isolation test means:

  • Connecting the ADSL modem directly to a telephone wall socket (i.e., no line filter) with a telephone lead no more than 3 metres in length.
  • Disconnecting every other device connected to any other telephone wall socket in the premises. This includes double adapters and extension leads.

Once you've completed the above two steps, powercycle the modem. Some modems take a while to successfully connect to the ADSL service, so please be patient. If the light goes solid, all well and good - move on to the one by one test. If it hasn't gone solid within five minutes, there are an additional two tests you need to try:

  • With the modem in isolation, replace the telephone lead connecting the modem to the telephone wall socket with another lead no more than 3 metres in length.
  • With the modem in isolation, relocate the modem (no need to move your computer!) to a different wall socket.

With the above two steps, you're trying to determine if a faulty telephone lead or wall socket are the cause of the problem. In each case, you need to powercycle the modem and wait for at least five minutes to see if the ADSL light will go solid. If it does, you've found (at least part of) the cause of the problem and you should move on to the one by one test.

One by one test

A one by one test should be performed after you've successfully managed to get your ADSL modem to connect up while doing an isolation test. Quite simply, a one by one test is the process of connecting devices back on to the telephone line one by one.

After you connect each device (making sure that you've connected it using an ADSL line filter), test the Internet connection for a good few minutes to ensure that it continues to work properly. After you're satisfied that it still works, connect the next device, test the Internet connection, and so on.

Should you find that after connecting a particular device your Internet connection slows down markedly or drops out, chances are there's a problem with the line filter.

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