How to Test DSL Filters

By Leighton Sawatzky

Malfunctioning DSL filters reduce the quality of your DSL connection.
i cable modem image by IKO from

Digital subscriber line (DSL) modems share lines in your house with phones, fax machines, answering machines and other devices. Information sent by one device sometimes interferes with your DSL Internet connection. This is why DSL modems often come with filters, which you install on phone jacks with anything besides a DSL modem plugged into them. If you notice your DSL connection getting worse or cutting out altogether, one of your filters may not be working properly. Here's how to test whether your DSL filters are working:

Step 1

Unplug all the devices in your home connected to phone lines except your DSL modem and one phone.

Step 2

Unplug all the DSL filter dongles from the phones and other devices in your home.

Step 3

Plug a DSL filter into a phone outlet and plug the phone into the filter.

Step 4

Make a phone call to a number you can tie up while you are testing your filters. Place the receiver near a stereo or speaker that is playing music or otherwise making noise.

Step 5

While the phone call is in progress, go to one of the speed test tools linked in the Resources section and click "Start Test" or "Begin Test." Choose a location close to you, if given an option. Take note of the speed rating given at the end of the test.

Step 6

Hang up the phone and replace the DSL filter with another, untested filter.

Step 7

Repeat steps four through six until you have tested all your DSL filters. If you noticed lower performance on the Internet speed test with one of the filters than the others, that filter is likely faulty.