How to Hook up a Fax Machine with a DSL Modem

By Keith Evans

Updated September 26, 2017

Operating a fax machine on the same line as a Digital Subscriber Line (DSL) high-speed data service poses a challenge for some owners. Because DSL operates in a higher--but still audible--frequency range on your voice telephone line, bleed-over sound can wreak havoc with the sound-sensitive modulator/demodulator (modem) of a fax machine. If you have DSL, you can still use a fax machine on your line with some special equipment (which may have already been supplied by your DSL provider) and a few easy steps.

Obtain a DSL line filter. Some DSL providers supply several line filters when your DSL service is installed. These filters are small, in-line filters that are plugged between your telephone line and the telephone wall jack. If you have any extra DSL filters lying around, you will not need to purchase an additional one. If you do not have a line filter readily available, they can be obtained at most chain retailers or electronics stores for a nominal amount.

Unplug your fax machine telephone line. Your fax machine is connected to the telephone wall jack by a thin (and most likely flat) wire with a modular plug at each end. This wire, known as an RJ-11 wire (or just a telephone wire), has a small plastic clip that holds it into the telephone line jack on your fax machine, and an identical clip holding it into your wall jack. You do not need to remove this wire from your fax machine, but you will want to remove it from the wall jack by squeezing the plastic clip and gently pulling the wire out of the jack.

Plug the DSL line filter into the wall jack. You will notice that the DSL line filter also has a small amount of RJ-11 wire and a modular plug identical to the one you just pulled out of the wall jack. Insert this plug into the wall jack until the plastic clip snaps into place. The wire should be firmly inserted into the jack, and should not easily fall out once it is plugged in.

Plug the fax machine line into the DSL line filter. The other side of the line filter you just plugged in will have a port identical to the port in your wall jack; the plastic modular clip on the end of the RJ-11 wire that's coming from the fax machine should fit perfectly into this port. As with plugging the line filter into the wall, push the plastic clip on the RJ-11 wire into the port on the line filter until it clicks into place. It should be securely in place and not prone to fall out once it is plugged in.

Your fax machine is ready to use. The DSL line filter serves to filter out any bleed-over noise caused by the DSL service. Without the interference of this noise, your fax machine should be able to send and receive faxes without interruption.

Items you will need

  • DSL line filter

  • RJ-11 (standard) telephone wire

  • Fax machine


DSL line filters can be obtained in several different models, including in-line filters and wall filters. The instructions provided here detail how to install an in-line filter, though more advanced users familiar with modular jack wiring may be interested in installing a wall filter for a smoother, cleaner appearance.