DSL filters

If you saw my recent Ooma posts you know I recently ditched my home phone and switched to VOIP.  Before the switch I had phone and DSL through AT&T, now I just have DSL through AT&T.  When you run DSL, they provide you a DSL filter for each phone jack.  These DSL filters come in different shapes and sizes, but often times they are a pigtail you plug into the wall.  On the other end of the pigtail are two female phone plugs, one for the DSL modem and one for your house phone.

Now that I no longer have a house phone, I only have DSL, the question is do I still need the DSL filter?  The answer is no.  The purpose of the DSL filter is to "filter out" the DSL frequencies from the standard voice frequencies.  Voice frequencies do not interfere with DSL communications, but without the filter you can hear a high-pitched squeal on the line.

About a year ago one of my DSL filters went bad and I had to replace it.  But being the nerd that I am, I took apart the old one.  I was surprised how simple it was inside.  There were just a few passive components (coils and capacitors) inside to filter out the unwanted frequencies.  It looked something like this.

I followed the traces on the circuit board.  The input line was immediately split.  One pair went straight to the DSL output jack, the other pair went through the passive components and then onto the output phone jack.  This is why I suspected the DSL filter is not necessary for DSL only (a.k.a. dry-loop DSL).

Of course the real test is, if I remove the filter does it still work.  So I removed my DSL filter and the Internet still works.  I'm a firm believer in simplify everything.  If you don't need it, get rid of it.  So if you're running DSL only without a standard phone line, you do not need the DSL filters.