Simple Telephone Filters

The telephone lines coming into our homes can carry high-frequency electromagnetic fields , besides the regular speech.This article shows how to set up a simple line filter to lower this unwanted electromagnetic fields.

Why use a phone filter?

Telephone wires run for long distances before they reach a home or office. Along the way they can pick up EMF from other phone lines and electrical wires, especially if they are also carrying high-frequency signals, as is the case with Internet

Some of these interferences can be heard on the phone, but most are so high a
frequency that they cannot be heard and the phone’s speaker cannot reproduce them. The phone wire coming into the building will act as an antenna and radiate out the high frequency EMF it carries, and so will the telephone itself. For people who are electrically sensitive, this may be a problem, or at least something to avoid.

To find out if there is high-frequency electromagnetic field coming from the phone line, use a simple cheap AM radio. The really cheap models are best for this purpose, as they are notso good at filtering out static, and static is what we are interested in here.A digital radio will not work as well.

Simply turn on the radio, make sure it is set for AM reception, and turn the dial to a place where no stations can be heard and there is very little static. Then put the radio close to the phone cord. When I did that, it sounded like a swarm of angry bees.

A basic ready-to-plug-in filter
A very inexpensive DSL line filter is available from some building supply stores, electronics stores, online, and by mail order (like from Digi-Key, see vendor listing). It costs only about five dollars. It is designed to block DSL-signals, for those who have DSL Internet service (called ADSL in some countries) and only want it on some lines in a house. This filter also dampens other high-frequency noise as well. It is very simple Simple Telephone Filters to use. It just plugs into a phone outlet and then the phone line plugs into it. A variety of styles are available, such as wall mounted filters or filters with extra ports for more than
one phone line.