Before everyone goes out and buys ferrite cores, keep in mind that they will not do anything for the majority of people. ADSL signals are differential-mode, i.e. equal and opposite polarities on the pair, whereas ferrite beads only filter out common-mode noise, where the signal is equal on both wires in the pair.

Modems already have ferrite beads inside. Adding extra cores on the cable will only make a difference if you're in a terrible RF area, e.g. there's a large AM radio station transmitting near you, swamping the front-end of your modem. ADSL runs at around 30kHz to 1.1MHz.

Choosing the wrong type of core will affect its performance too, if any. There are three main materials in use - mix 43, 64, and 77. Mix 43 covers 1MHz - 1GHz, which is what you'd want if you really wanted to try an extra ferrite core.

Ferrite cores are usually only used to prevent EMI leaking *from* devices, not to block them from entering devices.

Aluminium foil around the wire won't do anything unfortunately!

Any wire will receive RF, but the interference will be common-mode which will be ignored by good modems, unless you happen to be in an RF-poor environment that swamps your modem's front-end. That's why I'm saying, ferrite cores don't magically make your line more stable - you must be swamped by stray RF at just the right frequencies first, before ferrite cores will do anything.

It's like saying eating panadol will make you feel better. It won't - you must have a headache first before panadol will make you feel better.


hmm RJ11 is the plug used on CPE telephone wires...

This post has been edited by wired@genes: Aug 30 2010, 10:11 PM