Simple guide to getting rid of emi/rfi noise

EFI and RFI are two types of noise which can interfere with the adsl signal.

RFI stands for radio frequency interference.

EMI stands for Electromagnetic interference.

 A lot of noisy things can emit both types of noise, EMI which generally travels around in mains cables and RFI which generally travels around in the air, you may have to go to a lot of trouble to get rid of this noise, and sometimes nothing you can do will get rid of it, but in some cases trying the stuff mentioned in this guide can offer a huge improvement in speed and reliability.

Lets take a look at the two types of noise in a bit of depth.

 EMI or electromagnetic interference. 

This can be from various sources in your own home your neighbours home, ten streets away or even on the other side of the country, and it travels down power lines.

So how do you get rid of it ?

The most obvious way and easiest way would be to move or get rid of the source of the noise, if its from something you own then it is easy, I can not tell you how to get rid of other peoples noisy stuff, but we can start looking for things in the house and ways in which to tackle this.

Central heating switches are the most common electrical thing to affect adsl in an adverse way, this should be your first check.

Turn your heating on by the timer does your adsl drop, if so then it is likely this is the cause of the problems, get your heating equipment checked out and your timer replaced.

Not your heating at fault then you need to look at possible sources one at a time, after which you wait to see if it has made an improvement.

One by one go around your home turning things on and off, wait to see if your adsl has dropped, if it does turn the electrical device on and off again, does it do it again?

You have found your culprit, replace or repair it, you may need to carry on doing this as you may have other stuff in your house which emits EMI.

Before you start throwing out that printer because the stupid thing was causing your adsl to drop, have you got a printer or any other stuff that has a two way plug like this ?

Turning the printer end around can often get rid of EMI noise.

Your extensions can pick up noise if they are badly laid out or connected, a few rules to remember when laying an extension are as follows.

1. Try to keep your extension away from power sources.

2. If you have to lay your extension next to a mains cable arrange the extension so that it crosses the mains cable, never run alongside the mains cable this will make it far easier for any noise to transfer across and make your adsl signal go bad.

3. Try to keep your extension as short as possible.

4. Always use a good quality cable, a solid cored UTP (unshielded twisted cable) cable will suffice, but for the ultimate cable try to source some STP (shielded twisted pair) cable, you can find it hard to buy both types of cable in the high street, however B & Q sell 100M UTP rolls for £25 which will more than do for most peoples needs.

A power line conditioner can help for most of the stuff which is beyond your control (neighbours, street lamps, welding equipment, pantographs on trains, and mark1 ford escorts) but if it is outside your home it is going to be hard to get to isolate it.

Still have noise after all that, well here is were the fun starts... NOT

RFI or Radio Frequency Interference

If you have this you will notice that your connection disconnects at night or SNR level drops at night, why ?

It's all to do with the Sun and how it suppresses the evil anti adsl breaking radio waves, that are brought to you by the likes of evil radio stations like talk radio and five live, I am sure that the oldies who love listening to radios that share a birthday with God have it in for us adsl users.

Anyway how do we get rid of this ?

Most of the time it will be a near on impossible task, but you can try these methods...

Clip on Ferrite ring RF filters.

you can buy these from maplins.

This is a simple type of inductor, it will filter out mild RFI noise and should be placed as near to the source of the noise as possible, in this case at the start of the extension wire.

You wind the wire around the middle, the more times the wire passes around the case the more inductance you will have, A word of caution to many winds could result in to high an inductance and you could filter out some of the useful part of the adsl signal, as a general guide I have found about 5 turns to be enough to provide a slight improvement.

If your extension wire is to thick then strip down enough wire from the outer sheath to go around as many times as you need.

Another way to filter out noise is shielded wires, in a perfect world BT would have shielded wire running from the exchange to our homes, after all it is better to stop the noise getting in along 1/2 mile of wire than filtering it out in last 4 feet, however this is a real imperfect world and BT don't offer this, shame really.

You could try using STP in the hope that the interference is locally generated.

If you have radio noise on your line, then it is most probably  picked up this radio noise before it reached your home, although these two solutions may help, they often won't make much if any difference.