How to troubleshoot broadband interference sources

This guide only applies to broadband services delivered over your telephone line. This includes ADSL, ADSL2+ and VDSL2 fibre-to-the-cabinet (FTTC) services. Virgin Media cable broadband service does not suffer the same sort of interference issues and the ultra-fast fibre-to-the-Home (FTTH) services are not affected by radio interference.

Broadband services delivered over telephone lines can be affected by radio interference inside your home. This can cause slow downs or drop-outs to your broadband service. The most likely culprits are boilers, water heaters and anything with a motor in them, but interference can also be caused by other electrical devices such as TVs.

The interference is most likely to affect you if your broadband router, or telephone cabling runs next to or by the device causing it.

We have previously published a video explaining how you can fit an i-Plate which removes the 'ring wire' from extensions in the house, reducing the impact of radio interference on broadband connections.

Some basic tips

  1. Try to avoid placing the broadband router behind your TV or amongst a nest of mains cables.
  2. Where possible connect the router to the telephone line at the master socket.
  3. Ensure every device connected to your telephone line has a micro-filter used, unless you have a faceplate filter at your master socket.
  4. Remove unused telephone extensions, these can act like radio aerials picking up unwanted signals
  5. If you have to use a long RJ11 telephone lead to connect the modem to the telephone socket, make sure it is a twisted pair cable e.g. 10M RJ11 to RJ11 High Speed ADSL Broadband Cable - rather than the flat profile cable that came free with the router.
  6. Do not stack broadband hardware, e.g. broadband router with a mobile signal booster (e.g. Vodafone SureSignal) on top of each other.

Identifying Sources of Radio Interference

If you are finding that your broadband speed varies or it frequently cuts out for a few seconds, ensure that everything is wired correctly. If you still have problems, see if you can identify if anything in your home is possibly causing interference.

All you need is a simple analogue AM (MW in old units) battery powered radio, and by tuning this to around 600KHz the radio by nature of the directional ferrite rod antenna can help you hunt out sources of radio noise. If on tuning the radio in you find a radio station by chance, just shift the tuning away from the radio station slightly.

Generally noise from electrical devices will have a pattern to it; if there is just generic white noise this is likely to be just generic interference, our video shows the sort of noises to expect.

Local sources of electrical noise will be easiest to find during the daylight hours, as once the sun sets atmospheric interference come into play. As radio stations are generally a constant signal, broadband routers will notch out this part of the band if affected. The issue with local interference is that it can be intermittent causing drop outs and also occupy wide bands of frequencies reducing your broadband speeds.

If you find a lot of noise in a room, you may want to turn off all the electrical devices and turn them on one by one. Some people with particularly bad problems have found turning off a mains circuit for another floor in their home makes things easier to identify.

The sorts of devices that can produce RF noise that affects ADSL/ADSL2+:

  • Some Christmas lights - particularly flashing ones
  • Switched mode power supplies, e.g. phone chargers
  • Plasma and LCD TV's
  • Water pumps from power showers, central heating
  • Treadmills
  • Model trains
  • LED bulbs
  • Dimmer switches

..and the list goes on, almost anything electrical can give off radio interference.

The problem is knowing which devices are actually causing a problem, and unfortunately we cannot give you a sure fire guide, it is a case of trial and error. However, we have produced a video to show the steps you might take to identify the source

Watch our Broadband & Christmas Tree Lights video for a demonstration of how to locate AM noise:

If you do not have an AM radio, try one of these:

Common Questions

What do I do when I've identified the worst source and turning it off improves my broadband?

Well if the device is something you want to keep, then try to move it as far away from your telephone line and broadband router as you can (keep it away from other telephone extensions in the house too). You can also find using a twisted pair RJ11 cable to replace the flat lead from the microfilter to the modem reduces the noise pick up.

In the case of fluorescent lights you may find replacing the starter coil reduces the noise level when switching off.

The device is CE marked so why is it creating interference?

The CE mark does not mean that a device is not guaranteed to create no radio interference, just that it should be down to reasonable levels. If you find your new plasma TV is killing your ADSL2+ connection when the two items are a few metres apart then you may wish to contact the manufacturer (or ask if other users are seeing issues on our broadband forums).

I live in a flat/adjoining house and the noise was worst on the adjoining wall?

RF noise can travel some distance, so it is possible you may pick up interference from a neighbour. If you think this is the case, then if you can move the broadband hardware in your home first.

I picked up lots of interference from devices, but am not sure if it is affecting my broadband speeds?

Your provider should have given you a speed test estimate when you ordered the connection, if a speed test is within 10 to 20% of that speed then everything is probably fine.

If I upgrade to a FTTC based connection, will the noise that affects my ADSL connection still be a problem?

VDSL2 uses frequencies all the way up to 17 MHz (short wave band) so may be less affected by what causes problems with your ADSL connection. The short range of VDSL2 means that you should stick to the best practice rule of connecting the modem as close to the master socket as possible in your home.

My RJ11 modem lead has to cross some mains cables, what can I do?

When the telephone or broadband wiring crosses a mains lead it is best to do this so that the two leads are at ninety degrees to each other. You should avoid the common home entertainment system practice of bundling wiring into a single bundle. Use of a twisted pair RJ11 lead, and CW1308 specification telephone extension wiring helps to minimise the potential for noise pickup too.

How else can I improve my broadband connection speeds?

If you have more than one phone socket connected to the same phone line in your property, the wiring from the master socket to the other extension sockets can cause interference. This can sometimes be improved by installing a small device in the master socket called an i-Plate. Click here to see our i-Plate installation video.