Experiencing EMC interference?

Interference report montageRSGB wants to establish the full extent of interference to the radio spectrum from data-over-mains and other interfering devices; we are therefore asking everyone who is experiencing local interference to help us.


Most data-over-mains devices are “notched” so that they do not cause high levels of emissions on amateur bands. However, elsewhere in the shortwave spectrum there remains the possibility of interference.

We should all remember that there are other forms of interference to the enjoyment of our frequencies—from local switch-mode power supplies, some plasma televisions, electrical machinery, etc. Please also remember that there is a high level of natural noise on the lower frequency bands—particularly 1.8 and 3.5 MHz during the day time. In this questionnaire we are trying to establish the extent of interference you are experiencing from all these devices, and the following will help you identify these instances.

There are three simple steps to take:

1. Identifying the form of interference

You should first check that the equipment in your own house is not the source of the interference. There are “hidden” sources in many everyday pieces of electronic equipment. So we recommend that, if you can, you turn off all your power circuits at the circuit-breaker, except the one powering your receiver, and double check that there is nothing in your own home contributing to the interference. It is easy to overlook a small device that could be the source of the problem. If you switch off all the breakers except one, make sure there is nothing connected on the remaining live circuit, other than the receiver you are using. Be sure that you warn all other people in the household that the power, including lighting, may go off.

You should now try to determine whether the interference is caused by PLT—there are many other possible interfering signal sources.

So, tune across the affected bands, using the “AM” detector position on your receiver, and turn off the AGC. Compare the sound of your interference with the sound clips available on this website.

If you are reasonably sure that the interference comes from a PLA device (the sound clips may help), then tune outside the amateur band, and check if the level of the interference increases. What you should hear is that the interference increases rapidly as you tune outside of the amateur bands, and by as much as 30dB (i.e. about 5 ‘S’ points). If it does, it is more likely than not that you have identified a PLA device.

Make a note of the amateur bands affected, and the strength of the interference as indicated on your S-meter. You might also like to record the interference level on some of the short-wave broadcast bands.

2. Tell RSGB

Complete the simple form, pressing “submit” when you have inserted all the information. The RSGB cannot investigate your complaint, but may offer advice and in some cases assistance in preparing the information for a formal complaint to Ofcom. Just as importantly, the database which we build up from complaints will help us in our discussions with Ofcom. Remember we are interested in knowing of all forms of interference, not just PLAs.

3. Making a formal complaint to Ofcom

If we are to register the full effect of interference with Ofcom, it is really important that everyone affected complains. You can do this by going to the Ofcom website and completing the form. When you get to the free-text box at the bottom, headed “Please describe the interference and give any other comments” you should include the following:

  • “The interference affects the **details** Amateur Radio Service and/or **details** short wave broadcast frequency bands.”
  • Add, if you believe it to be true: “As far as I can ascertain it is caused by a nearby data-over-mains device (PLA/PLT)”

You should report all factual information that will help Ofcom in its duty. For example, any information that you have regarding the possible source of the interfering signals, and any investigation that you have carried out.

You will see that at the end of the form there is a statement: “Ofcom can investigate the interference to your radio system under our commercial charging terms.
The terms are that if we find the problem is within your own radio system or from something which we consider to be under your or the user’s control then we will charge for the investigation at £91.42  + VAT per man hour used”.
It is for this reason that you MUST ensure that the problem does not originate in your own home!

You can use the Ofcom form for reporting any form of local interference, but make sure it does not originate in your own home!

Further advice can be found at I am experiencing Interference