The major interference problem for beacon listeners occurs on the twenty meter frequency of 14100 kiloHertz. The IARU/NCDXF beacons have been on this frequency since 1979. The frequency was established before the tremendous advances in the popularity of the digital modes occurred and today the frequencies on both sides of 14100 kiloHertz are full of digital signals.
On the ham bands, no station has a legal right to exclusive use of any particular frequency. However, as the digital-mode signals began encroaching on the beacons, both the IARU and the ARRL incorporated into their official band plans the idea that the frequencies between 14099.5 and 14100.5 should be kept clear to protect the beacons at 14100.0. Almost every country that belongs to the IARU has adopted this band plan. In some countries these band plans have been adopted into the regulations governing amateur radio. In other countries, there is general agreement that a properly operated amateur radio station should normally operate within the recognized band plans and the vast majority of digital operators do so.
If you are listening to the beacons with a receiver whose bandwidth is designed for voice reception, the 2.8 kiloHertz bandwidth typical of such receivers will inevitably receive adjacent digital signals as well as the beacons. When this happens, the resulting interference should not be blamed on digital operators so long as their signals are more than 500 Hertz from the beacon frequency.
It is recommended that when you listen to the beacons you use a receiver with a CW IF filter of 500 Hertz or less. Such a narrow IF filter is primarily needed to reduce interference from digital signals on 14100 kiloHertz, but will help you to hear the beacons better on all bands by reducing atmospheric and other noise.
Unfortunately, not all digital operators are familiar with fact that the official band plan for twenty meters calls for keeping the frequencies around the beacons clear. Furthermore, some digital operators do not realize that their transmitted RF energy occupies frequencies which are different from the frequency which shows on their dial.
If you notice a station which is not abiding by the band plan and is transmitting RF energy too close to 14100 kiloHertz, you may, in a nice way, call that station's attention to the interference he is causing. The operator probably doesn't realize he is interfering. If the interference is intentional, you should report the operator to your local national organization or one of the monitoring stations listed below.
In some cases, interference may be caused by non-amateur operations in the ham bands. The IARU maintains monitoring stations in each of the three regions responsible for reporting non-amateur operation in the amateur bands to the appropriate authorities.
IARU Monitoring Service Contact Information:
If you observe interference to the beacons from shortwave broadcasters or illegal operations, please report the interference to the appropriate monitoring station.