ncdxf     iaru


 

Beacon Interference


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. Although these band plans do not have the full force of law, there is general agreement that a properly operated amateur radio station should normally operate within such band plans and the vast majority of digital operators do so.

If one listens for 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. He probably doesn't realize he is interfering. It is ironic that one such station was automatically forwarding DXing information while simultaneously interfering with a major tool for DXing.

You are welcome to send interference reports to the Beacon Committee.
In the typical case of a digital-mode interfering signal, the most useful reports are from stations which can actually receive the digital transmission and which include the time, the date, the callsign of the transmitting station, the mode being used, and the dial frequency used to monitor the transmission. It is also useful if you include the IF bandwidth you use for listening to the beacons.