Compatibility of FMCW Modulated HF Surface Wave Radars with Radio Services

High-Frequency (HF) radars are operated in the 3-30 MHz frequency range and have been used for several decades now. Sky-wave systems are able to keep large areas under surveillance, e.g. the whole northern coast of Australia. Some of these systems have caused severe interference to other radio services like the Russian ”Woodpecker”. Currently, a network of ground-wave HF radars is beeing installed along the US coast. Due to the large number of systems, they can no longer be operated on an experimental license and care must be taken to avoid radio frequency interference with other radio services and radars. This paper discusses different modulation techniques for HF radar range resolution and their compatibility with other users of the HF spectrum.