Correlation of HF interference spectra with range

The variation of HF interference spectra with distance on the surface of the earth has been studied by computer simulation and a field experiment. A computer model of the earth and the ionosphere over Europe has been constructed with randomly positioned transmitting stations. The received sky-wave-signal spectrum was then monitored as the receiving location was moved by up to 500km. In the field experiment, voice-channel interference was recorded at five receiving stations with separations up to 430km. The recordings were analysed spectrally and compared. Generally, good correlation of spectra at different receiving sites were observed in both the simulation and the field experiments. In both cases, the results were obtained using receiving aerials appropriate for high-angle sky-wave communication.