The ionospheric channel provides the connectivity for the links in an adaptive HF radio circuit or network. To provide proper utilization of this resource the radio system must operate on the ideal frequency or as close to it as practical. This may be the same frequency for a simplex circuit or two different but closely related frequencies for a full duplex circuit. Frequency changes will be dictated by the natural cycles of ionospheric propagation; diurnal, seasonal and sunspot variations. Natural or man-made radio interference may dictate unpredicted changes in the operating frequency. Also solar flares and geomagnetic storms may cause communications disruptions which will also require changes in the operating frequency.