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.
ITU-R F.1611 SPANISH-2003 Referenced Document
ITU-R F.1110 Adaptive Radio Systems for Frequencies Below About 30 MHz
ITU-R F.1337 Frequency Management of Adaptive HF Radio Systems and Networks Using FMCW Oblique-Incidence Sounding
ITU-R F.339 Bandwidths, signal-to-noise ratios and fading allowances in HF fixed and land mobile radiocommunication systems*， 2013-02-01 Update
ITU-R P.533 Method for the prediction of the performance of HF circuits*， 2007-01-01 Update