The feasibility of sustaining very wide bandwidth (~ 1 MHz) communications on short surface wave and skywave links is critically dependant on prevailing channel conditions. In this paper the main results of a review of the HF channel, external noise and interference characteristics are summarised. A wideband-channel model is proposed for use in the simulation of direct sequence spread spectrum (DS-SS) radio system performance. Potential difficulties in spectrum sharing with existing narrowband systems are also considered.