This paper describes an adaptive HF radio systems architecture, from concept through to implementation. The key to adaptivity lies in software, and some of the software issues which affect the design and realisation of an HF `software radio' will be discussed. This adaptive system has been developed with the aim of providing a flexible testbed upon which to test new techniques for automated HF radio systems. The requirements of such a testbed placed a number of constraints upon the adaptive system which affected the design and functionality. One of these requirements was that the adaptive system should comply with the US MIL-STD 188-141A standard for automatic link establishment (ALE). The relative performance of the adaptive system and commercial equipment operating to this standard shows that the flexibility offered by an adaptive system does not impair performance in the MIL-STD 188-141A interoperable mode. The operation of an automatic radio control system (ARCS) can be divided into 3 distinct phases. The radio link is set up using ALE procedures; once the link is in use the changeable nature of the HF channel makes some form of automatic link maintenance (ALM) necessary. In order to select the optimum channel upon which to establish the link automatic channel selection (ACS) requires some mechanism to sense or predict the current channel conditions. All 3 of these phases must be implemented in a system capable of providing a testbed for new techniques for ARCS, and must be implemented with some flexibility in terms of functionality and configuration if the system is to be either a useful testbed or an effective adaptive system