Some approaches to real time evaluation for HF data communications

A project is currently being undertaken in which techniques to evaluate the HF ionospheric channel in real time, with particular reference to the requirements of communications systems employing modern flexible modems (for modulation selection), are being investigated. Four approaches to the measurement of the channel dispersion characteristics have so far been considered and tests conducted on short range (approximately 300 km) paths within the UK. These techniques are described in this paper together with some results from the experimental work. So far in this project, consideration has only been given to measurement of propagation delay and frequency dispersion parameters.