On conditions of signal reception in short wave channels

Short wave or high-frequency (HF) radios are currently used for international broadcasting, various types of communications, over-the-horizon radar, and some scientific experiments. In the future, they can also be employed for communications among unmanned and manned stations on other planets with ionospheres. The reception conditions in the HF range are determined mainly by the short wave propagation and narrowband interference (NBI). Oblique sounding systems provide the most complete information on these conditions, thus greatly improving the reception quality. This paper presents background materials on the short wave propagation and NBI prior to introducing the first oblique sounding system that satisfied modern requirements. The system was developed in the USSR in 1966 and was the most advanced system then. It has influenced the progress of both all-purpose and built-in sounding systems. It also stimulated several theoretical findings that are still of interest to researchers and engineers. Despite that, most materials related to the system have never been published in English. This paper concisely explains theoretical and experimental results most important for future systems and provides information on the signal reception conditions in the HF range.