Studying the Parameters of Frequency Dispersion for Radio Links of Different Length Using Software‐Defined Radio Based Sounding System

Methods and relevant software were developed to study frequency dispersion parameters of wideband high‐frequency (HF) radio channels over propagation paths of different lengths: near vertical incidence skywave paths (up to 500 km) and long‐distance radio paths (from 1,000 up to 3,500 km). We developed a universal ionosonde (in terms of methods and signals) to do experimental research into HF radio wave propagation and dispersion using software‐defined radio technology and platform Universal Software Radio Peripheral N210. The multipurposeness of the ionosonde is manifested in the sounding methods used (oblique incidence and vertical incidence) as well as in the spread spectrum signals used (binary phase shift keying, frequency modulated continuous wave, and frequency modulated interrupted continuous wave). The characteristics of the megahertz‐bandwidth HF channels were studied. The dependences of the variation of the third‐order dispersion parameter on the time of day, the radio path length, and the channel carrier frequency were experimentally found. Key Points A method for obtaining dispersion characteristic and calculating impulse response of wideband channels depending on the dispersion parameters was developed Data on the third‐order dispersion parameters was obtained depending on a midband frequency of a megahertz‐bandwidth HF channel as well as on the path length The developed SDR‐based universal sounding system is an effective tool for studying HF radio wave propagation and dispersion in the ionosphere