Coherent Bandwidth of HF Communication Channels Enabling the Change of Intramode Dispersion Type

Paper presents the results of theoretical studies on the coherent bandwidth of wideband ionospheric HF channels and their availability under conditions of changing intramode dispersion. A mathematical model of group delay dispersion in the vicinity of the point where intramode dispersion type changes was developed. By numerically modeling the frequency dependences of group delay, it was found that on mid-latitude paths with a length of 500–3500 km, the coherent bandwidth can be increased by an average of 2.5-25 times, compared to channels that do not enable the change of intramode dispersion type. An analysis of the results on the availability of wideband channels showed that on Near-Vertical Incidence Skywave (NVIS) paths, coherent bandwidth up to 200 kHz can be ensured with a 0.9-1 availability during the day. For long-haul paths of 3500 km, coherent bandwidth increased up to 900 kHz with an availability level of 0.8-1.