Analysis of the electromagnetic availability of radio signal sources during propagation in the ionosphere radio channel
Authors: Мirtаlibov Т.А. , Pozdyshev V.Yu. , Razinkov S.N. , Тimоshеnkо А.V. 
Published: December 2023

Problem statement. Multi-channel automated short-wave radio communication networks are used to provide information support for the activities of critical facilities and the organization of information exchange between subscribers assigned to a large area, as well as the control of aircraft when flying at transcontinental ranges and sea vessels in remote areas of the world ocean. The probabilistic-temporal characteristics of the effectiveness of monitoring their dynamic states largely depend on the electromagnetic availability of radiation sources. The conditions of their electromagnetic availability must be determined by the values of the maximum applicable frequency and spatial-energy characteristics of the signals in the ionosphere radio channel. Time periods of stable reception must be set taking into account possible changes in ray trajectories and fading (fading) of signals due to refraction in ionized layers of the atmosphere during daily and seasonal fluctuations of electrical parameters. To determine the current values of the radio channel parameters, the International Reference Model of the Ionosphere and GOST 25645.146-89 “Earth's Ionosphere. Model of the global distribution of concentration, temperature and effective frequency of electron collisions”, which reflects the patterns of distribution of average values of the electron concentration in the Earth's ionosphere at different times of the year and day with changes in solar and geomagnetic activity. Goal. Evaluation of the electromagnetic availability of short wave emitters for monitoring posts based on a rational choice of operating frequencies and finding the spatial and energy characteristics of signal reception. Results. A predictive model has been developed for assessing the electromagnetic accessibility of radio signal sources by the values of the maximum applicable frequency and spatial and energy characteristics during propagation in the ionosphere radio channel. The profile of the ionized layers of the atmosphere and the structure of radio channel undergo changes depending on the mutual position of the Earth and the Sun, as well as solar activity and the latitude of the observation site. In the profile of the ionized structure of the atmosphere, four characteristic regions are conventionally distinguished – layers D, E, F1, F2. Due to the intrinsic fluctuations in the parameters of ionized layers under the influence of a large number of factors, ground-based complexes of vertical (inclined) sounding and a satellite system for observing the ionosphere do not provide the required reliability of data on its state in real time for the entire surface of the Earth. Based on certain values of the optimal operating frequencies and inclination angles of the ionosphere wave ray trajectories, the time intervals of the electromagnetic availability of transmitters located in different regions in the summer and autumn-winter periods were found. Based on the estimates of the maximum applicable signal frequencies in the ionosphere radio channel using an azimuth-elevation detector-direction finder located in the Central Federal District, the angles of inclination of the trajectories when receiving radio station signals meteorology information of airfield networks of the Russian Federation and neighboring countries were determined. The detector-direction finder used an active antenna array of 16 asymmetric vibrators 2.5 m high, located on an area of 200×200 m, and synchronized coherent radio devices with frequency conversion. Measurements were carried out in the Doppler ray separation mode when selecting signals at matching frequencies was carried out in accordance with the time schedule for the operation of radio stations. On routes with a length of about 1000 km, variations in the directions of arrival of signals along the elevation angle with 3 reflections from the ionosphere reach 15...20°, and in the azimuth plane - up to 4...5°. On routes with a length of more than 1000 km, the fading of signals is determined by the interference of beams commensurate in level; on routes with a length of more than 2000 km, as a rule, one beam prevails, and fading is due to a change in its heterogeneous-style in time. Practical significance. The predictive model for analyzing the electromagnetic availability of radio emission sources makes it possible to select the modes of operation of monitoring posts with the establishment of a period of time with the best conditions for receiving signals in given areas, based on the values of the maximum applicable frequency of radio channels and the angles of arrival of a sky wave with the highest power. The obtained results form the basis for improving the technology of monitoring the radio-electronic situation when receiving signals propagating over the ionosphere radio channel, and justifying the tactical and technical requirements for the characteristics of high frequency range direction finders.