A Method for Optimal Frequency Selection in HF Ultra-Long-Distance Communication

NVIS (Near-Vertical Incidence Sky-wave) is currently an effective method to solve the blind zone effect of high-frequency communication, but the effectiveness of its operation is closely related to the frequency selection. Aiming at the existing problems in frequency selection of the current NVIS system, this paper proposes a rapid frequency selection method for the NVIS system based on passive monitoring. This method can achieve both the accuracy and timeliness of frequency selection without sending any detection signals. It can realize the rapid tracking of the ionospheric parameter f0F2 and the capture of the spectrum "holes" during the communication gap, and dynamically adjust the communication frequency in real time. This paper measures and analyzes the experimental data of different antennas. The results show that this method is applicable to a variety of NVIS antennas, and has the characteristics of high frequency selection accuracy, fast speed, strong concealment, etc., which has important reference value for improving the communication effect of high-frequency near-vertical incidence skywave propagation.