A land-based hf transmitter for ionospheric propagation studies using superdarn radars

Abstract

The goal of this project is to design, build and characterize a low power High Frequency (HF) transmitter. The transmitter will be installed and operated in Antarctica to establish a beacon at the South Pole station to be received by the Super Dual Auroral Radar Network (SuperDARN) radar installed at SANAE IV. The transmitter is specified and designed to transmit at 12.57 MHz (continuous wave) from the South Pole. It must achieve a frequency drift of 41.8_mHz or better. The transmitter must operate normally under extremely low temperature conditions down to -40°C. The transmitted wave will be refracted by the ionosphere and received by the SuperDARN radar at SANAE IV. The ground distance between the HF transmitter and the radar is approximately 2000 km. The goal of the experiment is to form a bi-static radar configuration in order to study the ionosphere, especially travelling ionospheric disturbances (TIDs), which are signatures of atmospheric gravity waves (AGWs). A 25 dBm transmitter prototype was developed using a GPS disciplined oscillator in order to achieve the frequency stability required for this project. The HF transmitter proved to conform to the power and frequency stability requirements both during propagation tests conducted between Hermanus (34.4241° S, 19.2247° E) and Pretoria (34.0558° S, 18.4589° E) in South Africa, as well as when the device was exposed to temperatures that ranged from +40°C to -45°C. Although the antenna design was beyond the scope of this project, various determinations and considerations are presented in the link budget analysis, which have been confirmed during field tests. Therefore, certain recommendations on the antenna design are given. Propagation in Antarctica is expected to differ from the field tests conducted due to the differences in density and dynamics of the polar ionosphere, compared to the mid-latitude ionosphere.