High-power VLF transmitter facility utilizing a balloon lofted antenna

A 100-kW transportable very low-frequency (TVLF) transmitter facility has been used for magnetospheric wave-injection experiments from sites in Alaska, New Zealand, and Norway. A unique feature of the TVLF facility is the antenna which is a conducting cable lofted to an altitude of 1500 m by a 1000-m³helium balloon. The antenna is driven at its base as a monopole above a ground plane. The antenna cable also serves as the balloon tether. The lowest operating frequency in this configuration is 6.6 kHz, at which the radiated power is 100 W. At the highest operating frequency used in the experiments, 21 kHz, the radiated power is 10 kW. In Norway power lines were used as antennas. The minimum operating frequency was then 1 kHz and the radiated power is estimated to be about 0.5 W. The components and performance of the TVLF facility used with the balloon lofted antenna are described.