Extra-low-frequency radiation from the polar electrojet antenna

Abstract

There have been many recent reports on the detection of extra-low-frequency (ELF) radio waves in the immediate vicinity of powerful ionospheric high-frequency (HF) heating transmitters which are amplitude modulated at the ELF frequency^1–4. Results have also been presented which indicate that long path propagation (>3,500 km) of ELF signals from such heating facilities may be possible^5,6. However, no calibrations were provided with these measurements and it has thus not been possible to estimate the relative efficiency of these ‘wireless’ ELF generators compared with the more conventional long-wire antennas, although several theoretical estimates have been provided^7–9. Results are presented here of the simultaneous measurement at Lycksele and Kiruna, northern Scandinavia, of the ELF signals radiated by the polar electrojet antenna located near Tromsø. From these data, it has been possible to confirm the successful excitation of the Earth–ionosphere waveguide by the polar electrojet source and to make a first estimate of its radiated power—this is typically 1 W in the frequency range 1–1.5 kHz for HF effective radiated powers of 270 MW.