The Siple VLF transmitter as a multi-frequency probe of the earth-ionosphere waveguide

Receptions of subionospheric signals radiated from Siple, Antarctic in 1983 to stations at Palmer, Halley, and South Pole are reported which are shown to be strongly dependent upon azimuth and signal frequency. The results indicate that antenna properties favor the endfire direction (toward Halley) at the third harmonic of the antenna half wave resonance frequency, and in general demonstrate greater efficiency at higher frequencies. The present effects provide a means of extending the effective frequency range of the narrowband Siple antenna system and of selectively probing certain regions of the earth-ionosphere waveguide.