Very-low frequency signals (2-10 kHz) received at Palmer Station, Antarctica, from the 21.4 km dipole antenna at Siple Station, 1400 km distant

Radio signals transmitted from the unique experimental VLF transmitter at Siple Station (76°S, 84°W), Antarctica, as well as VLF signals from communication and navigation systems and waves that propagate in the ionosphere and magnetosphere in the whistler mode, are regularly received and analysed at Palmer Station (65°S, 64°W), Antarctica. The amplitude and polarization properties of the Siple signals are predicted using a ray optics analysis. The amplitude of the signal received from Siple varies with frequency; observed nulls in the signal spectrum, where thesignal amplitude/alls 5-10 dB below what might be expected, are explained by the ray analysis. The amplitude spectrum is observed to be very sensitive to ionospheric conditions. Whereas the arrival bearings of signals from VLF transmitters other than Siple are found to be within 5° of their expected values, which is consistent with their expected vertical polarization and the operation of the DF system, an approximately 90° anomaly in the apparent arrival bearing of the signals from Siple is attributed to the essentially horizontal polarization of the received signal. The anomaly is found to be consistent with the theory of operation of the DF system. Occasional anomalies greater than 90° are explained in terms of a combination of polarization error and a smaller multi-path error. Siple two-hop signals and whistlers propagating on a common magnetospheric path showed arrival bearings and other properties consistent with a path end point within 200km of Siple. This suggests that these signals were received at Palmer with essentially vertical polarization.