The Antenna

The geographic coordinates of the antenna are: Latitude 42.370 S, Longitude 147.218 E. As shown in Figure 1, the antenna is a 23 element log-periodic structure fixed in position and pointed to the celestial equator near the meridian. Its response pattern is broad enough to cover the whole ecliptic and to have reasonable hour angle coverage. The antenna's directivity is low, about 6 db/isotropic; its horizontal, E-plane pattern is about 90 wide and its vertical, H-plane pattern is more than 100 wide. The antenna has an opening angle of 90 at its apex, and a scale factor of 0.89. The longest dipole is 50.0m and the largest spacing between dipoles is 2.75m. These values decrease geometrically by the scale factor to the shortest, 3.05m, dipole. The height of the tower which supports the apex of the antenna is 21.4m. The geometrical bandwidth of the structure is 3 to 45 MHz but, since the radiating region spans an appreciable length of the structure at any single frequency, the RF bandwidth of the system is 3.3 to 40.9 MHz. Interference effects between the direct ray and the ray reflected from the ground, i.e. Lloyd's mirror effects, are observed, but the reception of the reflected ray is diminished by 5 to 20 db because of the antenna's directivity. These effects are calculated and partially removed in the data processing. The instrument is normally operated from 2200UT to 0630UT each day although the directivity of the fixed antenna limits the observing period to about six hours with good sensitivity.

© Copyright Astronomical Society of Australia 1997