CSIRO’s “On-axis” feedhorn
The high-quality TV output from Parkes was made possible by two things: the size of the telescope (which lets it capture lots of radio waves) and its very good receiving systems.
The TV vision was transmitted from the Moon as radio waves. The incoming waves were reflected off the surface of the Parkes dish and up to the ‘focus cabin’ that sits high above it. Here there were two feedhorns to capture the radio waves and turn them into electrical signals. The main ‘on-axis’ feedhorn sat at the centre of the focus cabin, while the ‘off-axis’ feedhorn sat to one side.
Both feedhorns were designed by CSIRO engineer Dr Bruce Thomas. The main on-axis feedhorn was of an innovative new design (a one wavelength, two hybrid-mode corrugated horn) that Dr Thomas developed. The new design increased the sensitivity and bandwidth of the receiving system.