HartRAO Home >
news >
Antenna Surface Panel Alignment 2004/09/02
Radio Telescope Upgrade
Antenna Surface Panel Alignment 2004/09/02
Initial alignment of the new surface panels has been proceeding since the
installation of the last of the 252 new panels making up the main parabolic
surface of the 26-m radio telescope on 2003 September 10.
The alignment has been caried out using a theodolite installed in the
"elephant base" under the Cassegrain cone housing the microwave receivers in
the centre of the telescope. In addition, a tape measure is used to set the
radial distance of the panels.
The basic alignment was carried out in normal working hours. Calibration
using astronomical radio sources show that the aperture efficiency of the
telescope doubled at its shortest operating wavelength (2.5 cm) after this
alignment.
However, the telescope expands and contracts during the day owing to the
differential heating heating of the structure by the Sun. Consequently, a
more accurate alignment has to be carried out at night.
The main part of the night alignment was carried out on the night of 2004
September 01/02 by Jonathan Quick, Jacques Grobler, Pieter Stronkhorst,
Piet Louw and Attie van Wyk. The images below show the action.
Click on image for large version
This picture, taken from the tetrapod support for the subreflector
(secondary mirror), looks down on the central Cassegrain cone and the top of
the 18 cm wavelength feed horn strapped to its side. To align the panels,
reference targets for the theodolite are mounted under four of the panels, so
these have been removed for the duration of the alignment. The aperture
left by one of the missing panels can seen on the left.
Click on image for large version
The theodolite is located in the "elephant base". Here Pieter Stronkhorst
is just visible aligning the theodolite.
Click on image for large version
Jaques Grobler is seen in close-up operating the theodolite.
Click on image for large version
Work started on the outermost ring of panels and moved inwards.
Click on image for large version
Piet Louw adjusts a panel.
Click on image for large version
Jonathan Quick adjusts one of the mounting bolts.
After completion of the night alignment, we change to microwave holography,
making use of a 12 GHz transmitter on a geostationary satellite as a
reference signal.
