The 26 m Telescope

The central instrument of the Observatory is a 26m parabolic antenna. This is a general purpose, fully steerable antenna with a solid reflecting surface and operates up to 22 GHz. The antenna is used at prime focus. The telescope is unusual for an astronomical telescope in that it has an XY mount rather than the more traditional Azimuth/Elevation (Az/El) mount.

History

The 26m antenna was built in 1965 by NASA and installed at the Orroral Valley Tracking Station near Canberra. This tracking station was part of NASA's world wide tracking and data network, operated for NASA by the Space Projects Branch of the Australian Department of Science, It maintained a 24 hour per day, 365 days per year tracking operation and during a typical day it made contact with more than a dozen different spacecraft. The 26m antenna was the largest antenna at the station, and was involved in programmes such as the Orbiting Solar Observatory (OSO), the joint US-UUSR manned Apollo-Soyuz mission of 1975, and the Space Shuttle program. It was responsible for tracking the re-entry of Spacelab over Australia.

A re-organisation of NASA facilities resulted in the Australian activities being concentrated at Tidbinbilla, near Canberra, and the closure of the Orroral valley station. The 26m antenna was surplus to requirements. NASA then donated the antenna to the University together with extensive support equipment. The antenna was moved from Orroral Valley to Mount Pleasant during the period from July 1985 to February 1986 and was officially opened on 13th May 1986.

Hardware

The observatory's main time and frequency standard is a Hydrogen Maser. There is also a GPS receiver linked to a "Totally Accurate Clock" which is used to compare observatory time with GPS time.

Spectral line observing is performed with a 1024 channel 1 bit auto-correlator (two polarisations can be correlated at one time, with 512 channels per polarisation). The correlator will operate at selected bandwidths between 0.156 and 20 MHz. A two bit correlator with 8192 channels (using the VLBA correlator chips) is being built.

As the observatory is involved in most Australian VLBI, there are three recording systems: Mark-II, Mark-III and S2.

Receivers

The 26m antenna is equipped with Helium cooled receivers that operate at 2.3, 6.6, 8.4 and 12.2 GHz. There are also room-temperature receivers that operate at 0.66, 0.84, 1.4 and 22 GHz (a cooled 22 GHz receiver is in production). For a list of receiver specifcations (system temperatures etc) see the Southern Hemisphere VLBI Telescopes - System Parameters page.

Computer Control

Presently the 26 m antenna is undergoing an upgrade of computing equipment. The new observatory software runs on two Sun SPARC workstations and a set of IBM PC clones running a real-time operating system (pSOS).