by Robert Brand
Before I mention what has been done at Ceduna, let me tell you I have had many calls / emails with NBN Co about their error with the closing date for Ceduna. At their request I had to dig into the internet and find credible references to prove to them the real date. That has been done, but as of tonight, the date in the press release from NBN Co has not been corrected.
I came across this item in an article by the University of Tasmania that uses one of the dishes from Ceduna. Telstra shifted the other one (Ceduna 1?). Someone might like to tell us where it ended up. Perth? It is interesting to see what UTAS have done with Ceduna and how it fits into their network.
UTAS Ceduna Radio Telescope
The University of Tasmania Ceduna radio telescope is a 29.6 metre diameter parabolic antenna designed and constructed by Mitsubishi in 1969, with an alt-az mount and feeds located at the Nasmyth focus. It is located near the coast of South Australia, some 850 km west of Adelaide, at longitude 133◦48′36.57′′ east, latitude -31◦52′05.04′′, and an altitude of 161 m above sea level. The facility was established by the Overseas Telecommunications Company (OTC) in 1969, as the Ceduna Satellite Earth Station and was later taken over by Telstra. The Earth Station provided the gateway between Australia and Europe for telephone and television communication, via the global satellite system set up by Intelsat that offered sophisticated and low-cost communication services around the world. The choice of Ceduna as the location of an Earth Station was dictated by the limits of the coverage zone of the Indian Ocean geostationary satellite, the need to be reasonably close to Australia’s populous south eastern region, and the need to be in a location free from man-made electrical noise. During 1984, almost half of Australia’s International telecommunication traffic passed through Ceduna’s Earth Station.
In October 1994, improved communication methods (notably fibre optic links) and a need to rationalise services saw the closure of the Ceduna Earth Station. In September 1995 Telstra donated the Ceduna Satellite Earth Station to the University of Tasmania for use as a radio astronomy observatory. At the time of the handover, the antenna drive and control systems were those originally installed in 1969 and power was provided by a set of on-site diesel generators. The facility’s conversion to a radio astronomy observatory was a significant undertaking and included the connection of mains electricity, modification of the cable twister assembly, and the installation of new antenna drive motors and controllers, angle encoding equipment, feeds and a range of specialised radio astronomy equipment. The new electric drive motors provide slew rates of up to 40 degrees per minute about both axes, with an elevation limit of 1◦. Angle encoding is highly repeatable and currently an
RMS pointing accuracy of about 20′′ is achieved. The COSMIC project is providing a large amount of additional pointing information which is expected to result in an improvement of a factor of two or more in the pointing accuracy. The antenna surface has been surveyed and adjusted to an RMS accuracy of about 0.8 mm.
During its operation by the OTC/Telstra, the Ceduna antenna provided simultaneous up and down-links to the Intelsat satellites using frequencies in the 4-6 GHz range (transmitting in the range 5.925-6.425 GHz and receiving in the range 3.7-4.2 GHz). The high-powered transmission amplifiers originally used with the antenna were oil-cooled and could not be tilted. This was the reason for the choice of Nasmyth optics, since the focus position of the antenna lies along the elevation axis, allowing the transmitters to be housed in the “upper equipment room” (see Figure 1). This design feature impacts upon the range of frequencies at which the antenna can operate. The dimensions of the hole in the elevation axis limits the diameter of the final section of waveguide feed, resulting in a lower frequency limit at Ceduna of 2 GHz. Corrugations in the large waveguide sections close to the tertiary mirror affect the propagation at higher frequencies, resulting in 22 GHz being the upper frequency achievable. We have designed and built a range of new terminating sections for the Nasmyth waveguide feed, which operate in the frequency bands of 2.2, 4.8, 6.7, 8.4, 12.2 and 22 GHz. For reliability and simplicity the dual circular polarization receivers at each frequency are uncooled and have a bandwidth of approximately 500 MHz (except the 22 GHz system). .
The Ceduna 30m antenna conversion project was largely motivated by the need to extend the Long Baseline Array (LBA). The LBA consists of the Australia Telescope The LBA is operated as a National Facility by the Australia Telescope National Facility National Facility, Parkes, Mopra and ATCA telescopes, the University of Tasmania Hobart and Ceduna telescopes, with regular participation of the NASA Tidbinbilla telescopes and the Hartebeesthoek telescope in South Africa.
The Ceduna antenna first participated in LBA observations in late 1997. It has significantly enhanced the imaging capability of the array, by increasing the number of baselines, and more importantly providing much needed east-west baselines. With the inclusion of Ceduna, the longest north-south baseline (1400 km from the ATCA to Hobart) is comparable to the longest east-west baseline (1500 km from the ATCA to Ceduna). Figure 2 shows a 6.6 GHz LBA image of the nucleus of the radio galaxy Centauraus A, in which the counterjet is clearly seen, as are a number of components along the jet (S. J. Tingay et al. in prep.). This image is of significantly higher quality than comparable images of Centaurus A made with the pre-Ceduna LBA (see for example Figure 1 of Tingay et al. 1998). The Ceduna antenna is currently equipped with LBA-DAS/S2 tape-based (Wilson et al. 1995) and Mets¨ahovi disk-based VLBI recording systems (Dodson et al. 2004).
For those interested, the full document is here:
Interested in what is happening at Ceduna (LIVE):