Radio Telescope on Track

This post was originally published by Australia’s Science Channel on 29th July 2016 but was removed when the website was updated.

David Gozzard is a PhD student who has found himself on an interesting journey to remote Australia. In this blog, he shares some of the fun work he’s been up to!

When I started my PhD in experimental physics, I knew there would be a lot of travelling involved, mostly to conferences, meetings and workshops both in Australia and overseas. What I did not realize was how often I would find myself travelling to remote areas of Australia and South Africa to conduct field work. I’m not complaining. The field work is both challenging and rewarding, it gets me out of the lab, and it means I get to visit some of the world’s premier scientific facilities.

And that’s where I am now. After a four-hour flight from Perth to Sydney, a short hop from Sydney to Tamworth, and a two-hour drive from Tamworth to Narrabri (lugging two heavy cases full of scientific equipment), I find myself at the Paul Wild Observatory, home of CSIRO’s Australia Telescope Compact Array, the largest radio interferometer telescope in the southern hemisphere.

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Antennas 1 – 5 of the Australia Telescope Compact Array.

Built in the 1980s, the Compact Array is a radio telescope comprising six 270-tonne
dish-antennas, five of which can be driven to various positions along a 3 km track in order to change their view of the sky. Although it’s not as famous as The Dish at Parkes, the Compact Array holds the distinction of being the most scientifically productive radio telescope in the southern hemisphere. In radio engineering, the plural of “antenna” is “antennas”. Biologists, calm down.

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Me, driving antenna 3 during an array reconfiguration (see video below).

This is my 3rd trip to the Compact Array. I’m here to test equipment developed for the Square Kilometre Array (SKA) radio telescope. Radio telescope arrays like the Compact Array and the SKA need high-precision reference signals from atomic clocks to be transmitted to each antennas in order for the array to function properly. Over long transmission distances, the precision of these signals can become degraded and when that happens, the array fails.

On something the size of the Compact Array (6 km from one end to the other), this is not a problem; but for the SKA, which will have antennas located up to 150 km away from the centre of the site, signal degradation is a big problem. The equipment I have brought with me is designed to compensate for the degradation of the reference signal by measuring how the reference signal has been perturbed and modifying the transmission to compensate.

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My signal stabilization test equipment setup at ATCA.

My supervisor and I have been developing this stabilization system over the past two years at The University of Western Australia, and we have tested its performance extensively in the laboratory. Now the time has come to plug it into a working radio telescope to confirm that it works in the real world!

Because this is a synthesis imaging telescope, every few weeks the antenna dishes are moved to different positions along a track to change how they image the sky. I was lucky enough to be allowed to take part in one of these array reconfigurations. Each of the six antennas weighs 270 tonnes and has a top speed of 4 km/h. Reconfiguration can take 1 – 2 hours depending on the extent of that day’s changes. Antenna 2 shown in the video was driven nearly 2 km in this reconfiguration job.

The Compact Array is the best facility to perform these tests because it was constructed with an almost unique receiver system that allows us to run the array using both its conventional reference distribution system and our stabilized reference system at the same time. Our system runs over an extra 77 km of fibre-optic cable to a communications hut and back. The telescope data from the conventional reference system can be compared directly with ours to see if the stabilization system is working as designed.

The Compact Array is the best facility to perform these tests because it was constructed with an almost unique receiver system that allows us to run the array using both its conventional reference distribution system and our stabilized reference system at the same time. Our system runs over an extra 77 km of fibre-optic cable to a communications hut and back. The telescope data from the conventional reference system can be compared directly with ours to see if the stabilization system is working as designed.

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Me, sitting in the ATCA control room.

Working with the CSIRO team is an absolute pleasure. Everyone is very professional, they all know the systems they are responsible for insideout, and they are very helpful. The experiments that I have performed at the Compact Array would not have been possible without the efforts they made to accommodate my test schedule and the modifications I needed on some of the antennas.

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This photo is the group of us who contributed to the work on this trip. The people in the photo are left-to-right: David Gozzard, Mike Hill, Sascha Schediwy, Peter Mirtschin, Jamie Stevens and Jock McFee (not pictured – Brett Lennon).

They also took a keen interest in the experiment itself. Many of the staff at the Compact Array reminisce about how it used to be, only a few years ago, when the site was buzzing with astronomers from Australia and around the world. Now, astronomers can operate the telescope remotely from Sydney or, in some cases, from the other side of the world. As a result, the onsite staff have seen their ranks halve as less support is needed. The engineers and other support staff miss being able to quiz astronomers about what they are using the telescope for, and what they are discovering.

Apart from the Compact Array itself, the observatory is home to a lot of Australian science history. The array occupies a site formerly used by the Culgoora radioheliograph (pictured below), which CSIRO used from the mid-60s through to the mid-80s
to perform groundbreaking studies of radio emissions from the Sun and solar outbursts.

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One dish of the Culgoora radioheliograph.

Most of the 96 dish-antennas from the radioheliograph still surround the site in a 3 km wide circle. Within that circle are also the Sydney University Stellar Interferometer, until recently used to make measurements of the size of distant stars; the CSIRO Applied Physics Solar Telescope, which studied the visible light from the Sun in conjunction with the radioheliograph; the Birmingham Solar Oscillations Network Telescope, used to study churning gas inside the Sun; and an IPS Radio and Space Services telescope, which monitors solar outbursts to forecast how they will affect space craft and radio communications.

As I write this, my time at the Compact Array is coming to an end. My experiments have worked, the stabilization system has performed well, and I am preparing to report the results to the SKA Office. And the results are looking good. The system reduces signal fluctuations to one part in ten trillion, over a 1-second period. If your wristwatch
was that stable, after 300,000 years it would be off by less than one second. This is more than 10 times better than the stability required by the SKA.

Now I just have to pack up my equipment and get ready for the journey home.

Further reading

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