Wednesday, May 26, 2010

First LBA antennas installed!

The first two LBA antennas have now been installed! The main installation, involving the construction of 96 LBA antennas, is scheduled for a couple of weeks' time, and will involve teams of postgraduate students from Portsmouth, Southampton and Oxford. It's a big undertaking, which requires a lot of preparation so that relatively unskilled volunteers can quickly get up to speed in getting antennas accurately placed, delicate cables correctly connected, and all of the components secured to withstand the weather.

Yesterday, a small group of us - astronomy staff and students from Southampton, Portsmouth and Hertfordshire - spent the day learning the details of the LBA installation process from the experts, Derek McKay, Mike Willis and Harry Smith, so that we can act as "team leaders" during the main installation. To begin with Derek McKay took us through a test build, running through the entire procedure step by step, on the test range away from the main LOFAR-UK site. Drilling into grass and soil to insert the custom-made "Chilbolton pegs" for attaching the dipole wires lulled us into a false sense of security about how easy the process was going to be... Here Bob Nichol drills a hole during the test build, while Harry Smith and Derek McKay look on:

After lunch, the plan was to run through the procedure for real, using one of the newly compacted LBA antenna pads. There are a number of steps in the process, which need to be carried out very carefully, with quality assurance checks at several stages. The main stages involve laying out the ground sheet (whose main purpose is just to prevent weeds from growing round the antenna), laying the ground plane (the metal grid that helps reflect radio waves towards the dipole wires), drilling holes and hammering in pegs to attach the dipole wires, setting up the antenna pole, and then finally attaching the LNA (low-noise amplifier) and dipole wires - here demonstrated by Martin Bell and me:

All went well until we reached the stage of drilling holes - the carefully honed procedure involving ensuring an accurate 45-degree angle for the pegs had to be scrapped when it became clear that there were impenetrable rocks that needed to be avoided in some parts of the LBA field. Luckily, introducing a bit of flexibility about the peg angle doesn't cause a problem for getting the correct tension in the dipole wires, and so after a bit of discussion we managed to complete the first LOFAR-UK LBA antenna, which will form part of the final station - an excellent achievement for an afternoon's work! This is the first completed LOFAR-UK LBA antenna, and (most of) the installation team: Bale Granville, Harry Smith, Hana Schumacher, Martin Bell, Mike Willis, Derek McKay, Judith Croston, Bob Nichol (in front). The second picture also includes Martin Murphy, Martin Hardcastle, and Mark Andrews.

We then went on to build a second antenna, to try to speed up the process and to give us all some more practice. By the end of the day we had two completed LBA antennas, a group of (hopefully!) well-trained team leaders, and a refined procedure for the main installation. And we're looking forward to getting the other 94 LBAs installed in a few weeks' time!

Admiring our work: Mike Willis, Harry Smith, Martin Bell, and me.

Pictures are courtesy of Martin Hardcastle.

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