Sunday, 8 July 2012

LBA field levelled and surveyed

The Low-Band Antenna array field has now been levelled. The next stage is then to mark out the location of the aerials. The aerials are scattered about in a 40-metre diameter circle. The scatter pattern is not random, even though it looks like it. The reason for this pattern is to improve the beam-shape of the sparse array. By spreading out the aerials, you can increase the resolution, but you need to do so carefully to avoid aliasing effects (called side- or grating-lobes) from becoming problematic.

The layout that we are using is modelled closely on that of the inner configuration of a Dutch Remote Station ("RS"). The two outlier antennas are brought into the array and two additional calibration aerials will be installed later. Although it looks like some of the aerials overlap, it is actually on the ground planes that intersect. The aerials themselves at the array centre are close-packed but do not physically interfere with each other.

Design of the KAIRA LBA layout. (D. McKay-Bukowski & J. Vierinen).

Each position has two survey pegs. The first at the northern edge of the aerial ground plane defines the position. The second constrains the rotation. We'll discuss this in a later web log post.

One of the survey pegs on the LBA field. Photograph by Arttu Jutila.

These survey positions were provided to a survey company who completed the layout of the pegs.

Marking the GPS points was finished rather quickly thanks to the GPS specialist.
This is a view of the LBA field taken on top of a HBA tile. Photograph by Arttu Jutila.

The next stage on the LBA construction is the installation of the cable trenching and ducts. However, there is also a lot of HBA work about to start up. Keeping up with the web log is always a major challenge over the busy Arctic summer build season. But there's lots to follow so do make sure you visit regularly and keep up to date with the progress.

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