Friday 13 July 2012

LBA trenching plan

One of the problems with building the LBA is dealing with the non-uniform arrangement of the aerials. As each aerial requires two cables, and these cables need to be buried to protect them, a detailed trenching plan needs to be worked out ahead of any digging operations.

On the morning of 10th July 2012, Mikko Tilja and Derek McKay-Bukowski took to the field with pen, paper, spray paint, field markers, templates, documentation and a lot of patience to devise a trenching plan. This is a non-trivial problem and there are lots of constraints such as:

  • Minimise lengths of cables required (we are cable constrained),
  • Avoid all anchor pegs (which are required to secure the aerials),
  • Avoid all survey pegs  (required for aerial placement),
  • No cable crossings (which cause deployment complications),
  • No more than 5 cable pairs per node (due to conduit capacity),
    Nodes cannot be placed under grids (for access),
  • Avoid tight cable bends (to protect the cable RF-integrity),
  • Keep a good distribution of the entry/exit points on each node,
  • Minimise the number of nodes (to conserve pipe),
  • Minimise the number of trenches (to conserve our morale), and...
  • Devise the plan in less than 2 hours!

However, despite these restrictions, we still managed to devise a good plan. The following is the plan schematic (click on the image for an enlargement).

The black dots (with white numbers) are the nodes. Each one has an access hatch, to allow the cables to be drawn. The shading is to help visualise the node sectors. The small black dots are the pegs (2 × survey pegs and 4 × corner anchors). Work has now begun on the trenching.

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