| There was considerable debate as how to
best earth the towers, and in particular the main 100' tower. It was highly likely that the tower would be struck by lighting, but the problem was the poor conductivity of areas like Tic Hill, that are mainly made up of rock and gravel, none of which is a good conductor. Just hammering in a ground stake may not do much, so it was decided to measure the ground conductivity. There is a standard way to measure ground conductivity by measuring 3 different earthed points to a single reference point, and then using a maths formula, the ground conductivity per metre can be calculated. This was done and the results were open circuit. There was no ground conductivity between earth rods pounded into the rock / gravel. The biggest problem was finding enough points just to get the ground stakes in. Two stainless steel ground rods were hammered into the tower trenchers and the conductivity measured. Once again open circuit as measured on a multi metre...! So was there any point in grounding the towers.....? WARG had been donated several stainless steel earth rods and it was decided to use them anyway, even though obtaining a real earth connection to earth was seen as impossible. However at least when the tower is hit by lightning it would travel down the tower and into the ground. After all it has to go somewhere. There was concern that without at least some "earthing" the concrete might be fractured with lightning strikes.  VK6RTH
tower earthing
The donated earth rods could be connected together and as luck would have it, where a Black Boy had been growing in the trench for the main tower, the earth rod could be driven into the ground for at least 3 to 4 metres. All legs were grounded, with one having the 3 to 4 metres into where the Black Boy had been growing. There must have been a fracture in the rock, and the Black Boy had taken advantage of this. So just how well this earthing is, is unknown, but it was all that could be done. I don't know if the shack rack was grounded to this but it was intended to do so. |