Problems Paths.
Take a look at the document I included but based and what you are telling me about the outage time and durration it seams that you are experiencing obstruction fading. The example is the second one on page one.
Do this, input the real centerline in in link files. Then go to the terrain data and input a tree and/or building at the controlling points. Use the typical height of the buildings and or trees you would find in the area you are crossing. For example if the path crosses over a banana plantation the add 7 meter trees at the controlling points. If the path crosses over an olive grove add 5 meter trees. If the path crosses over eucalyptus trees then add 30 meters, basically use typical height for typical trees in the areas. Then calculate the clearance and the obstruction fading. If the path crosses over a rice paddy then assume that you will have a layer of water on the ground and look for out of phase reflection points that are visible to both antennas.
Always do a path design with man-made structures, vegetation and cultivation along the links and look for potential problems. Then calculate the impact of the potential problem. If you can calculate a problem then you go out in the field and verify if your asumptions are really there. Let me tell you that along the valley you will find, trees, water from irigation and buildings.
As far as the weather goes the link you provided if for HF and VHF propagation, I don't know if this is applicable in your situation because the ducts they are talking about are high in the atmosphere, keep in mind that your links travel along the ground from 0 to 100 meters and what I said earlier is still true, the links are relatively short and not likely to suffer from ducting.
Let me know what you find and send me the link files with the real centerlines and where you think the trees/buildings are along the links and we can look at them again. Remember that you can see what is along the path by inserting the links in google like I did and then go along the paths and mark down where you cross large trees or buildings.
Let me know.
PS. I had to compress the file a lot to upload it. If you give me your e-mail I will send it directly.
Louie....
