ALOS, or line of sight, means just what it says - antennas can see each other. It does not mean that you can see a sparse outline of the target building through a forest of trees, or that you know where the building is even though you cannot actually see it.

For longer distances, clearance above objects at the center of the transmission path becomes important. The center path of the signal would be found if you were to imagine taking a string and connecting the antennas end to end. Clear line of sight includes clearance below the string and above all objects so that the radio signal can propagate without reflection over the path. A rule of thumb is to have 12 feet per mile of clearance at the center of the path between the two points you are connecting.

How can you obtain line of sight? The best way is to get on top of the building and look before you buy. Most often, if you can see the building or part of it, there is a way to obtain line of sight. Poles or towers can be installed, or you can hop to a structure that is a high point that can see both buildings to repeat the signal. In many cases permission to mount an antenna is only a phone call away.

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