The moment you go above 8 meters (26 feet) the signal via normal omni antennas may be insufficient on ground level for your handheld devices to receive.  Downtilt omni's don't cover the same horizontal distance at the same height but they concentrate more signal downwards so your usable signal on ground level covers a greater distance. The lightbulb with hat is a nice representation if that hat reflects the light rays downward to make them brighter. ... View more