I wonder abt antenna high. How do we count the antenna high? Is it
referenced from the ground, or the roof of a building. Say I put a 3 el yagi
on a mast connected to my roof, apx 5 meters above ground. Does this
distance from the roof to the ground count, or do I have to put it up
another 1/2 wave from the roof top ? Any experience?

Regards
Ken