[Elecraft] Vertical Beam Spacing

[W4YN@ARRL.Net]

I would suggest reading the ARRL antenna book. Usual spacing is 1/2 of
the length of longest element. 72 feet above ground is fine for 20
meters but for 40 and 80 you will have more radiation going up than
out! Also read the tower manufactures specs about derating tower load
as height above tower increases. Snow and Ice loads can easily double
weight and increase wind load dramatically. Check with antenna
manufacturers. 
73 Tim O'Rourke W4YN