[TowerTalk] VHF beam spacing?

[jim Jarvis]

Folks,

I've got an M2 6m5x,   5 elements on six meters, which will mount on  
a pole-mounted
rotor.  (G1000dxa).    I want to put a small 2m yagi above that.    
Does anyone have a
sense of minimum spacing required?

Obviously, I want to minimize the mast length above the rotor, so its  
a tradeoff between
isolation and physical load on the rotor mast-clamp.

Thoughts?

N2EA