[TowerTalk] Elevated Radials

[Bob Maser]

Does anyone on this reflector have a source of information regarding using 
elevated radials with a ground mounted 1/4 wave vertical?  My Hygain Hytower 
is at ground level but I would like to put 4-5 elevated radials up about 10 
feet on it.  How is the coupling between the radials and the feedpoint of 
the vertical achieved and how are the lengths of the radials calculated?

Bob Maser  W6TR