I currently use a homebrew 40/60/80m vertical consisting of a 5M aluminium tube with a multi tapped coil at the base. The ground plane is the metal roof at my house, and the antenna is not centered in it, but it's next to one of the edges.
I read that for center loading, the coil needs to be twice as big as for base loading. So I was thinking of adding another 5M length of aluminium tube and raising the loading coil to the center of the antenna. Since the required coil will be twice as big, but the antenna is now twice as long, the coil will be the same.
What I'd like to know is if there will be significant benefit of center loading the antenna, considering the hassle of raising a 10m tall radiator with a coil in the middle.
Also, how is the radiation pattern affected by not centering the antenna in the ground plane?