[Antennas] Collinear dipole info

[Mel Vance]

I am going to ask what will seem to be a very stupid question......

I have several antenna books....all talk very little about collinear dipoles.

Ounce upon I time, I knew how adding the phrasing sections and 1/2 wave elements to a 
dipole affected feedpoint resistance and reactance...but can not recall the effect....

Anyone recall the effect?

Anyone know of a good website that explains it?

Anyone know the formulas to calculate the changes?

Any help from anyone?

Mel
N7OKL