Well... J-poles can be 5/8 or 1/2 wave. The ones I have made are 1/2 wave, and are fed with a 1/4 wave matching stub. I have been told they are essentially end fed Zepp antennas. I have made 4 element collinears that are J-poles, and ones that have a ground plane. Ground must enter the equation somewhere. Glen K4KV