I'm sure this has been answered multiple times before but rather than chide you for not searching, here is the process:
I like to start all parts with default datums then offset as many as needed to define the overall envelope. In this case, I would have a top and a bottom that correspond the the finished ground length.
The first solid feature is a helical sweep with variable pitch. The first sketch is just a straight line that extends from .75 wire diameters below the bottom datum to .75 diameters above the top datum. Sketch additional points along this line so you can control the pitch. The pitch has to start and end equal to the wire diameter fro the closed ends then transition to the effective pitch diameter then be constant before transitioning back down to the wire diameter. The second sketch is just the wire diameter.
Once you have the helical sweep just do a revolved or extruded cut to trim the ends. You will end up with a 270 degree witness on the ends.
