This was one of the first antennas I built.
This is actually a close up of an alternative method to feed a J-pole, but works as a design in itself, just look at some other J-pole designs and adapt this diagram to it. It is an easy way to attach the s0-239 to one and works reasonably well. Since when i made one using this method I planned to be swapping out my feed line with other antennas I slightly modified the connection so instead of being soldered on it was bolted. To do this I used a small washer and drilled four holes in it to match the mounting holes on the s0-239 and then soldered the washer to where the diagram shows the so-239 connecting. Running the insulated wire through the pipe can be a bit tricky and to keep it easy to swap i simply clamped it onto the J-pole where it meets at point "A" the other end was simply wrapped very tightly around the clamp so I could undo it and feed it back through for removal. This did decrease the performance however.
note: Before soldering the feed to point "A" you might want to use a clamp and slide it around on the antenna a bit to find where you get the best signal.
note2: If you do solder the so-239 to the J-pole and are using one of the cheap ones from a place such as radio shack I suggest you file the "shiny stuff" off the so-239 especially where it will make contact, this will make soldering it to the copper much easier and be carefull with the heat it is easy to mely the insulation on the so-239 during this part if you are not carefull.