I did try and did not find how to tie this knot/hitch. The included instructions leave a bit to be desired for me to understand. Does anyone know the name of the strain relief knot to tie the radiator wire on to the dipole body?
I don't think that's a knot. Alpha Delta typically uses solid wire for their antennas (which can be a PITA). I believe that they are showing the wire stuck through the hole in the center insulator and then tightly wrapped around the incoming wire 3-4 times. With solid wire, the resulting connection is reasonably secure.
I've done the same kind of wrap/knot on some of my antennas using stranded wire. I just wrap it four times and on the last turn I pass it back between and pull it tight. Then I measure the distance of both wires back to the connectors and cut them the same length before I put the terminals on them. I've never had one come loose.