I know its not an approved method but when I use a larger pole like the OP had in the picture, I cut off a straight piece of the smaller mast about a foot long, stick it into the larger mast, and run a minimum of two large bolts with nuts completely through the entire thing perpendicular to each other using a drill bit first for the hole. I then tighten both until the larger mast is basically crimped against the smaller one on all 4 sides. Again, not approved but extremely sturdy.
I know its not an approved method but when I use a larger pole like the OP had in the picture, I cut off a straight piece of the smaller mast about a foot long, stick it into the larger mast, and run a minimum of two large bolts with nuts completely through the entire thing perpendicular to each other using a drill bit first for the hole. I then tighten both until the larger mast is basically crimped against the smaller one on all 4 sides. Again, not approved but extremely sturdy.

The wire from the top of the clamp goes to top of dish to tension it to keep it from flexing. This dish has been know to deform a bit when it would get hot. So the wire just helps to reduce that problem.