Q. Concrete Recommendations?
Our attorney makes us say that a Licensed PE savvy in concrete foundation experience wouldn't recommend specifics without knowing the details such as the type of soil and the wind zone. Then he/she would still need to be comfortable controlling the quality of the concrete and application. In addition, as this is likely a hand-mixed job with a 'who knows what' mixture of concrete, the quality assurance just isn't there. (no offense, of course!)
So, unless you are a Professional Engineer matching this requirement, and/or we don't want to call on our alumni club referral program for a ground-mount savvy PE (it puts them in an awkward place) then we can proceed with a set of general rules of thumb, that may mimic the directions on the Quickcrete bag, that we see work repeatedly for low-risk structures such as the DX Flagpole and DXV's.
As a conservative recommendation, again, for a low-risk structure, most of us handy folks should be able to come up with something serviceable here that works very well.
Here's further reassurance for you.
One of our engineer type friends with lots of experience with DX Flagpoles submitted the following reasonable approach:
"If it were me, as an amateur radio installer, just winging it, I'd go down to Lowes, get the biggest Sonotube diameter they sell (12 inches or 18 inches), dig a hole about a foot deeper than the base section, add some gravel, and some Quickcrete. Dump the gravel in first, then put in the PVC. Stir the Quickcrete with as little water as possible (it cures stronger with less water). Then put the concrete around the PVC. Put a section of aluminum in the PVC, put a level on it, and be sure its plumb. You can tie out the aluminum 3 ways to support it while the concrete cures. Or you can skip the Sonotube and just dump the concrete straight into the dirt too."