Total posts : 45366
“I have had far better luck with iron powder toroid and rod rod core wound inductors than with air cores. Others the opposite experience.”
I guess I’ll have to experience it for myself someday. The problem I believe I see with most air core loading coils is that the wire and core materials are two small, and/or the core is too conductive.
I went with insulated 18 AWG stranded wire, which seems to have the characteristics of spacing the winds by 2x insulation thickness (one on one wind, plus on on the next, excepting the end winds) on white 4″ sewer core, which is much thinner wall than schedule 20 PVC.
The combination seems to have less resistance than smaller gauge wire, stranding and decent wind separation for fewer and more diffuse eddies, 1/2 the material conductance of sch 20 PVC pipe, and larger diameter (more “air” and fewer winds, which I think may also reduce eddies), and seems to work very well. I did some estimates and massaging of the formulas to come up with what I thought should be the correct number of winds for my frequency, further reducing anomalies which may be associated with extra winds needed for a more generalized coil with taps . It’s still a lot harder to tune to peak resonance, though. However, I’m thinking a large multi-leaf variable cap with very limited range could fine tune with little penalty. Anyone happens to run across one with say 0-10 pF, don’t be shy.
One other thing to consider … great AM radio depends on great grounding/counterpoise techniques. A really good ground setup can cover a multitude of ‘RF sins’ 😉
As much as I’d like a wee bit more power with a mite fewer restrictions, I admit it’s been great fun because of dealing with those challenges. Gentlemen (say, BTW, where are the ladies of Part 15?), I tell you we have we have attempted to govern puny amounts of physical forces and still created great miracles 😉