ds,

Such coils are typically used in crystal radio receivers for the MW bands. High Q allows good system efficiency, which is important when only the energy being collected by your antenna system is available to drive the speaker allowing you to hear the signal.

Alternative technologies make this largely an exercise in geekiness. Some do it as a technical challenge, others as for historical recreation. I did it largely as a study of the physics of inductors.

Regards,

Alan

I am curios about the "purpose" of the coil once constructed. I am not a scientist. thanks in advance

Arv,

I've got some T200-0 cores (tan/natural phenolic material, mu ~ 1) I picked up from Kits and Parts but haven't found a use for yet. I'll have to give it a try, but yes that makes perfect sense from the geometry.

Winding toroids is a bit of a pain for a large number of turns. The commercial toroidal winders are very interesting machines, with an annular bobbin that carries the wire. The ring can be broken to insert the core then closed again, filled with wire and then reversed to spin the wire off onto the core. Check out the videos on YouTube of them in operation if you haven't seem them before. You could build something similar for manual use out of a piece of plastic channel section (maybe metal if it was flexible enough to be bent without fracturing).

Regards,

Alan

Alan

Another "reduced capacitance" type inductor is one which is wound single layer on a fairly large diameter torus. Since the center circumference is smaller than the outer one, the windings are naturally spaced a bit apart on the outer part of each turn. Of course larger wire diameters work better than smaller ones.

Arv

_._