Six years ago I needed to non-destructively reverse engineer a multi-tapped toroid inductor for an Ampeg SVT preamplifier clone that I was building.
Starting with the inductor's nominal inductance, the physical diameter of the magnet wire and the dimensions of the wound inductor, I was able to determine the ferrite material and standard core size, the length of wire, and winding recipe without disturbing my sample of the factory part.
All of this was for an audio frequency application, so the RF properties were not relevant. However, it was satisfying that my DIY inductor worked as expected, and I was able to determine the unknowns in the recipe with simple algebra.
Starting with the inductor's nominal inductance, the physical diameter of the magnet wire and the dimensions of the wound inductor, I was able to determine the ferrite material and standard core size, the length of wire, and winding recipe without disturbing my sample of the factory part.
All of this was for an audio frequency application, so the RF properties were not relevant. However, it was satisfying that my DIY inductor worked as expected, and I was able to determine the unknowns in the recipe with simple algebra.
I documented my build story here: http://www.frontiernet.net/~jff/SonOfSVPCL/DIYSVTBassPreampI...