[Elecraft] K2 Toroids not measuring correct inductance?

[Jim Brown]

On 6/1/2011 10:20 AM, rhapak wrote:
> I notice that many of my toroids do not measure near the stated inductance
> in the parts list but are wound with the specified amount of turns and would
> just like to know why??

In addition to the tolerance variations Eric mentioned, the measurement 
frequency also matters.  Ferrite and iron core materials do not exhibit 
pure inductance that is constant with frequency, there's also resistance 
from the core, and capacitance between the turns and the core, and 
between turns.

There's a discussion of this in my RFI tutorial, which has been 
incorporated into recent versions of the ARRL Handbook.  While my work 
has been dedicated ONLY to ferrite materials, powdered iron cores must 
follow the same laws of physics, but with different physical parameters 
-- that is, different values of mu, R, and C versus frequency.

73, Jim Brown K9YC