Owen Duffy wrote:

The '259B is no doubt a handy device, but very limited for measuring
components. Have you tried to measure at an inductance that has more than
250 ohms of reactance at some frequency of interest? Have you tried to
explore self resonance of a coil..., invariably it runs into the same
problem of inductive reactance going off scale way below the point at
which self resonance bites in.

When talking about ferrite or powdered iron cored inductors of reactance
over 200 ohms, where mu is frequency dependent and flux dependent, I find
the '259B nearly useless.


I've had just the opposite experience. I find the 259B to be extremely
useful in determining ferrite types and the impedances of inductors.
Generally a single "turn" (pass through the hole) is adequate for
measurement. For most toroidal inductors the impedance is closely
proportional to the square of the number of turns, so the value of
multi-turn inductors can be extrapolated with reasonable accuracy. Of
course, two or three turns can be used for measurement if the unit can't
resolve the impedance of a single turn.

The frequency dependence of the mu and loss is just why the 259B is so
useful -- I can find the impedance at the frequency or range of
frequencies it'll be used at.

I very seldom design magnetic components for applications where flux
density noticeably alters the impedance. If the signal is so large as to
permit this to happen, you'll be generating serious harmonics and, if
multiple signals are present, intermod. If the saturation is being
caused by DC, it's often possible to bias the core with the same current
while making measurements. And I've never hit a powdered iron core with
enough signal or DC to get anywhere near saturation. They tolerate much
higher flux density than ferrites.

I'd really feel handicapped in designing baluns and wideband
transformers, in particular, without my 259B or something similar.

Roy Lewallen, W7EL