An online expert held forth on the design of ferrite chokes and transformers, and to quote one paragraph:
Equally selfevidently we don’t want ANY real part of the reactance in a transformer and, for a practical transformer, we want the self inductance on each side (primary and secondary) to be at least j10*R(Load or Source) and the coupling to be as close to 100% from primary to secondary. It is the real part that heats up transformers a LOT and, since ALL of the current is seen by the ferrite in a transformer, not just the part that got reflected back on the outside of the coax in a choke, losses are abos-posilutely-undubiously NOT desired and the u”R needs to be as close to zero as we can get at the designed frequency for minimum loss and minimum power dissipation.
Setting aside the hyperbole and the wooly thinking, let’s drill down on u”R
needs to be as close to zero as we can get at the designed frequency for minimum loss and minimum power dissipation.
It is a pretty general statement without really specific quantities, needs to be as close to zero as we can get
and minimum loss and minimum power dissipation
does not give useful guidance of acceptable values of µ”, and may even impart the impression that the following chart is for material that is not suitable above perhaps 200kHz, if that.

Above, µ” is greater than 10 above about 200kHz, greater than 100 from about 2 to 100MHz. Is this what the quote condemns? Continue reading Selfevidently
Last update: 10th March, 2022, 9:45 AM