amdx wrote:
Hi All,

Info below from the following site----
http://www.ee.surrey.ac.uk/Workshop/...x.html#bhcurve

Unlike electrical conductivity, permeability is often a highly non-linear
quantity. Most coil design formulæ, however, pretend that it is a linear
quantity.

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My question is-

If I wind a transformer using the specified A sub L and then use that
transformer in a receive antenna where the voltages are very small, wouldn't
I be low on the curve and cause the transformer to function poorly
especially at the lowest frequency of the design?

Mike

PS Thinking about a Flag antenna, which has a small output signal.

Al is usually the value for low flux density. That is, it's the value
you'll have when the flux level is low. Permeability will drop from
there at high flux levels.

If you're making a broadband (untuned) transformer, you only need to
insure that the winding impedance is high enough. If you design it to
have adequate impedance at the lowest frequency, you should be ok for
frequencies above that. If you're making a tuned transformer, you'll
probably be using either powdered iron core or a ferrite core with a big
air gap in the magnetic path like a ferrite rod. Either will withstand
many orders of magnitude of flux density above what a received signal
will produce before there's any noticeable change in permeability.

The assumption of constant permeability is often a reasonable one.
Change in permeability with flux density is certainly nothing you have
to worry about in a receiving application unless you've got a lot of
turns and a lot of DC current in the winding.

Roy Lewallen, W7EL