"Roy Lewallen" wrote in message
...
Larry Benko wrote:
Roy Lewallen wrote:

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.


Not to nit-pick but the permeability of nearly all powdered iron
formulations actually rises with increasing flux levels (AC) and then
falls off. For #26 material (u=75), the effect is very much exagerated
with the permeability increasing nearly 300% at ~5000 Gauss and then
falling very quickly. However the permeability does drop for any value
of DC bias current and larger DC bias currents produce greater
reductions in permeability.

73, Larry Benko, W0QE

Thanks for the correction. The permeability monotonically drops with
increasing coercive force (H), but rises as you say with increasing flux
density (B) over some range of flux densities. This is true for ferrites
also.

Roy Lewallen, W7EL

Please see the following URL Page 6,
http://www.mag-inc.com/pdf/cg-01.pdf
note the graph for the toroid, the inductance decreases by 40 percent
going from 2000 gausse to 10 gausse.

Question 1.
I don't know where on that graph the published permeability would set the
inductance. ( to clarify--How many gausse is used to measure permeability
and set AL?)
Question 2.
Can anyone take a stab at how many gausse in a typical FT140-43 toroid
with 8 turns on the secondary, and 34 or 35 turns on the primary used on a
flag antenna with a low level signal.

Maybe if we have two points on that graph we can have a real number to
see how much inductance changes from published AL at low gausse.
Mike

PS. interesting how pot cores have very little inductance change with
changing gausse.