I have observed this phenomenon as well but it seems
to be mainly an issue with beads or shapes with small
holes. The bead magnetizes from the inside out.
Larger "toroids" with sizeable center holes don't magnetize
as easily. This make sense physics-wise since Ampere's
law says H is inversely proportional to radius.

Rick N6RK

"J M Noeding" wrote in message
...
Reposted due to changed URL

Hi
have noted the following measurement (from LA7MI) forAmidon
FB43-4301, and wonder if someone knows more available data for actual
ferrite- and iron-powder cores to be used in transmitters?

For a Amidon FB43-4301 the inductance drops by 50% for 1.2At. 3At for
75% reduction. One should keep the DC-current below the value of 0.5A
to keep the reduction below 0.5. In the example above this rule is
used, but the best is to use push-pull arrangement and the DC
magnitation is kept to a minimum level. The inductance reduction is
stored and the effect is called remanence, cores used for direct
current should have air-gap

Will write a page - http://www.noding.com/la8ak/12345/n12.htm (changed
URL) for constructing RF power amplifier based on an article written
by LA7MI and distributed to a local London radio club in 1992

73
Jan-Martin
LA8AK
http://home.online.no/~la8ak/c.htm