Topband: measuring transformer core inductance

[Richard Karlquist]

> I wouldn't want people to think this is a big problem with all cores, or
> even most cores we use. In my experience, this is a non-issue in the soft
> iron cores we normally use at higher frequencies.

The very popular Fair-Rite 43 is not immune from 
magnetization, as I have tested it.  I suspect
73 is at least as bad.  The issue comes up for
me because I use DC in my system to switch relays.
If the relay DC passed through the transformer due
to a short or wiring error, I can't just fix the
problem and ignore the possible core damage.
Also, the RF chokes used to feed the DC into
the coax cannot be wound on non-gapped ferrite
cores, like toroids.  I see this all the time
in commercial equipment supposed designed by
engineers.  My favorite is RF amplifiers that have
beads on a DC feed with 20 amps going through it.

Rick N6RK