[Milsurplus] Triad Choke

[Richard Brunner]

Thoughts on Swinging Chokes:  The only difference between a "standard"
choke and a swinging choke is the size of the air gap in the core.  Less
gap, more swing.  Think of the magnetic circuit in the core as analogous
to voltage drop in Ohm's Law.  The magnetic core has high permeability,
requiring few ampere-turns, and the air gap has no permeability
requiring many ampere-turns.  Thus, with a large air gap in the core
most of the ampere-turns are in the air gap, making it less sensitive to
dc, and there is not so much change in inductance as dc flows through.
With the small air gap, more magnetic flux is possible because of the
lower reluctance of the magnetic path, and the iron part tends to
saturate more quickly, causing the inductance to swing at high dc
currents.  Does that make sense?  FYI, it's hard to calculate
performance because of magnetic fringing at the air gap.

I have found that marked choke inductance is only nominal, and can vary
significantly depending on how well the core was put together.
Fortunately it seldom matters.

Richard, AA1P