[Boatanchors] is it a Choke or a Filter Reactor?

[Brian Clarke]

Yes, the inductance of a swinging choke varies with the level of dc carried. To do 
this, it has a larger air gap than a fixed inductance choke. To achieve a nominal 
inductance, therefore a swinging choke has to be bigger than a fixed choke 
because of the extra reluctance of the deliberate air gap.  In reality, the 
inductance of all iron-cored chokes varies with dc current.

So, the simple test is to measure the inductance [an ac test] while varying the 
dc carried. Isolate the inductance measuring device with a capacitor and allow 
for its reactance in the calculations.

A good oldie-goldie reference is Fritz Langford-Smith's 'The Radio Designer's 
Handbook', aka 'The Radiotron Designer's Handbook'.

73 de Brian, VK2GCE.

Glen asked:
  "Is there a sinple test to tell you how to distinguish
  between a normal power supply choke vs a Swinging choke"?   I am under the
  understanding that a swinging choke, has more fun, is wound differently than
  a nomal reactor. The reactance varies according to the current flowing
  through the inductor. Hope to hear from some real techno wizards.  Also, is
  there any reference reading on the subject.