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

[Brian Clarke]

Hey Paul,
You're absolutely right. That's what comes of half-remembered truths learned over 
40 years ago - the important details go.
I just had a look at Langford-Smith - he does suggest that one starts with an 
interleaved lam core and then experiment with the air gap to get the correct 
inductance at the low and high dc current points.
Thanks for reminding me!
Love the California sling-off.
73 de Brian, VK2GCE.
  Paul said:

  Hi Brian,

  You might want to recondiser your comments in this post. For a given core, 
  the smaller the air gap, the more quickly the core saturates with DC bias. 
  When the core starts to saturate, the incremental inductance drops... just 
  what happens with a swinging choke.  A large air gap will cause the 
  inductance to remain more constant with DC current. Think of an air core. No 
  change of inductance with current (unless have such a high current that the 
  wire structure moves...not a problem with anything most hams work 
  with..California excluded).

  The Radiotron Handbook is a good reference. For transformers and the like 
  Grossner's "Transformers for Electronic Circuits" 2nd. Edition is an even 
  better reference.

  Hope this is of help.

  73, Paul W9MEH

  My initial but slightly erroneous offering:

  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.