Topband: Coax Choke Balun

[Ward Silver]

>> Jim Brown K9YC wrote:
>> 
>> "There is a MAJOR advantage to using a ferrite core -- it makes the 
>> choke RESISTIVE rather than inductive."
>> 
> With respect, I don't believe this to be correct. A ferrite/dust iron cored inductor has exactly the same basic characteristics as an air cored inductor. It has 
> inductance, loss resistance and distributed capacitance.  For a choke (which is another word for a particular use of an inductor) to appear (almost) purely 
> resistive it must be operated as part of a resonant circuit, or be such a poor inductor that the loss resistance is predominant! 
> 
> 73 Roger
> VE3ZI

This depends on the type of ferrite material.  Some are designed for very low loss for use in transformer and inductors.  Others are designed to have significant loss characteristics for use as RF absorbers and common-mode chokes.  This is all laid out quite nicely in Jim's tutorial publications (http://www.audiosystemsgroup.com/publish.htm) and which are summarized in the RF Design Techniques chapter of the 2010 Handbook.

73, Ward N0AX