[TowerTalk] Measuring Common Mode Choke with Anritsu VNA

[Jim Brown]

Exactly right!  NA6O reported exactly the same comment to me in private 
email. Z is not a single-valued number, it is a variable and it is complex.

I'm currently in the middle of a project measuring chokes wound on the 
relatively new double-sized #31 toroid, and an important thing I'm 
learning is that the "double-humped" curve shape that results from 
dimensional resonance in the range of 3-5 MHz disappears below that 
range. In addition, the loss component also falls at lower frequencies, 
so as a result, chokes wound to cover 160M, for example, exhibit much 
higher Q, and thus much narrower bandwidth. I'm currently looking for a 
different ferrite mix whose loss vs frequency characteristics are 
optimized a decade lower in frequency for use on the LF bands.

73, Jim K9YC

On 1/2/2018 9:59 PM, Jeff Blaine wrote:
> The issue is not the value of the actual Z.  The issue is that the 
> reported peak Z frequency can be very far removed from the true value. 
> Hence the problem.  If you build a monster Z choke but it's narrow 
> banded, then the measurement error (with respect to frequency of the 
> peak) is important.
>
> 73/jeff/ac0c