[Elecraft] Toroids frequency range and baluns

[Jim Brown]

On Sat, 27 Sep 2008 09:21:11 -0600, James Duffey wrote:

>"Why are choke baluns wound as a coil vastly superior to choke baluns  
>made with a sting of ferrite beads? With the coil type, you're adding  
>additional coax loss... What am I missing here?"

>I didn't see an explicit reply to this on the list, 

In the interest of brevity on the list, I referred those interested in 
this to the tutorial I wrote on RFI and the use of Ferrite Chokes. That 
material is anything but brief, but I believe that it is quite clear 
and easy to study IF you understand the fundamentals of electrical 
circuits that include R, L, C, and Z. 

>but the short  
>answer is that with a coil balun, the inductance increases as the  
>square of the number of turns. With the beads, the inductance just  
>increases as the number of the beads. 

YES

>So, ignoring stray capacitance,

You CANNOT ignore stray capacitance, it makes a VERY major contribution 
to the behavior of ANY choke. 

>a toroid with 10 turns will have 10 times the inductance of the same  
>cable passed through 10 toroids (beads). You get more bang for your  
>buck by coiling the cable. The additional losses are not too great for  
>most applications.

YES.

BUT -- it is NOT about INDUCTANCE, it is about the RESISTIVE component 
of the impedance. And that RESISTANCE is the loss component of the 
parallel RLC circuit formed by the inductance of the choke, the 
capacitance, and the loss coupled from the ferrite core. It is the 
RESISTANCE that solves our problems, NOT the inductance. We use 
inductance in TRANSFORMERS and in resonant circuits that are part of 
radios. We use RESISTANCE in RFI suppression and in common mode chokes.

The tutorial is at http://audiosystemsgroup.com/RFI-Ham.pdf

73,

Jim Brown K9YC