Topband: Recycled ferrites for 160m

[Jim Brown]

On Wed, 21 Jan 2009 09:23:29 -0500, Dan Zimmerman N3OX wrote:

>If you have an antenna analyzer you can get a decent idea of how the thing
>works by winding a few turns of wire onto the core and measuring the
>impedance of that.   Shooting for a total impedance around 50 ohms is useful
>for something like the MFJ-259B which is more accurate around 50 ohms than
>way out in high and low impedance land.

YES.  One VERY important caution. Antenna analyzers typically have stray input 
capacitance on the order of 10 pF!  The equivalent circuit of a ferrite choke is 
a parallel equivalent circuit, and for most chokes the capacitance will be half 
that value. Thus, the analyzer can introduce considerable error. 

I suspect that the ferrite parts you are talking about are MnZn materials. If 
they are, they will probably have a strong dimensional resonance in the region 
between 0.5 MHz and 2 MHz. Study the data in my RFI tutorial and the data for 
ferrite materials and parts in the Fair-Rite catalog. 

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

Fair-Rite is http://fair-rite.com   Follow the bouncing ball to their on-line 
catalog, which is extensive and excellent.

73,

Jim Brown K9YC