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
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