On Sun, 4 Jan 2009 18:54:37 -0500, Dan Zimmerman N3OX wrote:
>I think you'd find it hard to measure the difference even with good lab
>equipment.
Ferrite chokes are VERY difficult to measure with reasonable accuracy.
Some of the difficulties and a couple of good measurement methods are
described in the tutorials on my website. The principal reason is their
high frequency equivalent cicuit, which is a parallel resonant circuit
that has very small values of capacitance, and a fairly large
resistance.
Fair-Rite, the mfr of nearly all ferrite parts sold to hams, has always
had a great catalog, available online in pdf format. A little over a
year ago they significantly upgraded it by adding multi-turn impedance
data (for 1-3 turns) for many of their suppression parts. This data
doesn't get you down into the HF range, but it does clearly demonstrate
how inductance, loss from the ferrite, and stray capacitance combine to
move the resonance down from around 200 MHz to the upper HF range.
73,
Jim Brown K9YC
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