This only works at low frequencies, well below resonance of the choke
that you've wound. AND -- it only yields the AL value at low
frequencies. Many materials with very different mu and mu' curves have
similar low frequency performance. Common mode chokes are used near
resonance, which is far more difficult to measure accurately.
There's one rather practical way to identify #31 core material with a
simple VOM. Measuring between two points on the core on a medium to high
ohms scale should read resistance values in the range of 50K - 200 K
ohms, because its bulk resistivity is fairly low. Most other materials
have much greater bulk resistivity. This characteristic is shown in a
table on early pages of the Fair-Rite catalog (downloadable from their
website).
73, Jim K9YC
On Mon,5/22/2017 1:08 PM, Don Wilhelm wrote:
Mike,
You may be over-thinking it.
Wrap 10 turns around the core and measure its inductance.
From that data, you can calculate the AL value. Match that AL value
against a chart of the values for various cores.
73,
Don W3FPR
On 5/22/2017 9:30 AM, Michael Walker wrote:
All
I am doing some work on a box of chokes I received and I am trying to
figure out just exactly what mix they are.
I have a tracking generator, so I am trying to figure out a test
jig. Do
I just wrap the choke in fleedline, have a common ground and then use
the
shield of the feedline to feed my signal over looking for the
attenuation
on the receiving end of the generator?
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