Are you suggesting that Fair-Rite's published data for this part is wrong?
Fair-Rite's data is correct.
In extensive measurements of certain of their parts, I've not yet
seen that.
I wouldn't know why. I've been using these parts since they first came out.
Prior to that I made my own out of 73 mix shield beads. I measure everything
I do.
I stand by my comments.
Your comments are incorrect.
That particular core material is primarily inductive below about 2.5 MHz,
the exact frequency varying with batch and core style.
Around 2.5 MHz, reactance and resistance becomes equal. In that particular
core, depending on batch, reactance of one pass is about 4.8uh or +j75 ohms
and resistance 75 ohms for a combined impedance of about 106 ohms at +45
degrees. Q is unity.
Looking for Q=unity is how I sort unknown cores, and verify new unmarked
cores. (I've had Krieger and others ship mixed parts.)
As frequency increases Q decreases. At some point, in this case around 10
MHz, Q is zero as the core transitions from inductive to capacitive. Above
that, core behavior is the same as if diamagnetic materials were used.
This behavior makes a transformer broadband, as opposed to an air core that
goes through a "real" resonance with high Q. The designer can use enough
turns for adequate impedance low in frequency, while avoiding winding
resonance at some much higher frequency.
What you call winding "resonance" and predict will move around significantly
with number of turns is actually the frequency where the core no longer
exhibits magnetic effects. If you wind one turn or five turns, the frequency
where the reactance changes signs will barely moves. Similar is also true
for the Q=1 frequency.
I suggest you (or anyone else) build, measure, and proof some transformers.
We can have winding resonances, but resonance requires a core have magnetic
properties on the frequency of resonance. We can't go several times the Q=1
frequency (where u' and u'' have crossed) in that core material and expect
we are seeing a winding resonance.
Please, let's not tell people one of the best cores to use (that hundreds
seem to already know is true) is the wrong choice. My first article using
this material core was published around 1980, and I was making them out of
beads for myself long before then. I always thought air core coils for
things like reversible Beverages was a bad idea for the 1970's.
73 Tom
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
|