Re: [TCML] Measured Q vs. Predicted

[Ed Phillips <evp@xxxxxxxxxxx>]

I recently acquired a nice LCR meter.  This meter happens to measure Q
factor.  I was noticing that there is a huge discrepancy between the
measured value and predicted value.  I was hoping you might be able to shed
some light on this.  Lets take my secondary as an example.  This is for the
bare secondary, no topload.

Predicted:
---------------------------------------------------------------
39.7637 Ohms = DC Resistance
19.131 mH = Ldc-Low Frequency Inductance
246 = Q

Actual
---------------------------------------------------------------
38.99 Ohms = DC Resistance
19.487 mH = Ldc-Low Frequency Inductance
2.785 = Q

Now this secondary is probably not the best secondary in the world, but it
certainly is not the worst.  Is there a reason why my measured Q is so much
lower than that given by JAVATC?"

    How does the meter measure Q?  At what frequency?   Seems to me the predictions and measurements agree remarkably well for the resistance and inductance since you don't necessarily know the dimensions of the coil accurately.  The Q is the ratio of the reactance of the inductor to the series resistance and hence is frequency dependent and unless you can control the frequency of the measurement the Q value is useless.

Ed


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