Calculating and Measuring Resonant Frequency / Inductance of Secondary Coil (magnifier)

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: dhmccauley-at-spacecatlighting-dot-com 

In the midst of my magnifier design, I came up with a discrepancy.

Secondary Coil Specifications:
Coilform Diameter:  16"
Wire Gauge:  14 AWG (0.064" wire diameter)
Turns per Inch:  9T (based on my finished magnifier)
Winding Length:  24"

When I calculate the inductance and resonant frequency of my secondary coil
(in magnifier coil) using either calculations, or TeslaCad, or WinTesla, I
get the following
numbers:

Inductance:  9.76mH
Fres:  365kHz
****************************************************************************
*
Now, when I measure this secondary coil using an Impedance Analyzer, I get
the following:

Plot of Impedance vs. Frequency
http://www.easternvoltageresearch-dot-com/images/mag1_sec_response.jpg
(Note:  Top vertical line of graph is 14mH and each vertical division is
2mH)

 >From graph, the flat portion of impedance curve is about 9.5mH which
corresponds to what I calculate.
However, when impedance is minimum (-2mH), the frequency is about 606kHz.
I'm using this minimum impedance point as
where the resonant frequency occurs.

These frequencies don't match one another, yet I would expect them to.  Am I
missing or doing something incorrectly here?
(The secondary coil was placed directly across the two probes of the
impedance analyzer when measuring.)

Thanks
Dan