we replaced U9 by an OP27 instead of AD797. The replacement AD797 and AD829 were oscillating at 12MHz and larger .
So if you replace U9 by an OP27in your model the noise will be slightly higher at high frequencies.
Did you subtract the instrumentation noise from your measurement @TP7?
If not then do it.
As far as i remember the noise level of the DAQ/preamp is/was about 4nV/sqrt(Hz). I guess the simulation will then match your measurement 
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Thanks, I modeled the LM336 and get almost the same measured curve at low frequencies. I'm on my way over to 40m in a matter of minutes to remeasure the noise with a lower noise amplifier to see if the entire curve can fit. I also have the model attached - the strange graphing frequencies were to match the ones I got with the measured data. I am also going to double-check the opamps used in the circuit currently. I already verified the resistor values - only R18 was incorrect (1k instead of 390).
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