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Entry  Thu Jul 15 14:13:01 2010, Megan, Notes, VCO, Matching Model and Measurement ModelMeasuredNoise.pngNoiseAll.fil
    Reply  Thu Jul 15 15:46:20 2010, Frank, Notes, VCO, Matching Model and Measurement 
Message ID: 221     Entry time: Thu Jul 15 15:46:20 2010     In reply to: 219
Author: Frank 
Type: Notes 
Category: VCO 
Subject: Matching Model and Measurement 

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

Quote:

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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