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11th February 2019, 09:09 PM  #411  
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Join Date: Mar 2005
Location: Blaricum

Quote:
But because phase is close to 90 degrees, a bit of noise on the phase doesn't hurt to calculate the imaginary from the complex modulus Z. Maybe it would therefore be even better to measure at 10kHz instead of 3kHz, because at this frequency phase is closest to 90 degrees, giving probably the highest accuracy in calculating L. Hans 

11th February 2019, 09:35 PM  #412 
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Join Date: Jan 2004
Location: Belmont MA

Hans with all due respect this statement is nonsense, the modulus is real not complex and you don't calculate the imaginary from something, you measure magnitude and phase Euler's equation gives you the direct correspondence to real and imaginary part.
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11th February 2019, 10:22 PM  #413 
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11th February 2019, 10:35 PM  #414  
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And with much respect from my side, the magnitude that is measured is Z and is real, being by definition the complex modulus of Z. And yes, with the phase you have to calculate from Z the re and the im magnitude. But the magnitude from im1=Zsin(88 degrees) differs only 0.04% from im2=Zsin(89 degrees). That's why I meant to take a frequency where the phase is closest to 90 degrees as possible, which is the case at 10kHz, getting L with the highest accuracy. Hans 

12th February 2019, 12:42 AM  #415 
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Sorry Hans we just have some kind of terminology problem, complex modulus makes no sense (to me). The modulus (magnitude) is a real number there is no imaginary part. It just makes a layer of translation for me to see what you mean.
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12th February 2019, 12:52 AM  #416 
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The ratio "A/R" turns out to be "problematic" at very low levels for the HP3577  may be owing to the way this 1984 instrument performs the calculation, noise, etc. (I'm guessing you don't have enough "bits" in the low range level.)

12th February 2019, 07:21 AM  #417  
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Quote:
That's true until we add the loss mechanism we are looking for. Then vector isn't 90 anymore so all bets off. I think we do need to measure phase unfortunately. LD 

12th February 2019, 09:58 AM  #418  
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Quote:
Complex modulus  Wikipedia Hans 

12th February 2019, 10:13 AM  #419  
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That would be a shame, when resolution turns out to be the deal breaker. The HP3577 spec's are a bit vague on that, but they mention that at levels between 90 dB to 100dB below Full Scale Input, resolution with 10Hz BW is still +/0.75dB. When taking +15dBm or 1.26V as Full Scale input, 100dB would be 12.6 uV. That is still above the 22uV that I was suggesting with the 40dBm setting + 40dB attenuation with 5K  50 Ohm. So do I make a wrong interpretation of the spec's ? Hans 

12th February 2019, 01:20 PM  #420  
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