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Cartridge dynamic behaviour
Cartridge dynamic behaviour
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Old 11th February 2019, 09:09 PM   #411
Hans Polak is online now Hans Polak  Netherlands
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Originally Posted by scott wurcer View Post
We need to look seriously at the sensitivity to model fit. Here is -10% on L and +10% on C. This would be buried in the noise that has been shown so far.
In the table below, one can see what 100% variation of the Cap and 10% variation in L does to the phase at 3kHz and at 10kHz.
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.


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Old 11th February 2019, 09:35 PM   #412
scott wurcer is offline scott wurcer  United States
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Originally Posted by Hans Polak View Post
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|.
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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Old 11th February 2019, 10:22 PM   #413
luckythedog is offline luckythedog  United Kingdom
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Originally Posted by scott wurcer View Post
At least we only need 200kHz or so, HP's accessories will all be intended for the full instrument BW.
This is true. It's well within DIY grasp.


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Old 11th February 2019, 10:35 PM   #414
Hans Polak is online now Hans Polak  Netherlands
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Originally Posted by scott wurcer View Post
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.
Scott,
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=|Z|sin(88 degrees) differs only 0.04% from im2=|Z|sin(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.

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Old 12th February 2019, 12:42 AM   #415
scott wurcer is offline scott wurcer  United States
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Scott,
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.
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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Old 12th February 2019, 12:52 AM   #416
jackinnj is offline jackinnj  United States
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Cartridge dynamic behaviour
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.)
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Old 12th February 2019, 07:21 AM   #417
luckythedog is offline luckythedog  United Kingdom
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Originally Posted by scott wurcer View Post
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.
Hi Scott what Hans is saying is that the real part of Z at 10kHz is << imaginary part. So magnitude of Z tells us what we wish to know ie magnitude of imaginary part of Z.

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.

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Old 12th February 2019, 09:58 AM   #418
Hans Polak is online now Hans Polak  Netherlands
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Originally Posted by scott wurcer View Post
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.
Hi Scott, no problem, but obviously I'm not the only one using this terminology Complex Modulus

Complex modulus - Wikipedia


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Old 12th February 2019, 10:13 AM   #419
Hans Polak is online now Hans Polak  Netherlands
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Originally Posted by jackinnj View Post
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.)
Hi Jack,

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 ?


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Old 12th February 2019, 01:20 PM   #420
scott wurcer is offline scott wurcer  United States
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Originally Posted by luckythedog View Post
Hi Scott what Hans is saying is that the real part of Z at 10kHz is << imaginary part. So magnitude of Z tells us what we wish to know ie magnitude of imaginary part of Z.

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.
Yes I apologize again for mis-understanding. The observed measurements presented sometimes show 10 or more degrees of phase error so direct application of minimum phase theory would possibly miss what we are looking for.
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