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Old 21st December 2012, 11:16 AM   #21
KSTR is offline KSTR  Germany
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Elvee,
please have patience, I'll come to normalization at the point when it really becomes a must. As can be seen in post #2, there is not that much to normalize out (flat up to 20Mhz), especially with 50dB vertical scale, also I left it off exactly to show the (small) effect of the jig.

Metalsculptor,
my NWA is a 75 Ohms system so the estimated mismatch to the TP won't be that much. The length of 1ft. was chosen with some care and from the impedance plot of it I see that it's still in the lumped, "electrically short" region dominated by the inductance, no sign of cable reflections ("comb filter" shape of the response) in the impedance is seen, up to the displayed freq. range of 10MHz. I did see these, though, when I attached an unterminated length of 10m 75R coax.

Last edited by KSTR; 21st December 2012 at 11:18 AM.
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Old 21st December 2012, 12:16 PM   #22
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by KSTR View Post
Elvee,
please have patience, I'll come to normalization at the point when it really becomes a must. As can be seen in post #2, there is not that much to normalize out (flat up to 20Mhz), especially with 50dB vertical scale, also I left it off exactly to show the (small) effect of the jig.
You'd be surprised. And once you taste it, you will ask yourself how you could dispense with it. Even at relatively low frequencies.
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Old 21st December 2012, 12:28 PM   #23
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BTW anybody reading own or has experience with a Bode 100 from Omnicron Labs?

jan
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Old 22nd December 2012, 01:20 AM   #24
gootee is offline gootee  United States
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Quote:
Originally Posted by KSTR View Post
Elvee,
please have patience, I'll come to normalization at the point when it really becomes a must. As can be seen in post #2, there is not that much to normalize out (flat up to 20Mhz), especially with 50dB vertical scale, also I left it off exactly to show the (small) effect of the jig.

Metalsculptor,
my NWA is a 75 Ohms system so the estimated mismatch to the TP won't be that much. The length of 1ft. was chosen with some care and from the impedance plot of it I see that it's still in the lumped, "electrically short" region dominated by the inductance, no sign of cable reflections ("comb filter" shape of the response) in the impedance is seen, up to the displayed freq. range of 10MHz. I did see these, though, when I attached an unterminated length of 10m 75R coax.
Klaus,

Any RF engineer would probably immediately make the same point as Elvee. It is such an ingrained habit, to "calibrate-out" everything but the DUT, every single time a network analyzer is used, and every time the frequency range is changed, etc, etc. (Of course, it's easier when you're working with DUTs that have RF connectors on them.)

Tom
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Old 22nd December 2012, 01:32 PM   #25
KSTR is offline KSTR  Germany
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I tried with and without, Tom, and there was close to nil changes seen with the measurements I did so far. Parameter settings proved to be more important with the analyser running almost it's full freq. span. I'm still learning there but making good progress.

Today I might continue experiments (this time checking a group-delay thingy of a rather esoteric tool named "Gabor-Link", where normalization of mag and more importantly phase is mandatory).

ATM the analyser is in "maintenance mode", though, partly disassembled as I need to replace the old and fully rotten NiCd backup batteries with a 3.6V Lithium cell -- disabling the recharging of course.
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Old 22nd December 2012, 03:02 PM   #26
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Quote:
Originally Posted by jan.didden View Post
BTW anybody reading own or has experience with a Bode 100 from Omnicron Labs?

jan
The lowest impedance I could measure with the Bode 100 is a milli-Ohm. With the AP I can measure to less than a micro-Ohm (which is pretty academic IMHO)

The Bode 100 will render "unwrapped phase" if you select. You can also attenuate the generator outputs, attenuate the inputs. It comes with a wide-band transformer, but the "current sources" with which to measure Zo and Tg are additional. With Tg you can measure the stability of 3 terminal regulators for which you can't access the feedback loop.

I have 3 analyzers, only the Bode was purchased new. I bought several Stanford Research units during the dot-com bust and sold all but one for a nice profit. I have an HP3577A with the S-Parameter test set as well.

Wandel & Goltermann -- if it's programmable via GPIB there are a lot of neat things you can do which make life simpler.

Folks should look for Christophe Basso's papers on loop compensation -- he's already written two text books on the topic and much of his material can be found on the web. Omicron Labs also has a number of application notes and videos on their website.
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Old 22nd December 2012, 03:54 PM   #27
KSTR is offline KSTR  Germany
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Jack,
GBIB is installed... but haven't checked it yet, need to order a USB-2-GBIB interface (or at least a plot grabber) first.

I haven't tried imp vs freq measurements with the AP Sys2 yet except for a quick check hooking up a speaker driver, if I wanted to go micro-Ohms with it which setup of output resistance (lowest?) and drive level (highest, close to over-current clamping?) is best, from your experience? Analyser in Bandpass mode?

Last edited by KSTR; 22nd December 2012 at 04:06 PM.
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Old 22nd December 2012, 04:03 PM   #28
KSTR is offline KSTR  Germany
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Quote:
Originally Posted by jackinnj View Post
Folks should look for Christophe Basso's papers on loop compensation -- he's already written two text books on the topic and much of his material can be found on the web. Omicron Labs also has a number of application notes and videos on their website.
Thanks for these pointers.
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Old 22nd December 2012, 07:05 PM   #29
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Quote:
Originally Posted by KSTR View Post
Jack,
GBIB is installed... but haven't checked it yet, need to order a USB-2-GBIB interface (or at least a plot grabber) first.

I haven't tried imp vs freq measurements with the AP Sys2 yet except for a quick check hooking up a speaker driver, if I wanted to go micro-Ohms with it which setup of output resistance (lowest?) and drive level (highest, close to over-current clamping?) is best, from your experience? Analyser in Bandpass mode?
I used a pair of 1,000uF caps back to back, with a 50 ohm resistor to couple the output of the AP2722 to the DUT. The voltage across the resistor gives you current. I built a pair of buffer amps, SSM2019 to read voltage and current, divided to get Z.

You need to allow for settling time of the analyzer, repeat the measurements and take an average.

I used the analyzer in both analog and digital modes and the measurements were about the same. Analog is more accurate, digital is faster.
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Old 11th January 2013, 03:13 PM   #30
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Fascinating!
Looking forward to your plots of various power supplies and regulators
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