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I nearly fell out of my chair when I saw the HP fixture prices. May I
suggest using these:



There is a lot of other goodies on his website, and I have found him very
easy to deal with.

Regards,


Charles.
VK1CM

Dave,

Where did you find the very large alligator clip shown in the photos in the document? My usual sources aren't turning up anything big enough to bite a bnc connector.

Just curious.

Andy

On Sun, May 18, 2025 at 11:39 AM, Dan Pate - AI5OL wrote:

I fabricated a test lead that is a coax that terminates in a pair of alligator
clips. I clip the leads onto a panel mount SMA connector to attach the
Open/Short/Load calibration standards to calibrate to the reference plane at
the alligator clips. I can then clip the leads to the connections of the coil
to test.

Alligator clips are OK if you just want to get a rough idea of the impedance of the device you are measuring. The problem with them is you have an impedance discontinuity from the coax to the clips which can only be partially "calibrated out". Also when you calibrate the clip separation and lead spacing is different that when you are measuring the DUT. This all results in a poor reference plane.

Below is a measurement I did of a small inductor. It was tested at 100 kHz. on a DE-5000 LCR meter and then measured using alligator clips and a proper test jig. The results and comments are in the graphs.

Roger

On Sun, May 18, 2025 at 02:29 PM, Team-SIM SIM-Mode wrote:

Here my plots of S11 and S21 measurement of the 4.63Kohm leaded resistor at
same time , same graphe , same scale
they are dramatically differents , and I prefer the S21 obviosly . May be i am
missing some thing.

Something wrong with your S11 plot. It should be much better than that. Here is a re-post of my previous plot. S11 is flat but is off by 3 to 4%. Note that S21 is much better estimate at low frequencies but rolls off.

Questions
-----------

1. Do you have a photo you can post of your test jig(s) for S11 and S21 measurements?
2. Are you using the enhanced response option in the menu?
3. What version of firmware are you using?
4. Try a 10K and see what you get.

Hi Roger

Here my plots of S11 and S21 measurement of the 4.63Kohm leaded resistor at same time , same graphe , same scale
they are dramatically differents , and I prefer the S21 obviosly . May be i am missing some thing.

73's Nizar

On Sun, May 18, 2025 at 04:13 PM, Roger Need wrote:

You also need a good test jig because stray capacitance and inductance can
affect the results.

An ideal test fixture would maintain a 50Ω impedance right to the device body. The Keysight high-frequency SMD fixtures come close to this ideal, the device interface center conductor is a disk, coaxial to and coplanar with a grounded ring which is the outer conductor, with an insulated gap between.
The calibration standards and device under test are placed across this gap to make measurements; there is also a shielding cap which bayonets on during calibration and measurements, to stabilize the stray capacitance and add shielding from interference.
In the photo the brass thing is the outer ring and the inner electrode is indistinguishable as it is 1 or 2mm across.
It would not be to difficult with someone with a lathe, etc. to fabricate a pretty good one. Even a piece of .250" semirigid cable sanded flush would be pretty darned good for small SMD devices or it could be soldered into a ground plane plate flush with the shield for larger components.
Other Keysight accessory links, for inspiration:
Lower frequency:
I used this one a lot for UHF and below:

73, Don N2VGU

Those leads account for about +j5 at 28 MHz. I'm giving the leads about 28
nH of inductance. The +j5 ohms is about 10 % of your measurement system
impedance of 50 ± j 0 ohms.

Dave - W?LEV

On Sun, May 18, 2025 at 6:21?PM Team-SIM SIM-Mode via groups.io <sim31_team=
[email protected]> wrote:

Hi Dave

It's a leaded resistor with 2cm legs

73's Nizar

--

*Dave - W?LEV*


--
Dave - W?LEV

On Sun, May 18, 2025 at 09:45 AM, Team-SIM SIM-Mode wrote:

You are right, i tested a 4.63 K Ohm serial resitor S21 gives me 5.35 Khom
+15.6% error but regular static value across the 30Mhz span , S11 shunt gives
me a very irregular values across the 30Mhz span , thats mean if we can
calibrate better S21 resistor function it will give better accuracy
measurements for hight values > 1K Ohm , I dont Know if there is a trick for
this possible S21 compensation ?
see illustrations below

Nizar,

The NanoVNA-H4 is only a one-way VNA so it does not calibrate for s22 and S12 and only does six point calibration. In order to get good S21 series measurements you need the source and load impedances to be 50 ohms or you have to do compensation adjustments using an exported Touchstone file. DiSlord has implemented enhanced response which helps somewhat to accommodate for the load impedance. You also need a good test jig because stray capacitance and inductance can affect the results. You need to keep the jig away from the bench to avoid capacitive coupling. Any phase shift errors arriving on port 2 (CH1) will also change the way the resistive and reactive values are computed.

I made some measurements today using my jig which I show in the photos below. Below are some measurements using 3.3K and 10K leaded resistors. The NanoVNA was setup to show S11 and S21 at the same time using the same grid scale. The S11 measurement will be 50 ohms high because it is measuring the series resistance of the DUT and the port 2 load resistance.

Observations
- Both methods were fairly close using the 3.3 K DUT
- The 10K had similar results at low frequencies but with the S21 method there was considerable rolloff with frequency. The S11 measurement was fairly flat but was 400 ohms low (4 % off) across the frequency range. Personally the S11 results are good enough for me and I don't have all the fuss associated with an S21 jig and the measurement issues.

Hello Dave,

I agree with Luc. Everything I've read about Smith Charts says that ABOVE the horizontal (resistance) centerline is Inductive, and everything BELOW is capacitive. But I still have a lot to learn about Smith Charts and maybe there's some situation where they are reversed.

Thanks for listening.

Larry, AE5CZ

I have used mine to measure the inductance of antenna load coils that I have made. I fabricated a test lead that is a coax that terminates in a pair of alligator clips. I clip the leads onto a panel mount SMA connector to attach the Open/Short/Load calibration standards to calibrate to the reference plane at the alligator clips. I can then clip the leads to the connections of the coil to test.

73 de Dan AI5OL

--
This email has been checked for viruses by Avast antivirus software.
www.avast.com

Hi Dave

It's a leaded resistor with 2cm legs

73's Nizar

Were you using a leaded or SM resistor in these tests?

A picture of the setup might be of value.

Dave - W?LEV

On Sun, May 18, 2025 at 4:45?PM Team-SIM SIM-Mode via groups.io <sim31_team=
[email protected]> wrote:

Hi Roger

You are right, i tested a 4.63 K Ohm serial resitor S21 gives me 5.35
Khom +15.6% error but regular static value across the 30Mhz span , S11
shunt gives me a very irregular values across the 30Mhz span , thats mean
if we can calibrate better S21 resistor function it will give better
accuracy measurements for hight values > 1K Ohm , I dont Know if there is
a trick for this possible S21 compensation ?
see illustrations below
73's Nizar .

--

*Dave - W?LEV*


--
Dave - W?LEV

Hi Roger

You are right, i tested a 4.63 K Ohm serial resitor S21 gives me 5.35 Khom +15.6% error but regular static value across the 30Mhz span , S11 shunt gives me a very irregular values across the 30Mhz span , thats mean if we can calibrate better S21 resistor function it will give better accuracy measurements for hight values > 1K Ohm , I dont Know if there is a trick for this possible S21 compensation ?
see illustrations below
73's Nizar .

Stabilize the S22 port with a 6 dB or greater attenuator for starters and
90% of the problems.

In addition any VNA has trouble measuring high impedances.

For measuring CMRR of my common mode chokes (transmission line
transformers), I use a spectrum analyzer with a tracking generator - a
transmission mode measurement.

Dave - W?LEV

On Sun, May 18, 2025 at 3:55?PM Roger Need via groups.io <sailtamarack=
[email protected]> wrote:

Nizar,

The NanoVNA H4 has difficulty making accurate S21 measurements for several
reasons that have been posted many times in this group. I suggest you try
measuring a 5K and a 10 K resistor using your test jig and S21 and see what
you get for results.

Roger

--

*Dave - W?LEV*


--
Dave - W?LEV

Nizar,

The NanoVNA H4 has difficulty making accurate S21 measurements for several reasons that have been posted many times in this group. I suggest you try measuring a 5K and a 10 K resistor using your test jig and S21 and see what you get for results.

Roger

Thanks, Nizar. There is almost no difference between the two methods for Z (|Z|), a bit more for R and I. This suggests that the residual shunt capacitance in your test fixture is negligible. The S21 method is noted as Ser, which stands for series-through (Snt for the shunt-through method comes next). I include R because some builders judge choke performance by it rather than |Z|. The I plot shows where the choke changes from being inductive to capacitive.

Brian

Hi Brian

Here S1p and S2P attached

73's Nizar

Hi thanks

Sent from Outlook for Android<>
________________________________
From: [email protected] <[email protected]> on behalf of Paul Hardcastle via groups.io <paul.a65dr@...>
Sent: Sunday, May 18, 2025 8:03:31 AM
To: [email protected] <[email protected]>
Subject: Re: [nanovna-users] mint 22.1 git install error

Hi Rod,

Confession - I'm not a software guy.

It does look like an issue with PIP/python rather than nanovna-saver.
Google tells me it is likely the libssl-dev was not installed when
python was built.

If you are happy with the version installed from the repos then stick
with that. I normally prefer to stick with a slightly older package
than disappear down a rabbit hole in an area I am lacking skill.

Cheers,
Paul



On Sat, 2025-05-17 at 23:46 -0700, Rod via groups.io wrote:

Hi Paul,

when installing nanovna-saver 0.7.3 from github I get the error shown
here:

a
Thank you again for helping me. I love the software.

Cheers, Rod

Nizar, please post the .s2p file. I'd like to see whether the Y21 method offers any improvement over the S21 method for your test.

Brian

Hi Roger

Thanks for all this papers and sharts, here my simple direct measurements comparaison of this morning for the same balun 1/1 commun mode impedances done by two differents methods :

1) S11 Shunt IZI responses ( commun mode connections).

2) S21 IZ_Seriall response ( commun mode on serial connection).

see illustrations attached below , it gives a very different impedances result , that's Why the S11 IZI is not usable here due to high values of impedance measurements where S21 Serial methode is still a very correct methode .

Conclusion : S21 Serial impedance or LogMag is the only correct methode to mesure the commun mode rejection of baluns Z> 1KOhm ( or any S21 derived nanoVNA graphes ) .

73's Nizar