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Hi Nizar,

Be careful with this NanoVNA accuracy sheet. It remains indicative, and as you say, accuracy remains dependent from hardware bridge and calibration load. The initial purpose of this picture here is to show that depending circumstances, it is sometimes relevant to choose another measurement method, than the common s11 one.

In the context of this topic (s11 measurement), you can't totally rely on these relative error measurement values. But for example if you get an X=1000 ohms value or higher, you are sure not to be in a confident frequency range, for capacitor or inductance measurement. Here, we have to consider this graph (configuration 1), as an helper here, no more.

73 - Jean-Roger

Hi Jean

Your NanoVNA accuracy Shart is Very Nice : imposed naturaly by the S11 NanoVNA hardware 50 Ohm bridge , indeed S11 accuracy is better around 50 Ohm bridge resistor : S11 accurate prety good 3% from 10 Ohm to 200 Ohm , Calibration Load should be known as accurate as possible.

73's Nizar

Thank you Dave. It is a quite interesting overview.

I just suggest to add an advice about having also an eye of the jX (reactance) value. The idea is to check that this value combined with R (Z module) remains in a relevant accuracy field of measurement for the NanoVNA. See captures below.

1: 10 pF capacitor @ 145 MHz : R and C values
2: 10 pF capacitor @ 145 MHz : R and X values
3: Indicative accuracy for s11 measurement (configuration1), suggested Z module limits for a maximum relative error measurement of 3%, between 10 ohms and 200 ohms. The previous capacitor result of the measurement respects this criteria.

73 - Jean-Roger

I just implemented a simple method to freeze the automatic scaling. While the numbers are the same, this capacitance comparison is much more compelling.

Brian

Thanks for all the information and suggestions. I will chose a low cost option and have learned to be more thoughtful and careful with this wonderful tool. I have learned a lot from it and have a replacement on the way. Thanks again for your expert advice.
Terry K3JT.

It was the H4 . Purchased from R&L. I accept the blame for the damage. The nano was not defective.

Here's an example of what the Y21 method can do. The plots are for an ATC 2.7 pF capacitor. The VNA was an HP 8722D with Inter-Continental test fixture and calibration kit. Self-resonance is about 9.4 GHz. The first image compares capacitance results for the Y21 method and the conventional S21 series-through method. The second image compares dissipation factor results. S11 and S22 are identical as are S21 and S12 at the 0.01 dB and 0.01 degree file resolution.

K6JCA's writeup on the Y21 method:



Brian

There is also a large family of low-capacitance limiter diodes from a
number of (non-Chinese) sources designed specifically for the purpose if
you choose to build your own. They are readily available from standard
suppliers like Mouser and Digikey. They are not expensive.

Again, the use of these limiters does not guarantee a silver bullet in
preventing damage.

Dave - W?LEV



On Fri, May 16, 2025 at 5:21?PM WS1M - bammi via groups.io <jbammi=
[email protected]> wrote:

As Dave mentioned limiters like mini-circuits VLM-33W-2W-S+ are a good
solution. Unfortunately these are hard to get as they are being
re-designed, and ebay sellers know this and have jacked up prices to mafia
levels.
Fortunately for us, another great solution is the equivalent TAPR, their
limiter can be purchased from here

Please *Note* that the TAPR version is only spec'ed up to 6M (54 MHz) and
is not as wide bandwidth as the mini-circuits that goes up much higher.
Please read the description on the above page before buying.

Another option is the receiver guard from DX engineering


This has an operating range 500 kHz to 150 MHz - still not as wide band
as the mini-circuits and has limitation on the lower frequencies unlike the
mini-circuits or the TAPR limiters. This unit has BNC connectors and not
SMA.

There are many pin-diode based limiters on eBay/Aliexpress, none of them
have clear specs, so buyer beware.

Also please note the presence of such limiters still does not guarantee
full protection due to limits of input power, output leakage, recovery time
and non linear behavior outside the defined bandwidth. In any case you
cannot willy-nilly pump watts into these, things will still go up in smoke!
You still need to attenuate and/or use a good quality sampler (see w2aew's
videos on these topics, all of his videos are so excellent)
If you are so inclined, I can suggest starting with this and then search
for all related videos


--
73 de ws1m
bammi

--

*Dave - W?LEV*


--
Dave - W?LEV

As Dave mentioned limiters like mini-circuits VLM-33W-2W-S+ are a good solution. Unfortunately these are hard to get as they are being re-designed, and ebay sellers know this and have jacked up prices to mafia levels.
Fortunately for us, another great solution is the equivalent TAPR, their limiter can be purchased from here

Please *Note* that the TAPR version is only spec'ed up to 6M (54 MHz) and is not as wide bandwidth as the mini-circuits that goes up much higher. Please read the description on the above page before buying.

Another option is the receiver guard from DX engineering

This has an operating range 500 kHz to 150 MHz - still not as wide band as the mini-circuits and has limitation on the lower frequencies unlike the mini-circuits or the TAPR limiters. This unit has BNC connectors and not SMA.

There are many pin-diode based limiters on eBay/Aliexpress, none of them have clear specs, so buyer beware.

Also please note the presence of such limiters still does not guarantee full protection due to limits of input power, output leakage, recovery time and non linear behavior outside the defined bandwidth. In any case you cannot willy-nilly pump watts into these, things will still go up in smoke! You still need to attenuate and/or use a good quality sampler (see w2aew's videos on these topics, all of his videos are so excellent)
If you are so inclined, I can suggest starting with this and then search for all related videos


--
73 de ws1m
bammi

Got it wrking now. It was a cable. I tried 4 till I got it wrk. And still only one firmware worked on it also

QUOTE:
Good overview. I think it is worth to add a little bit more to point 2
of the recommendations.
Because in case one is measuring a reactive component at a frequency
range of interest, which coincidentally is around the self resonant
frequency.
Maybe selecting a low frequency range first.
UNQUOTE

You're right, Kees. When I wrote the second "RECOMMENDATION", I seriously
considered including a caution to first do a wide sweep which may include
the self resonant frequency. I decided not to include that and keep the
thread focused on the task at hand to keep it simple for those unfamiliar
with these types of measurement. I did seriously consider adding your
suggestion. Thank you. Maybe after more comments, I'll go back and
incorporate additional information based on feedback.

Dave - W?LEV

On Fri, May 16, 2025 at 10:18?AM PE0CWK via groups.io <pe0cwk=
[email protected]> wrote:

Dave,

Good overview. I think it is worth to add a little bit more to point 2
of the recommendations.
Because in case one is measuring a reactive component at a frequency
range of interest, which coincidentally is around the self resonant
frequency.
Maybe selecting a low frequency range first.

73,
Kees PE0CWK


Op 16-5-2025 om 01:18 schreef W0LEV via groups.io:

I've had several requests on reading the values of inductors and

capacitors

using the NANOVNAs. I've put that together in the attachment to this
email. If you want to learn how it's done using the NANOVNA's and the
Smith Chart presentation, the attachment should be of interest to you.

For

the write-up, I've used the H4 version of the NANOVNA, but everything
should be applicable to any version of the NANOs or professional VNAs.

So,

don't belabor the point that .....waaahhhh....waaahhhh......I don't have
the H4. The technique is applicable to any vector network analyzer.

So, if interested, have a read of the attachment.

Dave - W?LEV

--

*Dave - W?LEV*


--
Dave - W?LEV

On Fri, May 16, 2025 at 09:18 AM, alan victor wrote:

You (I) can turn intepolation off.

That would be fine.

I think some of the L & C vendors that offer Touchstone files generate them from simulations, not from raw VNA data. I don't think they're trying to hide any issues with their parts. They may just want to clean up the data. Whenever S11 and S22 are identical, I suspect a simulation. I can also check with the Y21 series-through measurement method. It suppresses stray shunt capacitance. If Y21 and the usual S21 series-through method yield identical results, I think the data is simulated. I believe all component test fixtures, no matter how carefully designed and built, have some residual shunt capacitance.

Brian

Understood Brian. You (I) can turn intepolation off.
In any case, I suspect these measurements were done with TRL calibration on microstrip,

TRL cal does have bandwidth constraints and perhaps is the culprit introducing the gap.....

Which VNA. Some early versions on nanoVNA has spikes when switching from fundamental to harmonic mode. The fix was to lower transition frequency. Some other versions could not handle the high frequency limit. The fix was to lower STOP frequency.

Mike N2MS

Ted,
See Msg. #38300. I thot I'd messed mine up trying to upgrade the f/w by the DFU mode, but Stan talked me thru it, and now it works fine.

There's a lot of good help here.

jbl

Permanent installation of the following would go a long ways in protecting
the S11 or source port:

VLM-33W-2W-S+

From Minicircuits. It's presently under re-design, but is available and is
designed to limit large and possibly damaging RF levels on the ports where
it is installed.

Dave - W?LEV

On Fri, May 16, 2025 at 3:26?PM Dragan Milivojevic via groups.io
<d.milivojevic@...> wrote:

Which one? NanoVNA V2 frontend is quite different from H4 (for example).

On Fri, 16 May 2025 at 17:13, Terry Wassell #1398 via groups.io <k3jt.wv=
[email protected]> wrote:

Sad to report that, for the second time, my nanovna is broke from RF over
exposure or ESD. My question is: can I protect the input with some

fuse-

or similar over-load protection device? Yes, I will treat this one with
extra care.
Terry. K3JT

--

*Dave - W?LEV*


--
Dave - W?LEV

On Fri, May 16, 2025 at 08:30 AM, alan victor wrote:

You should most likely want to add interpolation, say spline.

Alan, I want the program to show what's in a file, not a sanitized version. Note that cubic spline interpolation, the kind of spline I'm familiar with, can yield points well away from a reasonable curve when things go wrong. It's quite tricky to tame. Be on the lookout for artifacts in any plotting program that uses it.

Your S22 curve looks like it has no gap. The S22 data actually does, just like S11. My unsanitized dot plot below reveals it..

I'm think the gap indicates some sort of problem with the VNA. I want to see these things because they call into question the validity of the rest of the data.

Brian

Sorry for the bandwidth.

Brian, two simulators failed to read the Johanson file correctly.
However, a Keysight simulator had no issue. Operated fine.
Here is s11,s22, and 20000 data points and of course the Keysight routine adds interpolation.

You should most likely want to add interpolation, say spline.
GL with the routine.

Which one? NanoVNA V2 frontend is quite different from H4 (for example).

On Fri, 16 May 2025 at 17:13, Terry Wassell #1398 via groups.io <k3jt.wv=
[email protected]> wrote:

Sad to report that, for the second time, my nanovna is broke from RF over
exposure or ESD. My question is: can I protect the input with some fuse-
or similar over-load protection device? Yes, I will treat this one with
extra care.
Terry. K3JT

Terry,

Can you please explain the RF exposure or ESD which caused the failure so
that I can take precautions?

73
Jon, VU2JO

On Fri, May 16, 2025 at 8:43?PM Terry Wassell #1398 via groups.io <k3jt.wv=
[email protected]> wrote:

Sad to report that, for the second time, my nanovna is broke from RF over
exposure or ESD. My question is: can I protect the input with some fuse-
or similar over-load protection device? Yes, I will treat this one with
extra care.
Terry. K3JT