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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


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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*


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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

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

Use a different USB controller on your computer and check the USB cable.

On Fri, 16 May 2025 at 16:04, Ted Garrett via groups.io <kq4ymd=
[email protected]> wrote:

It connects, firm ware is the latest for the H model, i fellow the steps
in the guide, the dfu demo software starts as normal starting delete phase,
takes 18 hrs, now im in down load phase and its 4 hrs into it and 6 %.

What firmware do you recommend?

It connects, firm ware is the latest for the H model, i fellow the steps in the guide, the dfu demo software starts as normal starting delete phase, takes 18 hrs, now im in down load phase and its 4 hrs into it and 6 %.

What firmware do you recommend?

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:

Dave

you'll have to swap the Above & Below in the first lines on page 2 ...

73
Luc ON7DQ

Delete phase? There is not normally a separate delete phase in nanova firmware loading. Most of the programming methods have you a) attach to nanovna in dfu update mode, b) Select and outload the new firmware file, and c) restart the nanovna in normal mode with new firmware. The programming software does do a bulk flash erase as the first part of the update process.

It is very hard to truly brick a nanovna.

Which software are you using to update the firmware? Are you able to get that software to connect to nanovna in dfu update mode?

I guess I bricked it. Nanovna H. 3 days of trying to reput the firmware back on it. Can't get it to even delete phase.

Thanks a lot Dave.

Shall go through it and get back to you.

73
Jon, VU2JO

On Fri, May 16, 2025 at 4:49?AM W0LEV via groups.io <davearea51a=
[email protected]> wrote:

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