开云体育

On 7/18/22 5:10 AM, Larry Martin wrote:

Jim Lux wrote:

The actual load may or may not be 50 ohms in the design circuit.

Hi Jim, thanks for a thoughtful response.? But I'm not sure transmission line effects play into this test at 13.56 MHz, where wavelength/10 is around 10 feet.? They could explain some things I see at UHF (915 MHz, wavelength/10 more like an inch).? There are fewer than 50 part numbers of HF/NFC RFID ICs in common use.? They are not specified by impedance but by capacitance, which must be balanced against their respective coils.? Most capacitance specs cluster around 15 pF or 50 pF, but the "50" pF rating does not relate to "50" ohm impedance.

Can you give a sample part #, and I'll go look at the data sheet.

Further, if we had to worry about tags' internal impedance, some tags would not work with some readers.? HF/NFC tags work with "any" HF RFID reader, not just ones that match the impedance or capacitance of the inlay design.? In this test, the NanoVNA CH0 stands in for the RFID reader, and should have a similar level of cross operability.

In a real reader, the requirement for the transmitter is "produce at least X magnetic field" and for the receiver "sense no less than Y magnetic field".

For a active reader passive tag, don't the tags just rectify the transmitted signal to produce DC to run the internal tag chip?

To me, the LOGMAG curves in the linked image () represent CH0 transmit power that is not reflected back to CH0 because it is coupled to the RFID tag and consumed by the RFID chip.? I'm trying to see what-all can be deduced from that measurement.

That's only sort of true. The VNA has a 50 ohm source impedance, so you'd need to take that into account.

Like I said, model it as a non-ideal transfomer (with some TBD turns ratio) that transforms some unknown load impedance which is a resonator with loss.

On 7/18/22 2:20 AM, Marc et Nicole Feuggelen-Verbeck wrote:

The value of an inductor is a given and depends on several factors, but CERTAINLY NOT on the frequency

An ideal inductor, perhaps, but any sort of practical real inductor with parasitic C between turns and the surroundings varies with frequency. The loss also changes with frequency due to skin depth changes (although that's a small effect).
There's also a small inductance change effect due to different distribution of current in windings due to skin effect.

Finally, if the inductor is on a core, pretty much every core material has frequency dependent properties.

On 7/17/22 11:26 PM, Ed G8FAX wrote:

Hi Victor,

“Connecting two identical baluns with unknown performance back to back is a very bad test procedure to use.
All that can be determined is the degree of mismatch at the unbalanced port and the insertion loss of the balun. This test procedure is incapable of revealing values for the mode conversion parameters which means that the CMRR cannot be calculated, and even worse, provides no conclusive evidence that the balun actually functions as a balun at all!

E.g. a "back to back" test of a pair of coax to banana jack adapter (which is not a balun) would show good S11 and S21.

For reference a LogMag reading of -14dB is the same as a VSWR of 1.5:1.
Any logmag reading less than -14dB is better and better. If you get a
logmag reading of -20dB then you are in very good shape. Several external
things can change the resulting logmag such as ground conductivity, height
of the horizontal leg of the antenna above ground, or proximity of the
vertical part of the antenna to nearby objects, and the number of ground
radials.

There is one telltale measurement that can point to the difference. Masure
the feed point impedance. The closer the impedance is to 50 ohms the lower,
the more negative, the LogMag reading. The impedance will be impacted by
the number of radials and ground conductivity.

The logmag is the return loss in dB. EXAMPLE if the forward power is 100
watts, +30dBw, and the reflected power is +10dB, 1 watt, then the return
loss, i.e logmag, will be -20dB.

Hope this helps,



*Clyde K. Spencer*

Inductance is independent of frequency. Inductance only depends on the materials used (this also means that the environment of the element is important). If you vary the frequency, the inductance NEVER changes.

Marco , F8VOA

Op 18/07/2022 om 14:18 schreef Reinier Gerritsen:

Inductance may vary with frequency, e.g. when there is a ferrite core. The core material's properties are frequency dependent. Also, the effect of the interwinding capacitance increases with frequency and that will change the observed inductance.
Reinier

On July 18, 2022 11:20 AM Marc et Nicole Feuggelen-Verbeck <f8voa54@...> wrote:

The value of an inductor is a given and depends on several factors, but
CERTAINLY NOT on the frequency

F8VOA , Marco

Op 18/07/2022 om 09:27 schreef Observer:

Its a fact, that inductance value, vary according to frequency.
How does the nanovna measure ?
Does it use the saved selected frequency range inside the nano ?

--

If You are not part of the solution , then You are the problem <<<

Inductance may vary with frequency, e.g. when there is a ferrite core. The core material's properties are frequency dependent. Also, the effect of the interwinding capacitance increases with frequency and that will change the observed inductance.
Reinier

Jim Lux wrote:

The actual load may or may not be 50 ohms in the design circuit.

Hi Jim, thanks for a thoughtful response.? But I'm not sure transmission line effects play into this test at 13.56 MHz, where wavelength/10 is around 10 feet.? They could explain some things I see at UHF (915 MHz, wavelength/10 more like an inch).? There are fewer than 50 part numbers of HF/NFC RFID ICs in common use.? They are not specified by impedance but by capacitance, which must be balanced against their respective coils.? Most capacitance specs cluster around 15 pF or 50 pF, but the "50" pF rating does not relate to "50" ohm impedance.

Further, if we had to worry about tags' internal impedance, some tags would not work with some readers.? HF/NFC tags work with "any" HF RFID reader, not just ones that match the impedance or capacitance of the inlay design.? In this test, the NanoVNA CH0 stands in for the RFID reader, and should have a similar level of cross operability.

To me, the LOGMAG curves in the linked image () represent CH0 transmit power that is not reflected back to CH0 because it is coupled to the RFID tag and consumed by the RFID chip.? I'm trying to see what-all can be deduced from that measurement.

Thanks for weighing in,
Larry Martin

The term "inductance" has two meanings. It may mean the inductance exhibited by a coil or circuit at a frequency of interest. It also may mean the inductance at a low frequency where variation with frequency is negligible. The two values can differ due to coil self-resonance, change in effective coil diameter with frequency, change in dielectric permittivity or core permeability with frequency, or other factors. The first value usually is just called inductance. The second may be called true inductance, ideal inductance, or low-frequency inductance. The confusion comes when it too is called inductance.

When referring to inductance in public, you can avoid confusion by stating which meaning you're using.

Brian

The NanoVNA will measure inductance over a frequency range, which you
configure in the sweep settings, just like with other measurements.

In theory, the inductance does not depend on the frequency, but the
inductive reactance does.
I'd like someone to correct me if I'm wrong, but from what I can see, VNAs
can't actually directly measure inductance (is there anything that can?),
and instead measures impedance, and then estimates inductance from
impedance. Since everything is an RLC circuit (in coils, don't forget the
resistance of the conductor, and the capacitance between the turns, which
affects the coil's self-resonant frequency), the estimate of the inductance
will change with frequency, sometimes drastically (again, keep the
self-resonant frequency in mind).

пон, 18. ?ул 2022. у 09:27 Observer <tvstreamdevice@...> ?е
написао/ла:

The value of an inductor is a given and depends on several factors, but CERTAINLY NOT on the frequency

F8VOA , Marco

Op 18/07/2022 om 09:27 schreef Observer:

Its a fact, that inductance value, vary according to frequency.
How does the nanovna measure ?
Does it use the saved selected frequency range inside the nano ?

--

If You are not part of the solution , then You are the problem <<<

Hello Roger,
I have two coaxial cables that came with the NanoVNA. I cut one of them to
make the solder. I use the cable I didn't cut to do the calibration and
after connecting the one I cut, I correct the delay. That's why the delay
is so low. When I do the calibration directly at the input of the NanoVNA
and connect my SMA cable, the delay correction is difficult for me, the
phase(pink curve) is triangular like in the attached picture. When I made
the calibration at the cable I didn't cut and I connect the cable I have
cut the phase is just shifted I don't have triangular thing on the curve.
Best regards.



Le ven. 15 juil. 2022 à 22:54, Roger Need via groups.io <sailtamarack=
[email protected]> a écrit :

On Fri, Jul 15, 2022 at 11:44 AM, Diane BONKOUNGOU wrote:

Hello,
Thanks for your response I've got -462ps for the delay correction is it
good?
Best regards.

Your display looks OK but 462 ps would be the value for a very short
transmission line - about 4.5 cm long. What is the length of your
transmission line and what kind of coax is it?

Here is a video you might find interesting. It shows how to measure an
antenna located inside a product...



Roger

Its a fact, that inductance value, vary according to frequency.
How does the nanovna measure ?
Does it use the saved selected frequency range inside the nano ?

yes, I do have the female to female . I was to quick to assume I had something missing.
And, yes, I am following that Absolute Beginners manual . Some slight insignificant differences in software.

Hi Victor,

Interesting reading about cmc models and ways of establishing by measurements and maths of obtaining values for the various elements of the models form the links you provided, thanks.

Dominguez-Palacios et al (DP) paper uses S21 Voltage measurements, whilst the Hal document works on S11 impedance measurements. Fig 2(a) of DP paper is equivalent to HAL Fig 3 (a) – T0 connection, or as you describe in your notes CM0 as you find no appreciable difference to CM3.

For DM, the DP paper makes use of two baluns. The equivalent in the HAL document would be fig 3 (b) = T1 connection, an arrangement close to my original suggestion for measuring CMC DM, the differences being what started our excellent discussions and something yet to be ascertained is if there is any appreciable difference of techniques. For sure if one considers a CMC filter (extra capacitance on the far side), yes I fully agree that the techniques are not comparable.

Thus, I see that the ‘open’ measurement of the DP paper (fig 2 (c) is part of a series of tests of a particular method for the purposes of modelling, not an alternative to more conventional means of establishing performance of a cmc. Just as are the additional configurations of the HAL document Fig 3 (c), (d) & (e) with T4 being equivalent to DP paper ‘open’.

Interesting to note that in the HAL document, the conclusion is that results not only depend on components (tolerances?) but also on respective positioning (lay-out).This reminds me of a quotation I heard many years ago (can’t remember where/who it came from) =”Theoretically, practice and theory are the same, in practice, they are not!”

I have also been refreshing and improving my knowledge on transmission line transformers (TLT’s) and found for me a very useful reference = Ruthroff transmission line transformers, Guanella baluns, lowpass and bandpass filters, and balanced transmission lines using multilayer technology, Riaz R Sobrany, M.Eng.



Although aimed at microwaves and MICC type technology, chapter 3 covers basic theoretical operation of various Ruthroff TLT’s and chapter 4 Guanella types. Of interest to me in particular is his notes on testing baluns(on page 136 of pdf).

“Connecting two identical baluns with unknown performance back to back is a very bad test procedure to use.
All that can be determined is the degree of mismatch at the unbalanced port and the insertion loss of the balun. This test procedure is incapable of revealing values for the mode conversion parameters which means that the CMRR cannot be calculated, and even worse, provides no conclusive evidence that the balun actually functions as a balun at all!
A procedure to test a balun using a conventional 2-port VNA which determines the CMMR but does not measure the insertion loss or the port reflection coefficients is detailed in [113]. This test procedure requires three precision resistors and the accuracy of the measurement is dependent upon the accuracy of these resistors.”

With ref 113 being “O. M. Woodward, “Balance Quality Measurements on Baluns,” IEEE Transactions on Microwave Theoiy and Techniques, vol. 31, no. 10, pp. 821-824, Oct. 1983.” I have not located this, so no further comment on the technique at present.

This to me raises questions concerning the validity of using baluns in the measuring chain; what exactly is being measured and is making back-back compensation measurements valid, especially if one is using home made baluns. The same might well apply to commercial ones.

I did a little research in to commercial baluns, “mini-Circuits” produce a very wide range of rf transformers (500+), there may be something suitable there, I have yet to explore possibilities


Summarising so far on the way to measure a cmc depends rather on the objective, is it to find parameters for a model or to evaluate performance, different approaches are required. There is no universally applicable model for cmc’s it depends if low frequency or rf application. Your own experiments and studies support this when you say “The 'equivalent' circuit maps the best my remeasurements is the model of Guanella (to ideal transformers; a transmission line to represent the DM and a reactance+resistance to represent the CM)”.


Kind regards

Ed, G8FAX

My quick notes about used foumulas in NanoVNA

Yes side-by-side as you put it. The NanoVNA is calculating all the parameters (SWR,
Return Loss (logmag format) and impedance (R, X) from the same scanned measurements.

Hello

I saw and verified that we can recalculate all the parameters from S11. Can you explain to me :
- What is the native measurement performed at the bridge level
- What is the first parameter produced by the nanoVNA from this native measurement
--
Fran?ois

-----Message d'origine-----

De la part de Roger Need via

Envoyé : dimanche 17 juillet 2022 22:33

Greetings, You may need a few adapters.MURATA MM126056 SWD / SWF TEST PROBE TO SMA FEMALE RF ADAPTOR fd5g59 | eBay


|
|
|
| ?50.00 | |

|

|
|
| |
MURATA MM126056 SWD / SWF TEST PROBE TO SMA FEMALE RF ADAPTOR fd5g59 ...

MURATA SPECIALIST TEST PROBE MM126056. SWD / SWF test probe - SMA female adaptor.
|

|

|

Very unlikely.? ? If you mate and remove a UFL about a dozen times, it no longer makes a good repeatable connection.? ?Really a connector designed to be used once during the assembly of a product.? Kent WA5VJB

Hello. I bought NanoVNA V2 Plus 4 Pro from tindle webpage.
In the package, I got cables and SMA calibration kit (4pcs). But this calibration kit is for SMA cables;



I have this Nordic NRF52840 Bluetooth kit. The kit has SWF RF connector for direct RF measurements.
My plan was to connect the NanoVNA to the SWF connector.

For better results, are there UFL or SWF calibration kits?
I use Murata MXHS83QE3000 SWF probe, and I want to calibrate the NanoVNA when this SWF probe is on.
But I can't find SWF calibration kit. Where can I find a SWF calibration kit?

Thank you, Gracias. Josele

On Sun, Jul 17, 2022 at 06:42 AM, Observer wrote:

another silly mistake !
I didnt realise that the short circuit cap is actually screwed in on the Ch0
and CH1 !!!

You should also have a barrel connector (threaded on both ends) to connect the cables together for the calibration through test. As a new user you should read the Absolute Beginners Guide to the NanoVNA.


Roger