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On Mon, Jul 18, 2022 at 03:27 AM, Observer wrote:

How does the nanovna measure ?

I believe it works like this:
It sends a pulse of RF at the Nano's 'start frequency' and analyzes the phase and amplitude of the return signal (like an echo?). Then it sends a pulse at the next frequency step, and so on for the number of steps programmed (usually 99, I think).
For each echo pulse, it calculates the L, C, etc. values from the phase difference between the transmitted pulse and the received pulse.
To see the data that actually results, look at the contents of an s1p or s2p file that the Nano can save (maybe only using the 'NanoVNA-Saver' program). (The -F nano can save s1p/s2p files to its own internal storage.)
--
Doug, K8RFT

On 7/19/22 5:09 AM, Miro, N9LR via groups.io wrote:

On Mon, Jul 18, 2022 at 05:40 PM, Jim Lux wrote:

I use the T1-1T-65X - 6 pin DIP package 200 kHz to 80 MHz - it's 1:1 with a
center tap. If you need 2:1 the T2-1T-65X has a secondary 2x the primary, with
a center tap.

You have a typo in the component name - it's "X65", not "65X", but great find!

Oops, yes..

I used those because I had an application where I wanted to be able to change the turns ratio, so I have a 6 pin DIP socket, and I can plug in the T1, the T4 (2:1), or the T16 (4:1).

And it's easier to solder to DIP pins if you're dead bugging it, than to some tiny SMT pad.

As someone mentioned minicircuits does have a minimum order, so one might need to do some scrounging around for a source or alternate parts if you only want one or two.

On 7/18/22 11:15 PM, Larry Martin wrote:

And of course, the RF interface spec for the chip is something you have to buy from NFC Forum. (for the princely sum of $600)

Yeah, the NFC Forum restricted those specs a while ago, for the good of mankind I'm sure. The 2011 and 2013 versions are still out in the wild on Google. But NFC Forum is not the chip company. This public NXP datasheet for the slightly newer Ntag213 includes the radio interface:

Well the data sheet doesn't say much about the electrical properties of the interface other than to say it's 50pF and compliant with the $600 spec..

However, this ap note on antenna design..



In particular Figure 5.

The document goes on to describe how to measure these antennas, including coupling with a 1 turn loop, just like you're doing.

But they talk about it in the context of making impedance measurements, not looking at the return loss compared to 50 ohms.

It's just a transformer with high leakage inductance...

So it sounds like your answer to my question is that I should SPICE model the system comprising the NR-loop and the tag. After a reality check, I should be able to deduce SPICE properties like the tag's internal capacitance, etc, based on the model, assuming I can quantify the coupling. Am I hearing you right?

That's a way.. the app note give a bunch of ways to look at it. I'm not sure I'd use SPICE.
It kind of depends on what you're trying to do. If you're trying to characterize different models of tags, it might be more a matter of turning S11 measurements in to lumped circuit equivalents, and going from there.

On Mon, Jul 18, 2022 at 05:40 PM, Jim Lux wrote:

I use the T1-1T-65X - 6 pin DIP package 200 kHz to 80 MHz - it's 1:1 with a
center tap. If you need 2:1 the T2-1T-65X has a secondary 2x the primary, with
a center tap.

You have a typo in the component name - it's "X65", not "65X", but great find!

And of course, the RF interface spec for the chip is something you have to buy from NFC Forum. (for the princely sum of $600)

Yeah, the NFC Forum restricted those specs a while ago, for the good of mankind I'm sure. The 2011 and 2013 versions are still out in the wild on Google. But NFC Forum is not the chip company. This public NXP datasheet for the slightly newer Ntag213 includes the radio interface:

It's just a transformer with high leakage inductance...

So it sounds like your answer to my question is that I should SPICE model the system comprising the NR-loop and the tag. After a reality check, I should be able to deduce SPICE properties like the tag's internal capacitance, etc, based on the model, assuming I can quantify the coupling. Am I hearing you right?

Jim Lux wrote: “google for "woodward balun balance quality 1983" “

Thanks, I no longer have academic access, so will need to buy or get site of the paper some other way. However, there might be alternatives/better solutions to pursue.

I found “Analysis and Performance of Antenna Baluns” by Lotter Kock

Victor Reijs might be interested in this. This models a balun as a delta-connected network of impedances, provides a good explanation of how the common mode current occurs (another question I think Victor has) as well as giving several means of testing, including back-back and the “Woodward” method, tabulating their usefulness.


Jim Lux wrote: “ I use the T1-1T-65X - 6 pin DIP package 200 kHz to 80 MHz - it's 1:1 with a center tap.? If you need 2:1 the T2-1T-65X has a secondary 2x the primary, with a center tap.
The 622-kk81 is a non catalog part. I'd find something that's in stock. If you need 3 isolated windings, I'm sure they've got something.”
It appears ordering direct from Mini-Circuits requires a minimum order value of $50. With shipping costs and import duties, the cost of 622-kk81 would be high, so thanks Jim for alternative part you use.

Neither part is available from Digikey or Mouser, so a look though what they have in stock to see if there is yet another alternative might be more fruitful and cost effective.
Kind regards

Ed G8FAX

On 7/18/22 1:42 PM, Larry Martin wrote:

Jim:

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

The tag in the photo is an NXP NTAG203 chip in a Smartrac Bullseye inlay, about 10 years old. Smartrac never published the exact part number of Ntag203 in inlay X, and doesn't really exist anymore since merging with Avery. Google shows many old hits on both devices.

And of course, the RF interface spec for the chip is something you have to buy from NFC Forum. (for the princely sum of $600)

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

Sure, which to me argues against transmission line effects within the tag, i.e. behind the secondary winding, being significant to the VNA trace.
I will read up on non-ideal RF transformers and see if anything "sparks" an idea.

It's just a transformer with high leakage inductance. That is, you can probably model it as an ideal transformer with some turns ratio, in series with a bulk inductance. Model wise, you can put the leakage L on either side of the transformer.

Typically, you'd put some C in the circuit to counter the leakage inductance.


Consider the "transmit direction"

You've got some voltage source that wants to push power to the tag. So you've got a big inductance in series with the transformer, which powers the tag. So the voltage at the tag is Xload/(Xload + Xleakage) - it's a voltage divider. To get the voltage higher, you add some C, so it's Xload/(Xload + Xleakage - Xcapacitance)

It's similar, in principle, to power factor correction; if that helps.

Same thing in the "receive direction" - the tag is pushing a voltage through the transfomer to the reader. Again, the extra leakage L is in series - it's L, so it's not lossy, but it still is a voltage drop. So if you can cancel it with a capacitor, then all is good.

Naturally, just like with PFC - a particular value of capacitor only works at one frequency - but hey, these are single frequency devices, and the "compensation" doesn't have to be perfect.

On 7/18/22 12:23 PM, Victor Reijs wrote:

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.

Indeed that is the reference I would like to read also. Does someone have a
copy?

google for "woodward balun balance quality 1983"

The paper works through the math of using a VNA to do the measurement as a 3 port device.

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

Yes, and they publish N-port VNA measurements. 4 port for most of the baluns.

I think the 1:1:1 T-622-KK81 can do the function.

I use the T1-1T-65X - 6 pin DIP package 200 kHz to 80 MHz - it's 1:1 with a center tap. If you need 2:1 the T2-1T-65X has a secondary 2x the primary, with a center tap.


The 622-kk81 is a non catalog part. I'd find something that's in stock. If you need 3 isolated windings, I'm sure they've got something.

I agree with Jim Lux. The inductance of an "ideal" inductor does not vary with frequency but any physical ("real world") inductor will have its inductance vary with frequency. In the case of an air coil the change will be small due to the skin effect and current distribution resulting from it but can still be measured as Jim pointed out in his reference.

In the case of an inductor made with some type of core material the change in inductance with frequency is much more noticeable especially with high permeability ferrite cores. With powdered iron or brass it will be much less than it is with a ferrite material. Attached are plots of 5 turns on a powdered iron toroid and 5 turns on a ferrite mix 43 toroid.

Roger

The answer(s) to your question depends on what you want to know about it and what type of Tuner it is.

For example, I have a homemade manual Tuner that I built many years ago, and, having learned a lot more about impedance by now, wanted to know what the characteristics of the Tuner were as far as impedance and the effect that it has when in line and in bypass. I calibrated the vna to the end of my patch cable to a 50 ohm dummy load over 2-30 MHz, then connected the load to the output of the Tuner and the cable to the input of the Tuner. It was pretty bad.... both in line and bypass. I cleaned up the wiring and improved it, although it is still not ideal.

The other way I use the vna with the Tuner is to find and record the settings for a range of frequencies in each band. For that, I use both channels displaying swr, logmag, phase and the Smith Chart. By observing the changes in the Smith Chart, I can dial in the settings for the desired frequency and tweak the response around it.. I like to try to get the logmag down to -40 dB at that frequency if I can, but that is only at the exact frequency.

Jim:

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

The tag in the photo is an NXP NTAG203 chip in a Smartrac Bullseye inlay, about 10 years old. Smartrac never published the exact part number of Ntag203 in inlay X, and doesn't really exist anymore since merging with Avery. Google shows many old hits on both devices.

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

Sure, which to me argues against transmission line effects within the tag, i.e. behind the secondary winding, being significant to the VNA trace.

I will read up on non-ideal RF transformers and see if anything "sparks" an idea.
Larry

Hello Ed,

Op ma 18 jul. 2022 om 08:26 schreef Ed G8FAX <ed@...>:

For DM, the DP paper makes use of two baluns.

Like the HAL document, Fig 16b.

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.

But if you have the values you can also calculate the CM rejection (CMR).
But at the end I think that these two articles are more power-supply Choke
and not Transmission Line Choke. Which has a slightly different set of
parameters). The power supply choke have a fCO1 and fCO2, while I think
that the Transmission line Chokes have only fCO1:

Just as are the additional configurations of the HAL document Fig 3 (c),
(d) & (e) with T4 being equivalent to DP paper ‘open’.

DP Open is an OC S21 measurement. While HAL Fig 3 (c) T2, (d) T3 & (e) T4
are reflection measurements (to determine 'individual' choke parameters).

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!”

Certainly for a Choke it is important what is around it. That is why I test
on a styrofoam platform. So it is influenced by other objects (including
hands, etc.:


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.

Looks an interesting link as it handles 4:1 Ruthroff and Guanella (I think
he only discusses 4:1 and 16:1 Guanella) Thanks. Will study it

“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.”

Indeed one needs to know how good these Baluns are. But one needs something
to go from unbalanced the VNA port to balanced (the DUT).
I was wondering: if one includes the baluns in the calibration, would that
not calibrate that setup?

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.

Indeed that is the reference I would like to read also. Does someone have a
copy?

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

I think the 1:1:1 T-622-KK81 can do the function.

All the best,

Victor

On 7/18/22 10:10 AM, Marc et Nicole Feuggelen-Verbeck wrote:

What you say is correct but that is nitpicking : The value of an inductor does not change with increasing or decreasing frequency . 100?H now equals 100?H just as 100KOhm is equal to 100KOhm .
If not , the laws of physics must be rewritten . F=1/2(pi)(sqrt(LC))
An inductor is *a passive electronic component that stores energy in the form of a magnetic field*. In its simplest form, an inductor consists of a wire loop or coil. The inductance is directly proportional to the number of turns in the coil , the used materials and the envirement but not the frequency.

ideal inductors have zero diameter conductors with zero resistance, and the inductance is
proportional (approximately) to *square* of turns, (if all the turns are equally well magnetically coupled)


The *inductance* of a real inductor most certainly changes with frequency (as captured in standard works like those of Rosa and Grover)


for a variety of reasons - mostly that with finite sized conductors, the current is not distributed evenly, and that distribution depends on the frequency.

There is also an issue of "effective impedance" in that inductance can be partly cancelled by capacitance (in the worst case it completely cancels at self resonance).

End of story
Marco
Op 18/07/2022 om 15:42 schreef Jim Lux:

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.

Marco is correct. The inductance L does not change with frequency (except
for the small non-linear effects of the core materials).

HOWEVER, all real inductors also have parasitic capacitance and resistance,
which causes the Z (impedance, not inductance) to change with frequency.
And these effects are real, and can be quite large. So when the VNA
measures an inductor across a frequency range, you will see the impedance
(not inductance) change from something close to the pure 'L' inductance at
very low frequencies, to where the parasitic capacitance completely cancels
out that inductance at higher frequencies (at the LC resonant frequency)
and then the C becomes dominant at even higher frequencies. So it is often
useful to measure this impedance (or apparent inductance) at the frequency
the inductor will be used - where the modeling of its required valued was
done.

At DC and low frequencies, the Z of an inductor is dominated by its
inductance, and the Z and L are essentially the same. But at higher
frequencies the Z will be dramatically different, and depends highly on the
materials and construction techniques used in the inductor.

The nanovna and other vna's (and/or the software used to control them)
calculate the Z from the measured S11 or S21 parameters, often with a good
degree of accuracy. Then they calculate the L from the Z. There are more
limitations to the accuracy of this calculation.

A good LCR meter is likely a better tool to measure the 'L' of an inductor.

Stan

On Mon, Jul 18, 2022 at 10:11 AM Marc et Nicole Feuggelen-Verbeck <
f8voa54@...> wrote:

What you say is correct but that is nitpicking : The value of an
inductor does not change with increasing or decreasing frequency . 100?H
now equals 100?H just as 100KOhm is equal to 100KOhm .

If not , the laws of physics must be rewritten . F=1/2(pi)(sqrt(LC))

An inductor is *a passive electronic component that stores energy in the
form of a magnetic field*. In its simplest form, an inductor consists
of a wire loop or coil. The inductance is directly proportional to the
number of turns in the coil , the used materials and the envirement but
not the frequency.

End of story

Marco


Op 18/07/2022 om 15:42 schreef Jim Lux:

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.

--

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

What you say is correct but that is nitpicking : The value of an inductor does not change with increasing or decreasing frequency . 100?H now equals 100?H just as 100KOhm is equal to 100KOhm .

If not , the laws of physics must be rewritten . F=1/2(pi)(sqrt(LC))

An inductor is *a passive electronic component that stores energy in the form of a magnetic field*. In its simplest form, an inductor consists? of a wire loop or coil. The inductance is directly proportional to the number of turns in the coil , the used materials and the envirement but not the frequency.

End of story

Marco


Op 18/07/2022 om 15:42 schreef Jim Lux:

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.

--

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

On 7/18/22 8:24 AM, Observer wrote:

I inserted my nanoVNA, ( fully calibrated as swr ) into the input of my ATU100 auto tuner, with power off.
I got anything but an swr reading. Am I doing it right ?
Before test, I inserted the 50 ohm load at CH0 , and it showed 49.70 ohms 1:1.0025 . So, I assume, my vna is calibrated ok

Some ATUs "remember" the tuning setting when power is off, others don't. (i.e. some use latching relays, others don't).

What you should see, looking into the tuner, is the S11 with a dip at the tuned frequency, and not other places. As you change the tuner's Ls and Cs, the dip moves both in depth and frequency.


In general, the NanoVNA doesn't put out enough power for an auto tuner to actually do the tune cycle. If you have a tuner with a serial remote control (or equivalent) like the AT200PC, you can send inductor up/down and capacitor up/down commands and run a tuning algorithm on a PC that looks at the NanoVNA's measurements.

This is non-trivial.

Thanks, you are right. My fingers were writing in dbW but my mind was
working with dBm.

Thanks,
*Clyde K. Spencer*



On Mon, Jul 18, 2022 at 9:58 AM PE0CWK via groups.io <pe0cwk=
[email protected]> wrote:

Hi Clyde,

Reading your message, may I correct your example?
I.m.o. +30 dbW -> 1000 Watt and +10dB*W* -> 10 Watt

-Kees, PE0CWK

Op 18-7-2022 om 14:53 schreef Clyde Spencer:

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*



On Sun, Jul 17, 2022 at 4:17 PM<cariboome@...> wrote:

Good day. I'm fairly new to both amateur radio and this marvelous

device,

the NanoVNA H4 v4.3 sold by Seesii on Amazon.ca
I find tuning my many inverted V antennas using a manual tuner extremely
effective using this Nanovna -- set to s11 on 3 parameters for logmag,
Smith and SWR traces.

My question is: for some tuning, I often show a very low SWR (<1:1.05)
with a logmag reading of -15 or thereabouts, and another tune showing

about

the same SWR but a logmag of -40, -50 or even -90 dB. The logmag trace
sometimes appearing as a very steep and deep notch, often at or in the

SWR

trace and other times just a shallow dip. The Smith typically shows a
fairly consistent 50 ohms plus or minus 1 or 2 at tuned resonance. Is

this

a representation of reflected loss and VSWR being shown real time side

by

side? Is it better to have a logmag reading of -90 dB let's say, as

well as

a very low SWR -- vs very low SWR and a "higher" logmag of -20dB for
instance?

I sincerely hope I'm expressing myself sensibly...
--
- Dave
-VA7WNW-

Thank you all. I've attached images of some early readings made with the NanoVNA as I explored. It's an extremely valuable tool. I'm pleased to confirm I am using it correctly. The traces I was getting looked, to my ignorant eyes, too good to be true! But it is true: my first two attempts at antenna making are wildly successful!

--
-VA7WNW-

Hi Clyde,

Reading your message, may I correct your example?
I.m.o. +30 dbW -> 1000 Watt and +10dB*W* -> 10 Watt

-Kees, PE0CWK

Op 18-7-2022 om 14:53 schreef Clyde Spencer:

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.