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Does the mfr provide a "how we measure it" document?

Test fixturing, sample circuits, etc. are important.

You'll see this kind of thing with devices designed for use in embedded systems - For instance, there are a lot of "monolithic WiFi" antennas, which are designed for 2.45 GHz, but only on a specific board layout in a specific environment. It's a tiny SMT "chip" with no connector, and if you put it into a SMT clip fixture, it probably doesn't read 50 ohm resonance.

If your measurements are showing more inductive, it might be that the mfr is assuming some capacitance to surroundings in the circuit. I notice in the picture that there's a bunch of capacitors and spots for capactiors. It might be that the mfr intends for you to add components for a specific application.

Hi Doug, having done quite a few RFID antennas, that 1 to 1 is rather optimistic.
One thing to consider, do you have any other metal within a foot or so of the antenna?? ?You can easily see a pair of pliers passing a foot or so from the loop.
Good luck with your project, Kent WA5VJB

I have a 125 kHz RFID antenna consisting of a coil and series tuning capacitor. The manufacturer supplied plots of the SWR and Z of the antenna showing a nice 50 Ohm 1:1 SWR at resonance. I have tried to replicate these plots using my newly purchased NanoVNA and I get radically different plots showing a load closer to 25 Ohms and a 2:1 SWR. Measuring the L and C separately gives about the same readings I get with my HP4801 vector impedance meter at 125kHz, but it is near the upper frequency limit of the HP4801 so results are shaky. I calibrated the NanoVNA over the same range as shown in the manufacturer's plots. My Smith plots are centered on the horizontal axis like I would expect them to be. The manufacturer's plots are shifted up to the inductive half of the Smith chart. Both show a nice resonant dip at 125 kHz.

Am I doing something wrong? Is the antenna manufacturer lying?

SherpaDoug WA1UWP

exactly !

Hey Dave,

I agree with you, my TI99/4A is still my favorite. (just kidding but I did use it for years) I now use win 7 and buy malware to keep it clean.

Mike C.

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

I would solder the coax shield to the area labeled GND in the antenna design, not to the ground plane nearby.

Hi Dianne,

What model/version of the nanoVNA do you have? many do not cover the 2.4GHz bluetooth frequency band.

What diameter/type of coaxial cable are you currently using? Type RG316 has diameter 2.5mm and RG178 diameter 1.8mm.

My advice is to test your antenna with a length of cable that will be used in the final product with a connector that will be used in that design.

I hope the above is of some help to you

Kind regards

Ed

Thanks for your reply.
I managed to correct the delay
I was asking the same question to my tutor about the size of the cable in
relation to the PCB. I am on an internship and I have to design a PCB trace
antenna. The company wants the antenna size to be as small as possible to
integrate into their IoT device for low-energy Bluetooth communication. I
don't think I can get a smaller SMA cable than this for soldering, I will
look if you have a proposal, I'm a taker. Attached is the antenna design
and the solder image.
Best regards

Le ven. 15 juil. 2022 à 15:35, Siegfried Jackstien <
siegfried.jackstien@...> a écrit :

You have to calibrate at the cable end with open short load
And with such big cable soldered to such a tiny pcb your results will be
at least questionable...
On so high frequencies even an sma to n adaptor will shift your smith 90
degrees around... A long cable if not calibrated out will show a handfull
of circles (as you can see)..
Dg9bfc sigi

Am 15.07.2022 14:20 schrieb dianebonk2@...:

Hello everyone,
I am a beginner in using the NanoVNA, I have a calibration problem after
connecting a transmission line into the VNA. You can see some pictures of
the result in the attached document after connecting the cable to the VNA
in the attached file.
Could someone tell me how to correct the impedance shift introduced by

the

cable? Thanks
I went to the "electrical delay" menu to correct the problem by adding a
delay but it got worse. I don't know what to do.

I want to solder the cable afterwards into a PCB where we have antenna
traces.

Hello,
Thank you for your answer. My DUT is a PCB trace antenna. Attached is a
picture of the antenna. I need to perform the measurement in the feed line
of the antenna. I am in an internship and the company is designing an
antenna for their Iot device(Bluetooth lower energy communication). They
want the antenna to be as small as possible. I am wondering if the size of
the antenna feed line can skew the antenna measurement.
I succeed to correct the delay I think.
Best regards.

Le ven. 15 juil. 2022 à 16:20, Douglas Butler <sherpadoug@...> a
écrit :

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

Le ven. 15 juil. 2022 à 18:22, Roger Need via groups.io <sailtamarack=
[email protected]> a écrit :

On Fri, Jul 15, 2022 at 05:58 AM, <dianebonk2@...> wrote:

Hello everyone,
I am a beginner in using the NanoVNA, I have a calibration problem after
connecting a transmission line into the VNA. You can see some pictures

of the

result in the attached document after connecting the cable to the VNA in

the

attached file.
Could someone tell me how to correct the impedance shift introduced by

the

cable? Thanks
I went to the "electrical delay" menu to correct the problem by adding a

delay

but it got worse. I don't know what to do.

I want to solder the cable afterwards into a PCB where we have antenna

traces.

The most accurate way is to calibrate at the end of the cable using a
short, open and a 50 ohm SMD or very small resistor with absolute minimum
leads.

The other way is to use the electrical delay to compensate for the length
of the cable With a 33 cm (12 inch) cable I had to set the edelay to 3.18
ns to get the open at the far right of the smith chart. Try 0.1
nanoseconds (100 picoseconds) for each cm of cable and then keep adjusting
until you get close to the far right on the Smith chart. The velocity
factor of the cable you use will have an effect so the 100 picoseconds is
just an estimate to get you in the ballpark.

Roger

On Fri, Jul 15, 2022 at 05:58 AM, <dianebonk2@...> wrote:

Hello everyone,
I am a beginner in using the NanoVNA, I have a calibration problem after
connecting a transmission line into the VNA. You can see some pictures of the
result in the attached document after connecting the cable to the VNA in the
attached file.
Could someone tell me how to correct the impedance shift introduced by the
cable? Thanks
I went to the "electrical delay" menu to correct the problem by adding a delay
but it got worse. I don't know what to do.

I want to solder the cable afterwards into a PCB where we have antenna traces.

The most accurate way is to calibrate at the end of the cable using a short, open and a 50 ohm SMD or very small resistor with absolute minimum leads.

The other way is to use the electrical delay to compensate for the length of the cable With a 33 cm (12 inch) cable I had to set the edelay to 3.18 ns to get the open at the far right of the smith chart. Try 0.1 nanoseconds (100 picoseconds) for each cm of cable and then keep adjusting until you get close to the far right on the Smith chart. The velocity factor of the cable you use will have an effect so the 100 picoseconds is just an estimate to get you in the ballpark.

Roger

What exactly do you want to measure? What is the Device Under test, DUT? Is it the PCB? Is it the cable? Is it the combination of the two? If you just want to measure the PCB you need to do the calibration through the cable.

You have to calibrate at the cable end with open short load
And with such big cable soldered to such a tiny pcb your results will be at least questionable...
On so high frequencies even an sma to n adaptor will shift your smith 90 degrees around... A long cable if not calibrated out will show a handfull of circles (as you can see)..
Dg9bfc sigi

Am 15.07.2022 14:20 schrieb dianebonk2@...:

I bought my NanoVNA in large part to have a solution looking for a problem to solve. My main use for this device was the SWR sweep capability for my antennas, but I soon discovered previously unknown problems that now needed a VNA solution. How pleasantly convenient.

Having a real time Smith Chart display is absolutely invaluable for getting a good feel on impedance for one. More, I have some SDR receivers that can be overloaded by a 50KW AM broadcast station a few miles away. The solution was to build custom filters. My first one, using an online passive filter design tool, was a 500 KHz LPF. It's quite satisfying whipping up a design and then see it perform. I found that even using 10% tolerance parts and tiny axial inductors, I could still produce an effective filter. The VNA proved to me that specifying a cutoff frequency with a good gap to the required cutoff frequency meant I could get by without strict tolerances and hi-Q torroid inductors.

My latest filter design was for a 22nd order 3.5 - 30 MHz BPF. I never would have ever tried that without my NanoVNA. And it works, knocking down the BCB and giving an excellent, although not as deep [nor needed], upper cutoff. This exercise was just as much about learning how to build and test the filter as its actual use.

Testing 455 KHz IF filters made for another fun experience, especially since I had to compensate for the wildly different 2K Ohm I/O impedances.

Yes the NanoVNA for me was a solution looking for a problem to solve. Kinda like going to school and learning how to solve a problem and then look for a problem to solve, lab exercises so to speak, but with immediate real world applications. Chicken or egg? Which comes first is not important. Just pick one and work towards the other.

Theory is always incomplete. It is said that the field of thermodynamics learned much more from the operations of steam locomotives than steam locomotives learned from thermodynamics. Often electrical building codes lag advances in electrical technology by decades. In my specialty of ship hull inspection there are always the ship design drawings and the "As Built" drawings. "We ran out of 10# plate so we used 12# plate until we could get more from the foundry."

Hello everyone,
I am a beginner in using the NanoVNA, I have a calibration problem after connecting a transmission line into the VNA. You can see some pictures of the result in the attached document after connecting the cable to the VNA in the attached file.
Could someone tell me how to correct the impedance shift introduced by the cable? Thanks
I went to the "electrical delay" menu to correct the problem by adding a delay but it got worse. I don't know what to do.

I want to solder the cable afterwards into a PCB where we have antenna traces.

Hello Ed,

Op vr 15 jul. 2022 om 11:23 schreef Ed G8FAX <ed@...>:

Hi Victor,

Oh wow, what a fantastic webpage you have, full of useful information.
Your attention to detail, investigations and experiments is exemplary and I
congratulate you for all your efforts.

Thanks, but when I get a better grip on the OCFD (aka being ableto model
and include in that moe the Choke) I plan to revisit teh webpage(as it is
now somewhat cluttered with all kidn of experiments I did. I think all are
valid but it coudl be better structured with the present knowledge I have;-)

I must confess, I have only read parts of it. What springs to my mind, is
the choice of ferrite material and power handling, this will alter any
model if capabilities are exceeded. I’m sure you are aware of that and if
not addressed this already, will do so.

I did not look at power issues (I think I will using my equipmentin the QRP
range), but I agree it could be extended with that. Who knows, when I have
the need.

Also, have you considered an open wire feed rather than coaxial? Again
forgive me if you have already looked at this alternative.

I did not do that (yet?). Also here I am planning to use coax and thus I
restricted intially to that.

When we are discussing models, the OC model comprises of a CM part and DM
part. The CM parts has parallel resistances and reactances. I’m sure you
are aware that these can be also be represented by equivalent series
circuits. Thus by translating the shunt inductors with the resistors, the
circuit could be re-drawn with a form similar to that of a transmission
line (TL). By the way I would call that configuration a “balanced Pi”
arrangement. Anyone following this discussion, not familiar with converting
parallel to series circuits, I refer in the first instance to

The 'equivalent' circuit maps the best my measurmenets is the model of
Guanella (to ideal transformers; a transmission line to represent the DM
and a ractance+resistance to represent the CM); see also Owen Duffy's page:


I am relatively new to the nanoVNA (I have H4.2) and still exploring the

very many menu options of firmware 1.2.00. It appears that the instrument
now has capability of presenting results in either series or shunt form, I
have yet to investigate this, and many more things. This might help when
producing values for a model.

I use NanoVNA Saver for that (or the s1p/s2p files and my excel
spreadsheet).

In respect of the G3TXQ link, I agree, it is not clear. What I do get from

reading it is that his chokes are coils made from coax cable wound on a
toroid and wonder as it is not a transformer arrangement if it is
applicable/relevant to our current discussion?

I think this is part of the dsicussion of terminology;-) 1:1 Guanella
(which I use and also G2TXQ) is lso a 1:1 transformer, but I call it a
Choke as I use it mainly as a choking device.

I also think there is a terminology issue with calling this ‘common mode’,
a point you raise on your lovely webpage, to me I see it more as a ground
loop between inner and out of coax line. Thoughts? Considering his test
arrangement and firmly bonding grounds of generator and measuring ports, I
wonder/think he connects croc clips to each end of the braid, as that is
where the ‘choking’ is required, else what what be measured on the inner
route and centre?

Teh 1:1 Guanella Choke (whihc is also used by G2TXQ on that page (indeed
coax on a toroid), can be used in the CM0 (crocs on both end of braid plus
shield) or the CO (crocs on both end of braid or crocs on both end of
shield) onfiguration (he is certainly not used CM2 or CM3 configuration)

I am not familiar with the ‘open’ measurement technique, to be honest,
never heard of it until you raised it in a previous post, so can not give
any helpful comments on how useful it is for determining CM & DM
performance of a CMC. I will study the ‘HAL’ link information and get back
to you.

The HAL article is nice and also this one:

I think the OC, DM and CM are nicely explained and modelled.
But IMHO this article and HAL's are abouvt power-supply chokes (a lot of
windings), whcih are build a little different than RF chokes (more aligned
with transmission line).

All the best,

Victor

P.S. just received the toroids, need to test the complex mu so I can design
these 'ideal' Transfomers for the DM measurement.

“In theory there is no difference between theory and practice, while in practice there is “
Benjamin Brewster

Hi Victor,

Oh wow, what a fantastic webpage you have, full of useful information. Your attention to detail, investigations and experiments is exemplary and I congratulate you for all your efforts.

I must confess, I have only read parts of it. What springs to my mind, is the choice of ferrite material and power handling, this will alter any model if capabilities are exceeded. I’m sure you are aware of that and if not addressed this already, will do so.

Also, have you considered an open wire feed rather than coaxial? Again forgive me if you have already looked at this alternative.

When we are discussing models, the OC model comprises of a CM part and DM part. The CM parts has parallel resistances and reactances. I’m sure you are aware that these can be also be represented by equivalent series circuits. Thus by translating the shunt inductors with the resistors, the circuit could be re-drawn with a form similar to that of a transmission line (TL). By the way I would call that configuration a “balanced Pi” arrangement. Anyone following this discussion, not familiar with converting parallel to series circuits, I refer in the first instance to

I am relatively new to the nanoVNA (I have H4.2) and still exploring the very many menu options of firmware 1.2.00. It appears that the instrument now has capability of presenting results in either series or shunt form, I have yet to investigate this, and many more things. This might help when producing values for a model.

In respect of the G3TXQ link, I agree, it is not clear. What I do get from reading it is that his chokes are coils made from coax cable wound on a toroid and wonder as it is not a transformer arrangement if it is applicable/relevant to our current discussion? I also think there is a terminology issue with calling this ‘common mode’, a point you raise on your lovely webpage, to me I see it more as a ground loop between inner and out of coax line. Thoughts? Considering his test arrangement and firmly bonding grounds of generator and measuring ports, I wonder/think he connects croc clips to each end of the braid, as that is where the ‘choking’ is required, else what what be measured on the inner route and centre?

I am not familiar with the ‘open’ measurement technique, to be honest, never heard of it until you raised it in a previous post, so can not give any helpful comments on how useful it is for determining CM & DM performance of a CMC. I will study the ‘HAL’ link information and get back to you.

Like you, I have also been wondering about suitable baluns (transformers), if there are any reasonably priced commercial items available or how to make one, so very interested in what core you use, number of turns and wire gauge. I think some experimentation is required and happy to give it a go, but my schedule means in August or later. I was also wondering if a suitable CMC wired or used in voltage mode would be a suitable item as a transformer here, thoughts?


Kind regards

Ed, G8FAX