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The NanoVNA doesn't have a separate Source and receiver ports, so you can't do the external amplifier, coupler approach in the Rackley paper.

Is there a reason you need high power for the test? (that is, can't you just push the mighty milliwatt from the VNA into the antenna)

What you might be able to do is sequentially make S21 measurements, switching the second port (CH1) of the NanoVNA to the various ports of the directional coupler (with attenuators as required). The challenge is that the power amplifier will be "outside the calibration plane", so you'd need to separately characterize it and then do the math to remove its contribution. A complication is that the PA's characteristics probably change with the load impedance.

The techniques in the paper rely on having multiple coherent receivers that are separately accessible, which the NanoVNA doesn't have - two of the three receivers are "dedicated".

Now it's true that you could probably go in and do some surgery on a NanoVNA (they're inexpensive, and you're collecting data into a computer, so you could get the one with the small display) and bring out the different ports you need. (basically, the inputs to the mixers fed from the stimulus, and the bridge on CH0) - you could replace the circuitry with a little board with the same input circuit that CH1 has (which is, I believe, a resistive pad and some coupling capacitors).

You could then use software (Scikit-rf in python for instance, has the libraries) to do the calibrations, etc.; using the modified NanoVNA just as a data collector.

Another approach would be to build up an equivalent system using some inexpensive SDRs all locked to a common reference - A programmable source (the NanoVNA) and 3 or 4 RTL-SDRs might work

From amfone :;wap2
John K5PRO:
Before the days of plastic antenna analyzers, you either used a GR bridge or a slotted line (for VHF), or just knew the SWR from a cheap wattmeter or Bird, or if you were lucky, a Delta OIB-2. This is the cousin of the famous OIB-1 and OIB-3 used by by broadcast engineers. Freq range is 2-30 MHz, 1 kW thru-power. Reads +/- 500 ohms resistive and up to +/- 800 ohms of reactance, and includes the meter amplifier for precise null

And the modern version using a Hp8753C with a DIY directional coupler , 2 Attenuators , and RF amplifier:


Newbie as I am on NanoVna , it will be beneficial if some can suggest how to use the NanoVna to achieve OIB measurements like the ones mentioned on the paper

Thanks Jim, now I understand better.

So, I will build a LC tuning circuit and I will measure afterwards to adjust it.

--
73 s Christian F8GHE

I've added impedance measurements to the S-parameter plotter. It now includes the one-port reflection method and the two-port series-through, shunt-through, and Y21 methods. Y21 cancels stray port reactance. The plotter includes reference impedance renormalization. You can measure a component at 50 ohms and see the response at its design impedance. I include a utility to merge files for forward and reverse S11 and S21 measurements to obtain S11, S21, S12, and S22. This lets you use a NanoVNA to fully characterize a component that may have an asymmetrical response, such as a ceramic filter.

The program is at the top of the following page. See the bottom of the page for downloading instructions.



Brian

Roger,

Thanks. I thought I had replied yesterday but apparently not. Well, let me shop some 0603 resistors and ferrites and I'll come back once I get something decent.

Also, my board is scrap.
1- I chose the wrong construction material when I ordered.
2- My transmission line does not have a proper return path. The strip on the next layer is way too narrow.
3- I need to remove those square pads at the antenna base points, they are for the surface mount version of this antenna.
3- My ground plane is 74mm long, as per datasheet, this should be 84mm

Perseverance, the first quality I teach my son... I'm too far in, I'll get to the end :)

Some of those techniques are more about measuring a high impedance component, so they wouldn’t work.

You’re making an S11 measurement - it’s just challenging because for end fed antennas, there’s more to the antenna than the wire you’re at the end of.

It’s the same as trying to measure the Z of a top hat loaded vertical or a vertical of any kind - where does the “other terminal” connect?

In the case of an end fed, the “other half of the antennna” is often the feed line.

Jim thanks very much for your advise.
During this afternoon I found these urls and now I don't know what is the best way to measure my end-feed antenna : Your or one of these :
-
-
-
--
73 s Christian F8GHE

Also ensure that the cable that you are using is a data cable and not just
one capable of only supplying power. Many cables can only supply power
unless specifically stated, so I use a cable tester to make sure that it is
capable of data.

The one supplied with your device should be a data cable as long as you got
it from a reputable seller.

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On Wed, Feb 26, 2025 at 7:41?PM Roger Need via groups.io <sailtamarack=
[email protected]> wrote:

On Wed, Feb 26, 2025 at 10:52 AM, Len Ward wrote:

Mine is not seen by Win 10 device manager. ( tried 2 cables and

machines) I

heard there is a way to get it out of DFU mode internally?
Mine did not die updating firmware, but it was hooked up to PC using

"saver"

program I think.
I installed the dfu se demo and file manager, but it's useless since PC

can't

see the device

NanoVNA Saver does not touch your firmware so it could not have damaged
your device. Your device cannot be "bricked" because the DFU loader is
built into ROM on the microprocessor.

Does your device boot at all or is it just a black or white screen? Can
you talk to it using the USB COM port and a serial program like Putty?

To get the H4 device into DFU mode you can do one of the following:
- Select DFU from the menu
- Push the jog switch down with the power off and then power on
- Open the case and short the VDD and Boot0 pins, then power on and remove
the short

When you do one of the above and are connected to a Windows PC you should
hear a "bing" in Windows. If you go into Device Manager you should see
that your device is recognized. One of two drivers will be installed. One
works with DFUse and nanoVNA app for firmware loading and the other works
with STM Cube. You can search this group and the group Wiki for the many
messages on how to install drivers and use these programs.

Also suggest you read the Absolute Beginners Guide to the NanoVNA in the
Files section of this group.

Roger

Roger

On Wed, Feb 26, 2025 at 10:52 AM, Len Ward wrote:

Mine is not seen by Win 10 device manager. ( tried 2 cables and machines) I
heard there is a way to get it out of DFU mode internally?
Mine did not die updating firmware, but it was hooked up to PC using "saver"
program I think.
I installed the dfu se demo and file manager, but it's useless since PC can't
see the device

NanoVNA Saver does not touch your firmware so it could not have damaged your device. Your device cannot be "bricked" because the DFU loader is built into ROM on the microprocessor.

Does your device boot at all or is it just a black or white screen? Can you talk to it using the USB COM port and a serial program like Putty?

To get the H4 device into DFU mode you can do one of the following:
- Select DFU from the menu
- Push the jog switch down with the power off and then power on
- Open the case and short the VDD and Boot0 pins, then power on and remove the short

When you do one of the above and are connected to a Windows PC you should hear a "bing" in Windows. If you go into Device Manager you should see that your device is recognized. One of two drivers will be installed. One works with DFUse and nanoVNA app for firmware loading and the other works with STM Cube. You can search this group and the group Wiki for the many messages on how to install drivers and use these programs.

Also suggest you read the Absolute Beginners Guide to the NanoVNA in the Files section of this group.

Roger

Roger

Nico,

You mentioned that you are just starting off with RF design. You have picked a difficult starter project because at 900 MHz. there are many factors that come into play that are not big issues at lower frequencies like HF.

Many things can affect your measurements.
- improper calibration of the VNA
- your PCB transmission lines not being 50 ohms
- your ground plane does not meet manufacturers specs.
- stray capacitance and inductance
- SMA connectors not properly torqued
- impedance bumps due to male/female SMA connections
- objects near the antenna
- the test coax outer shield becoming part of the antenna

I suggest that you get familiar with de-embedding your cable using small SMD cal loads and then try measuring some known resistance components like 75, 100 and 150 ohm to get a feel for how sensitive things can be at these high frequencies.

Don't use a short cable and mating SMA connectors and edelay to extend the reference plane. De-embed the cable by doing short and open first and then solder a single 50 ohm 0805 to the end to finish the cal. Then solder on a 100 ohm and see of you get 2:1 SWR and measure close to 50 ohms. Then remove it and solder to the board with very short shield/center conductor connections.

You need to verify that your transmission line on the board was calculated correctly and is close to 50 ohms. Those offshore boards are cheap so design one with a number of transmission lines that are laid out the same way that you are doing now. Solder some 0604 50, 75, 100 and 150 ohm resistors to the end. Then verify you get the proper SWR..

W0LEV gave you some tips for testing for common mode current on your RG174 test cable. Try some Fair-Rite Mix 61 binocular cores from DigiKey and loop the coax through them.

Roger

Mine is not seen by Win 10 device manager. ( tried 2 cables and machines) I heard there is a way to get it out of DFU mode internally?
Mine did not die updating firmware, but it was hooked up to PC using "saver" program I think.
I installed the dfu se demo and file manager, but it's useless since PC can't see the device

The feedline is still part of the antenna. The best you could do with this
setup (the first image) is to decouple immediately after the SMA connector
(ideally before the connector). 61 or 52 material ferrite clamp-ons? A
small diameter (1/4-inch or less) single layer coil of possibly three turns
right after the SMA might also do the job. You need to get the outer
surface of the coax out of the picture. As it is, it forms part of the
antenna.

With the setup in the first image, lightly grab the coax and run your hand
up and down the coax between the PCB and the VNA with your fingers around
and touching the coax. Does anything on the VNA change? If not, you're
sufficiently decoupled. If so, and things change on the VNA while doing
so, you need to decouple the outer surface of the coax shield from being
part of the antenna.

Dave - W?LEV

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On Wed, Feb 26, 2025 at 3:57?AM Nico via groups.io <nicolassimard=
[email protected]> wrote:

Wow ! Thank you so much to every one for taking your time in helping me. I
truly appreciate it.

@Siegfried @John
I finally did it. I've cut down my RG174 down to the shortest length I
could (35mm). I'v calibrated at the end of an RG316 I have, then connected
the "board-to-pcb adapter". I added a 180ps Edelay. I tried to double the
value (for round trip) but with no differences.

@WOLEV : The Whole board measures 100mm and the ground plane measure 74mm
in length. I'm realizing at writing this this could be a part of the
problem ? If this is a 1/4 wave monopole, then it should needs the
equivalent as a ground plane, that could mean my ground plane is not long
enough ? it should be 84 according to the datasheet. mmm I may have to
reorder some pcbs !

@Jim
1- No, unfortunately I don't have the evaluation board. I'm on my own, I
know almost nothing in RF !
2- This antenna is designed for high volume applications. In my case the
"high volume" will be 2 units !, Anyways, this antenna is sold in either
through hole or surface mount. There are squares as pads for the surface
mount version. I may have to remove them as I use the through hole one.
Unfortunately, I won't have access to any design tools in that field. Even
if I had one, I would not know ho to operate it to extract valuable data...
If my LoRa (20mW of extreme power !) module is not 50Ohms on the output, I
will never know and there won't be any ways I'll be able to measure it.

@Roger
1)My pcb stack is a standard 4 layer from JLC PBC with controlled
impedance option selected. They offer the calculator for the appropriate
trace width. As per the datasheet of the antenna, the transmission line
from the RF module to the antenna itself has a ground plane on layers 2 and
3 to offer the return path for the feedline. This is what is recommended in
the datasheet. This is what I did and know I understand the reason. So, in
theory, from the LoRa module to the antenna, this should be a transmission
line and not a part of the radiating element. Thanks for pointing out ;)
2)With my short 35mm adapter tonight, I tried 180ps and 360ps as Edelay
with no differences.
3) I tried yesterday to calibrate with the cable shorted, opened and then
loaded with a combination of a 47 + 3 ohms of 0805 chip resistor I had on
hand. I don't remeber exactly and I don't have any pictures but by memory
it gave me negative values as the R. Assembling two chip resistor to make
one, not the greatest idea. I will have to order som 50Ohms chip resistor .
Question : Can I use 0805 it should definitely be 0603 ? I've somewhere
there could have capacitance effect on a too big of a chip.
4) Thanks for the info on ferrites. I'll give them a look.

So here is my progress so far:
- Tonight I'v cut the cable to 35mm but calibrated at the end of my 30cm
RG316. Look at the pictures to see the results.
- I've realized that my ground plane may be too short and have to modify
the boards and order new ones.
- I've ordered an RF inductor and capacitor kit for the CLC matching
network. I'll give it a try and see from there where it goes.

To be continued...

--

*Dave - W?LEV*


--
Dave - W?LEV

One way might be to use a transformer. ?Minicircuits has small, inexpensive transformers in a DIP package in ratios up to 16:1 or 25:1.

1:25 CORE & WIRE Transformer, 0.02 - 30 MHz, 50? | TT25-1-X65+ | Mini-Circuits ( )
minicircuits.com ( )

( )

That will get you from 50 ohms to 1250 ohms.

End fed antennas are tricky to measure (and model), because in most cases, the outside of the feedline winds up being part of the antenna.

Hi,
Currently trying to design and tune a 1/2 end fed antenna (RF is applied on one end), I am looking for the correct method to measure its impedance. As this one is very high I don't know the right méthode !

The result of this measurement should allow me to create a Stub with SimNEC to tune it.
Thanks in advance for your help

--
73 s Christian F8GHE

I recently wrote a program to renormalize S-parameter impedance. This lets you measure a filter with a 50 ohm VNA even though the design impedance is higher. In the course of testing the program, I needed to plot S-parameters. I searched extensively for suitable viewers, desktop or online. The ones I located were either incomplete, frustratingly awkward, or had bugs.

I decided to write my own Windows S-parameter plotter. It's near the top of the following page. See the bottom of the page for downloading instructions.



The first image compares group delay for two Murata ceramic filters. The next images show the benefit of phase unwrapping.

Brian

Wow ! Thank you so much to every one for taking your time in helping me. I truly appreciate it.

@Siegfried @John
I finally did it. I've cut down my RG174 down to the shortest length I could (35mm). I'v calibrated at the end of an RG316 I have, then connected the "board-to-pcb adapter". I added a 180ps Edelay. I tried to double the value (for round trip) but with no differences.

@WOLEV : The Whole board measures 100mm and the ground plane measure 74mm in length. I'm realizing at writing this this could be a part of the problem ? If this is a 1/4 wave monopole, then it should needs the equivalent as a ground plane, that could mean my ground plane is not long enough ? it should be 84 according to the datasheet. mmm I may have to reorder some pcbs !

@Jim
1- No, unfortunately I don't have the evaluation board. I'm on my own, I know almost nothing in RF !
2- This antenna is designed for high volume applications. In my case the "high volume" will be 2 units !, Anyways, this antenna is sold in either through hole or surface mount. There are squares as pads for the surface mount version. I may have to remove them as I use the through hole one.
Unfortunately, I won't have access to any design tools in that field. Even if I had one, I would not know ho to operate it to extract valuable data...
If my LoRa (20mW of extreme power !) module is not 50Ohms on the output, I will never know and there won't be any ways I'll be able to measure it.

@Roger
1)My pcb stack is a standard 4 layer from JLC PBC with controlled impedance option selected. They offer the calculator for the appropriate trace width. As per the datasheet of the antenna, the transmission line from the RF module to the antenna itself has a ground plane on layers 2 and 3 to offer the return path for the feedline. This is what is recommended in the datasheet. This is what I did and know I understand the reason. So, in theory, from the LoRa module to the antenna, this should be a transmission line and not a part of the radiating element. Thanks for pointing out ;)
2)With my short 35mm adapter tonight, I tried 180ps and 360ps as Edelay with no differences.
3) I tried yesterday to calibrate with the cable shorted, opened and then loaded with a combination of a 47 + 3 ohms of 0805 chip resistor I had on hand. I don't remeber exactly and I don't have any pictures but by memory it gave me negative values as the R. Assembling two chip resistor to make one, not the greatest idea. I will have to order som 50Ohms chip resistor .
Question : Can I use 0805 it should definitely be 0603 ? I've somewhere there could have capacitance effect on a too big of a chip.
4) Thanks for the info on ferrites. I'll give them a look.

So here is my progress so far:
- Tonight I'v cut the cable to 35mm but calibrated at the end of my 30cm RG316. Look at the pictures to see the results.
- I've realized that my ground plane may be too short and have to modify the boards and order new ones.
- I've ordered an RF inductor and capacitor kit for the CLC matching network. I'll give it a try and see from there where it goes.

To be continued...

And also remember line lengths on/in the dielectric are shortened by the
reciprocal of the SQRT of the dielectric constant (I assume
FR-4?....nominally 4.2).

Dave - W?LEV

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Virus-free.www.avg.com
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On Mon, Feb 24, 2025 at 9:57?PM Jim Lux via groups.io <jimlux=
[email protected]> wrote:

I don't know that shortening it even more makes all that much difference.
You can guestimate the loss and to a first order, you're looking for
reasonably flat S11 across your band, right? So if 174 it's <1 dB round
trip, and you get -10 dB S11, then it's probably really something like -9.

How picky is your source about reflected power?(most low power sources
aren't very picky)
-10 dB is only 10% reduction in radiated power (assuming it doesn't
reflect back to the antenna and get radiated <grin>)
Those antennas aren't super efficient anyway.

-----Original Message-----
From: <[email protected]>
Sent: Feb 24, 2025 10:21 AM
To: <[email protected]>
Subject: Re: [nanovna-users] Am I in the right track ?

Let me apologize if my yesterday's post was not clear. The pictures I
posted are actually the result of the recommendation you gave me. I took a
30cm RG-316 cable I have and calibrated at the very end. Then I made a 6in
RG-174 from that end that connect on the pcb. I added a 760ps delay to
compensate for the RG-174. Tonight I will try to shorten it as much as I
can and some measurements.

The radio transceiver I intend to use has a 50ohm output. The feedline I
created on the pcb should also be a 50 ohm line. I made the pcb fabricated
with controlled impedance. This way, the fab house provides the dielectric
constant of the pcb stack up and provide trace width recommandation to
achieve the desired impedance, which I followed. The antenna I chose is
also 50ohm.

I will follow up.

Thanks again

--

*Dave - W?LEV*


--
Dave - W?LEV

Nico,

A couple of points to consider.

1. I can't tell from your PCB photo if you had tracks on both sides of the board in order to implemented a transmission line from the matching network to the helical antenna. This is required because a single track will make for an additional radiating element. Attached is the manufacturers layout for your antenna.

2. The edelay on most of the NanoVNA products is the round trip delay. You used 760 ps which is only one way. On my NanoVNA I have to enter 1.52 ns. To verify your edelay is correct short the end of 6 inches of RG174 and see if you are on the far left of the horizontal line on the Smith Chart. Adjust your edelay until you are.

3. The edelay method will be OK for Return Loss and SWR measurements. Your impedance measurement (R & X) results will be MUCH better if you calibrate right at the end of the cable with an open, short and 50 ohm SMD chip. Then solder to your board. The edelay at 900 MHz. will not give you good estimates of R and X because of slight loss in the cable and impedance bump at the SMA connection. Try this yourself by measuring a 100 ohm SMD resistor using both methods.

4. You need to use ferrites on the cable which are appropriate for the frequency of operation. I suggest a number of Fair Rite Mix 61 as shown in the attachment. A binocular core with holes big enough for a few turns would help reduce common mode current.

I don't know that shortening it even more makes all that much difference. You can guestimate the loss and to a first order, you're looking for reasonably flat S11 across your band, right? So if 174 it's <1 dB round trip, and you get -10 dB S11, then it's probably really something like -9.

How picky is your source about reflected power?(most low power sources aren't very picky)
-10 dB is only 10% reduction in radiated power (assuming it doesn't reflect back to the antenna and get radiated <grin>)
Those antennas aren't super efficient anyway.

Let me apologize if my yesterday's post was not clear. The pictures I posted are actually the result of the recommendation you gave me. I took a 30cm RG-316 cable I have and calibrated at the very end. Then I made a 6in RG-174 from that end that connect on the pcb. I added a 760ps delay to compensate for the RG-174. Tonight I will try to shorten it as much as I can and some measurements.

The radio transceiver I intend to use has a 50ohm output. The feedline I created on the pcb should also be a 50 ohm line. I made the pcb fabricated with controlled impedance. This way, the fab house provides the dielectric constant of the pcb stack up and provide trace width recommandation to achieve the desired impedance, which I followed. The antenna I chose is also 50ohm.

I will follow up.

Thanks again