Re: Am I in the right track ?
Once again,
Thanks to all of you for your inputs. Poorly translated from french, I would say that I did not know in what type of gearbox I was going to put my finger in !
Well, I ran some other experiments tonight. Here is what I've found.
The antenna is an helical monopole where the pcb copper pour serves as the antenna ground plane. I really made sure to follow the manufacturer's layout recommendations. The feed line (as pictured in my original post) shows the feedline also, designed as suggested by LINX. I've included the PI matching network at the very end of the ground plane as also recommended.
This is the datasheet link:
I did what you guys suggested. I've cut a 6in piece of RG-174 and the used a 30cm RG316 extension I have. I did the SOL at the end of the extension and added a delay of a few pico seconds for the remaining piece that attach to the pcb.
@Roger Need: Thanks, Oh, I forgot to mention some board details. I attached pictures of my pcb. My cable is attached where the LoRa radio module will go, as seen on the bottom side. The feedline to the antenna should be a 50 ohms impedance feedline, it goes to a matching network (as recommended by the manufacturer) and then to the antenna. The ground plane dimensions are specified and the distance of the antenna from the ground plane border also, which I've respected. It is a 4 layer PCB. Layer #2 has a ground strip line under the trace that goes along with it that should form the 50 ohm line right down to the antenna itself.
@John, Thanks for your input. could you point me out to some ferrite cores ? I would not know what to look for exactly. If you know some specs and a good source for it, that would be awesome.
Well, I get some interesting result but I'm not sure if I understand what is happening. As you can see with the pictures, if I hold the board in my hands, I get what I would call a "proper" response. But once I lay the boar on the top of the pole, the signal looks like crap. Putting the pcb back into its enclose does not make any significant differences, good or bad.
By holding it and then read something better, does that I mean that my body becomes the ground plane it needs ? Would that mean then that the pcb ground plane is not sufficient in size ? That would be weird as the pcb ground plane is slightly larger than what is recommended by the manufacturer.
Once again, thanks to all of you for lighting up lantern, I truly appreciate your advices.
RF has a steep learning curve ;)
Nicolas
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Re: testing non-50 ohm filters was Re: [nanovna-users] NanoVNA port renormalization
Can you show a closeup picture of the TEST JIG for your NanoVNA please. ________________________________ From: [email protected] on behalf of CLIFTON HEAD via groups.io Sent: Sunday, February 23, 2025 5:01 PM To: [email protected]Subject: Re: testing non-50 ohm filters was Re: [nanovna-users] NanoVNA port renormalization ________________________________ From: [email protected] on behalf of Roger Need via groups.io Sent: Sunday, February 23, 2025 1:26 PM To: [email protected]Subject: Re: testing non-50 ohm filters was Re: [nanovna-users] NanoVNA port renormalization On Sun, Feb 23, 2025 at 07:52 AM, Team-SIM SIM-Mode wrote:
MFJ company says that MFJ259 antenna analyser becomes inaccurate when
measuring reactances below 7 Ohm or above 650 Ohm, i am really impressed with
the good S21 responses you have even with a high value Z Renormalisation as
440 , Congratulations, may be NanoVna-H4 has a little more dynamic range then
MFJ instrument
I own an MFJ259, a RigExpert AA-55 and a NanoVNA H & H4. The MFJ is the poorest performer of the bunch and not really useful for measuring resistance or reactance to any degree of accuracy. The RigExpert and NanoVNA are much better when used as one port VNA's for impedance measurements over a range of 1 to 3000 ohms. Some plots of the NanoVNA measuring components is attached. Results are quite good in my opinion.
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Re: testing non-50 ohm filters was Re: [nanovna-users] NanoVNA port renormalization
Can you show a closeup picture of the TEST JIG for your NanoVNA please. ________________________________ From: [email protected] on behalf of Roger Need via groups.io Sent: Sunday, February 23, 2025 1:26 PM To: [email protected]Subject: Re: testing non-50 ohm filters was Re: [nanovna-users] NanoVNA port renormalization On Sun, Feb 23, 2025 at 07:52 AM, Team-SIM SIM-Mode wrote:
MFJ company says that MFJ259 antenna analyser becomes inaccurate when
measuring reactances below 7 Ohm or above 650 Ohm, i am really impressed with
the good S21 responses you have even with a high value Z Renormalisation as
440 , Congratulations, may be NanoVna-H4 has a little more dynamic range then
MFJ instrument
I own an MFJ259, a RigExpert AA-55 and a NanoVNA H & H4. The MFJ is the poorest performer of the bunch and not really useful for measuring resistance or reactance to any degree of accuracy. The RigExpert and NanoVNA are much better when used as one port VNA's for impedance measurements over a range of 1 to 3000 ohms. Some plots of the NanoVNA measuring components is attached. Results are quite good in my opinion.
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Re: Am I in the right track ?
as shorfter the cable as better your setup
dg9bfc sigi
Am 23.02.2025 um 20:32 schrieb Nico via groups.io:
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Show quoted text
These are very interesting points, thank you very much for that.
I was questioning myself wondering if my technique was appropriate. Thanks again for confirming it can be improved.
I will follow up on that once I could have put my hands on some connectors...
Regards,
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Re: Am I in the right track ?
Nico,
You don't necessarily need more connectors.
You could calibrate at the end of your RG174 cable by detaching it from your board, then using a small 50 ohm chip capacitor, an open circuit, and a direct short as your standards. If the leads are kept very short this should work reasonably well at 900MHz.
Once re-attached to your board, ferrite cores near the antenna end of the cable would be a good idea, too.
--John Gord
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On Sun, Feb 23, 2025 at 11:32 AM, Nico wrote:
These are very interesting points, thank you very much for that.
I was questioning myself wondering if my technique was appropriate. Thanks
again for confirming it can be improved.
I will follow up on that once I could have put my hands on some connectors...
Regards,
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Re: Am I in the right track ?
On Sun, Feb 23, 2025 at 12:36 AM, Nico wrote:
My board is hooked up to the vna through an RG-174 I had laying around. It is
2 meters exactly. I have added an E-Delay of 10.1ns as per a calculator I
found on the Times microwave website. I don't know if there is a bug in the
vna's firmware but I had to put 0.66 as the velocity factor in order to make
it display 2.00 meters as the cable length. If I put 66 as in 66%, it shows
200 meters. Anyways, I'm not sure if that part is that relevant.
When you use the edelay feature in a NanoVNA to move the reference plane from the SMA connector to a distant point you really need to have a short cable so the attenuation is minimal. This is not the case with 2M of RG174 at 900 MHz as others have pointed out. You really need to establish the reference plane at the end of the cable by "de-embedding" and doing the SOL calibration with the cable open, shorted and using a 50 ohm SMD load. The other problem you have is what you are attempting to measure. From the pictures it looks like a helical antenna with a short connecting PCB trace that will be a loading inductor. The "other half" of the antenna looks like the ground plane of the PCB. When you connect your RG174 cable to the board the outer surface of the coax shield and the NanoVNA will now be part of the antenna, will radiate and affect your measurement results. You need to slide many ferrite beads of the correct mix over the cable near where it attaches to the board to act as an RF choke. If you shorten the RG174 and see the results change (after calibrating at the end again) then this indicates this kind of problem. Another thing to consider is that the manufacturer does not specify an antenna with a 50 ohm feedpoint impedance. Maybe the antenna suggested is an end fed half wave and they have a matching circuit. I am only guessing here. Roger
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Re: Am I in the right track ?
These are very interesting points, thank you very much for that.
I was questioning myself wondering if my technique was appropriate. Thanks again for confirming it can be improved.
I will follow up on that once I could have put my hands on some connectors...
Regards,
|
Re: testing non-50 ohm filters was Re: [nanovna-users] NanoVNA port renormalization
On Sun, Feb 23, 2025 at 07:52 AM, Team-SIM SIM-Mode wrote:
MFJ company says that MFJ259 antenna analyser becomes inaccurate when
measuring reactances below 7 Ohm or above 650 Ohm, i am really impressed with
the good S21 responses you have even with a high value Z Renormalisation as
440 , Congratulations, may be NanoVna-H4 has a little more dynamic range then
MFJ instrument
I own an MFJ259, a RigExpert AA-55 and a NanoVNA H & H4. The MFJ is the poorest performer of the bunch and not really useful for measuring resistance or reactance to any degree of accuracy. The RigExpert and NanoVNA are much better when used as one port VNA's for impedance measurements over a range of 1 to 3000 ohms. Some plots of the NanoVNA measuring components is attached. Results are quite good in my opinion.
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Re: testing non-50 ohm filters was Re: [nanovna-users] NanoVNA port renormalization
Hi Jim
MFJ company says that MFJ259 antenna analyser becomes inaccurate when measuring reactances below 7 Ohm or above 650 Ohm, i am really impressed with the good S21 responses you have even with a high value Z Renormalisation as 440 , Congratulations, may be NanoVna-H4 has a little more dynamic range then MFJ instrument what can explaine this even if we loss 10 times the accuracy when we are away from 50 Ohm , but in this case we should pay some attention to the thermal stability of the NanoVNA , give it some time to startup before calibration and measurements, anyway i am happy with this Z-renomalisation functions.
73s Nizar
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Re: Am I in the right track ?
May be it's a new version in program, that you must enter the velocity factor as .66 and not in percent. Your measured data are ok, but the 2m RG174 has a loss of 2dB @ 900 Mhz. So the real mismatch at your antenna is -2.34 dB. (You must add 2 x 2 dB). That is very bad for an antenna. A better way will be to use the 2m RG174 with a connector at the end and make a calibration at this end. Thn use a very short cable from that connector to your PCB.
Am 23.02.2025 um 04:46 schrieb Nico via groups.io:
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Show quoted text
Hi,
Is my setup ok ? Is there any monstrous mistakes in my montage ? I'm quite new to the nanoVNA. Well, I am totally new on VNAs themselves. I did not know their exitance 2 months ago ! Well, I want to match my antenna because so far, it is pretty horrible. But, before ordering some matching network component and then screwing everything because I am missing something obvious, I would like someone to point me to the rookie mistakes I could have made.
The project is a LoRa module (902-928MHz) connected to a small antenna mounted on a pcb. The pcb is inside a small polycarbonate box. I have followed the design rules for this antenna from the manufacturer. I have calibrated my nanoVNA-F V2 (from sysjoint) using the supplied calibration set, straight at the S11 connector. My board is inside its final box and mounted on a wood plank that mimic the final location. My board is hooked up to the vna through an RG-174 I had laying around. It is 2 meters exactly. I have added an E-Delay of 10.1ns as per a calculator I found on the Times microwave website. I don't know if there is a bug in the vna's firmware but I had to put 0.66 as the velocity factor in order to make it display 2.00 meters as the cable length. If I put 66 as in 66%, it shows 200 meters. Anyways, I'm not sure if that part is that relevant.
So, by looking at the pictures, does anyone can see some obvious mistakes ?
Thank you so much
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Re: Am I in the right track ?
it?s close ... but you will get much better results if you use a short cable ... and calibrate at the end of that cable
dg9bfc sigi
Am 23.02.2025 um 04:46 schrieb Nico via groups.io:
toggle quoted message
Show quoted text
Hi,
Is my setup ok ? Is there any monstrous mistakes in my montage ? I'm quite new to the nanoVNA. Well, I am totally new on VNAs themselves. I did not know their exitance 2 months ago ! Well, I want to match my antenna because so far, it is pretty horrible. But, before ordering some matching network component and then screwing everything because I am missing something obvious, I would like someone to point me to the rookie mistakes I could have made.
The project is a LoRa module (902-928MHz) connected to a small antenna mounted on a pcb. The pcb is inside a small polycarbonate box. I have followed the design rules for this antenna from the manufacturer. I have calibrated my nanoVNA-F V2 (from sysjoint) using the supplied calibration set, straight at the S11 connector. My board is inside its final box and mounted on a wood plank that mimic the final location. My board is hooked up to the vna through an RG-174 I had laying around. It is 2 meters exactly. I have added an E-Delay of 10.1ns as per a calculator I found on the Times microwave website. I don't know if there is a bug in the vna's firmware but I had to put 0.66 as the velocity factor in order to make it display 2.00 meters as the cable length. If I put 66 as in 66%, it shows 200 meters. Anyways, I'm not sure if that part is that relevant.
So, by looking at the pictures, does anyone can see some obvious mistakes ?
Thank you so much
|
Am I in the right track ?
Hi,
Is my setup ok ? Is there any monstrous mistakes in my montage ? I'm quite new to the nanoVNA. Well, I am totally new on VNAs themselves. I did not know their exitance 2 months ago ! Well, I want to match my antenna because so far, it is pretty horrible. But, before ordering some matching network component and then screwing everything because I am missing something obvious, I would like someone to point me to the rookie mistakes I could have made.
The project is a LoRa module (902-928MHz) connected to a small antenna mounted on a pcb. The pcb is inside a small polycarbonate box. I have followed the design rules for this antenna from the manufacturer. I have calibrated my nanoVNA-F V2 (from sysjoint) using the supplied calibration set, straight at the S11 connector. My board is inside its final box and mounted on a wood plank that mimic the final location. My board is hooked up to the vna through an RG-174 I had laying around. It is 2 meters exactly. I have added an E-Delay of 10.1ns as per a calculator I found on the Times microwave website. I don't know if there is a bug in the vna's firmware but I had to put 0.66 as the velocity factor in order to make it display 2.00 meters as the cable length. If I put 66 as in 66%, it shows 200 meters. Anyways, I'm not sure if that part is that relevant.
So, by looking at the pictures, does anyone can see some obvious mistakes ?
Thank you so much
|
Re: Adapting the LiteVNA for SAR?
Use S21 mode with an amplifier.
People have been using VNAs as radars for years.
The NanoVNA just makes it easier.
Dealing with the big first reflection is tricky. One way is to use a separate cancellation path that is adjusted to null the first reflection. ?That’s what we did for the FINDER victim detection radar.
FINDER: Radar for Locating Disaster Victims ( )
jpl.nasa.gov ( )
( )
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On Feb 17, 2025, at 08:51, KENT BRITAIN <WA5VJB@...> wrote:
? Hi Larry
I have worked on several GPR projects.? One is currently looking for land
mines in SE Asia.
A LOT of loss going though dirt.??? And a big impedance bump at the
air/dirt interface.
They really need much more power than the Nano puts out.?? And since the
same port is Tx and Rec, an amp will not be simple.????? But lots of neat
stuff down there.?? Kent
On Monday, February 17, 2025 at 10:17:28 AM CST, Larry Rothman via
groups.io <nlroth@...> wrote:
Folks,
Using the NanoVNA as a signal source for Ground Penetrating Radar (GPR)
was discussed a couple of years ago. Today on Hacker News, there is an
article about a home-built Synthetic Aperture Radar (SAR) unit using a
freq around 6GHz.
The article discusses theory and the problem of finding a suitable Rcv
A/D. The LiteVNA has the freq range, is capable of resolving nS time (to a
certain amount), can measure phase and is programmable.
The big issue is probably the switching time of the generator/reflection
ICs in the front-end of the LiteVNA. As for the A/D spec, would the
heterodyne method and DSP used be a limiting factor?
So - might it be feasible to make use of the LiteVNA in a simplified radar
setup using an external controller and appropriate antennas?
Could the TDR routines be adapted?
Could the LiteVNA be used with a TinSA-Ultra and a controller for
something?
Just thinking out of the box here. In my 60+ years of Tech, I have always
looked at repurposing stuff. So, instead of "not possible" answers, I
would rather hear what might need to be changed (electronics /software) to
achieve a minimal proof of concept. Thinking caps on....
... Larry
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Re: testing non-50 ohm filters was Re: [nanovna-users] NanoVNA port renormalization
You have noted the shortcomings of* ANY* VNA, including those from the "big boys" at $$$$$. Nothing new, here. Yes, the VNA deals with impedances. Frequency analysis best be accomplished using a spectrum analyzer, not a VNA. Time analysis best be accomplished using an o'scope. Impedance domain......frequency domain......time domain...... Dave - W?LEV On Sat, Feb 22, 2025 at 2:47?PM Team-SIM SIM-Mode via groups.io <sim31_team= [email protected]> wrote: Hi
We have the impression that the NanoVNA is as an impedance meter, a
Q-meter or a frequency analyzer, while it is only a transmission line
network analyzer, that is to say we have to do with impedances that turn
around 50 Ohm with a SWR that can go to 10:1 max beyond which the
precision loses much of its meaning,
in fact the S11 measurements are made at the base of a physical 50 Ohm
resistive divider bridge, it is sufficiently precise around 50 Ohm but it
loses its precision as we move away from this value, saying very correct
measurements is between 5 and 500 Ohm otherwise the interpretation of the
measurements becomes very compromised,
thus the Z-renormalization should not used to the extrem much from 50 Ohm
and it will be tedious as we are moving away from 50 Ohm, so renormalizing
the Z to 440 Ohm is really at the limit of validity of these ingenious
calculation methods which facilitate the measurements with the greatest
simplicity and least chance of implementation errors.
so with this good results, we are already Happy .
73's Nizar
-- *Dave - W?LEV* -- Dave - W?LEV
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Re: testing non-50 ohm filters was Re: [nanovna-users] NanoVNA port renormalization
Indeed, it is optimized for 50 ohms, but I don’t know that I’d say the precision loses much of its meaning as you get away from that.
Can you quantify your assertion?
Ultimately, the accuracy is determined by the uncertainty of the raw I/Q measurements, which is around 1 part in a few thousand, and then whatever that does when calculating reflection coefficients. At big mismatches the signal into the reflected port of the bridge is large, so the SNR is high (70-80 dB?) which is 1 part in 10,000.
As they say in school, show your work - give an example of a measurement uncertainty with an unknown near 50 ohms, and then one of one near, say, 500 ohms, and 5k.
The Copper Mountain folks have an article on various ways to measure Z, and there’s differences in how the errors stack up whether you’re doing series or shunt techniques. That might be a place to start.
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On Feb 22, 2025, at 06:47, Team-SIM SIM-Mode via groups.io <sim31_team@...> wrote:
?Hi
We have the impression that the NanoVNA is as an impedance meter, a Q-meter or a frequency analyzer, while it is only a transmission line network analyzer, that is to say we have to do with impedances that turn around 50 Ohm with a SWR that can go to 10:1 max beyond which the precision loses much of its meaning,
in fact the S11 measurements are made at the base of a physical 50 Ohm resistive divider bridge, it is sufficiently precise around 50 Ohm but it loses its precision as we move away from this value, saying very correct measurements is between 5 and 500 Ohm otherwise the interpretation of the measurements becomes very compromised,
thus the Z-renormalization should not used to the extrem much from 50 Ohm and it will be tedious as we are moving away from 50 Ohm, so renormalizing the Z to 440 Ohm is really at the limit of validity of these ingenious calculation methods which facilitate the measurements with the greatest simplicity and least chance of implementation errors.
so with this good results, we are already Happy .
73's Nizar
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Re: Starting trouble for NanoVNA!
I'm starting to think that adding the washers, (in other words increasing the space between the NanoVNA's front/top cover and the touchscreen just a teeny bit) solved the start-up problem as well, because when I press the menu on-off/toggle control while I turn the power on, I get the same blank screen as described above.
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Re: testing non-50 ohm filters was Re: [nanovna-users] NanoVNA port renormalization
Hi
We have the impression that the NanoVNA is as an impedance meter, a Q-meter or a frequency analyzer, while it is only a transmission line network analyzer, that is to say we have to do with impedances that turn around 50 Ohm with a SWR that can go to 10:1 max beyond which the precision loses much of its meaning,
in fact the S11 measurements are made at the base of a physical 50 Ohm resistive divider bridge, it is sufficiently precise around 50 Ohm but it loses its precision as we move away from this value, saying very correct measurements is between 5 and 500 Ohm otherwise the interpretation of the measurements becomes very compromised,
thus the Z-renormalization should not used to the extrem much from 50 Ohm and it will be tedious as we are moving away from 50 Ohm, so renormalizing the Z to 440 Ohm is really at the limit of validity of these ingenious calculation methods which facilitate the measurements with the greatest simplicity and least chance of implementation errors.
so with this good results, we are already Happy .
73's Nizar
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On 22/02/2025 09:42, werthercaro via groups.io wrote:
-=-=-=-=-=-=-=-=-=-=-=-
Thanks for the reminder. Upgraded OK and working on an H4/MS. David -- SatSignal Software - Quality software for you Web: Email: davidtaylor@... BlueSky: @gm8arv.bsky.social, Twitter: @gm8arv
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Re: Starting trouble for NanoVNA!
My version appears a bit different. 73 Jon, VU2JO On Fri, Feb 21, 2025 at 10:08?PM Barry Leonard KN4JRF via groups.io <w9jbl= [email protected]> wrote: Fixed the jumpy menu (kinda). Put two 0.7mm/0.027in flat washers as thin
spacers on rt. side on NanoVNA (see foto) to keep cover from pressing on
touch screen.
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Roger Need
schweppe
Barry Leonard KN4JRF
David J Taylor
