NanoVNA Custom Software

[joeqsmith]

The fixture is 3d printed. I think I have saved some fusion 360 or stl files, if needed.

I could see that being helpful to a few people.  If you wanted to take the time to detail it, I could add a table of contents to the starting post that links to it. 

[joeqsmith]

...

The nanovna 2 excels at this kind of measurement. However its not a "grid dip meter" obviously that is based on ancient technology. But the effect is the same and it has the potential to be much more precise. (if you adjust the stimulus parameters to give you high detail in the range you want to look at.

(The graphs I get when using it thethered - via USB are gorgeous.)
...

Consider my grid dip meter was most likely from the early 50's.  My HP8754A VNA from the 70s.  My PNA from the early 2000.  We have come a long way in RF tools in a very short time.   Much of what I show is just a ballpark.  Many times the VNA isn't calibrated.  If it is typically I stay with the ideal models.   

The following was a recent link from RF cafe,  July 1958.   
https://www.airplanesandrockets.com/electronics/approxi-meter.htm

Fun site..
https://www.rfcafe.com/

[joeqsmith]

Shown with the same ATC 100B390JW 39pF capacitor but place it in parallel with a CoilCraft 0805CS-680X 68nH.   The same 1pF NPO coupling capacitors were also used.  This should get us just under 100MHz.   Data sheet for the inductor shows a Q of about 45 @ 100MHz. 

Using the grid dip meter, it seems to resonate around 90MHz. From the datasheet, Q would be around 40.  It's difficult to use the grid dip meter to make this measurement.     

Measuring with the Lite after calibration, the peak measures 90.29MHz.  The 3dB delta is 2.4975MHz giving us a Q of 36. 

Looking at the group delay with an average of 10, it's roughly 130ns which gives us a Q of 37.

Should be easy enough to replicate.   

[joeqsmith]

Noticed some chatter about the H4.  Mine has never worked well enough to use it.   Similar to my V2Plus, I suspect just poor firmware.   I downloaded  NanoVNA.H4.v1.1.00.dfu  which appears to be the latest.

https://github.com/DiSlord/NanoVNA-D/releases/tag/v1.1.00

After programming this into the H4,  it does show the correct version but it no longer sweeps, or rather sweeps VERY slow.  Guessing several minutes to run a sweep with what ever the defaults are.   Its almost appears likes its default IFBW is below even 30Hz.  Rolling back to  NanoVNA H4 v1.0.38.dfu and it appears to be back to normal.    Reprogram in the latest, again hung.  Takes maybe 3 - 5 minutes to show a trace on the screen.   Setting BW to 4kHz no effect.  Setting number of points to 101, no effect.  Clear config and Reset have no effect.   Move the center freq to 300MHz and 1MHz span has no effect.   There's no software being used and the  H4 is not connected to the PC. 

As I said, it's never worked very well but seems it's much worse now.  Those of you trying to get the H4 to work with my software, or just in general, good luck. 

[joeqsmith]

My grid dip meter can measure just over 300MHz.   Plan was to do one last LC that resonates near the meters upper limit.   Rather than the 68nH, a 6.8nH was used with the same 39pF ATC part.   This should be a bit over 300MHz except for the parasitics, tolerance.....

Pic1 showing one of the the weak coupling caps.  These are a 1pF NPO  06035A1R0CAT2A.  See datasheet:
https://datasheets.kyocera-avx.com/C0GNP0-Dielectric.pdf

Pic2 removing mask and adding a small extender tab for the inductor to rest on.

Pic3 showing the 300MHz coil on the grid dip meter along with the new tank.

Pic4 Looks like it resonates just under 300MHz.   

Pic5 showing completed tank attached to the LiteVNA

Capture3 Running an uncalibrated wideband sweep to get some idea what it looks like.   Looks like it resonates near 295MHz.

Capture4 The LiteVNA has been calibrated.  The peaks centroid measures 294.838MHz.  The width measures 7.25MHz giving us a Q of 40.7.   The data sheet shows it around 30 at 300MHz (Capture2).

Capture5 showing the group delay (50 averages) of 44ns.  This gives us a Q of 40.7.

Not sure why the Q is so good.  Then again, these are typical numbers.

 
   

[joeqsmith]

My original NanoVNA does a fair job below 300MHz.  The firmware I have will allow 1.5GHz but results are really poor as you go beyond 900MHz. 

Shown is using a 3.3nH 0805CS Coil Craft part with the resonance at 800MHz.  Just below where the Nano changes bands.   Data sheet shows a Q of 40 typical.

First two pictures show the original Nano compared with the Lite with the tank attached after power up, no calibration.

Picture 3 shows the original Nano measuring a Q of roughly 36.   Making the same measurement with the Lite gave a Q of 37. 

[cyp_eev]

The fixture is 3d printed. I think I have saved some fusion 360 or stl files, if needed.

I could see that being helpful to a few people.  If you wanted to take the time to detail it, I could add a table of contents to the starting post that links to it. 

I've found the stl files for the double H-field probe.
The loop is made of RG178. These connectors seem to be the same type I have used:
https://www.ebay.com/itm/194989969715?hash=item2d664ed133:g:8DUAAOSwTBBiX269

I hope to find some time this weekend and upload a video with more details.

[joeqsmith]

The end of Solver64.  We hardly knew you. 

[buta]

I am sorry to hear you will not support the Solver3264.

Let the market force tell them it may be a smart decision or not.

[joeqsmith]

Why does the LiteVNA shift up and down near 750MHz?  Both of mine appear to do it.   As you can see, it has nothing to do with my software.   The switch point has a fair amount of jitter and appears like quantization noise. 

[joeqsmith]

Plan was to try a higher Q tank above 300MHz and again compare the Lite with the original Nano.   Showing group delay with 100 averages.   

[Kosmic]

The end of Solver64.  We hardly knew you. 

Would the community edition be an option ?

[joeqsmith]

When I looked into it, I thought I read that the community edition required an internet connection and would stop working if one was not provided.    There's no way I would invest any time into it based on that.  All it would take is for them to pull the plug on it.  After them changing their licensing, I have lost all trust in their leadership.   Without a perpetual license, I am locked into the versions I own. 

That whole NXG SNAFU tells you how disconnected they are from their remaining customers.  I wonder how much they had invested into that.  Lots of bad choices on their part.     

Looking forward, I see no reason for the schools to offer it.   I suspect things will start to dry up fairly quickly now.    We have already dropped all of our contracts with them.  I wonder how many companies are doing the same. 

All my opinion.  We will see how it plays out over the next few years. 

[Kosmic]

Yeah, they want to transition to the software as a service model but they are just not providing anything new or more.

[joeqsmith]

They do have their big parties and conferences if that's your thing.   

[Kosmic]

And apparently nobody's working during the weekend. Their website is down since yesterday 

[DiSlord]

Why does the LiteVNA shift up and down near 750MHz?

I think this related to MAX2871 switch
MAX2871 can generate in 3G-6G range, less frequency get from divide on 2, 4, 8, ....
750M - result 3G / 4 (at this point switch from 6G/8 to 3G/4)

Check 375M, 1.5G, 3G frequency

PS i not see this on my LiteVNA

[joeqsmith]

Why does the LiteVNA shift up and down near 750MHz?

I think this related to MAX2871 switch
MAX2871 can generate in 3G-6G range, less frequency get from divide on 2, 4, 8, ....
750M - result 3G / 4 (at this point switch from 6G/8 to 3G/4)

Check 375M, 1.5G, 3G frequency

PS i not see this on my LiteVNA

I'm not sure how I would test it at other frequencies (outside of constructing unique tank test circuits).    I'm not surprised you were unable to replicate it.  It appears to be a very unique case.

Injecting an RF generator into port2 sweeping the signal looking at the peak, first we cut the problem in half (removing the drive side) but I do not see the step.    I tried using a step attenuator to see if I could replicate it on a wider range or just at the 750MHz, no luck. 

I can tune the LC tank off that 750MHz (lower to 700MHz) and the step will go away.    The problem appears related to that 750MHz and appears to require a changing amplitude signal to replicate it.   

I tried to reduce the drive strength one level and the step goes away.   I then placed a step attenuator in series with the LC tank and again lowering the  signal causes the step to go away. 

I wonder if that high Q tank is causing some problem but only at certain frequencies.  Really strange.    Maybe one of the RF gurus can replicate it. 

[joeqsmith]

And apparently nobody's working during the weekend. Their website is down since yesterday 

When I tried, it appears it was a planned outage.

[joeqsmith]

Testing a tank at 350MHz, we can see the same step.  What is interesting is as I reduce the drive, the location of the steps narrows (move closer to the peak).   

***
I would show you this without the PC attached but I find it very difficult to scale what is on the screen.

[joeqsmith]

Showing a higher Q tank with the same resonance as the last one (yellow trace).   As we change the span from 100MHz down to 20MHz, we can clearly see the steps in the phase. 

[joeqsmith]

Zooming into the step.   (Note, I changed the delay slightly to show it is not as some unique phase point).     

[joeqsmith]

The more I looked into it, it appeared to be tied to the fact it's a high Q rather than the frequency it is running it. 

Shown with a Q of around 40 at 225MHz.   

The second plot showing the exact same settings and same LC tank circuit.  I have removed the two protection diodes on the front end. 

Makes sense now.   

[DiSlord]

I think you see gain step. V2 models use fixed gain settings for various ranges. This not allow get good resolution.

My last firmware changes - add AGC mode.
Exist one problem - not possible get perfect results on switch step due nonlinearity OpAMP gain. On V2 you also have this errors but not visible (you can see this near 140MHz on V2 most big jump and on 100MHz on Lite).

On start i made gain calibration (you can see it on DMSG screen as GAIN0-GAIN3) on fixed frequency.

How big step you see? My results near 0.01 to 0.05dB i thin this not critical

[joeqsmith]

>>How big step you see? My results near 0.01 to 0.05dB i thin this not critical

With last tank, 0.043 dB.  About  1 deg of phase error.  Of course -1/2pi*dP/dF..  That one degree phase step causes some pretty large spikes in the group delay.   I tend to agree.  Its a low cost unit and there's nothing really critical.  It's more just something to be aware of.   

I am still using the same firmware from Feb.  If you would like me to try a different version just post a link.