NanoVNA Custom Software

[gf]

Reference = N ean shift trace 0 position to to N*Scale from bottom screen, yes not good

Thanks, so it is from the bottom of the screen. That's the detail I did not remember anymore (at the moment my NanoVNA is out of reach for a while, so I cannot verify).
Honestly, when I needed to use it for the first time, I was initially confused either.

[joeqsmith]

Of course, its not really from the bottom of the screen.  Say you enter 1 and things more up 1 unit.  Now you enter 1 again. It does not use the new bottom of the screen and more up 1 more unit.  It stays the same.  You would need to enter 2.  So its from some fixed location, not related to the current screen.   Where's that in the manual?   If you change the scale, better be ready to try and find your new reference.     I would have guessed there was a way to change the view with the touchscreen or jog switch but if there is, I couldn't figure it out. 

Still, IMO usable.  Just not the most intuitive or well documented product I have ever seen. 

[joeqsmith]

An example of some very poor cables.  All I am doing is moving them slightly.   With the error you are seeing, I would be checking to make sure that there are no problems with your setup.

[joeqsmith]

I tried a some short cables made from RG223 and noted little difference above 8GHz.   Its a bit too stiff. 
https://www.pasternack.com/flexible-0.216-rg223-50-ohm-coax-cable-pvc-jacket-rg223-u-p.aspx

You may have seen me use this cable as well.  It's much more flexible than the other double shielded cable I had been using.  Using this cable with all the adapters shown and careful calibratio, the cheap 20dB attenuator is still within a half dB sweeping from 1MHz to 6GHz.   Once we get into the harmonic mode, things fall apart but still useful.   

https://www.pasternack.com/flexible-0.122-rg188-ds-50-ohm-coax-cable-ptfe-jacket-rg188-ds-p.aspx

*** Note the two short RG223 cables to left

*** Letting the Lite run for a bit with the attenuator, seems stable. 

[DiSlord]

The mode of operation on harmonics is not the standard mode of Lite, the 3rd and 5th harmonics are used for measurement, because of which the dynamic range suffers (this mode just optional, but can be useful for example in TDR measures  for get better resolution). It is better to calibrate at these frequencies at high AVG values, this will reduce the noise in the calibration data, as well as in the measured data).
In general, you can get ~ 50dB in these modes, but there is a very long calibration
My 40 and 50dB measures

[Alextsu]

Hi, Joe,
Do You use a SMA fixed-torque wrench to attach the cables & DUTs every time or fix them by hand?

[Mechatrommer]

The mode of operation on harmonics is not the standard mode of Lite, the 3rd and 5th harmonics are used for measurement, because of which the dynamic range suffers (this mode just optional, but can be useful for example in TDR measures  for get better resolution).

if i buy a tool expecting to behave as in spec, and then the seller offers me a broken toy as a gift, i will happily accept that. i bought LiteVNA because 6.3GHz, now you offer 9GHz i will gladly accept that as bonus however broken it is. some application i can use eyeball or PC regression/averaging app to predict dut's behavior beyond 6.3GHz.. if you hear complaint from mourners you can ignore them. if they dont want the gift, they can always set stimulus to maximum of 6.3GHz.. btw i just asked Zeenko Store to ask Hugen to upgrade again NanoVNA-QT to support 9-10GHz, i hope they will listen.

[joeqsmith]

Hi, Joe,
Do You use a SMA fixed-torque wrench to attach the cables & DUTs every time or fix them by hand?

Normally, I try to leave the cables attaches to avoid wear.  For the Lite, I did install a couple of extensions to try and further minimize the wear.   

https://www.digikey.com/en/products/detail/amphenol-rf/132171RP/1011924

The adapters and cables are all torqued properly.   As for torquing  the DUT and cal standards, it depends.     Notice the cables I show that I claim are bad.  If you were using them below a few hundred MHz, you may find you get very good results with them.  Again, the lower the frequency, the less critical the mechanics which includes proper torque.  So to answer your question, it depends on what I am doing.  Just like calibration, a lot of times I won't do it or it's about the last thing I do.  Again, depends what I am after.

[joeqsmith]

The mode of operation on harmonics is not the standard mode of Lite, the 3rd and 5th harmonics are used for measurement, because of which the dynamic range suffers (this mode just optional, but can be useful for example in TDR measures  for get better resolution). It is better to calibrate at these frequencies at high AVG values, this will reduce the noise in the calibration data, as well as in the measured data).
In general, you can get ~ 50dB in these modes, but there is a very long calibration
My 40 and 50dB measures

I had someone recently write me about using one of these low cost VNAs to tune some filters.  These would have a fairly steep skirts and I would expect very low gains in the stop band.  Communications...   They were telling me how they were planning to use the average.  I was thinking to myself, if I were trying to tune a filter like this I would want the screen to be updating several times a second.   It will be interesting to see if they decide the one they bought was good enough for their application.   

[joeqsmith]

Pulsing S21 asynchronously with one and two firmware averages.  Maybe in the future we can have a trigger in and out.   

[joeqsmith]

Just for the fun of it, here's some sort of an attempt to use the Lite beyond 10GHz.  My software for the original 8754A supported using external mixers.   I built a test set back then that allowed me to experiment beyond 2.5GHz but even 20 years or so later, I would say I'm still just generating garbage.   

Shown looking at a S21 normalized with a 20dB MWM.  Then inserting an SMA T adapter (some sort of stubish notch filter).     

No cal standards along with poor cables, connectors and components.  I don't put any stock in it.  Fun but not useful.

[realfran]

I hope rev.3 of the software full integrate the Lite-VNA inclusive of the harmonic mode.
What is the setup on the Lite? Rev. 3 does not use the calibration on the FW.

[joeqsmith]

I hope rev.3 of the software full integrate the Lite-VNA inclusive of the harmonic mode.
What is the setup on the Lite? Rev. 3 does not use the calibration on the FW.

None of the software I have released to the public for these low cost VNAs allows you to select the internal calibration.  Nor do I support any feature that requires the touchscreen, buttons, jog switch or card readers.   I also only support a very small subset of the commands.  Just enough to get the data out of the unit. 

Obviously, the Lite was not sending the raw data but this has been corrected.  I'm not sure if they have support.  Read Dislord's firmware interface document: 
https://www.eevblog.com/forum/rf-microwave/nanovna-custom-software/msg3888317/#msg3888317

[realfran]

Yes, version 2.08 take is the measurement on. Thank you for the information, I use only with the PC.
Hope to get the rev.3 with the new feature.
Best regards.
Frank.

[joeqsmith]

Yes, version 2.08 take is the measurement on.

Every version including 3 will display what ever the VNA sends up.  If the VNA sends calibrated data,  my software uses it.   It does not know if the VNA was calibrated or not.   

For the original NanoVNA, I support the Recal function (allowed me to load any of the internal calibrations).  When I decided to open it to the public, I knew leaving a feature like this was going to confuse users,  so I moved it off the main page to try and save the antenna analyzer group the grief.   The manual warns about it.   I'm sure it's caused problems for a few people.   

[realfran]

I see on V.3 there is the averaging function that is good to use when required, the possibility to use on harmonic mode is one other possibility if the bridge permit.
One question: use one external mixer and directional coupler HPF filter like one of your videos suggests? will be too complicate?

[joeqsmith]

2 X mixers were used, one mixer to up convert and one to bring it back down.   There is also HP, LP, splitter, LO and directional coupler, depending what you are trying to do.   Mixer losses are 7dBish each, so a wideband amplifier is used.  In my example with the Lite looking at S21, no directional coupler was used.  For the old HP8754A looking at S11, a directional coupler was used.   

In concept, it's not too complicated and putting something together wouldn't be too difficult.   When playing around with some wire and transistors on a breadboard, I made this video showing a basic software model I wrote to demonstrate LeCroy's Digital Bandwidth Interleaving.   Roger Delbue of LeCroy chimed in.  The reason I mention this is it shows the basic concepts. 

[realfran]

Thank you for the very good video.

[joeqsmith]

Glad you enjoyed it.

[Alextsu]

FYI: a discussion about VNA calibration  error models goes here:
https://groups.io/g/nanovna-users/topic/34237712

This paper seems directly related to the Unknown Through Calibration error model, as I understand:
https://www.researchgate.net/publication/358164808_Measurement_Uncertainty_in_Network_Analyzers_Differential_Error_Analysis_of_Error_Models_Part_4_Non-Zero_Length_Through_in_Full_Two-Port_SLOT_Calibration

[joeqsmith]

Thanks.  I had read that email chain and was talking with a friend about it the other day.  The translation makes it difficult for me to follow.   It will require I spend a lot of time to try and make sense of it. I did not download the tools and source code to try and replicate their tests.   I also didn't read their final report.  There were some other nuggets I found in that mail chain but again, it takes time to research.   Did you read it and attempt to follow? Were you able to rebuild their code as well?   

[joeqsmith]

The Lite's internal averages compared with my software average and smoothing filter. 



https://www.microwaves101.com/encyclopedias/smoothing-is-cheating

[DiSlord]

I can suggest made calibration on big avg settings, this allow get less noise calibration data -> and as result less noise measured data after calibration.
I use minimum x10 avg on calibration.

Also 1001 points and 1x avg by sweep time equal 101 points and x10 avg. So if need more fast update better use less points.

PS sweep speed after 6.3G decreased, need more wait generator ready.

[joeqsmith]

I show the VNA without calibration for a reason.  No doubt that reducing the noise in general is a good thing as long as there is no loss of information. 

Because I don't tune a lot of filters, I'm not sure what people would generally consider an acceptable update rate.  I would imagine instant feedback is desired but maybe once every few seconds is good enough for a few.   Personally, I couldn't use something that slow to make several adjustments.  Giving up data points for faster feedback is certainly something users would consider when trying to use it to tune a filter.         

PS sweep speed after 6.3G decreased, need more wait generator ready.

Also, the SNR improves as we move below that.  Its less of a problem.   

As I mentioned, the one person who wrote was planning to average to increase the dynamic range.  The one thing they never mention is what they required.    It was a communications application so I would assume that they would need something better.


I was thinking I could take a filter and run it on the Lite using the firmware calibration (what ever parameters/procedure you recommend) and store the Touchstone data to the SD card.  Then run it with my software.  Repeat it with the V2Plus4 and maybe my old VNAs.   So I pull out a SD card go to slide it into the slot and it disappears into the unit.     I remove the 4 screws to recover my card and then make sure I fits.  No problem.  I then put the case back together and try to insert the card but discover the card is too short and I need to use something to push it in deeper than the case allows to get it to lock.     The experiment was doomed before it got started. 
 

[joeqsmith]

You can get the card to lock with the stylist.   I attempted to use a 64G SD card but was presented with a write error.  Lucky for me, the 121GW DMM  Dave offers uses a small card which worked fine.     

We can try to look at the difference of the dynamic range of the Lite using the firmware's calibration.  Anyone could repeat that test compared with some filter I have laying around.