NanoVNA Custom Software

[joeqsmith]

The cts use is supposed to be simple. The crux: I've got that 3V cts wire loose, not telling program that expected hardware(transfer relay) is connected. The rts is successfully toggling 3->0->3V as needed to initiate port switching.  I want to get rid of the error light in the program.

So you do actually need someone to tell you to wire that CTS pin to ground.       Imagine that, a TTL signal that is pulled up to 3V and you ground it to get a different state.   Who would have ever guessed that....

That's derisive.   

***
Added more detail in case it was not derisive enough!
Note to self.... Learn to spell... 

[joeqsmith]

I was suspecting my coupling caps were the primary cause of why my attempt to reproduce the CMT paper was a bit low.   Replaced the 4 X 22pF TH coupling caps with 2 X 1pF NPO that were mounted to the fixture.  (same caps used to replicate cyp_eev's experiment).   Jumpers shown could be about a pF... 

Q is now 14.388M / 750k = 19.2  Right on par.   

 

[jspencerg]

I've never experienced or read about the meaning of "asserted" in the context of digital signals.

I would thank you for the detail except it feels like you used the answer as another opportunity to heap scorn.

Considering the words of encouragement you've offered me does not balance these harsh interactions. 

No need to deride me further.  I will not be back.

[cyp_eev]

That article is somehow confusing. They are also using S21 for the calculation..

They are comparing the two methods against calculated values.

Interesting fixture. 

Yes, indeed, you are right!
The fixture is 3d printed. I think I have saved some fusion 360 or stl files, if needed.

I've never tried the capacitive coupling method, but great to see it's working. Thanks!

For fun attempting to replicate your test except following the paper.   I am using a 39pF ATC capacitor.   Your couple of uH makes no sense with the 37.6MHz.   Looks like we need something around 450nH.  I cut one that measures 509nH.   Whole setup seems to resonate around 35MHz.  Close enough.

Looking at the group delay, I  get roughly 2us or a Q of 217.

Yes, sorry, I have not calculated nor measured that L  , just cut a piece of wire and wrote "few uH" , so you are right.
I have also used a high quality cap from EXXELIA (https://www.digikey.com/en/products/detail/exxelia/501CHB390FCLE/14112408)
Obviously your L has higher Q.

Re: Checking PIN diodes
This wireless method was what Copper Mountain discussed,  but did not use in their experiment.  Thanks for showing actual application of wireless measuring.  So many questions:
What is point of break in coaxial sheath?  Was break location by trial or by principle?
I'll have to study on coupling before I can appreciate other details.  Thanks for showing results from both programs.

This article describes shielded and unshielded loops and also explaines the gap.
https://incompliancemag.com/article/shielded-vs-unshielded-square-magnetic-field-loops-for-emiesd-design-and-troubleshooting/

The PIN Diodes I have mentioned, are fast protection diodes, used to protect the MRI receivers from high RF energy fields.
In this case they are used in so called passive detuning circuits.
I try to simplify that.. So imagine the resonator I have used in the experiment as a receiver antenna and solder two diodes antiparallel on top of the capacitor. On low voltages,
under normal receiving conditions, this diodes have a very low conductance (aprox. 50uS). So the Q factor of the loop should be high.
Not so the defective diodes, with a lower resistance that decreased the Q factor.
The diodes should get conductive only when the MRI is transmitting and the voltage is rising. So they are basically clamping the capacitor, detuning the antenna thus protecting the receiver.

Happy Easter everyone!

Cyprian

[realfran]

Hello, I think will be simple to put your two-transistor NPN driver diagram with the FTDI cable to drive the transfer relay.

From the manual:The transfer relay is controlled by the state of the RTS pin. When RTS is de-asserted, Port 1
and 2 of the VNA will route to Ports 1 and 2 of the transfer relay. When RTS is asserted, Port
1 and 2 of the VNA will route to Ports 2 and 1 of the transfer relay. The software expects the
transfer relay to always assert the CTS pin, or it will set the transfer relay error (XferRly Err)
Transco PN# 82152-70070200 Driver
The Transco relay requires 24V and is a latching type relay. A simple DC-DC converter was
designed using a 7400 gate that boosts the USB voltage to 24V and charges a large capacitor.
This capacitor holds the charge needed to drive the relay.
Figure 93 shows the DC-DC converter made from a 7404 hex inverter. The two remaining
gates are used to buffer the signals to drive the relay coils. This is not meant as a reference to
base your own design from. Rather this is what I put together with what I had on hand

Reading the manual get some idea from the picture

[joeqsmith]

Re:  the meaning of "asserted" in the context of digital signals.

RS232 came out long before my time.  I remember playing with a UART from Radio Shack in the 70's.   The term assert in that context is common. 

https://en.wikipedia.org/wiki/RS-232
https://www.maximintegrated.com/en/design/technical-documents/tutorials/8/83.html

Still, you only have two states to choose from and if the software is telling you that the state of CTS is wrong, common sense should have prevailed and you would have grounded the pin and moved on.   

One question begs if software doesn't care about the state beyond setting the error so why use it at all?   I still have several serial devices.  Having the CTS signal always asserted isn't something common so I use it as a quick check to make sure I have the correct port selected.   

... This is not meant as a reference to  base your own design from. Rather this is what I put together with what I had on hand...

Reading the manual get some idea from the picture

You have seen my setup.  That controller was a quick SPICE and built in a few hours.  It sits inside a plastic bag...  Nothing is mounted to any sort of structure.   Goal was to demonstrate some decent performance with an off the shelf device over my previous attempts at building one from scratch.

I didn't ask what averaging was.  I asked if you used linear averaging and asked if you had considered exponential averaging.  You responded with a video explanation of how to average a list of numbers.

As we have seen, your questions typically leave me guessing as to what you are actually asking.  Sometimes its easier to show things at the child's level and go from there.   Sure you took offense to it.  Oh well. 

Some questions like this one, I left open assuming you would sort it out on your own.

Re: FIR smoothing
How many terms does the filter use?  Please specify algorithm,  ie Hanning, after Tompkins&Webster, etc.

I would imagine even the random button pushers would have figured it out in a few minutes and it goes something like this:   

Wait, a tab titled "Filters".  I wonder what that could possibly be..   Let's select it.   Smooth Taps, Smooth Cutoff, Smooth Window, Smooth Type.   My house and cars have windows.  Whats a Smooth Window?  Let's select it and see.   What on earth is a Blackman Nutall.  I just want to measure my antenna's SWR.   Why does the Joe Smith guy make things so complex? 

[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.