NanoVNA V2 aka S-A-A-2 Bug List and Suggestion for Improvement

[Mechatrommer]

if anyone found bugs on their NanoVNA V2 unit feel free to report here... let me start. after complete calibration is made. S11 plots (R and X) for "Open" condition give nasty result all over the screen, see 3rd attachment (open.jpg), plot for 50 ohm Load and Short is OK. if this is not a bug, feel free to explain because my Deepace KC901V VNA is not behaving like this, at open R is Inf at all frequencies (line on top screen) and X is -Inf (line at the bottom screen), not going up and down all over the place.

Suggestion:
please provide plot (trace) format Log |Z|, Log R and Log X, so impedance 0-Inf (or/and -ve Inf) can be fitted in one screen.

i'm slowly will dig into the FW source code if i have time and if i can do something about it. cheers.

[Verticon]

Hi Mecha,

your S11 curve in the "load" picture looks very bad. I would say either a bad calibration or a device failure.

Here are my corresponding plots including a thru plot

[Mechatrommer]

you are using V2 Plus 4 better hardware, mine is V2 Plus with 2.8" LCD, no metal enclosure. but FW still same bug (Open).

[Verticon]

Yes, I am using the brandnew V2 plus 4.

Concerning the "open" plots the problem could be noise. I attached another plot (Open-2) where I changed the scale for X and R. This is appropriate because R is expected to be very high. The traces are now much more steady but especially in the lower frequency range they are very noisy. And this is definitively random behaviour and no real structure.

I tried to smooth it by applying average mode. But even with 40x average the big random amplitudes remained. So it seems that at least for R and X measurements the average mode has a does not work properly.

[bicycleguy]

@Mechatrommer
You need to do a calibration at the sweep params.  I don't see the vertical SOLT on the left side as in @Verticons.

[Mechatrommer]

C*D is that in old FW. dont worry i know how to do SOLT calibration, otherwise i will not get near straight line plot on 50 ohm and short load. why i got disturbed by this is because my KC901V doesnt do this. and another thing is we cant just calibrate T alone on NanoVNA and hope it will get correct S21 plot, we need to do complete SOLT calibration, unlike my KC901V we can do SOL and T calibration separately. i'm not sure why SOL has anything to do with forward transfer plot. but i have accepted this as "trap for young players" and accept it the way it is, maybe different calculation method is used.

[bicycleguy]

Not sure what's going on with the R and X.  Mine is the same.  I have recently upgraded my v2.2 to v2 Plus.  I don't remember it doing that on R & X before so maybe a bug or the result of better sensitivity.  Unfortunately I didn't make b4 and after pictures with the upgrade.

[KD0CAC John]

Just got a new nanoVNA v2 4plus in the mail , after being on the waiting list , ordered about 2 weeks ago through Tindle , I chose this one & source because it was reported to be some money was getting back to one of original people ?
This version has a 18650 battery holder under the metal case .
Issue is install a 18650 battery voltage at 4.1 - it will not power up .
So plugged in to Macbook USB and powers up .
Measured power battery in off holder-connectors 4.1 volts .
Looked at pulling the unit out case and the mounting studs - spotwelded to lower case go threw one board to brass standoff into 2nd board / display and then screws on top .
So appears to have to take out boards separately - screws , display , standoffs , then 2nd board ?
Just doing some checking before calling seller , checking any other bases ?  
Haven't loaded any software on the Mac , but again the only way to power up . 

[Kean]

Just got a new nanoVNA v2 4plus in the mail , after being on the waiting list , ordered about 2 weeks ago through Tindle , I chose this one & source because it was reported to be some money was getting back to one of original people ?

Correct - it supports HCXQS and in turn OwOComm.

This version has a 18650 battery holder under the metal case .
Issue is install a 18650 battery voltage at 4.1 - it will not power up .
So plugged in to Macbook USB and powers up .

I don't have one of the plus4 units, but I understand this is a known issue.
The following note was recently added to the Tindie listing after others reported this problem
"After inserting the battery, you need to plug in USB power at least once to activate the battery management IC."

So as long as you don't remove the battery (and it doesn't go completely flat) you should then be OK after kickstarting it with USB power once.

Edit: mentioned here https://groups.io/g/NanoVNAV2/topic/78660927#670

[KD0CAC John]

Thanks for saying , I'll check it out .
Yes I did remove the battery before plugging to USB - Mac , Thanks

[KD0CAC John]

Thanks again .
Put battery back in , plugged in USB , turned on , turned off , unplugged USB , now turns on with battery

[Hydron]

Aha, I noticed something similar which confused me at the time but now makes sense:
- I bought a battery, didn't work when I tried it the first time
- Discharged battery externally to test it, found it was ~2/3 full straight from supplier - very confusing that it hadn't worked!
- Put battery back in NanoVNA V2 plus 4, plugged in USB to charge it (took quite a while from empty)
- Seems to work fine from then on, with or without USB plugged in

[switchabl]

i'm not sure why SOL has anything to do with forward transfer plot.

A plain response calibration (thru-only) is technically possible (maybe not implemented) but would be less accurate than an "enhanced response" calibration which relies on SOL as well to correct for mismatch of the source port

[KD0CAC John]

Dang back again , not a bug - but self inflicted " dead bug "
I did several searches to find something that could help with this , did not find , so new thread .
Seemed to bricked my nanoVNA , just received a couple weeks ago , and started just exploring / clicking around , there were a number of clicking tabs that I did not recognize , as an example DMESG etc.
After a few days of poking around I bricked the unit / or made mostly non responsive , I can bring up the touch options on the right side and go & click on everything .
But the screen is sweeping faster than normal , has many , or all of the color of sweeps all over the screen , the only effect I can make , is to pause sweep .
I tried pulling the battery & turning on , figuring some type of reset - no change .
I mainly only use a Macbook Pro , with no kind of Windows on it , haven't found any software to use with Mac , so assuming that I can not reload / updater firmware 20201013 ?
Next issue , have a old Toughbook CF-19 with Windows 7 Pro , last used a few yrs. ago , and I can not get it to recognize my hotspot , things are piling up ;(

For some reason the iPhone did not focus on the last photo , error screen .

 

[hajkrem]

I ran into the same issue as KD0CAC John. The VNA (v2plus4, from official tindie store) measured garbage when the frequency range changed to use the ADF4350 (~140 MHz and up). Further symptom was the lack of any output on that frequency range. This is my repair story.

Probably unrelated, but during disassembly the device stopped working completely. After measuring around, I realised the +3V line was missing and the 3V LDO died. I changed it to a pin-compatible MCP1700T-3002, which helped (MCU got juice), but the original problem still persisted.

After the disassembly, I set the device to CW 150 MHz, and I could measure around:
 - none of the ADF4350s were locked (blue leds on lock detect pins were off)
 - both ADF4350 got the reference clock (24 MHz) and SPI commands
 - however the SPI lines of the TX ADF4350 looked funky (see image, clk signal)
By touching the series resistors of the SPI line (R607,R608,R609), the ADF4350 randomly got locked (blue leds on). By this time I was pretty sure the problem is the capacitive loading of the SPI lines, so I removed all the parallel caps (C620-C622). This fixed the issue, and the PLLs locked every time.

I don't know what happened, I bought my unit about 6 months ago, and worked fine up to last week. Anyway, those SPI signals looked unhealthy for sure. I ordered some 0402 33pf replacements, I'll solder them in later.