NanoVNA Custom Software

[joeqsmith]

I made an attempt to try the Scan command using the comments below.  The Nano responds with a "?" which suggests that it does not understand the command or the syntax is invalid.   I've been avoiding looking at the firmware but it appears that this is really the only source of documentation for it.  Github seems to be down at the moment but I'll have another look later.   

 

I added one command to the eddy firmware to enable on demand scans of
arbitrary length (yes, you can scan with one million steps or much more if you want)

Usage:
First pause the continuous scanning with "pause" and the use the "scan" command
to scan [from frequency in Hz] [increment frequency in Hz] [number of steps]
The frequency increment step is for now an integer
The scan command outputs

start
frequency s11_real s11_imag s21_real s21_imag
done

during the scan the calibration is NOT used so the output are uncalibrated numbers
allowing alternative calibration strategies

Example:
ch> pause
ch> scan 5000000 20 5
ch> start
5000000 0.001503840 0.000420701 -0.306770563 0.018568072
5000020 0.000695601 0.000503197 -0.306792527 0.018579231
5000040 0.000532656 0.000520238 -0.306793421 0.018573865
5000060 0.000495833 0.000512704 -0.306819111 0.018593480
5000080 0.000520689 0.000523833 -0.306812644 0.018576323
done

ch>

[joeqsmith]

Typing Help, Scan is not listed as a valid command.   Makes sense.   Github was back up so I downloaded the source and had a look at Main.c   

    { "gain", cmd_gain },
    { "power", cmd_power },
    { "sample", cmd_sample },
    //{ "gamma", cmd_gamma },
    //{ "scan", cmd_scan },
    { "sweep", cmd_sweep },
    { "test", cmd_test },
    { "touchcal", cmd_touchcal },

So while it looks like they may have considered adding this feature, it is not supported.   There may have been no benefit to something like this versus using my segmented approach.    Still, the upgrade is well worth it just for that one bug fix.   The system is now fairly stable. 

[radiolistener]

yeah, just tested, it is missing from the firmware 20-SEP-2019, so it will be added in the next release

[joeqsmith]

After adding 900M-1.5G into the mix, the noise from 500M to 900M doesn't seem so bad.   

Video clip showing the scatter plot:
https://www.youtube.com/watch?v=1xzNyqJ1T30&feature=youtu.be

[joeqsmith]

I have some abilities to filter the data.   Shown with a simple smoother.    There no penalty for the screen update rate as it ran across individual scans.   

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

I should mention that I have yet to try averaging the data.  The problem is how slow the Nano is.   Early on, I had tried a few things, like turning off all the traces to try and improve the sweep rates but it appeared to be fixed.   With the new firmware, it's slightly faster because I no longer have to throttle the data rate to keep the Nano from sending bad data.  Still, the improvements are not significant enough to try and average the data. 

[Bicurico]

"NANOVNASAVER SOFTWARE WALKTHROUGH + NANOVNA FIRMWARE UPDATES BRING 1.5 GHZ MAX RANGE"

https://www.rtl-sdr.com/nanovnasaver-software-walkthrough-nanovna-firmware-updates-bring-1-5-ghz-max-range/
https://github.com/mihtjel/nanovna-saver
https://github.com/ttrftech/NanoVNA

[Bicurico]

I compiled the firmware - not tested, yet - and it does compile without errors.

Attached for everyone's convinience.

Update: Just noticed i can't flash this, as it is not a DFU file! The instructions are wrong for compiling/flashing this. Don't want to use the ST-LINK V2 right now...

The FW that was linked a few posts earlier already increases apparently up to 1500MHz - I just did not try.

Also, while compiling works, I end up with a *.bin file instead of a *.dfu file. The difference is of course that teh DFU mode expects a file with the the corresponding headers, which are not present in the *.bin file. How do I compile a DFU file?

Regards,
Vitor

[joeqsmith]

People still ask for my LabView interface but I'm not sure why.  The open sourced Python seemed to really be what people were asking for and it certainly seems like they have made a progress with it.   Anytime I've asked what features they are missing, I never get a response.  They may just not be aware of the open source project.   

[Bicurico]

That's the point: I first saw people asking for feature and considered it an opportunity to write a donation-based software.

But then I looked at the existing applications and found them to be of a pretty high quality, so I asked people what they were unhappy with.

The only one responding was you, mentioning the not so nice screen refreshing. Other than that, I got no reply.

Then I thought I could implement the single feature I was not seeing: being able to sweep with more than 101 points. While I did implement that (slow), I noticed that this project I linked today, already does that, too! And there are FW forks to implement the sweep command you mentioned.

This is why I basically gave up on developing anything for this device: there are already too good alternatives!

Regards,
Vitor

[joeqsmith]

I added that narrow band or what I now call segmented sweep to increase the number of data points when I was working with SPICE and trying to get a decent demo going for that third video.   It will be very interesting to see if this new high resolution sweep will improve things or is it going to be so slow it is useless (much like my segmented sweep).   

I noticed they appear to have information about building the source with Windows but I haven't tried it.  I did however get the screen to go white again today and had to power cycle the unit.  So it's more robust but still could use some improvements.   

Sigilent's website shows them taking orders for their new VNA.   $3400 or so USD, without the cal kit, no TDR and no VNA software included.  Look like you more into the $5K when it's all said and done.    Plus you still have the problem of it not being a full 2-port system.   Hoping this time around that they give the unit to people who can actually show the practical justification of the higher cost when compared with this $50 unit.    

https://siglentna.com/spectrum-analyzers/sva1000x-spectrum-vector-analyzer/

[joeqsmith]

TOKO America, PC# 4DFB-915E-10=P
Description   Value      
Maximum Insertion Loss   2.7 dB      
Cut-off/Nominal Frequency Upper Range   800 to 1000 MHz      
Cut-off/Nominal Frequency   915 MHz      
Impedance   50 Ohm      
Maximum Pass Band Ripple   1 dB      
Operating Temperature   -40 to 85 °C      
Category   Filter Misc      
Manufacturer   TOKO America

https://www.digchip.com/datasheets/parts/datasheet/484/TDFM2B-915E-10_P-pdf.php

[joeqsmith]

I spoke too soon.  While playing around with this filter, I had the screen once again turn white which required a power cycle to recover.   Worse, I am once again seeing corrupt data sets.   This is not just my software.  I see it happen on the Nano's screen as well.  Slowing it down does appear to help.    Maybe it has something to do with the span, or the fact I am straddling the 900MHz region. 

Oh well, I was being too optimistic.  Hopefully the people working on the firmware can get something robust.

[ogden]

Sigilent's website shows them taking orders for their new VNA.   $3400 or so USD, without the cal kit, no TDR and no VNA software included.  Look like you more into the $5K when it's all said and done.    Plus you still have the problem of it not being a full 2-port system.

You get what you pay for. Anyway standalone SA with S11+S21 3GHz VNA for $4000 is hellova good offer.

Hoping this time around that they give the unit to people who can actually show the practical justification of the higher cost when compared with this $50 unit.

Perhaps manufacturers which are looking for dependable instrument having better than 60 70dB dynamic range? Not even mentioning freq range. Of course - many hobbyists are fine with nanoVNA, but not every buyer of VNA is hobbyist.

[edit] Comparison of $50 vs $50000 VNA: https://nuclearrambo.com/wordpress/comparing-nanovna-with-the-keysight-fieldfox-n9952a/

[hendorog]

Sigilent's website shows them taking orders for their new VNA.   $3400 or so USD, without the cal kit, no TDR and no VNA software included.  Look like you more into the $5K when it's all said and done.    Plus you still have the problem of it not being a full 2-port system.   Hoping this time around that they give the unit to people who can actually show the practical justification of the higher cost when compared with this $50 unit.    

https://siglentna.com/spectrum-analyzers/sva1000x-spectrum-vector-analyzer/

You are an optimistic man if you think the Nano will get to 3.2 GHz
The nano is a nice 300MHz device.

Also you might have missed this:
"Vector Network Analysis from 10 MHz – 1.5 GHz / 100 kHz – 3.2 GHz (Now included as standard)"

[radiolistener]

3.2 GHz is good. But 1.5 GHz for 50 USD is good enough for a radio amateurs

[hendorog]

[edit] Comparison of $50 vs $50000 VNA: https://nuclearrambo.com/wordpress/comparing-nanovna-with-the-keysight-fieldfox-n9952a/

That review raises an interesting point. They observe that the nano performs worse when used in full span. I've noticed this as well.

A user on another forum explained it in SA terms. Where a narrow span on an SA has a lower noise floor due to a narrow RBW being used.

That theory makes no sense. There is no variable filtering in the nano and the sampling is the same regardless of span as far as I can tell.

However wider spans with the same number of points take larger frequency steps. I wonder if the Si chip needs a longer time to settle when making larger frequency jumps? Maybe simply increasing the wait time prior to sampling will improve things in wide spans?

[OwO]

Yes, all PLL synthesizers take longer to settle when the frequency jump is larger. And yes, the nanoVNA will eventually reach 3GHz (and at a similar price I've heard). I know definitely that it's going to be based on the adf4350 + si5351.

[hendorog]

Yes, all PLL synthesizers take longer to settle when the frequency jump is larger. And yes, the nanoVNA will eventually reach 3GHz (and at a similar price I've heard). I know definitely that it's going to be based on the adf4350 + si5351.

Good point - I was referring to the current hardware obviously.

I expect the adf4350 version will be far superior to the current one above 300MHz.
Edit: But still not in the same class as the SVA family.

[ogden]

And yes, the nanoVNA will eventually reach 3GHz (and at a similar price I've heard). I know definitely that it's going to be based on the adf4350 + si5351.

To me "same price" seems to be way too optimistic. ADF4350 is expensive, VNA needs two. SA612 (3pcs) also have to be replaced with better mixers, like LT5560 or similar. Where we can follow information about next generation of nanoVNA? Any pointers?

[radiolistener]

I wonder if the Si chip needs a longer time to settle when making larger frequency jumps?

yes, large frequency jump needs to reset PLL, it takes some time for PLL lock. But it works fast enough.

[OwO]

ADF4350 costs about $0.4 each. I've seen the design and the 3 mixers are replaced with one higher spec mixer that is switched between the 3 channels. A variable gain amplifier is added at baseband using one opamp and switched feedback resistors for improved dynamic range. Audio codec is removed and the stm32 built in ADC is used instead. So overall there are quite a few components removed compared to V1 but I heard the performance should be comparable or better.

EDIT: mixer is probably going to be the ad8342.

[radiolistener]

Audio codec is removed and the stm32 built in ADC is used instead.

This change will reduce ADC dynamic range from 100 dB to 70 dB. So, it seems that the new NanoVNA will be worse...

[ogden]

ADF4350 costs about $0.4 each.

Where exactly you can get (genuine & new) ADF4350 for 0.4$? AD web: $6.05 @1000+

I've seen the design and the 3 mixers are replaced with one higher spec mixer that is switched between the 3 channels.

Right, MiniVNA Tiny. Existence of such design does not mean it is good. Problem with such approach - leakage through switches. Search this forum to see how bad this VNA actually is.

A variable gain amplifier is added at baseband using one opamp and switched feedback resistors for improved dynamic range. Audio codec is removed and the stm32 built in ADC is used instead.

Again - do not agree to such design decision. ADC of stm32 have barely 11 bit ENOB and 69dB SNR. Such VGA-augmented ADC will have worse linearity and temperature stability comparing to literally any generic audio ADC. Not to mention that VGA acting as part of ADC may slow sampling speed down because some/many points needs to be sampled at least 2 times while correct VGA gain is found.

[radiolistener]

ogden, there is also nightmare to capture samples with proper sample rate and low jitter with integrated ADC.

[ogden]

ogden, there is also nightmare to capture samples with proper sample rate and low jitter with integrated ADC.

This is not audio application, thus "right" sample rate is not required. Just pick closest to target number sample rate (round to ADC clock) and that's it. Yes, clock PLL of stm32 have inherent jitter which may ruin your day in high sample rate ADC applications, yet in this case it is low <= 50KSPS, ENOB of ADC is low. So ADC aperture jitter is not an issue. Yet anyway it is good idea to use new generation "stm32" IC's with improved clock jitter specs, rather than for example stm32l072 with it's +/- 600ps.