Sub $1000 VNA for antenna matching

[joeqsmith]

While looking for software that would make it easier for OP to match their antenna, I came across this VNA/software.   I didn't check but the description talks about being able to download the software and run it without the VNA using their test data.  Maybe it supports Touchstone.   

https://www.megiq.com/blog/item/47-vna-match-function-has-adjustable-components

[joeqsmith]

Attached showing the calibration probe.  Keeping in mind that the OD of the coax shield is 0.086".   A small sewing needle was placed along the coax and then wrapped with 30AWG wirewrap wire.   Then the whole assembly was soldered.   These two probes have a 90 degree bend in them, which is why the shrink tube is slanted.   

I may chop up a PCB to get the correct ground plane and then cut the shield so it can be installed and just see what difference we get. 

When looking at the radiation pattern, you can imagine this big chunk of coax hanging out the side and large ground plane behind the board along with the missing shield is going to have an effect.    A better measurement would be to look at the end product running and mounted to a turntable.  Then measure the pattern with a receiver.   With the OP limited to a $1000 budget, that's about an hour of lab time.  Guessing that's not part of their plan.   

[joeqsmith]

I've mounted the radio to a sectioned board with the proper layout.  Attached photo shows my hack job on the shield.  I found a bit of Arlon (not sure the part number) and epoxied the sectioned board with radio to it.  This will allow easy mounting to the rotor's mast.   Once this dries, I will repeat the calibration and measurements with the LiteVNA.   

[joeqsmith]

I've attached a photo showing the setup.  Note that the shield was soldered to the coax.   

Looking at the return loss, the Red trace was just after calibrating the VNA.  The Yellow trace is using yesterdays calibration.  There's a bit of difference which I'm not too surprised.  This time I was using some copper foil tape rather than the PCB.    The bigger change was due to all the other changes in the setup. 

The 2D plot would be how I would normally use the radio.   

[joeqsmith]

please follow this post... https://www.eevblog.com/forum/rf-microwave/clone-85033e-vna-cal-kit-measured-against-pico-cal-kit-using-librevna/msg4475422/#msg4475422 i have yet to get a good answer on why the ringy plot of LibreVNA output file. the last time we were discussing among VNA users that the ringy plot is due to internal mismatch (tracks are not 50 ohm impedance)... the way i see it, its internal problem and difficult to cancel from external tricks, unless the designer takes care of this internally or in FW. ymmv.

I was reading the LibreVNA group yesterday and it seems they have new hardware.  Someone posted an AB compare that may be of interest.  

https://groups.io/g/LibreVNA-support/topic/what_is_the_spec_defrance/95474170?p=,,,20,0,0,0::recentpostdate/sticky,,,20,2,0,95474170,previd%3D9223372036854775807,nextid%3D1666293968019920350&previd=9223372036854775807&nextid=1666293968019920350

[Mechatrommer]

please follow this post... https://www.eevblog.com/forum/rf-microwave/clone-85033e-vna-cal-kit-measured-against-pico-cal-kit-using-librevna/msg4475422/#msg4475422 i have yet to get a good answer on why the ringy plot of LibreVNA output file. the last time we were discussing among VNA users that the ringy plot is due to internal mismatch (tracks are not 50 ohm impedance)... the way i see it, its internal problem and difficult to cancel from external tricks, unless the designer takes care of this internally or in FW. ymmv.

I was reading the LibreVNA group yesterday and it seems they have new hardware.  Someone posted an AB compare that may be of interest. 

https://groups.io/g/LibreVNA-support/topic/what_is_the_spec_defrance/95474170?p=,,,20,0,0,0::recentpostdate/sticky,,,20,2,0,95474170,previd%3D9223372036854775807,nextid%3D1666293968019920350&previd=9223372036854775807&nextid=1666293968019920350

still look ringing to me on both plot, is that a Through test? not really clear..

[joeqsmith]

Agree, not at all what I would expect.  With the other posts showing difference in cal standards causing it, compared with what I show using various loads, I wonder if it's a user problem.  Maybe a problem with their math.  

They really should have sent one to someone that knew what a VNA was.

[Smokey]

...
FYI on the Lite.
The first one I bought worked well and met the suppliers specs.  A friends had very high noise.  They bought a second and shipped me theirs.  Their second one also had high noise.  After some testing, I found the Lite was very sensitive to the input voltage level from the USB port.  Basically, to get around it, I made a USB cable with a diode in series with the power to lower it.  This solved the problem.   
...

I'm looking at getting one of these LiteVNAs.  What should I be looking at, performance wise, to determine if a unit has an issue with the USB voltage? 

[joeqsmith]

...
FYI on the Lite.
The first one I bought worked well and met the suppliers specs.  A friends had very high noise.  They bought a second and shipped me theirs.  Their second one also had high noise.  After some testing, I found the Lite was very sensitive to the input voltage level from the USB port.  Basically, to get around it, I made a USB cable with a diode in series with the power to lower it.  This solved the problem.   
...

I'm looking at getting one of these LiteVNAs.  What should I be looking at, performance wise, to determine if a unit has an issue with the USB voltage?

I've posted data showing the problem, how I collected it and also how to mitigate it.  Did you have a specific question about that?  I understand they released an update to the hardware to improve its performance.  Someone had asked how it compared with what I had shown.  There was no response from the designers and all went silent.  You can find that on the LiteVNA groups.io.   

[Smokey]

Cool.  Thanks for the info.  I think this is the forum post regarding the power supply update:
https://groups.io/g/liteVNA/topic/the_new_litevna64_which/93138117

The last messages are from 11/11/22 and claim the distributors like randl.com have the 64.0.3.1 version.

[joeqsmith]

Yes, that is the thread.   Looks like it grew a bit. 

If you buy one, I would be interested in having you run a simple test just to get some idea how much they improved it compared with my stock one. 

[Smokey]

Yes, that is the thread.   Looks like it grew a bit. 

If you buy one, I would be interested in having you run a simple test just to get some idea how much they improved it compared with my stock one.

It's on it's way.  I'll update when it gets here.

[joeqsmith]

Sounds good.

Did you order the large display or small?   I'm not sure if there would be a difference in performance between the two.   Also the firmware is not compatible between them. 

You wouldn't think that would be a big deal but I found with the P2Plus/4, I had no problems with the firmware for the large display version.  The small display version took a lot of trial and error to find something stable.   Based on what I have seen from Dislord, I doubt we would see the same level of problems but I have no experience with that smaller Lite.

I do not know how any of the open software handles the calibration.   If you want to start with what ever software you like, we can start there.  If there is a major improvement, I may  install the same software you are using just to remove that variable.

[Smokey]

LiteVNA64 from here:
https://store2.rlham.com/shop/catalog/product_info.php?products_id=75669

[joeqsmith]

Perfect.

[Smokey]

Arrived.  Got the new "64-0.3.1" label style on the case (image from store site):



Firmware version it shipped with = v1.3.07
Build time = Aug 30 2022 - 10:14:02

[joeqsmith]

Good deal.

Once you have what ever software you plan to use installed and running, set the Lite to full sweep and calibrate it.  Terminate the two ports and measure S21.  Then upload the touchstone file for it.   Basically, I would like the Touchstone file for what is shown in that photo you attached except you may as well run it down to 50kHz.  1001 points is fine. 

I had tried this with my friends Lite using the SD card and running it stand alone before I sorted out the problems with the USB voltage.   You could try running yours standalone as well.  This may provide us with even lower noise.   

[Smokey]

I feel like I'm missing something about firmware versions.

This looks like DiSlords's github, but there is no liteVNA repo: https://github.com/DiSlord

The liteVNA groups.io doesn't appear to have the wiki setup and I'm not seeing a firmware section: https://groups.io/g/liteVNA

There was a link to a google drive in one of the posts, but it's not clear what versions are on it, and all the files appear quite old: https://drive.google.com/drive/folders/10lU5xnwmHDnPX98z21ky09N8nb_cEOk4

There is a nanoVNA beta groups.io page, but it's invite only: https://groups.io/g/nanovna-beta-test

What am I missing?

[joeqsmith]

ZeenKo links the GoogleDrive you provided, which should have the latest release from the manufacture.

https://www.zeenko.tech/litevna?spm=a2g0o.detail.1000023.1.b5a97ff8tHYEOr

Dislord is a member here and has uploaded test versions for us from time to time.  This was their last upload:

https://www.eevblog.com/forum/rf-microwave/nanovna-custom-software/msg4579603/#msg4579603

If you like testing code, it may be worth your time to look into the beta group you mention.