Open source vector network analyzer

[profdc9]

Hello,

I made a two port open source vector network analyzer that works between about 200 kHz to 500 MHz with about 50-60 dB of dynamic range.  I am still fiddling with the upper range of it because the SI5351A is a bit finicky.  It is available at

http://github.com/profdc9/VNA

The software and hardware is open source.  You can build it yourself from the schematics and gerbers.  It uses an optional ILI9341 touchscreen for input or output, or connects via USB and takes USB serial port ASCII commands.

Also, I made a theremin too

http://github.com/profdc9/MCTheremin

Best,

Dan

[Doctorandus_P]

I glanced briefly over it and it looks quite impressive.

I wonder if it would be fitting (and if you'd be interested in) admitting a pull request for this to be added to:
http://www.kicad-pcb.org/made-with-kicad/

A howto for the pull requests are on the top of that page.

[kentfielddude]

Thanks for sharing! I just ordered the pcb for it. I ordered five of the smt version of the pcb. If anyone in the US wants one I can send you one but you have to pay for shipping.

[OwO]

How are you getting up to 500MHz with the SI5351? The datasheet says it's rated to 160MHz...

[profdc9]

I sent a pull request to the kicad website git repository.

The VNA is able to get up to 500 MHz by using the third harmonic of the SI5351 signal.  The intermediate frequency of the third harmonic occurs at 3 times the intermediate frequency of the first harmonic, and so the microcontroller filters on the 3rd harmonic instead.

I'm having some trouble reliably switching the SI5351 in and out of extended range (> 150 MHz) mode so right now the firmware is limited to 450 MHz maximum frequency but this is sufficient for the 70 cm band.  There's something weird in the SI5351 control code I have yet to track down.

Dan

[radiolistener]

How are you getting up to 500MHz with the SI5351?

si5351 produces very good square wave with 1 ns rise time, it means that it has up to 1 GHz harmonics with good level.
Since this is vector analyser, you can use high-order harmonics from si5351 in order to measure frequencies higher than 200 MHz. 

This technique works good in EU1KY_AA_V3 antenna vector analyzer:
https://bitbucket.org/kuchura/eu1ky_aa_v3/wiki/Home

I assembled this EU1KY_AA_V3 antenna analyzer, works good from 5 kHz to 450 MHz. 
This is very popular and must have equipment.

There are also a lot of clones of EU1KY_AA_V3 on aliexpress: https://www.aliexpress.com/item/new-arrival-Mini600-5V-1-5A-HF-VHF-UHF-Antenna-Analyzer-0-1-600MHz-SWR-Meter/32915438007.html

The datasheet says it's rated to 160MHz...

Old si5351 were rated for 160 MHz max. But Silicon Labs updated datasheet and all new si5351 according to the datasheet supports 200 MHz. You can check the latest datasheet. It happens long time ago, so the risk to get very old si5351 with 160 MHz limit is very low.

Here is the latest datasheet: https://www.silabs.com/documents/public/data-sheets/Si5351-B.pdf

Generates up to 8 non-integer-related frequencies from 2.5 kHz to 200 MHz

[eddiesomesan]

This is a really nice and useful VNA - a must have. It has it`s disadvantages but it works quite good. It can go so high because it`s using harmonics, but with higher losses and lower precision.
We have around 3 complete and functional pieces here, and 3 more to go as a kit. PCB`s purchased separately, components also. 
Still, the 3 pieces that are complete and functional, although they were calibrated the same, have slightly different reading results. They are not so far apart so we can use them without any problems.
I hope I can post some pictures after I start building the next one.
73 de YO5VAE - Edy
PS. There are also 3`rd party modded firmware versions which work good, and can be installed really easy. Worth a try.

[profdc9]

I'm sorry, are you talking about the EU1KY analyzer or the VNA I designed?  I am just curious, if you built the VNA I made I would be open to suggestions.  I am guessing the EU1KY because as far as I know the design I have does not have any third party mods (yet).

One of my main motivations for making a separate VNA than the EU1KY is to make it out of simpler cheaper parts so it might be cloned and sold widely.  Using the cheapest parts you can get away with helps make that possibility more likely.

Dan

This is a really nice and useful VNA - a must have. It has it`s disadvantages but it works quite good. It can go so high because it`s using harmonics, but with higher losses and lower precision.
We have around 3 complete and functional pieces here, and 3 more to go as a kit. PCB`s purchased separately, components also. 
Still, the 3 pieces that are complete and functional, although they were calibrated the same, have slightly different reading results. They are not so far apart so we can use them without any problems.
I hope I can post some pictures after I start building the next one.
73 de YO5VAE - Edy
PS. There are also 3`rd party modded firmware versions which work good, and can be installed really easy. Worth a try.

[eddiesomesan]

Hello Dan.
Yes, i was talking about EU1KY on which this it`s based.
After I finish the one I`m working on from EU1KY, I`ll give this one a try because it looks really nice and promising, using easy to find parts and easy to assemble. Maybe i`ll be able to do some comparison of the results.
As for feedback, the only thing I can see until now are the RF connectors on the THT board. I would use N or SMA connectors, as the BNC`s are not so popular among hamradio operators. Also, for BNC, there are 75 ohm versions that can`t be identified as 50 or 75, in case someone`s using salvaged components.
Thanks you your efforts and for sharing your work. You put a lot of effort in this. I`ll try to keep you updated.
Edy