VNA test jigs and fixtures? - Page 1
Forum section: electronics / rf-microwave

author: cdev
author_rank: Super Contributor
timestamp: July 08, 2020, 02:49:47 am
content: I would like to build some test PCB boards for testing individual compnents in a controlled impedance way, testing self resonsnce, etc.Also, how you made them.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 08, 2020, 03:22:57 am
content: Hi,You can the board I use in this picture:In the top left of the board, there are three 3resistors in parallel, This is to make a low inductance 1standard.This is from this thread:https://www.eevblog.com/forum/projects/high-bandwidth-current-injector-for-impedance-measurements/msg3026052/#msg3026052Also look at this thread:https://www.eevblog.com/forum/projects/shunt-measurement-of-capacitor-esr-and-resonance-frequency-with-a-vna/Forum member, graybeard, does some component measurements with a VNA.Regards,Jay_Diddy_B

author: mark03
author_rank: Frequent Contributor
timestamp: July 08, 2020, 03:32:37 am
content: HP has a nice app note on the subject:https://www.electro-photonics.com/images/products/AN1287-9.pdfAlso check out Henrik Forsten's blog:https://hforsten.com/trl-measurements-with-homemade-vna-and-open-source-software.htmlHere he walks through the measurement of a surface-mount capacitor's S parameters. The results are a remarkably good match to the data sheet.Even if your VNA only supports the basic OSLT cal, you can still play with TRL and others using scikit-rf and python.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 08, 2020, 03:57:09 am
content: I was attempting to make a jig for testing some crystals. This is what I ended up with:https://www.eevblog.com/forum/rf-microwave/fun-with-crystal-filters/msg3076877/#msg3076877Simple series and parallel jigs:https://www.eevblog.com/forum/projects/20db-rf-attenuator-seeking-feedback-to-improve/msg2974530/#msg2974530Demo of measuring a part with one of these jigs using a cheap NanoVNA.https://www.eevblog.com/forum/projects/20db-rf-attenuator-seeking-feedback-to-improve/msg2976830/#msg2976830

author: joeqsmith
author_rank: Super Contributor
timestamp: July 08, 2020, 04:02:57 am
content: One of member rf-messkopf's fixtures. He was very helpful in getting my home made standards sorted out and has a good website you may want to check out.

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 08, 2020, 04:22:47 am
content: what bandwidth? i've made one "out of the" world class real (semi processed) wood quality + fiber FR4 hybrid test fixture, maybe good up to a GHz or two... edit: updated version on later attachments...

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: July 08, 2020, 11:13:02 am
content: If you can push up to a high enough frequency, TRL is the way to go for any custom jig-specific calibration. Downside is that you need a line that is a quarter wavelength or so long, so it is not really realistic under a few GHz.

author: cdev
author_rank: Super Contributor
timestamp: July 08, 2020, 12:35:40 pm
content: @joeeqsmithI notice you are using toroids to couple to your crystal test fixture. Do you just calibrate the test with the balun? do you use a resistor of the appropriate value for the load? (50 ohms, 200 ohms, ?) what kind of resistor do you use thats non-reactive?----------------------------@mechatrommerGood idea to place them all together one way or another. So they are not lost immediately! (they would be on my desk right now)Thats a major worry of mine, if I don't make some good way to keep them together.I'm concerned about making a calibration standard where all of the needed components are right together.I can easily see myself losing individual tiny SMA ones. So I think I am going to make up my own.Unfortunately, it seems most of my SMA hardware is likely some other metal than gold :{Seems that I should buy some real gold plated SMAs for my standard-making, though.Quote from: Mechatrommer on July 08, 2020, 04:22:47 am

author: cdev
author_rank: Super Contributor
timestamp: July 08, 2020, 04:47:56 pm
content: Your software is much much nicer on the eyes than the nanovna softwareQuote from: joeqsmith on July 08, 2020, 04:11:07 am

author: joeqsmith
author_rank: Super Contributor
timestamp: July 08, 2020, 07:35:13 pm
content: Quote from: cdev on July 08, 2020, 12:35:40 pmYes it is calibrated with the two impedance matching transformers. Yes, I calibrate with some resistance but then verify with other parts. ALL parts are reactive but at DCish where I am workin, its not really a factor. There's a fair bit of detail posted in that thread with the 20dB attenuators where I show some really crude builds for a reference.

author: profdc9
author_rank: Frequent Contributor
timestamp: July 13, 2020, 02:30:35 am
content: I designed a component testing jig using a ZIF socket. There are also spots for other components as well. I used it up to about 200 MHz with good results and 400 MHz with decent results, the limitations being the standards you can fit in a ZIF socket.https://github.com/profdc9/VNA/tree/master/fixture

author: Smokey
author_rank: Super Contributor
timestamp: December 04, 2023, 05:24:56 am
content: This fixture is only $60 from aliexpress:https://www.aliexpress.us/item/3256802374699500.html

author: DaJMasta
author_rank: Super Contributor
timestamp: December 04, 2023, 09:40:36 am
content: Those fixtures are configured for LCR meters, so they've got the interface for it and probably a lot less bandwidth than you'd want for RF characterization. While proper fixtures are normally quite expensive, every so often you can find someone clearing out an RF lab with a bunch of custom fixtures for sale - may not be perfect for the parts you're thinking of, but probably cheap and designed for high bandwidth.If I were trying the same, the PCB route seems like the best option. It will be the closest to the configuration in circuit and you can build your reference planes on the same material/process, plus SMA PCB connectors are super cheap, so it's easy to just make a few boards and solder in parts under test.