Using the VNA to sweep for a resonant frequency

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Willow_Martin
Posts: 1
Joined: Sun Oct 25, 2020 7:36 pm

Using the VNA to sweep for a resonant frequency

Post by Willow_Martin » Sun Oct 25, 2020 7:58 pm

I'm trying to do a very simple experiment, measuring the resonant frequency of a quartz tuning fork hooked up in series with a resistor, all connected on a breadboard, which is in turn hooked up to the VNA module. I've already since measured the resonance frequency of this QTF using an SR830 Lock-in Amplifier and found it ~32.7kHz; however, I'm not seeing any peak in the DUT plot around this frequency when I try to take a measurement with the FPGA hooked up to the VNA module. I'm very new to this software and would deeply appreciate any insight. Thank you!

pavel
Posts: 623
Joined: Sat May 23, 2015 5:22 pm

Re: Using the VNA to sweep for a resonant frequency

Post by pavel » Sun Oct 25, 2020 9:01 pm

According to the specifications at this link, the Red Pitaya VNA module doesn't work for frequencies below 500 kHz.

You will need to use a different test fixture for the 32 kHz frequency.

A very simple series fixture can be assembled from a few resistors and SMA or BNC connectors and it'll work at low frequencies without any problem.

Here are the links to a couple of web pages showing some very simple test fixtures:
http://www.scottyspectrumanalyzer.us/fu ... ystal.html
https://destevez.net/2017/09/measuring- ... -lite-vna/

Other solutions can be found in the documents linked from my notes about the VNA application:
http://pavel-demin.github.io/red-pitaya-notes/vna/

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