Friday, August 26, 2022

Vector Network Analyzer ( VNA) - 1 - Intro

Recently i received my Vector Network Analyzer (LiteVNA) and am very happy to finally have this interesting device.

Information and explaining in detail what is a VNA, what you can do with it (and how) can be found on internet and is probably better explained by other who have much more experience with this topic. However as i want to post some first results when testing my VNA on my blog, and for visitors of my blog who don't know anything about VNAs i first need do start with "Vector Network Analyzer ( VNA) - 1 - Intro". 

A Vector Network Analyzer (or VNA) is an electronic measurement and testing device that generates and measures frequencies so you can do measurements on things like antennas and (radio) frequency filters.
With modern electronic and some smart people made it possible to buy now a VNA in the 50 Euro range to do some measurement that where some years ago only possible with equipment of thousands of euros. The LiteVNA that i got costs around 100 Euro as this device works up to 6 GHz. My first 3 attempts some months ago to buy a VNA failed. After ordering i received a message it was not possible to deliver and my money was returned. I even did think of buying a VNA with lower frequency range if it was available. However, after some weeks waiting, i tried again at another store and they could deliver relative fast! The VNA came with a Short Open and Load connectors and some cables.

The VNA has two connectors. One connector acts as a combined output and input. A signal is provided to a DUT (Device Under Test)  and the signal is measured. The frequency of the signal can sweep in a frequency range and this way you can determine frequency characteristics of an antenna.
The other connector can act as input and by placing a DUT (a filter circuit) between the output and input you can observe how the DUT (filter circuit) behaves at different frequencies.

Calibration of the VNA is very important and the VNA also reacts on other changes e.g. cable length. A common calibration is the SOLT calibration  (Short, Open, Load and Thru).
Short Open and Load calibration is done by using a shorted circuit, open circuit or a load (e.g. 50 Ohm) on the combined input/output and running the appropriate calibration.
Calibration of Thru is done by connecting the two connectors without the DUT running the Thru calibration.

The LiteVNA can be used stand alone (powered provided by build in Lithium power cell) or via USB connected to a computer. Usng the computer you have a much bigger screen and you can easy export the measured data or  the pictures. The LiteVNA also as a memory slot for additional storage.
As recommended by some internet tutorial I placed additional connectors on the original connectors for protection.

In my next blog post i will post some results using a RF Demo Kit board. 

Some findings in the limited time that i have played with the VNA:

  • It is nice that the PC software can display a graph of the battery power of the VNA.
  • The LiteVNA (at least mine) can become very warm. Perhaps some settings (output power) can or need to be adapted to reduce this. I could not yet find if the temperature can be monitored (like the battery power). I don't know if and and how measurements are influenced by this temperate.
  • Measurements seems to be quite sensitive to things like cable length and the connection.

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