|
Re: Pitfalls of measuring components with the NanoVNA
#measurement
This is very good. Thank you for sharing!
-- VE6WGM |
|
Re: nanoVNA - Measuring Inductors and Capacitors (Vers. 3)
#measurement
#tutorials
#video
Hi Mike
Here is a brief textual overview of what I shared in the video.. To measure an inductor or capacitor, use a shunt configuration (basically attach the component to your nanoVNA using “alligator leads” so as to be able to make S11 measurements... hahaha! Oh yeah, I said that! Sorry RF Engineers.) Measure the capacitive or inductive reactance at a frequency where the reactance of the component is equal to the characteristic impedance of the system you are using to measure the inductor or capacitor (most likely 50 ohms). This will correlate to a phase angle of 90 degrees as measured by the VNA (positive for an inductor, and negative for a capacitor). This strategy places the impedance being measured within the nanoVNA’s abilities to measure accurately, and ensures that the measurement is performed well below the self resonant frequency of the component. You’ll get correct results so as to be able to label an unknown inductor or to verify the value of a capacitor. Where the use of such ‘crude’ test fixture will break down is if you happen to be measuring components that require a relatively high frequency in order for the reactance to be 50 ohms... in that case, the high frequency unfriendly alligator leads will need to be replaced with a proper test fixture. -- VE6WGM |
|
Re: nanoVNA - Measuring Inductors and Capacitors (Vers. 3)
#measurement
#tutorials
#video
References were given as convenient clickable links in the description below the YouTube video.
-- VE6WGM |
|
Pitfalls of measuring components with the NanoVNA
#measurement
I thought it might be interesting to start a post dealing with how to accurately measure components like inductors, capacitors and resistors on a NanoVNA. As an RF engineer I have made mistakes over the years using trial and error methods. By reading technical books/articles and posts by from others skilled in this area I learned about some of the pitfalls one can easily make and how to avoid them. So I hope some of you will jump in and share your tips and knowledge.
It is easy to make a mistake or draw a false conclusion about a component's characteristics when using a VNA. This can be due to many factors including the following: - limitations of the NanoVNA hardware and software - limitations of the test jig - quality of calibration load and calibration method - excess lead length - misconceptions about the component under test - insufficient technical knowledge Rather than discuss each of these individually it might be more interesting to do some tests on actual components and point out the pitfalls and things to watch out for when making these measurements. Here is a test I did on a 47 pF SMD capacitor using a NanoVNA-H4 with the DisLord 1.0.45 firmware. The PC software used was the NanoVNA app by OneOfEleven. Both of these individuals have done an excellent job developing this software and thanks for sharing it with the user community. The test fixture used was a female SMA connector with a small header row attached. Cal loads were made using male pins and a SMD 49.9 ohm cal load. The idea originally came from a post by Owen Duffy on his blog. A annotated photo of the setup is attached. A sweep from .05 to 900 MHz. was done and the reactance plotted (graph attached). A graph converting the reactance to "apparent capacitance" is also shown. A pitfall made by those new to VNA's is to assume this is the actual capacitance vs. frequency of the part. This is not the case because a physical capacitor also has some inductance associated with it as shown in the simplified capacitor model. This results in positive inductive reactance adding to the negative capacitive reactance and a faster rise in total reactance with frequency than just the capacitor alone. In the graph below note the rapid reactance increase with frequency as we get close to the self-resonant frequency (SRF) of the capacitor. Now one might think it is reasonable to measure at a very low frequency in order to get the actual capacitance but this is not possible because the capacitance reactance is so high at low frequencies that it cannot be actually measured by the VNA. By looking at the markers you can see that we can only start making accurate measurements around 2 MHz. for this part. Another instrument in my lab a DE-5000 can make these measurements at low frequencies (below 100 kHz.) and the part measures close to 47 pF in this range. The frequency at which accurate measurements can be made will be based on the capacitance of the device under test. Larger capacitors can be measured at a lower frequency and smaller ones like 10 pF at a higher frequency. If we wish to determine the frequency of self resonance we can look for the frequency where the reactance is zero. This is when the capacitive reactance and inductive reactance are equal and opposite in sign and result in zero at the SRF. This is also the frequency where the S11 phase angle abruptly changes from - degrees to + degrees for this example. For those familiar with Smith charts this is a data point on the horizontal line of the Smith chart. Roger |
|
Re: NanoVNA Testboard kit VNA Test Demo Board
#applications
I was referring to hwalker's post in this thread on Apr 18, 2020. This is the link in that post:
|
|
Re: nanoVNA - Measuring Inductors and Capacitors (Vers. 3)
#measurement
#tutorials
#video
Thank you for these videos.
toggle quoted message
Show quoted text
On Wed, Feb 17, 2021, 10:24 PM Gregg Messenger <techgreg@...> wrote:
For those of you who didn’t like my first two attempts at this video.. I |
|
Re: nanoVNA - Measuring Inductors and Capacitors (Vers. 3)
#measurement
#tutorials
#video
For those of you who didn’t like my first two attempts at this video.. I think I’ve done a much better job on this one of explaining why I take my readings at 90 degrees phase angle on the smith chart
:-) -- VE6WGM |
|
nanoVNA - Measuring Inductors and Capacitors (Vers. 3)
#measurement
#tutorials
#video
Version 3
-- VE6WGM |
|
nanoVNA - Measuring the resonant frequency of a crystal
#measurement
#tutorials
#video
A video I did up last summer on how to use the nanoVNA to measure the resonant frequency of crystals.
The intended audience is those who are not wanting a complete and exhaustive characterization of crystals, rather, a quick and simple method to take a handful of random crystals and to determine the resonant frequency so as to be able to sort and label said crystals. Also includes a simple explanation of parallel and series resonant modes of crystals. -- VE6WGM |
Gregg Messenger VE6WGM
Roger Need
Mark Adler
Martin Glazer