NanoVNA: Testing Coax For Characteristic Impedance And Distance To Fault (Length)

NanoVNA: Testing Coax For Characteristic Impedance And Distance To Fault (Length) is my attempt to simplify and demystify some the the cool things you can test on transmission line with the NanoVNA. This is just one of a group of videos I'm doing on this amazing little tool. For most of us in the Amateur Radio Hobby, every new thing we do brings forward all sorts of learning and experimentation. This is just one video I am making in this journey of discovery!
If you want to purchase the NanoVNA shown in the video, it's available on Amazon Prime here: amzn.to/3t9zsB2
And of you are trying to get the majority of the adaptors you need to run tests on different devices, here is a good kit. I wish I had found this when I was digging up all the stuff I needed for testing. You probably will want to buy at least two of these to get setup for both sides: amzn.to/3J8sBxq.
Thanks for watching and hope to hear you on the air!
Chapters:
0:00 - Intro to NanoVNA: Testing Coax For Characteristic Impedance And Distance To Fault.
1:38 - Using the NanoVNA in Smith Chart mode to test coax characteristic impedance.
7:25 - Let's break out the calculator.
8:35 - Proof by example. Testing non 50Ω coax.
12:48 - Testing for length to fault with the NanoVNA.
13:33 - Setup NanoVNA for Time Domain measurements.
15:08 - Formula to calculate the stimulus settings.
17:46 - Taking the measurement.
19:16 - What are the additional 'bumps' on the screen?
22:20 - Closing thoughts.

[@robertehartley9691]

Thank you very much for the most elegant and concise way of determining the characteristic impedance of a transmission line! Other people's solutions involved way too much math. With your method, I was able to quickly and easily confirm that a nice and inexpensive "supposed" RG316 coax was actually 50 Ohms impedance, and some of my old coax was about 75 ohms, which I expected but used as a test to ensure I was doing it right. This has releived so a chunk of frustration. Thank you again! -VK4SSE, Rob

[@AG6AG]

Glad it made it a little easier! Stu AG6AG

[@GoGlennR]

A great informative video, Stu. 😊Thanks & 73's de Glenn DL8FG/WB5FDJ

[@AG6AG]

Glad you liked it! Stu AG6AG

[@vicshier4841]

I'm working on a project and this was very helpful. Thanks!

[@AG6AG]

Glad it was helpful!

[@tomsmith4100]

Stu great educational video. I use nano all the time but this is some new to try....thanks

[@AG6AG]

Hi Tom, Glad you enjoyed it! I have to admit I'm constantly surprised as to what this little $100 thing can do. Stu AG6AG

[@robertatpierpontbeach]

Stu, thanks for another instructive video about using the nano. I liked how that sneaky "4" jumped into your formula to suggest that the cable was 300 ohms; another common type. Keep 'em coming and 73.

[@AG6AG]

Yeah, those 4s get me every time... I think we will do some more Oscilloscope stuff. Then take a poke at the Spectrum Analyzer. Thanks for your comments! Stu AG6AG

[@gcollatz]

What is that cool calculator that you are using? Great video have learned a lot from it and will watch several times again.

[@AG6AG]

That is an Android app called Panecal Plus. It's a great scientific calculator. Stu AG6AG

[@W2AYZ]

Good video Stu. I have always used MFJ 269 to test and find out the length or broken point, but your video shows how it can be calculated using nano VNA. Very informative. I guess you have a 4" screen version of it for the video. Mine is the smaller version and I often have hard time reading it.

[@kevinmatthews2620]

bang on timing there Stu, i am about to buy a nano vna off of a local amateur sale site close to me, and as you have been spot on with the log4om v2 videos for easy setup, and i have reffered to you videos for mine & a friends setup, this video could not have been better timing, as i have numerous bits of coax that could do with testing,Thanks in Advance Stu

[@AG6AG]

Glad it is helping! Stu AG6AG

[@KingLoopie1]

Thanks for the info, Stu! I just bought a nanovna h4 and trying without much success how to decode the menu to do the coax length. Good explanation (since I don't have the software for it yet...)! Gonna download this video for reference until I get more time in on the nano...

[@AG6AG]

Glad I could help! Make sure you report back and let me know if you have any other questions!

[@dalebertdurando1496]

This is good. Works for twisted pairs too (sometimes important when winding baluns). There are a few other methods for measuring cable impedance. One of my favorites is to put a potentiometer at the end of the cable and reduce the circle to a dot. The pot resistance is the impedance. The open/short method is also popular. For typical coax, just measuring the capacitance per foot is quick and dirty. There are tables showing capacitance for a given coax impedance. For cables with a sudden change in impedance (bad shield or splice) the TDR method is best for me. I can see the impedance vs length (requires a fast rising pulse and oscilloscope). For a real challenge use wire that is lossy (nickel wire or very small gauge wire). : )

[@AG6AG]

Good points. Thanks for posting! Stu AG6AG

[@f-7670]

What's the calculator you use? I like it!

[@AG6AG]

Hi- Panecal calculator program for Android. I love it! Stu

[@user-kw9ec1dr5q]

WAIT you said you hooked the coax to the nano vna, but is there a load or any thing on the other end of the coax? When i hook my coax up my little circle is as big as the largest circle on the smith chart ....

[@AG6AG]

Hi Robert, Yeah I hid that statement away in the calculator part of the video. Here is where I give away that there is a 50ohm dummy load on the end of the coax. kzbin.info/www/bejne/hYPEiqtvlsdpsMksi=ZJMZBp4u-nw8KCan&t=455 Sorry for the confusion, Stu AG6AG

[@user-kw9ec1dr5q]

ok thanks NS9T@@AG6AG

[@kevinmatthews2620]

could you not try the measurement by plugging a 50 ohm dummy load on the other end ?? to do the measurement with for distance, just a thought Stu, good video Stu keep them coming :)

[@AG6AG]

Hi Kevin, You can do the measurement with the far end either shorted or open. I don't think you could accurately measure the distance with a 50 Ohm load on the end. You certainly could try it, but I think the measurement would be a bit off... My next project related to the coax length is to try measuring a coax with an antenna on it to see if there is a bump where the connector to the antenna itself is. In theory, the big jump will be at the end of the antenna, but I think I will still see a small jump at the connector at the end of the coax. If you test it with a 50 Ohm load on the end let me know your results! Stu AG6AG