Impedance, Reflection Coefficient, Return Loss and VSWR (SWR) (069)

[@WECB640]

Ralph is one of the best teachers / mentors. A rare commodity. Keep up the excellent work OM. 73

[@eie_for_you]

Thank you so much! 73! 🙂

[@SpinStar1956]

Been busy and away, but now 'catching-up' on all your GREAT videos! Thanks Ralph, SO much for continuing to make such valuable and insightful lessons! 73...

[@eie_for_you]

@@SpinStar1956 Glad you made it back! You are very welcome!😁

[@TheRein10]

You're excellent teacher, difficult things become clear.

[@eie_for_you]

Thank you for the encouragement! 🙂

[@U812-k7j]

Great information, Ralph. In my daily amateur radio tinkering over the last 40+ years of hamming, I haven't and probably won't use the majority of these formulas. They sure are fun to run through to keep the gray matter functioning. 👍👍

[@eie_for_you]

Yeah, I don't use a lot of them often. But, in the playground I play in, I use them a bit. We have to keep the brain juices flowing! 🙂

[@Fireman9143]

Thanks for a very direct and well described explanation! This helps

[@eie_for_you]

You are very welcome, my friend! 🙂

[@Will256]

This was incredibly helpful! Thank you for explaining these topics in a precise but easy to digest manner

[@eie_for_you]

I'm glad you found this helpful! You are very welcome, it is my pleasure! 🙂

[@W1RMD]

I'm going to need to watch this again! (and again). Thanks for putting this all together for us. Using Smith charts is gold in understanding all of this, and you have some great videos on Smith charts. Also, a NanoVNA will display this very nicely on one screen. The rest is all Greek to me! Thanks a lot. 73 and have a great day! Nice shirt by the way.

[@eie_for_you]

True, the nanoVNA is an awesome tool! We just need to know what we are looking at. 🙂

[@IK8XOO--Paolo]

Great! I always suggest you videos to my students. 73s

[@eie_for_you]

WOW! Thank you! 🙂

[@gregwmanning]

Excellent video thanks for attached formula sheet

[@eie_for_you]

Thank you so much! I'm glad you appreciate the formula sheet. 🙂

[@ornithopterindia]

👍Thank you sir.

[@derdoktor7123]

Thanks Ralph, again a very good explanation of a confusing relationship between different ways to measure the results of impedance mismatch! (and again no chair turn😊)

[@eie_for_you]

You are so very welcome! When you use the nanoVNA Saver program with the nanoVNA and save the data to a file, it exports the Reflection Coefficient values (Re+jIm) from which you can calculate everything else. Yes, and no chair turn! 😀

[@derdoktor7123]

I have a Siglent SVA1032 and I did some SWR measurements, last try was with a chinese AD831 module to find a impedance matching at a specific frequency. I found a LC solution with the help of some online calculators and could reach a SWR of 1.4 ( before 17!!!) but I have no idea how to calculate it by myself.

[@eie_for_you]

@@derdoktor7123 First, I'd make real sure that the impedance you are measuring is done with stimulus levels that are within the capabilities of the chip. It is amazing how often this gets overlooked and it can make a huge difference in the measurement. Second, this is a much wider topic than I can cover in a simple reply to a comment. How you go about doing it depends on a lot of variables. What I am going to do is point you to this website which has a totally awesome tutorial on how to do impedance matching: handsonrf.com/ 🙂

[@derdoktor7123]

Thanks for your advice! My tests run with -20 dB stimulus and I think this was ok for the AD831 (with respect to the data sheet)

[@eie_for_you]

@@derdoktor7123 Cool that! Thanks for letting me know! 🙂

[@hadiehsani9338]

really good, thanks

[@eie_for_you]

Thank you so much! 🙂

[@gregorharrison1806]

A video describing the physical cause of the reflection would probably be helpful to many people.

[@eie_for_you]

Thank you for the suggestion. It certainly *does* sound like an interesting topic. Unfortunately, this would be getting into a lot of transmission line theory and wave theory that I am not prepared to speak on with any real confidence. As helpful as this might be to some, I'm going to have to pass on this one lest I lead anyone astray. 🙂

[@PixelSchnitzel]

Awesome and very educational video as usual! I'd like to call out one thing to add to your opening statement, as I understand it (please correct me if I'm wrong): Impedance is an independent quantity relevant to any RF source, load or transmission line component at some interface point. The other measures describe the *relationship* between components when energy is transferred between them. Is that a fair statement?

[@eie_for_you]

Thank you so much! I'm am very glad that you found this useful!🙂 You are absolutely correct, impedance is an independent entity upon which all the rest rests. 🙂 So, this is a good note. Unfortunately, KZbin does not allow creators to update a video. We can totally delete a video and then issue a new video, losing all history of the original video.😞

[@rdson1621]

Hello Ralph There is one question I have had for many years that nobody could answer so far: Why do we characterize the impedance of a transmission line by the magnitude of the impedance only? Since it is the sqrt of R² + X² there is a plethora (if not infinite) of combimations of those two giving, e.g. for a coax, 50 ohms. And these have a huge impact on the characteristic of the line! Is R big or small, is X positive (inductive) or negative (capacitive). The 50 ohms alone do not tell me much at the end. Where is my mistake in that thinking? Any hint? Best regards. PS Edit: maybe not truely infinite but all combination on the half circle with a radius of 50 (ohm) from -90° (purely capacitive), going trhough 0° (50ohm purely resitive) to +90° (purely inductive).

[@eie_for_you]

Thanks for the great and thought provoking question. It made me think ... I had to noodle on that a bit. Maybe it is because the actual complex impedance is completely dependent on the electrical length of the coax at a specific frequency. If we follow the SWR = 1:1 around the 360 degrees of the Smith Chart, you are right, the actual complex impedance (r + jx) combinations to yield a magnitude of 50 Ohms is, indeed, and infinite number. And this is totally dependent on the frequency in question, the physical length of the coax and the velocity factor of the coax.🙂