Video: Basics of the Impedance & Admittance curves on a Smith Chart

[w2aew]

This introductory video describes how complex impedance and admittance are represented on the Smith Chart, and how to convert between them.  A VNA is used to illustrate the complex impedance representation on a live smith chart with variable resistive and reactive components. 

Note that I did "mis-speak" about the circles in the chart - I described them as concentric, but I should've said tangent...

[slurry]

That was an excellent description Alan 

[bd139]

I watched this yesterday when it popped up on YouTube. I had a mortal fear of Smith Charts before and now I don't. Great work as always 

[Yansi]

Ya'll probably get the mortal fear of em right back when you get into the deeper purpose of the chart. I hope W2AEW will make some more detailed videos in the future about these. For example about the reflection coefficient, how the chart was derived, how to use them for impedance matching, etc... That will be more fun and I am looking forward. Thanks!

[denverpilot]

Liked the video Alan / @w2aew. I never liked the way those things are tested on tests, but they’re useful occasionally in real life.

VNAs are VERY useful in real life.

[German_EE]

Hi Alan and thanks for the video, I have one question and one suggestion:

Q: I know about the inductive above the line and capacitive below but I have seen two versions of the Smith Chart. The normal chart is like yours with a horizontal line, the other version has the line as two semicircles, one above the 'horizon' and one below similar to figure 4 in this document: http://highfreqelec.summittechmedia.com/Mar06/HFE0306_Rhea.pdf similar to the Asian Yin and Yang symbol. Which is correct?

A suggestion (as previously mentioned). During one of your future videos please could you cover the situation where the only things known are a) forward voltage b) return or reflected voltage and c) the phase difference between the two signals. Please show how this is plotted on a Smith Chart.

Thanks in advance, I'm looking forward to the future videos.

[w2aew]

Hi Alan and thanks for the video, I have one question and one suggestion:

Q: I know about the inductive above the line and capacitive below but I have seen two versions of the Smith Chart. The normal chart is like yours with a horizontal line, the other version has the line as two semicircles, one above the 'horizon' and one below similar to figure 4 in this document: http://highfreqelec.summittechmedia.com/Mar06/HFE0306_Rhea.pdf similar to the Asian Yin and Yang symbol. Which is correct?

Both are correct, they're really the same thing.  The "yin and yang" semi-circles are not delineating the inductive or capacitive regions of the Smith chart. They being used to illustrate the regions of impedance that can be matched using the L-section configurations shown.  If you look very carefully at figure 4, you'll see the "Type 1" figure (upper left) shows the colored line connecting the ends of the semi-circles along the circumference of the chart, thus creating a closed shape/area in the upper part of the Smith chart.  This indicates that the impedances within this closed are are those that can be matched with the "series-L, shunt-C" network shown.  The "Type 2" diagram in the upper right encloses an area on the lower portion of the chart, indicating impedances that can be matched with the "series-C, shunt-L" type network, etc.

So, there is really only one chart.  This figure is simply highlighting regions of the chart to help with impedance matching circuit selection.

A suggestion (as previously mentioned). During one of your future videos please could you cover the situation where the only things known are a) forward voltage b) return or reflected voltage and c) the phase difference between the two signals. Please show how this is plotted on a Smith Chart.

Thanks in advance, I'm looking forward to the future videos.

I will certainly try to cover that.  Pretty simple though.  Gamma, the reflection coefficient, is simply the ratio of the reflected wave to the incident wave.  In other words, reflection coefficient is Vr/Vi, where the voltages are complex values (including phase).  The reflection coefficient, gamma, varies between 0 and 1 and is plotted as a "ray" from the center of the Smith chart.  The value of 1 is the outer perimeter.  The scale for the reflection coefficient is one of the radial scales along the bottom of the chart - thus you can draw the gamma ray on the chart using the length and angle from the calculation.  Then, simply read the impedance value at the end of the ray from the curves on the chart...

[Dino KL0S]

BTW, if anyone is interested in Part 2 of the article you can see it at (http://highfreqelec.summittechmedia.com/Apr06/HFE0406_Rhea-part2.pdf).  73 - Dino KL0S