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...