Zack Lau transmatch

[Scott Parker K7LU]

Sorry that this is a few days later than I had promised, but here it is, the tuner article that I mentioned on last Thursday's net.  It is based on the principle that you can match anything with just two components, but you have to be able to change the configuration of those two components.  This tuner does the latter by treating the tuner connections like a patch panel (as opposed to one that's always for the transmitter and another that's always for the antenna.) 

If you're at all familiar with Smith charts, the graphics on this page show the different ranges of impedances that the different two-component configurations will match.  (And if you look, you'll see what I meant about the Smith chart looking like a Yin Yang symbol when you shade out the region that a given configuration will not match.)  Also, if you want to learn more about the Smith chart, that page has a lot of relevant links.

Also, looking at how these two component matching networks operate gives some insight into how the three component tuners, like the popular T network tuners (series C, shunt L, series C) work and how they avoid the "forbidden region" of impedances that an L cannot match.  The T can be viewed as two L networks, one series C/shunt L and the other shunt L/series C.  In choosing the range of components, the designer picks an intermediate impedance, higher than any expected load.  The generator side L network transforms the generator impedance to the intermediate and the load side L network transforms the intermediate down to the load. (Notice how the Yin Yang Smith charts of the two L networks are complimentary.) In the final product, the two shunt components in parallel can be rendered as a single component, variable over the required range.  Now we see why the T network matches a broader range of impedances.  The forbidden regions are eliminated....