Thanks to Al N1AL, Jack W6FB, and Dave AB7E for great information that helped me a lot.
I'm in the circuit simulation business, after all, and I confess that I was just being lazy, so I ran some simulations that confirmed what Dave, in particular, had said. As suggested by Dave, I chose typical Q values of 100 for the inductor and 1000 for the capacitor. Then I simulated as many points as I could on the entire Smith Chart to see 1/ if the tuner could tune each point to 50 ohms, and 2/ what the power loss was in the tuner at each of those points. Then, I discovered that K6JCA had already done this on his excellent blog at: https://k6jca.blogspot.com/2015/03/notes-on-antenna-tuners-l-network-and.html . The guy is totally professional and exhaustive in his discussions. I really admire his work. Anyway, it turns out you can make a graph of power lost in the tuner versus phase angle of the load. As you might suspect, 'easy' loads of 5 or 500 ohms resistive (SWR = 10:1) don't tax a tuner as much as reactive loads do. In fact, they're near (but interestingly, not at) the areas of *minimum* power loss. Whenever an antenna tuner is reviewed in QST, resistive mismatched loads are usually used. I'd like to see tuners tested with reactive loads, but the number of loads required to do this from 160 to 10 meters would be enormous. I see why resistive loads are preferred, because you can re-use the loads on every band. I'm frustrated by imprecise statements like, "This tuner will tune an 8:1 mismatch." What does that mean? There has to be a better way for manufacturers to spec the exact impedance ranges that their tuners will tune. I like the method that I used, which shades a Smith Chart in color based on the two criteria I listed above. One picture would tell you all about a tuner's effectiveness. No real tuner can tune the entire Smith Chart, but the more of the chart that is covered, the better the tuner. And if you can shade the areas of higher tuner loss in red, then that would also tell you an important piece of information. (However, to generate such a plot through measurement you'd probably need a very expensive load-pull setup, which is a totally separate discussion.) For the L-network I simulated, a particularly difficult 10:1 load was near the 7 - j30 ohm point, which is toward the bottom edge of the Smith Chart at a phase angle of 282 degrees (or -77 degrees), and a similar point near the top edge. The lower impedances with capacitive reactance were definitely the most difficult (using power loss as the measure of 'difficulty') for the tuner to handle, which Dave stated in his post, while the high impedances with inductive reactance were generally more difficult. If your antenna must be mismatched, and you're using an L-network tuner, you want it to be > 50 ohms with a little bit of capacitive reactance, or below 50 and inductive. By the way, K6JCA actually put the Elecraft KAT500 through this simulated evaluation and it tested so well that he ended up buying one. Al W6LX/4 ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
