What is the difference between LC(CL) and CLC antenna tuning unit as power loss is concerned ?
2 Answers
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LC or its counterpart CL ensures that at match, Q is as low as possible. Low Q means low loss.
CLC allows Q to be higher than necessary, and still match source to load. The higher Q means more power is lost heating the tuner element(s). If you tune it for minimum Q and impedance match, one of the "C's" tends toward redundancy, and the network looks like LC or CL.
It is possible to cascade two LC stages (or CL stages) when source impedance differs from load impedance by a large factor.
The intermediate impedance between LC stages would be $ \sqrt{Z_S \times Z_L} $. Each LC stage has low Q; lower than Q of a single LC stage. So even though this network has four components, losses are low.
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When I read Glenn Geek's answer I was confused by his use of the term "Q" . My only knowledge of it was as a figure of merit, in a tuned circuit a high Q is usually desirable. In that usage it is power stored in the reactance/power dissipated in the resistance. Terman called the difference between input power and output power in a matching circuit "delta". When this is viewed as input power over output power the result is a pure number, a value that can be called Q, a figure of merit. The lower the Q, the lower Terman's delta, and the more efficient the matching network. When an LC circuit is used as a matching device it is tuned slightly off from the resonate point, lowering the maximum Q of the LC circuit ( This usage of Q is the power stored/power dissipated one) meaning the LC circuit is more lossy, but viewed from the point of Terman's delta, or matching unit Q, (the input power/output power) the unit performs better. Here is a better explanation of Q, as Glenn used it in his reply. It may also answer some parts of the question. http://www.antentop.org/w4rnl.001/gup14.html
