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From: Bill KT4YE
Date: 20 Mar 2002
Time: 09:15:18
Remote Name: 12.93.230.32
Hard to imagine an autotuner with NO moving parts unless the device consists of a bloody great resistor such that the "antenna" impedance stays within acceptable limits over the entire frequency range. Of course, such a scheme doesn't radiate very well, since most of the transmitted power goes into the resistor. :)
Two approaches I know of: 1. A "conventional Pi/L tuner with circuitry to detect excess mismatches. Motorized coils and/or inductors are controlled by the circuitry and compensate for antenna mismatches. The better designs are mounted AT the antenna, since losses in the coax, and shunt capacitance to ground can eat up most of the transmitted signal.
2. Similar circuitry to detect mismatches. The circuitry controls either a tap point on the loading coil -- like you asked about earlier -- or the physical length of the antenna. Sometimes both
I'm sure there are a few hundred other ways to auto tune an electrically short antenna.
Hope this helps.
73 Bill