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Below is a picture of the internals of the MFJ-989D ANTENNA TUNER, 1.8-30 MHZ which you hook up between your HF transceiver and antenna. Notice the large variable roller inductor pictured at the bottom. The knob for changing the inductuctance is just visable on the left. The two large devices in the middle and top left are variable capacitors.
|MFJ-989D Antenna Tuner Internal View|