TUNABLE_VLF

Published:2009/7/16 3:16:00 Author:Jessie | From:SeekIC

TUNABLE VLF-Gives tuning range of 10kHz to 150 kHz without bandswitching, for WWV transmissions on 20 and 60 kHz and for operation on no-license amateur band around 1750 meters. Uses inductive tuning with toroidal ferrite core L1-L2 that is magnetically biased by pair of 1/2-inch diameter button-type permanent magnets. Rotating one of magnets with respect to other varies flux through toroid, changing its permeability and inductance. Toroid uses 100 turns of stranded wire to give inductance variation from 100 μH to 12 mH (120:1 range). Ferrite cores with higher permeability require fewer turns. Converter output on 15 meters feeds into communication receiver. Local oscillator uses FT-243 7-MHz crystal in third-over-tone mode to give 21 MHz. Antenna is directly coupled or coupled through capacitor to improve matching to long antenna. -G. Ruehr, Tuned Very Low-Frequency Converter, Ham Radio, Nov. 1974, p 49-51.1



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