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We present experimental results of a novel time-varying antenna to broadcast very-low-frequency (VLF, 3–30 kHz) signals. The antenna consists of a 275-m-long dipole interrupted with a high-voltage (HV) switch somewhere along the line. The switch was operated to force the charge to remain near the tip rather than reflect and return to the load. On-antenna measurements show the operation of the switch in trapping charge. Magnetic field measurements indicate that the time-varying system boosts the generated fields. Signals were detected in the far-field. The antenna demonstrated a broadband transmission and also allowed frequency hopping. The antenna was horizontal along the ground which greatly limited efficiency, and the results are discussed in this context.
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Whitmore et al. (2025) studied this question.
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