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In this paper, the problem of designing switched oscillators at four different frequencies (200, 300, 400, and 500 MHz) has been addressed. These oscillators are quarter-wavelength long coaxial transmission lines with a nitrogen spark gap switch at one end. Two of these switched oscillators at 200 and 500 MHz with a charge voltage of 30 kV have also been fabricated. These two oscillators are modeled using PSpice and their output into a 100 Ω load is estimated and tested by fabricating a 100 Ω transmission line. Use is made of a modified commercial helical antenna with a bandwidth of 400-600 MHz and a switched oscillator has been integrated into this helical antenna. Measurements have been made of the S 11 , the voltage into the antenna, and also the transient fields at two distances. Indeed, starting from electrical power from a 12 V battery, electrical field strengths in excess of 10 kV/m with damped sinusoidal waveforms at 500 MHz (for example) have been demonstrated.

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