An aerostat‐supported ELF/VLF transmitter

Abstract

A demonstration of an aerostat-supported extremely low frequency/very low frequency (ELF/VLF) transmitting antenna was performed. At ELF the vertical electric dipole (VED) antenna radiated at least 100,000 times more power than would a horizontal electric dipole having the same moment. That efficiency was achieved with an altitude of 12,500 feet (3810 m). Calculations show that the radiated power will increase as the fourth power of aerostat altitude. The tether antenna exhibited a corona onset voltage of 180 kV and was resistant to the degrading effects of ELF corona. Prolonged in-corona operation is therefore possible. The antenna was continuously tuned, despite changes in height and capacitance caused by the aerostat flight dynamics. The huge 300-H ELF tuning inductor posed no problem. Enhanced VED moments were achieved at ELF by operation at voltages up to 260 kV, 40% above the corona onset voltage. At VLF the antenna emulated a monopole that had a radiation efficiency greater than 90%. The measured bandwidths were large: 1.5 kHz at 23 kHz and 3.5 kHz at 34 kHz. The antenna height exceeded one-quarter wavelength at VLF, so the antenna could be tuned capacitively and required relatively low base voltages. At both VLF and ELF the measured fields agreed closely with predictions.

Model Predictive Control of Five-Phase Permanent Magnet Assisted Synchronous Reluctance Motor

“…As skin-depth is inversely proportional to the frequency, the situation can be alleviated by using extremely low frequencies such as ultra-low frequency (ULF) and very-low frequency (VLF). But this will result in larger antenna sizes and typical ground to submarine ULF/VLF transmitters are constrained by practical limitations the antenna size and power consumption requirements [75,76]. A recent Defense Advanced Research Projects Agency (DARPA) programs has declared a separate program to investigate the feasibility of "A Mechanically Based Antenna (AMEBA)" systems as solution for the aforementioned problem [74].…”

Penetration of ELF currents and electromagnetic fields into the Earth's equatorial ionosphere

“…4, April 1974, p. 353 -587). As discussed in detail by Field et al [1989], at ELF frequencies and depending on the ground conductivity and frequency a Vertical Electric Dipole (VED) antenna radiates five more orders of magnitude than an HED having the same moment. In examining the results of our analysis of the interaction of the injected ELF pulse with the equatorial ionosphere, we note that the interaction resulted in the generation of both of boundary layer vertical as well as horizontal currents that will couple directly to the EIW modes.…”

Risk Assessment and Experimental Light-Balloon Deployment of a Stratospheric Vertical VLF Transmitter

“…The first method was successfully employed by prof. Adolf Slaby as early as 1897, when airship-supported wires (up to 400 m of length and up to 280 m of altitude) were allowed to establish a telegraphic communication link [ 11 ]. A new adaptation of a similar design—an aerostat-supported antenna wire—was proposed in 1989 and later in 1997, with new tuning technology and elaborated ground-plane radials [ 12 , 13 ]. Fully airborne vertical long wire antennas were frequently employed by the zeppelins in the beginning of the 20th century [ 14 ].…”