Wireless communication systems

The feasibility for producing ELF signals in the earth ionospheric waveguide, by downconverting HF pump power in the ionospheric plasma has been investigated. We have found that: (1) Interaction regions of horizontal width approx. 100 km, localized inside an ionospheric density gradient, can deplete the pump for pump powers above a threshold value. Minimum threshold is achieved for pumps propagating almost perpendicular to the density gradient (very oblique incidence) at 100 km altitude. The threshold power required is between 3-10 MW of HF, (2) The conversion efficiency from HF to ELF in the ionosphere could reach values of the order of 0.01, and (3) The scheme can operate either as an ELF generator if we use an HF pump with power 3-10 MW and a lower HF sideband with power 100 kw, or as an amplifier of ELF signals from weak ground transmitters (such as the Wisconsin test facility), or from weak space or balloon based antennas. A variation of the scheme can operate as a broadband ELF generator for jamming purposes.