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For much of the twentieth century, high-frequency (HF) radio was the primary means of global communication. Satellites displaced HF from the 1970s onward by offering higher data rates, more predictable links, and simpler operation. Yet satellites are expensive, carry finite lifespans, and face a growing set of threats: anti-satellite weapons tested by multiple nations, jamming of fixed-frequency transponders, solar flares that can physically damage spacecraft, and persistent coverage gaps in polar and heavily forested regions. These realities have spurred a broad reassessment of HF as a resilient, infrastructure-independent alternative that can reach any point on the planet via the ionosphere. Modern developments — particularly wideband waveforms supporting up to 48 kHz channels with data rates reaching 240 kbit/s, and fourth-generation automatic link establishment that automates frequency management and link negotiation — have addressed many of HF’s traditional shortcomings. This white paper explains the physics of ionospheric propagation, surveys the satellite vulnerabilities motivating HF’s return, and details the technical standards and techniques that are making reliable, automated HF communications a practical reality.
