Ionospheric distortion of HF signals

The channel transfer characteristics of high-frequency (HF) radio signals propagating through the disturbed ionosphere were measured in a series of experiments conducted in the polar cap, auroral, and equatorial regions. Transmissions over one-hop F layer paths were observed to be distorted in the range (propagation time) and Doppler domains on the order of hundreds of microseconds and tens of hertz, respectively. A frequency-modulated continuous wave (FMCW) waveform was used for oblique sounding purposes, and a pseudorandom noise phase modulation with a 20-kHz bandwidth was used to measure range and Doppler spreads. The oblique sounding data were used to define a three-layer quasi-parabolic model of the ionospheric electron density profile, which in turn was used in the calculation of the channel scattering function to compare with the observed range and Doppler spreads.

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