HF Satellite Sound Broadcasting - A Preliminary Assessment

This paper examines in a preliminary way the technical factors associated with the use of the HF band for satellite sound broadcasting. Numerical results are presented for an example geostationary satellite system operating in the 26 MHz band. An analysis of the electrical characteristics and the far-field pattern of a whip antenna used on low-cost HF portable receivers is presented in order to connect receiver noise-limited sensitivity measurements and signal quality objectives with incident field strength requirements. It is shown that a minimum usable circularly polarized field strength of 390 μV/m is required for an elevation angle of 5° in a noisy urban environment, decreasing to about 130 μV/m above 15° elevation in a quiet rural area. A simplified satellite mass model is used to estimate the minimum mass of a satellite to provide a field strength of 1000 μV/m at the edge of the coverage area. The optimum antenna size is determined as a function of the antenna parametrics, e.i.r.p., and frequency. For the conditions assumed, the spacecraft on-orbit mass will be on the order of 14 000-17 000 kg, and the antenna diameter will be about 600 m. The Appendix contains analyses showing that refraction, scintillation, and absorption caused by transionospheric propagation are the principal mechanisms degrading the received signal quality. An analysis using ray tracing techniques shows that refraction will reduce coverage to about 40 percent of the earth\´s disk during the daytime for periods when the smoothed sunspot number is 100. Nighttime coverage will; because of refraction, extend beyond the visible horizon. Nighttime scintillation in the equatorial region is expected to be severe. Based on an extrapolation of data taken at higher frequencies, the envelope of the received carrier will exhibit Rayleigh statistics with fade depths on the order of 10 dB occurring on the average of one every 10 s and lasting for about 1 s. Absorption of t- ansionospheric signals occurs primarily in the region of the ionosphere and amounts to a nominal 2 dB of loss. During periods of sudden ionospheric disturbances due to solar flares the absorptive losses may approach 40 dB.