4.2 Telecommunication System Impacts Due to Self-Focusing Instabilities In addition to changes in the ionosphere due to ohmic heating, the SPS microwave power beam may create striations or irregularities in the ionospheric electron density resulting from thermal self-focusing instabilities. These irregularities, if they occur, could scatter radio waves in the HF, VHF, and UHF portion of the spectrum. Telecommunication systems operating in these bands could suffer performance degradation due to interference from scattered signals. These scattered signals could travel over great distances and give rise to interference to systems operating remote from the SPS power beam. Experiments to assess the impact of self-focusing instabilities on telecommunication systems were conducted in March and April, 1980. The results obtained are discussed in detail by Basu et al. (11). 4.2.1 Satellite-to-Aircraft Measurements. Satellite-to-aircraft transmission measurements were made using the Air Force Avionics Laboratory Cl35/662 aircraft operated by the 4950 Test Wing at Wright-Patterson Air Force Base, Ohio. This aircraft is equipped to monitor signals transmitted from the LES-8 satellite (249.2 MHz) and the FLEETSATCOM satellite (244.0 MHz). Both amplitude and phase can be measured under test conditions (12). Figure 5 provides a simplified illustration of the aircraft reception of a satellite signal that passed through a portion of the ionosphere modified by the Platteville Facility. The flight track of the aircraft was coordinated with the operation of the Platteville Facility in order that east-west and north-south tracks could be flown during times of facility “ON.” This enabled estimates to be obtained of the horizontal extent of the ionospheric scintillation induced by the facility operation. In addition to transmitting underdense radio waves, periods of time were allotted at the facility to the
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