equivalent to the SPS power for ionospheric heating. This is possible because the heating is inversely proportional to the square of the heater frequency. Experiments related to SPS effects on telecommunications have been conducted at Platteville, where the communications environment is representative of environments in which the SPS microwave-beam transmission would typically occur. Many different types of communications signals are monitored while the Platteville facility is heating the ionosphere. Because the current Platteville facility provides SPS comparable power density only to the lower ionosphere, the telecommunications experiments performed so far were directed toward obtaining performance information for those systems whose radio waves are significantly affected by the structure of the lower ionosphere. The telecommunication systems chosen for investigation were representative of those operating in the very low frequency (VLF, 3 kHz-30 kHz), low frequency (LF, 30 kHz-300 kHz), and medium frequency (MF, 300 kHz-3 MHz) portions of the electromagnetic spectrum. The results obtained indicate that the SPS, as currently configured with a peak power density of 23 mW/cm2, will not adversely impact upon the performance of VLF, LF, and MF telecommunication systems. The currently available ionospheric heater facilities are limited in power and frequency range and cannot simulate SPS effects in the upper ionosphere. Modified and expanded facilities would be required to simulate SPS heating of the upper ionosphere, verify the frequency scaling theories, and study the limitations on power density in the ionosphere. The electron density of the ionosphere likely would be decreased by rocket effluents in the vicinity of the SPS launch sites creating "ionospheric holes." Theoretical predictions of electron depletion and data from Skylab and missile launches suggest that a wide range of communications services could be affected following SPS rocket launches. ELECTROMAGNETIC COMPATIBILITY Electromagnetic compatibility is achieved when the capabilities of radio, radar, and other electronic systems are maximized with a minimum of interference between systems. The satellite power system would be designed and operated in ways which would satisfy established national and international rules for using the electromagnetic spectrum. Nevertheless, there would be a potential for producing interference because the amount of microwave power transmitted from space to earth for the Reference System would be unprecedented, and the size of the microwave beam would be very large at the earth's surface. The SPS field intensity would be one volt per meter at a distance of 30 kilometers from the center of a rectenna site. Communications systems generally operate with received-signal strengths of several microvolts per meter so communications systems within about 100 kilometers of an SPS rectenna could receive sizable signals from the satellite
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