objective of these tests is thorough characterization of radiated power in the range from approximately 1000 MHz up to the frequency where radiation in the SPS main beam is no more than the amount equivalent to the satellite's passive thermal radiation as seen from the surface of the earth. These measurements would include harmonic signals and noise products, as well as any nonharmon- ically related spurious emissions. This characterization is needed to permit calculations of the impact of SPS on radio astronomy, space research and other radio services. ASSIGNMENT OF SPS HARMONIC FREQUENCIES The power density level of the SPS at the primary transmitting frequency and at the next several harmonics will be so great, and the spectral characteristics at the harmonic frequencies so uncertain, that the allocation of frequency bands containing the 2nd, 3rd and 4th harmonics will likely be necessary for SPS use. The existence of the extensive series of grating lobes throughout the United States, Canada and Mexico is a further complicating factor which may require international coordination in order to assure that harmful interference will not be experienced by services operating at or near the harmonic frequencies 4.90 GHz, 7.35 GHz, 9.8 GHz, etc. TIME-VARIABILITY OF SPS OFF-AXIS RADIATION AND INTRINSIC MULTIPLE SATELLITE EFFECTS The interference and overload potential of the SPS Reference System is significantly increased should its off-axis signals become time-varying on the same time scales as are used for astronomical observations, as it can then mimic the expected behavior of the observations. As presently defined, the Reference System has such an intrinsic time-variability. In the Reference System, all 60 satellites transmit at 2450 MHz. However, it is not possible to phaselock the satellites in such a way that the off-axis radiation from different satellites will remain phase-constant for all ground-based observers. Each satellite pair, considered as a transmitting interferometer, will have an off-axis fringe pattern. Unavoidable station-keeping motion will cause this fringe pattern to sweep across the United States in a complex and partially unpredictable pattern.
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