The International Radio Regulations limit the power flux density at the Earth's surface from satellites. These regulations are designed to protect radio services on the Earth's surface fromS destructive interference from satellite transmission in the same frequency bands. Section 470 NGA of these regulations indicates that, for frequencies between 1670 and 2535 MHz, the power flux density from the SSPS must not exceed -168 dBw in any 4-kHz band. This is to protect fixed services using tropospheric scatter which apparently is the most sensitive system in that band. From Equation (4): From the above equation and Figures 77 and 78, the results for Cases (a2) and (a4) filtering are obtained. It can be seen that tropospheric scatter communication can operate within ± 1500 MHz from the fundamental for two-section filtering and ± 400 MHz for four-section filtering where a single SSPS is deployed (see Figures 81 and 82). An indication of the effect of a large number of SSPS units (100 SSPS) is shown to increase the noise 20 dB. For a four-element filter, the tropo service can operate to within ± 765 MHz of the fundamental. From Equation (4) and Figures 77 and 79, we obtain the results for Cases (b2) and (b4) filtering. It can be seen that operation is possible within ± 85 MHz for two sections and ± 60 MHz for four sections where a single SSPS is deployed. The International Radio Regulations also indicate the limit of harmful flux densities in the case of radio astronomy. On page 433 of the regulations, there is a table which indicates that, in the range of the SSPS fundamental frequency, an average level of harmful flux is defined as > -175 dBw/m2 for an isotropic.antenna. Antenna gains in this operation can run to 55 dB as a typical example. This means that the SSPS noise flux density must be kept below -230 dBw/m2 in order not to interfere. Also in this case, the bandwidth is typically 10 MHz. From Equation (4) and Figures 78 and 79, we have
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