SECTION 10 FREQUENCY INTERFERENCE AND ALLOCATION The frequency interference and allocation aspects of an MPTS are of great importance because of the potential impact on the design and the cost benefit of an SPS. Asa general rule the lower the frequency, the greater the effect on established users of the spectrum. It has been shown that the higher the frequency (above 3 GHz) the greater the risk of brownout in heavy rain. The system analysis and evaluation in a following section indicates the region in the vicinity of 2 GHz will provide a comparatively cost effective solution. Figure 10-1 provides an overview of the spectrum utilization in the areas of interest, the details of which are given in Reference 10-1. Of special interest are the radio astronomy bands, and the USA industrial band from 2.4 GHz to 2. 5 GHz centered at 2. 45 GHz. The radio astronomy bands imply tighter specs on noise interference due to the high gain receiving systems, and also pose difficulties in allocation if the band is associated with naturally occurring phenomena in space. The latter is the case for the 1. 4 GHz and 1. 7 GHz bands which correspond with hydrogen and hydroxyl resonance lines. The 2. 7 GHz and 5. 0 GHz bands are simply "windows" established for the convenience of the astronomy community in making observations in that general frequency region. The astronomers actually carry out observations throughout the RF spectrum with particular sites covering certain bands more frequently than others. The industrial band at 2. 45 GHz is the recommended location for the MPTS. It is near optimum from component and system points of view and follows a precedent for this type of usage. The following paragraphs cover the impact of this choice on users outside of this band for one satellite power source delivering 5 GW to the ground. For additional systems, e.g., 100, the noise and harmonics generated would increase by 20 dB. Impact of this on the equipment and other users requires further in-depth investigation.
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