6. Di scussion (i) The following comments may be made on Tables 1 and 2. (a) If a large radio telescope is directed so that an SPS lies within its main beam then the receiver will be damaged unless protected by a filter to ensure that the power level at the parametric amplifier is less than 1W (a rejection of at least 25 dB at 2.45 GHz for the worst case). (b) Observations within 5° of an SPS will only be possible with severely reduced sensitivity. (c) Observations in directions more than 5° away from the SPS but on a frequency within 10% of 2.45 GHz will have reduced sensitivity because of the filtering requirements. The radio astronomy band at 2.7 GHz would be affected and also the satellite communication bands at 2.2-2.3 GHz which are also used for radio astronomical observations. (ii) The estimates in (i) refer to the circumstance where only the fundamental 2.45 GHz signal from the SPS is significant. Any appreciable harmonic content in the signal beamed to Earth would increase the complexity of the filters required and might extend the limitations considered in 6(i) to other frequency bands reserved for radio astronomy. The seriousness of this cannot be assessed until the characteristics of the space transmitters are defined. (iii) The calculation of interfering levels and rejection needed have been based on the characteristics of the 250ft Mk IA radio telescope at Jodrell Bank. These figures may be taken as typical for parabolic reflectors now in use as radio telescopes. For smaller reflectors the area of forbidden sky around SPS for the various cases considered would increase approximately linearly as the aperture of the telescope decreases. For combinations of radio telescopes used as interferometers or in aperture synthesis networks, the effect of the SPS signal on the system needs more
RkJQdWJsaXNoZXIy MTU5NjU0Mg==