telescope are therefore those appropriate to the SPS frequency of 2.45 GHz. For simplicity we take the characteristics of the Mk IA radio telescope at Jodrell Bank. On 2.45 GHz these are - Beam width to 3dB points = 5 arc min. Mean sidelobe level to 5° off axis = -30dB with respect to main beam. Sidelobe level beyond 5° = -60dB with respect to main beam. Effective area of the collector = 3 x 10 m . We assume that the telescope is far enough removed (say more than 100 km) from the SPS terrestrial collector that it can be considered to be only in the far-out zone flux of the SPS. The power delivered at the focus for the maximum and minimum limits considered in 4(a) can then be calculated for typical circumstances. Table 1 gives the power delivered to the focus for three values of 9 - the angle between the axis of the telescope beam and the SPS. Table 1 Power delivered to the focus of the radio telescope at different values of 0 for two levels of the far-out zone field of the SPS. The power delivered to the focus of the telescope from a celestial source (assuming a limiting sensitivity of 10 W m Hz and a typical bandwidth of 4 MHz) will be of the order 10 watts. Thus the power input from the SPS into the telescope focus will be from approximately 10 to 10 times greater than that from the celestial source which it is desired to study.
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