5.1 Potential interference to terrestrial or earth station receivers from deep-space station transmitters Fig. 4 shows power flux-density at the surface of the Earth caused by deep-space stations with characteristics as shown in [CCIR 1974-78b]. These stations typically use low gain, wide beam antennae while near Earth. After a time not exceeding six hours from launching, they are usually at a sufficient distance for the power flux-density at the surface of the Earth to be less than the maximum permitted by Radio Regulations for protection of line-of-sight radio-relay systems. For example, the MARINER Jupiter Saturn spacecraft is expected to use the low gain antenna until 4.2 x 107 km from Earth, at which time the power flux-density would be - 198 dB(W/m:) in 4 kHz after switching to the high gain antenna. FIGURE 4 - Power flux density at surface of Earth from space station transmitter When the transmitting space station is using a higher gain directional antenna, there is the potential for interference with sensitive terrestrial receivers if their antennae are directed in the ecliptic plane. A space station operating at 2.3 GHz with an e.i.r.p. of 51 dBW at a distance of 5 x 108 km could create an input of -168 dBW to a transhorizon receiver (27 m antenna, main beam). The duration of such interference would be of the order of. a few minutes, once a day, because of the rotation of the Earth. 5.2 Potential interference to near-Earth satellite receivers from deep-space station transmitters Considerations of this interference are similar to those for the space station to terrestrial receiver case, § 5.1, with the exception of the path geometry. Depending on the changing conditions of that geometry, occasional brief interference is possible. 5.3 Potential interference to deep-space earth station receivers from terrestrial or earth station transmitters Interference to deep-space earth station receivers may come from terrestrial or earth stations over line-of-sight paths, by transhorizon phenomena, or by rain scatter. For co-ordination considerations see § 2.3. Other services with high power transmitters and high gain antennae are potential interference sources. Radiolocation stations are an example. Earth station transmitters are less likely sources of interference, depending on e.i.r.p. in the direction of the deep-space earth station. Co-ordination should enable adequate protection from radio-relay stations to be provided.
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