TABLE VI - Interference protection for deep-space station receivers TABLE VII - Potential interference in Earth-to-space bands 4.1 Potential interference to terrestrial or earth station receivers from deep-space earth station transmitters The normal maximum total power for current US deep-space earth stations is 50 dBW. For a typical minimum elevation angle of 10°, the e.i.r.p. directed towards the horizon does not exceed 57 dB(W/4 kHz), assuming the reference earth station antenna radiation pattern of Recommendation 509. For spacecraft emergencies, the maximum total power may be increased to 56 dBW, giving not more than 63 dB(W/4 kHz) at the horizon. These values of e.i.r.p. meet the requirements of No. 470F of the Radio Regulations. Aircraft stations within line-of-sight of a deep-space earth station will encounter total power flux-densities as shown in Fig. 1. For an aircraft altitude of 12 km, the maximum line-of-sight distance to an earth station is 391 km and the total power flux-density at the aircraft can never be lower than -83 dB(W/m2), again assuming the antenna pattern of Recommendation 509. Depending on distance and earth station antenna direction, the aircraft station may experience much higher flux-densities and interference levels. Co-ordination with airborne stations is generally not practicable. Tropospheric phenomena and rain scatter may couple deep-space earth station transmitting signals into transhorizon, space system and other surface stations. When practicable, co-ordination should provide sufficient protection for terrestrial receivers and earth station receivers. See § 2.3 for co-ordination considerations. \ 4.2 Potential interference to satellite receivers from deep-space earth station transmitters Satellites that come within the deep-space earth station beam will encounter power flux-densities as shown in Fig. 1. When the earth station is tracking a spacecraft so that the antenna beam passes through the geostationary satellite orbit, the flux-density at a point on that orbit will vary with time as shown in Fig. 2. For example, the total power flux-density will be -95 dB(W/m2) or more, for 32 minutes. The figure assumes a transmitter power of 50 dBW, a 64 m antenna, and the reference earth station pattern of Recommendation 509. An important observation is that the minimum flux-density at the geostationary satellite orbit within line of sight of a deep-space earth station is - 122 dB(W/m2), regardless of the antenna pointing direction. The duration and magnitude of signals from deep-space earth station transmitters which may interfere with satellites in non-geostationary orbits depends upon those orbits and the particular deep-space tracking at that time. 4.3 Potential interference to deep-space station receivers from terrestrial or earth station transmitters Terrestrial or earth station transmitters within sight of a deep-space station are potential sources of interference. Fig. 3 shows the space station distance at which interference power density from such a transmitter equals the receiver noise power density. For example, a transhorizon station with 93 dB(W/10 kHz) e.i.r.p. in the 2.1 GHz band could interfere with a space station receiver at ranges up to 4.1 x 109 km (600 K noise temperature, 3.7 m spacecraft antenna). The possibility of interference at such a great distance poses a threat to space missions to planets as far away as Uranus. Stations with lower e.i.r.p., or with antennae pointing away from the ecliptic plane, have less potential for interference.
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