tween 5° notifies the assignment to the IFRB, and the Board registers the and 25°. assignment in the MIFR, provided that the assignments are in Accordingly, these values have been adopted as a mandatory accordance with international agreements and subject below sharing constraint upon the fixed satellite service at 4GHz wherever 26/8 Radio spectrum management Satellite INTERFERENCE MODE 3 Y GHz Y GHz INTERFERENCE X GHz EARTH MODE 4 X GHz STATION X GHz Y GHz Y GHz INTERFERENCE INTERFERENCE MODE 2 MODE 1 Figure 26.3 Interference modes between a fixed-satellite network and terrestrial links (Wanted signal paths are shown in broken line) the frequency band is allocated internationally, with primary status, 26.4.2.5 Frequency co-ordination around earth stations for the fixed service; see Figure 26.8. Slightly less stringent con- straints have been agreed for down link bands at higher frequencies. There are agreed limits on the power radiated from earth stations at low angles of elevation in frequency bands shared with the fixed service. These limits are a sharing constraint, designed to keep 26.4.2.4 Constraints on terrestrial transmitters within reasonable bounds the distances at which interference to terrestrial stations can occur. However, the limits are high, and they Constraints on the power of fixed service transmitters operating in are unlikely to have much impact on the design of modern satellite bands below 30GHz allocated for fixed satellite service up links networks. (interference mode 4 in Figure 26.3) have been adopted to limit The methods used in managing microwave spectrum for the fixed interference to satellite receivers for the same reasons as led to service assume that the incidence of interference will be relatively power flux density limits for satellite down links. The constraints are as follows: predictable and interference distances will be relatively short. Thus, administrations discuss proposed new assignments with their imme- diate neighbours, if it is thought necessary, before notifying the 