o atmospheric conditions. Limited line of sight com- on the earth's surface to that of the transmitting or receiving station. munications, typically 10km. Limited usage, mainly short distance If the distance and great circle bearing is calculated using Equations speech and data links but increasing usage is likely. 27.10 and 27.11, the elevation and distance of the satellite can also be calculated. In addition to the free space loss, the loss due to atmospheric attenuation must be taken into account, and this will 27.11 References depend upon precipitation conditions in the earth station area. Typical values at 11GHz would be 1.0dB for an "average year" Boithias, Lucien (1987) Radio wave propagation, North Oxford increasing to about 1.5dB for the worst month. The actual figures to Academic Publishers. be used should be calculated from local meteorological data and the Braun, G. (1986) Planning and engineering of short-wave links, 2nd attenuation curves given in Figure 27.12. Ed. John Wiley & Sons, Chichester. Calculation of satellite paths is not often required as operators Budden, K.G. (1985) The propagation of radio waves, Cambridge usually publish "footprint" maps showing the received power con- University Press. References 27/15 Cannon, P.S. (1987) The evolution of meteor burst communications Johnson & Jasick (1984) Antenna Engineering Handbook, McGraw systems. J. IERE. 57 (3) (May/June). Hill. CCIR (1978) Man-made radio noise, Report 258- 3, ITU, Geneva. Longmire, C.L. (1978) The electromagnetic pulse produced by CCIR (1982) Volume V, Propagation in non-ionised media, Geneva. nuclear explosions, IEEE Transactions on Electromagnetic CCIR (1984) World distribution and characteristics of radio noise, Compatibility, EMC-20 (1) (February). Report 233-1, ITU Geneva. Maslin, N.M. (1987) H.F. Communications, A systems approach, Damboldt, T. (1975) A comparison between Deutsche Bundespost Pitman, London. ionospheric h.f. propagation predictions and measured field Millington, G. (1949) Ground wave propagation over inh