ting were "perfect." Gaseous absorption loss (or atmospheric absorption) varies with frequency, elevation angle, and altitude of the earth station. As one would expect, the higher the altitude, the less dense the air and thus the less loss. Gaseous absorption losses vary with frequency and inversely with elevation angle. Often, for systems operating below 10 GHz, such losses are neglected. Reference 3 suggests a 1-dB loss at 7.25 GHz for elevation angles under 10° and for 4 GHz, 0.5 dB below 8° elevation angle. Example of a Link Budget. Assume the following: a 4-GHz downlink, 5° elevation angle, EIRP is +30 dBW; satellite range is 25,573 statute miles (sm), and the terminal G/T is +20.0 dB/K. Calculate the downlink C/No. Remember that geostationary satellite range varies with elevation angle and is minimum at zenith. 9.3 SATELLITE COMMUNICATIONS First calculate the free-space loss. Use Eq. (9.4): = 96.6 + 20 log FGHz + 20 log Dsm = 96.6 + 20 log 4.0 + 20 log 25, 573 = 96.6 + 12.04 + 88.16 = 196.8 dB. Example Link Budget: Downlink EIRP of satellite +30 dBW Free-space loss -196.8 dB Satellite pointing loss -0.5 dB Off-contour loss 0.0 dB Excess attenuation rainfall 0.0 dB Gaseous absorption loss -0.5 dB Polarization loss -0.5 dB Terminal pointing loss -0.5 dB Isotropic receive level -168.8 dBW Terminal G/T +20.0 dB/K -148.8 dBW Boltzmann's constant (dBW) -(-228.6 dBW) 79.8 dB On repeatered satellite systems, sometimes called "bent-pipe satellite systems" (those that we are dealing with here), the link budget is carried out only as far as C/No, as we did above. It is calculated for the uplink and for the downlink separately. We then calculate an equivalent C/No for the system (i.e., uplink and downlink combined). Use the following formula to carry out this calculation: (9.24) Example. Suppose that an uplink has a C/No of 82.2 dB and its companion downlink has a C/N0 of 79.8 dB. Calculate the C/N0 for the system, (C/No)s. First calculate the equivalent numeric value (NV) for each C/No value: NV(1) = log-1(79.8/10) = 