through the antenna and is directed towards a footprint on the ground. Generally the power received in the centre of a footprint is larger than towards the edge. Equivalent isotropically radiated power (EIRP) is a measure of the effective power transmitted from a satellite in the direction of a specific region within the footprint. EIRP can be calculated by combining the transmission power from a Satellite Communications Figure 11.3 The earth station antenna at Ceduna, South Australia [8]. Source: Nachoman-au. GFDL (http://www.gnu.org/copyleft/fdl.html), CC-BY-SA-3.0 Figure 11.4 A satellite's spot beam footprint Broadband Telecommunications Technologies and Management 47 dBW 48 dBW 46 dBW 49 dBW Figure 11.5 Spot beam footprint EIRP map transponder and the antenna gain aimed at a particular geographical area. Figure 11.5 shows a typical EIRP for a regional footprint of an Intelsat satellite. It shows that the radiated power from a satellite directed towards Sweden is larger than 49 dBW (79 dBm). Similarly signal energy directed towards Portugal is 42-44 dBW (72-74 dBm). Ground station antennas are chosen to deliver a desired signal to noise ratio (SNR) for a designed reception quality. These can calculate the received SNR based on the published EIRP value and the path loss. Transponder Transponders are frequency convertors and amplifiers and are placed on-board satellites. Their function is shown in Figure 11.6: they receive a signal at one end, down-convert it to a different frequency by a fixed amount, amplify the signal and send it downlink. Figure 11.6 shows a K -band satellite transponder frequency allocation. Uplink signals are received at the satellite in the 14.0-14.5 GHz band, and the downlink signals are transmitted in the 11.7-12.2 GHz band. Transponder channels are paired, and every uplink slot is separated from its down- link pair by exactly 2.3 GHz. A total of 24 transponders exist in the K band, and each tran- sponder has a bandwidth of 36 MHz for a total effective bandwidth of 864 MHz (vertical and