Q4Satellite Communication

Uplink frequency is deliberately chosen higher than downlink frequency (e.g., 6 GHz uplink / 4 GHz downlink in C-band) because higher-frequency signals experience greater free-space path loss and atmospheric/rain attenuation; since the earth station has access to large power amplifiers and effectively unlimited electrical power supply, it can readily transmit at the higher power needed to overcome this greater path loss at the higher uplink frequency. In contrast, the satellite's onboard transponder is severely power-limited (constrained by solar panel/battery capacity and the need to minimize onboard heat dissipation), so the downlink is assigned the lower frequency band, minimizing the power the satellite must expend to deliver an adequate signal level at the earth station receiver.