Question T8B02
From subelement T8 - T8B
What is the impact of using excessive effective radiated power on a satellite uplink?
Why is this correct?
Excessive uplink power blocks other users because satellites use automatic gain control (AGC). When a very strong signal hits the satellite, the AGC adjusts to that level and sets a higher receive threshold, preventing weaker signals from being relayed. With reasonable power levels from all users, the AGC doesn't activate and the satellite can relay many signals simultaneously, allowing shared access.
Memory tip
Compare your downlink signal strength to the satellite beacon - they should be roughly equal. If your signal is much stronger than the beacon, you're using too much power. This self-monitoring technique works because proper uplink power produces a downlink signal comparable to the beacon's strength.
Learn more
Satellite transponders operate as linear repeaters with limited dynamic range. The AGC system protects the spacecraft's receiver from overload but creates a 'capture effect' where strong signals suppress weaker ones. In practical operation, this means monitoring your own signal on the downlink frequency and maintaining power levels that keep your signal strength similar to the satellite beacon, ensuring equitable access to the transponder's frequency privileges for all stations within the footprint.
Think about it
Why do you think satellites don't simply use separate AGC circuits for each individual signal instead of one overall AGC system?