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Satellite telecommunication links cover astounding distances; ESA missions need to communicate with spacecraft orbiting at distances up to 900 million kilometres away. The uplink signal must be strong enough to travel these enormous distances and still deliver data to a satellite's receiver. High Power Amplifiers (HPAs) are used at ESA ground stations to provide the requisite high power levels required for the uplink.
HPAs have certain distinctive characteristics. They are heavy (up to 1500 kg), energy intensive (up to 100 kW) and they must be handled with a lot of care - any mishandling can lead to severe damage not only to the amplifier itself but also to the station - or, in the worst case, even cause serious injuries or death station personnel.
This forum provides a short introduction to high-power amplifiers and their technology, to solid state power amplifiers, why we still use klystrons (a vacuum tube invented in the 1930s) and the usage of HPAs at ESA ground stations.