Apollo Spacecraft S Band Communication System, Part 2

Communications from the Apollo spacecraft to ground stations were via an S band microwave link with a radiated power of 11.6 watts. The signal sent to the antenna was produced by the transponder unit and amplified by a traveling wave tube. This episode digs into the radio frequency (RF) power amplifier, explains its complicated system of relays providing redundancy, and describes how a traveling wave tube works and why they remain in use on contemporary spacecraft.