Voice transmissions from astronauts on board Apollo spacecraft were encoded as a frequency modulated (FM) signal which was, then, multiplexed onto the S band microwave downlink from the spacecraft to ground stations. In Part 10, this signal was extracted and decoded using modern communications gear, but that wouldn’t do—can original Apollo-era NASA ground test equipment do the job more than fifty years after it was built?
Just as present-day engineers are amazed at what was accomplished with the technology available to designers in the Apollo era, those designers would be awestruck by the capabilities of the 21st century test equipment such as microwave spectrum analysers and software-defined radios used to illuminate the genius of their work.