The original USB — Unified S-Band, a common communication channel used during the Apollo missions. With just 20 Watts, they could communicate with Houston from the moon. And a single antenna combined voice, television, command, tracking and ranging. From the Future Ventures’ 🚀 Space Collection.

This fully redundant Command Module S-Band Amplifier output was routed to the High Gain and Omni-Directional antenna’s on the CSM. It is stamped Serial No. 0006

Even today, this type of specialty vacuum tube is among the most efficient and compact types of RF amplifier. As a result, many high-tech satellites still feature these devices.

This photo and detailed analysis come from the Ken Shirriff blog, which became popular with places like Hackaday:

“How did the Apollo astronauts communicate 240,000 miles back to Earth? With an amplifier that was just 20 watts, built from special traveling-wave tubes. I look inside this amplifier in my latest blog post”

2 responses to “Apollo Command Module USB TWT Amplifier”

  1. jurvetson Avatar
    jurvetson

    TWT Schematic: Vintage photo of stack, with cover removed:

    Reply
  2. precious amount Avatar
    precious amount

    Cool hardware and images.

    When you hear the recording, "One small step for man…" there’s a bunch of crackling noise noise on the transmission. I’d heard the link from the Lunar Excursion Module didn’t have enough isolation from transmitter to receiver, (receiver desensitization). The noise on the transmission sounds like desensitization. I don’t think it was the S-band but the terrestrial Lunar hop, that was messed up. Do you know of any documentation showing what caused the desensitization on the first Apollo mission to the moon?

    Reply

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