It’s been fifty years. Let’s recall Apollo 11 radio communications systems, including the wonderful Unified S Band and local VHF that really worked. 

I can barely believe it’s been 50 years since I watched Neil Armstrong and Buzz Aldrin walk on the moon. You have probably seen lots of TV specials remembering this achievement. For something different, I thought I would write about Apollo 11 radio communications and how it worked.

Radio in space started with Sputnik in 1957, which broadcast beacons on 20 and 40 MHz received by many hams. Not me, though, I was only six at the time!

With the Mercury and Gemini programs, V/UHF took over and over the years spacecraft got crowded with all sorts of increasingly heavy collections of different radios. You will find that when Apollo came along, everything changed radio-wise. It was time for better range, more bandwidth and less power and weight.

Apollo engineers created two systems that worked seamlessly. The first system was for local communications on VHF in the 200 MHz band. But the second was the broadband, multi-channel, multi-mode Unified S Band (USB) system developed for NASA by Collins Radio.

USB operated on 2 GHz. Engineers aggregated all of Apollo’s long distance communications requirements into one system using a single transmitter, receiver and antenna. USB contained channels for voice, television, telemetry, range and direction finding, transponders, biometrics and so on.

Apollo 11 Radio Communications – Amazing Stuff

USB was a large microwave repeater and multiplexer. Most of the local communications from the Lunar and Command Service Modules were repeated back to earth on 2 GHz. Modulation schemes included AM, FM, PM and PSK.

Wideband FM was used for video and scientific data. Television pictures used 500 kHz bandwidth for black and white, and 2 MHz for color. Local VHF gear ran at 5 watts, while the 2 GHz USB link ran 15-20 watts.

You will see that the Command Module had an array of four 31″ dish antennas with 25 dB gain. Lunar module had a 26 inch dish at 16-20 dB. In addition, astronauts erected a 10 foot diameter 34 dB gain dish on the lunar surface to support color TV pictures.

NASA did a wonderful job of coordinating some very complex systems for Apollo 11 radio communications. Here is a overview description of all the propulsion and communications systems used.

Oh, yes. Astronauts also had a Morse Key for emergency communications. And they also had high frequency gear (10-15 MHz) for backup during recovery and landing.