{"id":53301,"date":"2022-07-11T11:33:13","date_gmt":"2022-07-11T15:33:13","guid":{"rendered":"https:\/\/swling.com\/blog\/?p=53301"},"modified":"2022-07-11T11:33:13","modified_gmt":"2022-07-11T15:33:13","slug":"ken-reverse-engineers-the-apollo-spacecrafts-fm-radio","status":"publish","type":"post","link":"https:\/\/swling.com\/blog\/2022\/07\/ken-reverse-engineers-the-apollo-spacecrafts-fm-radio\/","title":{"rendered":"Ken reverse-engineers the Apollo spacecraft’s FM radio"},"content":{"rendered":"

\"\"<\/a><\/p>\n

Many thanks to SWLing Post<\/em> contributor, Paul, who shares the following post from Ken Shirriffs’ Blog:<\/strong><\/p>\n

Reverse-engineering the Apollo spacecraft’s FM radio<\/a><\/h1>\n
\n
<\/div>\n<\/div>\n
\n

How did NASA communicate with the Apollo astronauts, hundreds of thousands of miles from Earth? The premodulation processor1<\/a><\/span>\u00a0(below) was the heart of the communication system onboard the Apollo spacecraft. Its multiple functions included an FM radio for communication to the astronauts, implemented by the Voice Detector, the module second from the top. In this blog post, I reverse-engineer the circuitry for that module and explain how it worked.<\/p>\n

The Apollo communication system was complex and full of redundancy. Most communication took place over a high-frequency radio link that supported audio, telemetry, scientific data, and television images.2<\/a><\/span>\u00a0NASA’s massive 85-foot dish antennas transmitted signals to the spacecraft at 2106.4 megahertz, an\u00a0S-band<\/a>\u00a0frequency, giving the system the name “Unified S-Band”. These radio signals were encoded using phase modulation;3<\/a><\/span>\u00a0onboard the spacecraft, a complex box called the transponder received the S-band signal and demodulated it.4<\/a><\/span><\/p>\n

The voice and data signals from Earth were combined through a second layer of modulation: voice was frequency-modulated (FM) onto a 30-kilohertz subcarrier while data was on a 70-kilohertz subcarrier, so the two signals wouldn’t conflict.5<\/a><\/span>\u00a0One of the tasks of the premodulation processor was to extract the voice and data signals from the transponder’s output. These voice signals went to yet another box, the Audio Center Equipment, so the astronauts could hear the messages from the ground. The data signals were decoded by the Up-Data Link, allowing NASA to send commands to the Apollo Guidance Computer, control onboard relays, or set the spacecraft’s clock.<\/p>\n

Many systems worked together for communication, but I’m focusing on a single module: the voice detector inside the premodulation processor that performed the FM demodulation. [Continue reading the full article…]<\/a><\/p>\n<\/div>\n","protected":false},"excerpt":{"rendered":"

Many thanks to SWLing Post contributor, Paul, who shares the following post from Ken Shirriffs’ Blog: Reverse-engineering the Apollo spacecraft’s FM radio How did NASA communicate with the Apollo astronauts, hundreds of thousands of miles from Earth? The premodulation processor1\u00a0(below) was the heart of the communication system onboard the Apollo spacecraft. Its multiple functions included […]<\/p>\n","protected":false},"author":15,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[8,5984,3],"tags":[7136],"class_list":["post-53301","post","type-post","status-publish","format-standard","hentry","category-articles","category-aviation","category-news","tag-apollo-radio"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/pn3uc-dRH","jetpack-related-posts":[{"id":33006,"url":"https:\/\/swling.com\/blog\/2018\/06\/discovering-the-apollo-survival-radio\/","url_meta":{"origin":53301,"position":0},"title":"Discovering the Apollo Survival Radio","author":"Thomas","date":"June 28, 2018","format":false,"excerpt":"In a previous post, I mentioned that I visited the US Space and Rocket Center in Huntsville Alabama last week (a museum I highly recommend to anyone interest in spaceflight). While perusing numerous displays in the\u00a0Saturn V Hall at the Davidson Center for Space Exploration, I noted this little radio\u2026","rel":"","context":"In "News"","block_context":{"text":"News","link":"https:\/\/swling.com\/blog\/category\/news\/"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2018\/06\/Huntsville-Space-and-Rocket-Center.jpg?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2018\/06\/Huntsville-Space-and-Rocket-Center.jpg?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2018\/06\/Huntsville-Space-and-Rocket-Center.jpg?resize=525%2C300&ssl=1 1.5x"},"classes":[]},{"id":48687,"url":"https:\/\/swling.com\/blog\/2021\/04\/a-shortwave-audio-archive-tribute-to-apollo-11-astronaut-michael-collins\/","url_meta":{"origin":53301,"position":1},"title":"A shortwave audio archive tribute to Apollo 11 astronaut Michael Collins","author":"Thomas","date":"April 28, 2021","format":false,"excerpt":"Today we learned that Michael Collins, the American astronaut who flew the Apollo 11 command module Columbia around the moon, has passed away at the age of 90. For those of us who've always looked to the sky and dreamed of exploring our amazing universe, Michael Collins was a hero.\u2026","rel":"","context":"In "News"","block_context":{"text":"News","link":"https:\/\/swling.com\/blog\/category\/news\/"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2021\/04\/E0E7h6bXIAQ-Vas-1.jpg?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2021\/04\/E0E7h6bXIAQ-Vas-1.jpg?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2021\/04\/E0E7h6bXIAQ-Vas-1.jpg?resize=525%2C300&ssl=1 1.5x, https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2021\/04\/E0E7h6bXIAQ-Vas-1.jpg?resize=700%2C400&ssl=1 2x"},"classes":[]},{"id":38581,"url":"https:\/\/swling.com\/blog\/2019\/07\/from-the-shortwave-radio-audio-archive-voa-on-the-10th-anniversary-of-moon-landing\/","url_meta":{"origin":53301,"position":2},"title":"From the Shortwave Radio Audio Archive: VOA and BBC on the anniversary of moon landing","author":"Thomas","date":"July 20, 2019","format":false,"excerpt":"There are a hundreds of fascinating off-air radio recordings in our Shortwave Radio Audio Archive. One of our frequent contributors, Tom Laskowski, has digitally converted numerous magnetic tape recordings from his personal collection to share with the archive. Tom made the following recording of the Voice of America on July\u2026","rel":"","context":"In "News"","block_context":{"text":"News","link":"https:\/\/swling.com\/blog\/category\/news\/"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2019\/07\/800px-Apollo_11_Lunar_Module_Eagle_in_landing_configuration_in_lunar_orbit_from_the_Command_and_Service_Module_Columbia.jpg?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2019\/07\/800px-Apollo_11_Lunar_Module_Eagle_in_landing_configuration_in_lunar_orbit_from_the_Command_and_Service_Module_Columbia.jpg?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2019\/07\/800px-Apollo_11_Lunar_Module_Eagle_in_landing_configuration_in_lunar_orbit_from_the_Command_and_Service_Module_Columbia.jpg?resize=525%2C300&ssl=1 1.5x, https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2019\/07\/800px-Apollo_11_Lunar_Module_Eagle_in_landing_configuration_in_lunar_orbit_from_the_Command_and_Service_Module_Columbia.jpg?resize=700%2C400&ssl=1 2x"},"classes":[]},{"id":38588,"url":"https:\/\/swling.com\/blog\/2019\/07\/apollo-11-ham-radio-special-event-stations\/","url_meta":{"origin":53301,"position":3},"title":"Apollo 11 ham radio special event stations","author":"Thomas","date":"July 21, 2019","format":false,"excerpt":"Many thanks to SWLing Post contributor, Randy (KS4L), who writes: Don't know if you're aware, but there are a number of Special Event Stations on the air this weekend commemorating the 50th anniversary of the Apollo 11 landing on the moon. This includes W4A at the US Space and Rocket\u2026","rel":"","context":"In "Ham Radio"","block_context":{"text":"Ham Radio","link":"https:\/\/swling.com\/blog\/category\/ham-radio\/"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2019\/07\/W4A-QSL-Card-e1563706390102.jpeg?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2019\/07\/W4A-QSL-Card-e1563706390102.jpeg?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2019\/07\/W4A-QSL-Card-e1563706390102.jpeg?resize=525%2C300&ssl=1 1.5x, https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2019\/07\/W4A-QSL-Card-e1563706390102.jpeg?resize=700%2C400&ssl=1 2x"},"classes":[]},{"id":14836,"url":"https:\/\/swling.com\/blog\/2015\/09\/shortwave-radio-recordings-voa-on-the-10th-anniversary-of-apollo-11-moon-landing\/","url_meta":{"origin":53301,"position":4},"title":"Shortwave Radio Recordings: VOA on the 10th anniversary of Apollo 11 moon landing","author":"Thomas","date":"September 15, 2015","format":false,"excerpt":"Many thanks to SWLing Post and SRAA contributor, Tom\u00a0Laskowski,\u00a0who shares this recording of the Voice of America; recorded on July 20, 1979 at 0500 UTC on the 31 meter band. Tom notes: \"The first 4:30 is from a VOA newscast that aired before the main part of the program. The\u2026","rel":"","context":"In "News"","block_context":{"text":"News","link":"https:\/\/swling.com\/blog\/category\/news\/"},"img":{"alt_text":"Apollo_11_lunar_module-001","src":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2015\/09\/Apollo_11_lunar_module-001.jpg?resize=350%2C200","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2015\/09\/Apollo_11_lunar_module-001.jpg?resize=350%2C200 1x, https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2015\/09\/Apollo_11_lunar_module-001.jpg?resize=525%2C300 1.5x"},"classes":[]},{"id":42794,"url":"https:\/\/swling.com\/blog\/2020\/04\/today-on-the-50th-anniversary-of-apollo-13-nasa-streams-real-time-audio\/","url_meta":{"origin":53301,"position":5},"title":"Today: On the 50th Anniversary of Apollo 13, NASA streams real-time audio!","author":"Thomas","date":"April 11, 2020","format":false,"excerpt":"Many thanks to SWLing Post contributor, Wilbur, who shared the following message on Twitter: NASA has posted the Real Time audio of the Apollo 13 Mission on the 50 Anniversary of the launch. Lift off is just after 2:00 PM EST today! (Saturday April 11) https:\/\/apolloinrealtime.org\/13\/ WOW! Thank you so\u2026","rel":"","context":"In "News"","block_context":{"text":"News","link":"https:\/\/swling.com\/blog\/category\/news\/"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2020\/04\/Apollo_13_liftoff-KSC-70PC-160HR-1018x1024.jpg?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2020\/04\/Apollo_13_liftoff-KSC-70PC-160HR-1018x1024.jpg?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/swling.com\/blog\/wp-content\/uploads\/2020\/04\/Apollo_13_liftoff-KSC-70PC-160HR-1018x1024.jpg?resize=525%2C300&ssl=1 1.5x"},"classes":[]}],"jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/swling.com\/blog\/wp-json\/wp\/v2\/posts\/53301","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/swling.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/swling.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/swling.com\/blog\/wp-json\/wp\/v2\/users\/15"}],"replies":[{"embeddable":true,"href":"https:\/\/swling.com\/blog\/wp-json\/wp\/v2\/comments?post=53301"}],"version-history":[{"count":0,"href":"https:\/\/swling.com\/blog\/wp-json\/wp\/v2\/posts\/53301\/revisions"}],"wp:attachment":[{"href":"https:\/\/swling.com\/blog\/wp-json\/wp\/v2\/media?parent=53301"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/swling.com\/blog\/wp-json\/wp\/v2\/categories?post=53301"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/swling.com\/blog\/wp-json\/wp\/v2\/tags?post=53301"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}