Apollo Comms Part 3: Inside the S-Band Transponder – GSM FRP

We take a closer look at the S-Band transponder from the Apollo command module, and marvel at the 5 transmitters and receivers it contains. The transponder was manufactured by Motorola, and is entirely solid-state.

0:00 Recap of previous episodes
1:56 Overall block diagram
5:49 Looking inside
11:18 Detailed explanation (with elevator music!)
16:28 Every wire of the transponder explained (in technicolor!)

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Music credits: Crinoline dreams by Kevin Macleod

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33 thoughts on “Apollo Comms Part 3: Inside the S-Band Transponder – GSM FRP”

  1. Interesting, I was a SDDS ( Signal Data Demodulator system ) technician at the time at a tracking station during Apollo. The equipment you are showing was unknown to me as I was downstream from the USB antenna system, about a half mile away, at the the actual tracking station where all the data was sent, decoded, and recorded and equipment called a PCM decoded all the down linked digital data. These signals had sub carriers PM and FM which contained voice and video which also had to to be decoded further by the SDDS for the digital and video data to be recorded and sent to Houston. It has been a long time, but I still remember some of the equipment and procedures. You might not be aware of it but all the timing for these systems used a Cesium beam time standard calibrated to the NBS time standard at Ft. Collins Colorado, because the spacecraft tracking with the USB required very precise timing.

  2. I don't have a clue what the hell Marc just said but I absolutely love it. I hope he keeps doing more of these style videos. I love getting into the fundamentals of how things work. Fascinating.

  3. The wiring doesn't look as bad as the time I hooked up a 5.1 surround sound system…with two phonos, a dual tape deck, CD changer, 4K TV, LaserDisc player, Blu-Ray, reel-to-reel/8-track, ChromeCast, external antenna, XBox 360, and DCC player. It all makes sense to me. 😀

  4. Wow, thanks for producing and sharing this kind of content. I bet this was black magic tech back when it was designed, built and used – and shrinking this RF tech down from size of a table full of equipment into these shoeboxes was even moar black magic at these days…

  5. Marc; i'm an avionics tech in Australia, no idea how I stumbled on these, I'm not normally a YouTube watcher, but I have been binge watching everything over the last month and am compleaty hooked. Fascinating stuff, I'm entertained and learning something! An uncommon achievement 😝 keep up the good work.

  6. As with every Video of you and your team, I am highly astonished on the technical details you come up with. Needles to say, that you presentation and all of your "old school" engineering skills are an inspiration !

  7. I have an Electronics Degree and an Amateur Radio licence and to be honest I have to concentrate on following some of these videos. Ironically you don't need to be an expert or even knowlegable to enjoy them which I what I love about Marc's channel.

  8. Designed by guys in white shirts and tie, a cig hanging from left lip and a slide rule in their hands . A brilliant designed piece of equipment for its time.. and to the people who questioned why we spent the money if they just could realize all the spin off's that came off of things like this we enjoy today.

  9. Holy crap! What an incredible job, both on your part, and of course the MANY engineers who built this thing! Amazing that so much of that can be done in a chip or two today

  10. It is nice to have a little rest after watching this video. Only fifty years before this Apollo radio was made, wireless communications used CW Morse code.

  11. Goodness me ! when you think of it in 1968/9 being able to replace a glass valve in a radio was a big thing to most people. Transistors were still a new thing.

  12. thank you marc for sharing all of your fantastic discovers and you curious mind.
    you have a talent for speaking into videos. a calm voice and the right rythm of speaking…
    i'm not an english-speaking (french)person but with help of the subtitles i could learn and understand many technical words

    You and your team are awesome. thank you
    thanks and hope you make another good things.

    and like said the pro-fet : Ic=B.Ib


  13. Wow! The ABSOLUTE GENIUS it took to design and build this system in the 1960s — hell, it'd still be difficult to do TODAY! I can't imagine what it took to get it done in the '60s. Seriously, SERIOUSLY impressive stuff here!!

    The more I learn, the more I realize how much I don't know. Absolutely LOVE these videos! Keep 'em coming!!

  14. I've got to admit – I'd love to see inside those modules! I'm fascinated to see how they managed to create this masterpiece with the components they had available back then. The compact size for such a complex device makes this a masterpiece IMO.

  15. I read microwave Comms at university. I still have the text books above my desk to remind me of how little I understand of how the damned things work.
    My lecturer did pay me the highest complement I had at uni though: "You have one of the finest research minds of an undergraduate I have met in many years." I just wish my mental health had been in a place where I could have made a run at an EngD. Oh well. The paths left un-trodden.

  16. ive been playing with SDR for a few years now… thought i knew a fair bit about modulation… first time ive heard of Phase Modulation with this vid!.. i know about phase but didnt realise you could modulate it to send data on..Apollo still teaching us 50 years later! 😛

  17. i wish we had a change to see it working 😛 may be trying to stream a youtube video using it 😛 and whats the limits ie distance and bitrate limits 😛
    but probably that's not possible because of used out of allowed power and frequency limits 😛

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