Greeting earthlings. If you follow the channel, you know that we love all things Apollo,
and that during our last visit to Steve Jurvetson’s amazing space collection,
we were given the opportunity to take two holy boxes of Apollo electronics to our lab.
These are the boxes that brought you voice, data and live TV from the moon, and should
be early masterpieces of microwave electronics, the blackest of black arts in analog electronics.
Over the many previous episodes, we explained the basics of the Unified S-Band communication
system. We opened up the amplifier and showed how it worked - but we stopped short of turning it on,
as we did not have the proper high power load and directional couplers. However, newsflash:
we do have them now, thanks to a donation from the company R&D Microwaves in New Jersey.
So thanks so much R&D Microwaves, link below, and stay peeled for more on the amplifier.
We then got the transponder fully up and running.
After turning our attention to the ground side of the link, we were able to establish
the bidirectional microwave link between the Earth and the Moon side of things. Phew,
that was a boatload of work on a very complicated system, and took most of the 15 previous episodes.
But on the grand scheme of things, we have just scratched the surface. What we have
worked on so far are the two boxes in yellow, which is the microwave transmission front end.
The complete communication system is much, much more complicated.
See here, our two boxes are just an itsy bitsy part of the system,
which includes a whole bunch of other boxes.
The other boxes’ job is to transfer the actual communication information
in and out of the Earth to Moon microwave link we have just established. We previously showed how
data and voice were modulated on the earth side, for the uplink. It was mighty complicated, and we
reproduced it thanks to modern Keysight equipment, plus our genuine NASA updata link test box.
Crew alert! Abort, abort, abort!
[Capcom] Apollo 12 Houson, try SCE to Auxillary, over.
So the uplink was already complicated enough.
But brace yourself, because that’s nothing compared to the reverse direction, the downlink,
which has many more modes and input sources. That’s why it takes so many boxes.
But guess what: Marcel, our other intrepid collector and team member, loaned us most
of them for restoration. Marcel has given us the Premodulation Processor, the Audio Center,
the Uplink Data, and the Telemetry boxes. I have since acquired the Central Timing Equipment.
So we have practically everything, save for the data recorder
and the SCE - the famous thing that Apollo 12 had to switch to AUX after they got hit by lightning.
All this to say that in this episode, we are going to try to bring up the next box,
the Premodulation Processor. The Premodulation Processor, or PMP,
is at the center of both of the audio and data system. And you guessed it,
it’s complicated. We’d be lucky if we could get just the basics going in one episode.
[Marc] So we have Eric and Mike,
and Eric is holding the box we're going to try to open today, which is the...
[Eric] Pre-modulation processor.
[Marc] Pre-modulation processor. Mike, you have the amplifier, because we found there was a nipple
on it. This is the only nipple we can show on YouTube, as Eric says [laughter]. See if see we
can... Ah, it won't focus, hold it! There you go, I have it. And Eric, your box has a nipple too,
which seems to be the same. And we're wondering how we unpressurize the thing. So we're going
to have a look at what that nipple is. Because it it looked like it was blind: there's a hole,
but it goes blind. And we can't remember how we depressurized that one, because Ken did it.
[Mike] I think that Ken did it by just loosening all the screws on the lid.
[Marc] It seems that this is what happened.
Poink! There we go, it's out.
There is a little thread in there. And that's of course the amplifier that we did in episode 1.
[Eric] With the custom lid.
[Marc] Ah, it's a plug! So this is just a plug, with a ring, and it's blind. Which means,
if the other one is still pressurized, and I'm taking the ring out, it's going to fly in my face.
Which means that Ken just probably did exactly what you said: he just loosened the bolts and let
it depressurize. Which brings another question: how are we going to repressurize this thing? How
did they pressurize it in the first place? I would think a pressure chamber. So they wouldn't have
a fragile valve mechanism in flight, right? Mike, you said the transponder had a valve?
[Mike] Transponder has a valve, DSKY has a valve.
[Marc] And the Uplink box has a pinch tube.
[Mike] Yes, the box has a pinch tube.
[Marc] So every uses a different way.
[Eric] It's totally non-standard.
[Marc] Everyone makes a different thing.
Would be also interesting to look, serial number 16. So 16 is a pretty early
unit. Yeah, so, 1966. All right.
[Eric] But that's the contract date, because here there are inspection stamps with a 1967 on it.
[Mike] It's gonna be the... This is the original date of manufacture, and then they've
changed the dash number. So it's been upgraded to a later revision.
[Eric] And then somehow repressurized.
[Mike] Yeah.
[Marc] Because you see it over printed on it?
[Mike] The 006 here is very clearly different from the ME 478-0068 that is the base part number.
[Marc] Oh, yeah.
[Mike] That's where that handle would help though.
[Marc] You have to take it from the... Oh it doesn't go in.
[Eric] Yeah because the paint is quite thick.
[Marc] Yeah, there we go, you got it.
[Mike] All right we're gonna alternate between...
[Eric] I don't know what they painted it with, but it's awfully thick.
[Marc] So it's all loosey-goosey, but hasn't popped up.
[Mike] Yeah we've got all the screws loosened, but it hasn't so separated yet.
[Marc] So, time for some coercion.
Tap, tap, tap. No. I think I'll use - as last time.
[Hiss of gas escaping]
[Mike] Ah!
[Marc] OK,
you're good to go.
[Mike] All right!
[Eric] You know, we can certainly try to get a whiff of the inside once we lift the lid on that.
[Marc] Yeah. They smelled nothing. None of the stuff smelled anything. The AGC was odorless,
the transponder was odorless. I would think they test for outgassing. Because
we have to do that for military parts. So I think it's by design, not a happy accident.
Grand opening?
[Eric]
Is there some wiring that it's hanging up on?
[Mike] I think there might be.
[Marc] Yeah, we might have to take the connectors out.
[Eric] I see modules.
[Mike] Yeah, well, the circuitry is all exposed,
it's not completely potted. So that's very good for us.
[Marc] Connector removal?
[Mike] Yeah, I think so.
[Marc] We tried with an adjustable wrench first, but it was of course
spaceflight tight and it became obvious that we would risk damaging the box.
So instead I machined a custom tool that would be much safer.
So I
machined ourselves a little tool.
And... Somebody holds the box, somebody holds the connector.
Yeah, a piece of cake! Okay, one connector done with no damage.
[Eric] One out of four!
[Marc] What? Oh yes, there is some stuff in it! This is glued down.
[Eric] Yeah that's what's causing all the problems.
[Marc] Yeah, all right.
[Eric] On to the next one!
[Marc] Last one before we can finally see what's inside. OK, you have it Mike?
Yay. Oh-oh!
Okay, go for opening.
[Mike] All right, here we go!
[Eric] Oh!
[Marc] Wow! That is serious looking hardware once again!
[Mike] Pull the gasket off.
[Eric] Oh did it grab back on?
[Mike] I think so. Here it comes!
[Eric] I've got a couple more coming your way. These little clips.
[Mike] Yeah. It's like trapezoidal washers.
[Marc] Half moon washers.
[Mike] Yeah.
[Eric] So it just fits in like that.
[Mike] So the chassis here has studs, threaded studs sticking up,
and then these little caps screw down onto them to hold the thing in place.
[Marc] Wow, and there's springs at the bottom.
[Mike] Yeah they are leaf springs.
[Marc] It's welded. This is a weld, it's not soldered.
Actually it's a combo: some are soldered, some are welded.
[Eric] Yeah, the wires up here and these are all soldered in place.
[Marc] These are welded.
[Eric] And the components are welded on.
[Marc] So: Receive, Data and Voice.
Voice Relay - that's to switch from CSM voice to relayed LM voice via the CSM. That is send.
Limiter, FM mixer: that's FM modulation obviously. Bi-phase modulation: this is BPSK,
this is data modulation. Principal data modulation, alternate. SCO,
I'm not sure what that is that is. This is the actually the scientific data modulation section.
Anything on the other side?
[Mike] Yes, the recessed modules are named on that side.
[Marc] Okay. TV, Key. So that's the morse [code], right.
[Mike] If we pull all the modules, then we can...
[Marc] Oh, so the wiring might stay intact. Oh, we might have lucked out!
All right!
[Mike] We're going to need a bigger jar!
[Marc] The longest bolt in history [of space flight].
[Mike] Here we go!
[Marc] Wow, piece of cake!
[Mike] Our power supply module.
[Marc] Beautiful!
This is probably the most beautiful construction we have seen. It's really pretty!
It is definitely the best mechanical construction of them all. Gee!
Ready for the reverse engineering?
[Ken] I need my lab coat!
[laughter]
[Marc] PCBs are widely overrated, you don't need any to fly to the Moon!
Alright, we didn’t even get to powering up anything yet. Given the complexity of the thing,
we divvied up the next tasks. Ken did his reverse engineering, and has posted a superb article on
his blog which I will link in the doodely doo. Head over there if you want to know what every
single module does. I will also try my best at an overview sweetened by elevator music in the
next episode. Mike spent two weeks beeping every single connector wire, making sure our schematics
actually matched the real box, something we had found lacking with our transponder.
I got to figure out how to hook it up and test it,
aided by my incredible collection of colored markers.
And Eric is making a reproduction of the section of control panel switches
that we need control this very complicated animal.
This should keep us busy for a while, and we’ll see you in the next episode.