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.
Over the previous episodes, we got them running and we now have a solid Apollo microwave link
running between the transponder and the original NASA ground test equipment.
Then we got more help from another collector, our friend Marcel, who gave us the many other
boxes that complete this complicated system.
We are now focusing our attention on bringing them up, and first in line is the Pre-modulation
Processor, or PMP.
It is the central node in the system and every signal gets connected through it: voice up,
voice down, command up, telemetry, the flight recorder, TV, LM relay and more.
In fact, it is so complicated that it took us the entire previous episode to go over
its functionality and identify all the connections.
We are now at a point where we can attempt to power it up.
The most challenging aspect is the very high number of control lines that have to be set
up to make it work.
No wonder, as it took a whole panel section of switches to interact with it.
So for this initial power up, we are going to first go for a minimum setup, to do the
main checks.
Mike which one is that?
[Mike] This is the power supply module for the PMP.
Takes in 28, puts out 18 volts for the rest of the modules, and for external switches
to control.
[Marc] So that's a switcher, you tell me.
[Mike] Yep.
[Marc] So we just go, right?
We put a load on it.
We go?
[Mike] Yeah.
Nothing.
Hmm...
[Marc] Okay, try again.
[Mike] Okay, trying again.
There we go!
[Marc] Okay, so our scope probe was not put all the way in.
18 volts point 0!
All right.
So nothing blew, except our ego when we didn't get it right the first time.
Okay, so first step, as usual it's good, the power supplies are just right where they should
be.
And we look at the AC and it's a very very quiet supply, we're at five millivolts per
division.
And I don't believe the low frequency stuff is from the supply, I think it's from the
lab.
[Mike] Yeah.
[Marc] I think it's the WiFi.
It's random.
[Mike] Do you want to try the auxiliary power supply?
[Marc] Uh, of course, of course!
That's true, there's two power supplies, right?
Is that why there are two transistors?
[Mike] Yeah.
It's duplicated across halves of the module here.
[Marc] So two power transistors, a bunch of stuff.
Can you flip it around again so we can see the [other side].
So at the back, at the very back, I suppose that's the relay that that chooses one or
the other power supply?
[Mike] Yeah.
[Marc] We just counted the transistors: there's three here, three here, one there, so it's
seven per power supply.
With two of them.
That's it?
[Mike] Yeah!
[Marc] Just change the pin?
[Mike] Just change the pin!
[Marc] And it comes through the same wire because the relay will switch it?
[Mike] Yes.
[Marc] 18.02, even better!
Okay, all right.
So both primary and auxiliary power supplies work.
[Mike] Nice!
[Marc] Very good!
So Mike has put back the PMP together, and we are doing some wiring to it.
What we're trying to do is - so it's a complicated animal.
It connects to just about everything.
So, I am trying to see if we could get some of the subcarriers.
There is one for voice, there is one for data on the PM, there is one for data on FM, and
there's a few for analog scientific data.
And to turn them on, we have to turn [on] all those wires.
So right now I think I have voice in - actually I don't have voice in, I just have the switch
to voice.
And then I hope to see the subcarrier at 1.25 MHz.
And for that I should only need - where is it?
- 512 kilohertz.
And, not this one, because that one is for data.
It's buried in there.
There it is, the 512 kilohertz for voice.
Over here - sorry Mike - I have: frequency, 512 kilohertz.
Actually I have it already wired up to the two inputs.
And then I am looking at the output, that's my little yellow wire to the oscilloscope.
It's one to two megahertz, it's fairly low frequency.
And that should give me a subcarrier.
And Mike, you wired it?
So you have power, and the green wire is the voice wire, the voice switch?
[Mike] Yeah.
So one side of the green wire goes to the 18 volt output from the PMP, and then we're
looping it back around into the switch input.
[Marc] Yeah, and that's how it's supposed to work.
Actually the PMP gives its own reference signals.
If you survived the last episode, we are looking at the PM downlink output, and if everything
works according to plan, we should see two subcarriers.
I’m trying to first turn on the green one for voice at 1.25 MHz, and in a second step
the blue one for data at 1.024 MHz.
And the hope is that we have gotten our wires correctly.
And so we turn it on, and see if 1.25 megahertz appears?
Mike?
Want to try it?
[Mike] Oh boy!
[Marc] Yeah, that's the simplest test we could imagine.
It's quite complicated.
So, well, give it give it a quick on, and just watch the current, that it doesn't go
into current limit.
OK.
190 mA.
No output.
What did I do wrong?
Oh, I know why!
I don't have the...
Do it again, I didn't have the output yet.
And of course, I forgot to turn on the 512kHz reference input, which I dutifully pointed
out in the last episode.
It’s easier to see here, the red 512 kHz wire from the CTE.
Nothing works if there is no reference signal.
[Mike] Okay, on!
[Mike] All right, so we see - oh I have the two carriers!
So I have the 1.25 [MHz].
I'm right on it.
So we have one subcarrier, but it looks like I have the second one, I have the data one
too.
And I thought we did not turn that one on yet.
But I think we did.
So that's 1.25, and I bet you the other one is 1.024.
Yeah, 1.022 MHz.
Huh, okay.
So we have voice and data subcarriers.
Okay, we think there's another quick experiment we can do, check FM.
Once again, a traumatic flashback from the previous killer episode, we are now looking
at the FM downlink output, and there it’s more complicated, I should see a the blue
1.024 MHz carrier for the data playback from tape, there should be nothing yet in the middle
for the voice playback, but we should get the 3 green scientific channels.
Maybe, perhaps, we hope.
It's a fairly toothy connector.
[Mike] R, S, T, U, V...
W, X, Y, Z...
[Marc] So, Mike thinks he has found the pin that turns off the FM channel.
So, on the FM channel, they sent the recorded data and also the scientific data.
So we should have a whole bunch of subcarriers for the scientific analog signals.
And I have to switch myself from PM to FM.
Yeah, I have signal in, so I should be good to go.
All right, so I should get 1.024 MHz and then llittle subcarriers that are the analog channels,
scientific channels.
Want to go for it?
[Mike] Allright, here we go!
[Both] Woah!
[Mike] That's a signal!
[Marc] These are my analog carriers, my three analog carriers.
So what I have here, I'm not sure.
So we have 1.024, that's correct.
We should have my 100 kilohertz-ish, yeah, that's it.
It's 150 100.
Ss that intermodulating somehow?
200 kHz.
95 kilohertz, 125 kilohertz, and 165 kilohertz.
I think those are the three subcarriers, but they are very ringy.
Yes, yes, 95, 125, and 165 kHz, that’s what it says!
So we see our SCI Data subcarriers.
I also have the 1.024 MHz data subcarrier.
However I see a lot of extraneous peaks, so the jury is still out on this one.
Are they supposed to be there?
Did we not turn the controls properly?
But I have a lot of garbage in baseband, and I have a lot of stuff in the upper band too.
So I see them here, but I see them mirrored over here, which I don't quite understand.
Pull your wire out, does it disappear?
[Mike] All right, I'm gonna take off the 18 volts.
[Marc] Yep!
So we were tickling the right pins and doing the right thing.
But these modes are complicated, so until we redo the whole control panel - because
there are several things you are supposed to toggle at the same time - we peobably won't
know.
Okay, so far so good, we have FM, we have PM.
We were just looking at the schematics, because I don't think we turned on the PM correctly.
We saw the two signals, but looking at the footage, it was -40 or -50 dBm, right.
[Mike] Right.
[Marc] And I think they were gated behind amplifiers, and we confirmed that.
So it turns out you have to enable a pair of the purple, or one pink, or one peach - we
have all the colors.
Okay, so let's try to add one more of those lines and see if we can get it ungated, and
get our signal.
[Mike] All right!
[Marc] Mike, you have put the additional wires?
[Mike] Yes, just one additional wire for now.
I wired this one into PMP off.
[Marc] PMP off, so we should have voice only.
We should have 1.025 [MHz].
Well, we just turn it on I guess, right?
[Mike] Yeah.
[Marc] You want to press the button?
[Mike] All right, here we go!
[Marc] And...
[Mike] Oh, I didn't plug it in.
[Marc] Okay it's not me, last time I forgot to get the signal out.
[Mike] All right, try again.
[Marc] Oh yeah, there we go!
Zero dBm, poof, right there!
Okay, so that's what was wrong.
And I bet you if you pull that wire it's, going to go away.
Uh, hold on don't pull it down yet, I'm going to figure out if it's the right signal.
Yeah, we have -1.8 dBm at 1.248 Megahertz, that's correct!
So we did it right!
You want to change your pin to do PCM plus voice?
[Mike] So instead of pp, I need little r, which is going to be...
Uh, little r, where are you?
I think I got it.
The letters printed on the connector are very tiny.
I think that should do it.
[Marc] Okay, so I'm still on.
512 kilohertz, three volts.
Yeah, there it is!
We see the same thing as we have on the other one.
There's a lot of cross modulation.
[Mike] Interesting
[Marc] They pushed the voice up to 1.3 dBm.
And here is data, 1.020.
So that's correct.
So that's very similar to the FM channel, where we saw a lot of interaction and cross
products between all the frequencies.
It has so many inputs, so many outputs, so many switching...
[Mike] It's all interconnected and entangled!
[Marc] Right, so we figured out that, okay, now we have to redo a few rows of switches.
They are all at the bottom right of the control panel.
And so we went to find out, what switches did they use?
Because they are very annoying: they are three position multiple switches, which is not easy
to find.
[Eric] Three pole, three throw.
[Marc] And Mike, of course, was able to get us a drawing - and is furiously looking for
it.
And Eric, you said: "oh I have some in my collection!".
[Eric] Right, the switch in the drawing looked really familiar.
And so I went back home and I dug around in my one of my many boxes of switches...
[Marc] And so you brought your collection of switches.
[Eric] And they are basically identical to each other with the difference of the actuator.
[arc] Yeah, very similar.
And if you turn it this way, you can see how it matches.
So it's made with a collection of hermetic switches, the same that we found on on the
ground switches, like on some of the ground switches.
And you can stack them however way you want.
They're delicious to operate, can you operate one?
[Eric] Oh yeah.
[Marc] Click, click.
Keep doing it because I didn't focus right.
Most of these are three positions, three throws.
And in order to do that, there is no such thing as a 3 positions 3 throw switch.
You use dual position, dual throw with on-on-on lever.
And so with two dual throws you make one triple throw, that's basically what happens.
And this is still how it's made today.
You can find those switches.
It's still made by Honeywell, right?
[Mike] Right!
[Eric] Yeah, you can buy them brand new.
[Marc] Yes, and it was a mere five hundred dollars a piece, or something like that.
[Eric] Something like that.
[Mike] Yeah, there's so here's the two-pole version, I think.
[Marc] Yeah, that's a cheapo, it's like $300 and something.
Oh, $292.
Hey, affordable!
I guess they're still used for avionics or something like that.
[Mike] Yeah.
[Marc] And so we decided, unfortunately, we're not going to reuse these to make our rows
of switches.
But I found some more reasonably priced ones - they were still expensive - on eBay, that
we are going to be able to make our panel with.
And after we've done that, then we can test the PMP.
Eric here has gotten the short straw.
[Eric] But just this little section down here, all those switches.
[Marc] Yeah, you're reproducing the schematics that was behind the things?
[Eric] Yep, so here we are: lots of wires, lots of switches.
[Marc] Since then Eric has been hard at work and has almost finished the control panel
we need to properly hook up the PMP.
We'll then try to make them in the new gray color that our PCB sponsor PCBWay has just
introduced.
So stay tuned for the next episode!