Greeting Earthlings.
If you follow the channel, you know that we are hard at work restoring the Apollo communication
hardware.
Over the last year and a half, you might have followed our steady progress.
We achieved bidirectional lock of the microwave carriers way back in part 13.
This is the backbone of the Apollo transmission link, on top of which a complex mix of signals,
including ranging, voice, data and television, is added, using a complex modulation scheme.
We have been busy ever since, getting these various individual channels going.
We transmitted up-data in part 14, got television working in part 21, and central timing in
part 25.
But to have everything working simultaneously, we needed to bring up two key pieces of equipment:
the pre-modulation processor, or PMP, on the spacecraft side, and the interface simulator
on the ground side.
These two very complicated boxes are the linchpin of the modulation system: they are responsible
for managing the many signals and subcarriers for transmission over the main microwave links.
We got the PMP going in part 20, and the interface simulator in part 24.
One more thing stood in our way before we could attempt to assemble the complete system:
we needed a control panel.
So we set out to reproduce a portion of the command module control panel in part 23, so
we could control the complicated communication system just like the astronauts did.
We are now ready to begin assembly of the complete system.
Okay, so we have reconfigured ourselves.
We have put the interface simulator on top of the transmitter.
So, that's our transmit station.
Here, we have the two receivers: the PM and the FM.
For the inputs, we have voice and we have the command data uplink box.
And we have also the ranging.
So we're getting fairly complete here, on the transmit side.
On the receive side, we have now put the transponder in its righteous place, in the transponder
mount.
So we can make space for the control panel, and eventually the PMP.
Several days later...
[Marc] You guys are hooking up?
[Eric] Yeah, we did some tests on the control panel, to make sure it's not doing anything
bad with the voltages.
So far it looks good, so we're going to try it out.
[Mike] Yeah!
[Marc] What would be the first experiment to do?
What should I hook up as analog stuff into it?
Or voice or...
[Mike] Right.
[Marc] Once we...
[Eric] Oh, you're getting ahead of us!
(laughter)
Moments later...
[Marc] So, we're about to flip the switch on, but we have to connect a little bit of
stuff.
It needs a reference, 512 kilohertz, and that will eventually come from the CTE.
And it also has a voice input: it's an A at 440 Hertz.
And I'm monitoring the outputs on PM on the spectrum analyzer.
So, we should be able to see a few modes.
Want to try it?
[Eric] Let's give it a shot!
[Marc] 28 Volts...
[Eric] Okay.
So the PMP is turned off right now.
I have to flip this switch to turn it on.
[Marc] Okay, I see nothing yet, because actually, I should not see anything.
Okay.
Ah!
[Eric] Yes, 18 volts!
[Marc] Yes!
I saw...
I see something, but I think it's fairly low.
[Eric] Voice is off right now.
[Marc] Yes...
Just a quick refresher from the previous episodes.
On the way down, voice is on the green subcarrier at 1.25 MHz and data is on the blue subcarrier
at 1.024 MHz.
So we are going to look for signs of the subcarriers and evidence of modulation on the spectrum
analyzer, as we exercise the various switches on our new control panel.
Okay, so it's just leaking at this point.
And now if you turn voice on...
[Eric] Well, there's something there!
[Marc] Why is it off to the side like this?
Uh-oh.
This is not giong according to plan.
Turning voice on should produce a nice narrow subcarrier peak at 1.25 MHz.
Instead I see a potato shaped signal at around that frequency.
[Marc] I thought we had it clean before...
I am perplexed.
It's vaguely at 1.25, but I am not...
At one point... Wait, wait, wait...
There we go!
[Eric] Bad connection?
[Marc] Yep.
[Eric] Oh, you were right.
Ha!
[Marc] Okay, it's our homemade connector, over here.
All right, okay, so now it's back.
We're back!
We have 1.25, we have voice.
[Eric] Would you like to hook up the sine wave?
[Marc] Yes.
[Eric] Let's get some voice going
[Marc] One volt...
There you go.
All right!
Yes, I see it now.
So this is where the signal is.
So if I do clear-write, there we go, we have modulation.
If I turn the voice off, that's correct.
So key.
If I go start 250 kilohertz, stop 750 kilohertz.
Give me some key.
[Eric] All right, make sure we are in key mode first.
[Marc] Okay.
[Eric] So here's key.
[Marc] And...
Oh! There sure is key!
All right.
You can Morse!
So the morse key mode is no joke.
If the whole complicated modulation system had a failure, you could disable everything
and revert to the most primitive form of radio communication: morse code.
The astronauts’ morse key was simply their push to talk button on their suits cord.
[Marc] It's a complicated animal.
[Eric] Yeah!
[Marc] And then I have my own cheat sheet over here.
So far we have exercised voice, that works.
We have exercised key, that works.
Ranging, I saw the increase in noise, so it probably works.
And we did PCM when we had the reference, so that worked too.
And then we have downvoice backup, we checked that.
All right, next demo is to try to check the upvoice, which we never did.
On the way up, in the other direction, the subcarriers are at completely different and
much lower frequencies.
Up data is on 70 kHz, and up voice is on 30 kHz.
Unless you are on backup mode, and the two are switched.
The PMP is able to demodulate voice all the way to baseband, so if all goes well, we may
hear a tone for the first time.
[Marc] And I just recreated a 30 kilohertz subcarrier, which I'm going to modulate.
And, it's at 30 kilohertz, and I have the modulation section over here.
So I have to FM modulate it.
[440 Hertz tone can be heard]
And it works perfectly!
And, we just checked that the squelch was working.
So, I'm below the squelch.
And if I put more amplitude, it works.
So they used that to turn off the noise.
Okay, we have that.
And then, I can also check the 70 kilohertz, by going to upvoice backup.
So I'm going to switch to the backup mode, which is 70 kilohertz subcarrier.
And then now, voice and data have been switched, which allows me to test data.
So I go to upvoice backup, and there it is!
And on that one, squelch shouldn't work.Yeah, squelch doesn't work.
[Mike] Makes sense.
[Marc] And now if I switch to data, go to 30 kilohertz...
And it's squelched!
Okay, so we have the up path working, we have the down path working.
Do you have SCE to AUX?
[Eric] Yeah, it's right here!
[Marc] SCE to AUX.
Yeah, so in case of emergency...
[Mike] We could put PMP to AUX as well.
[Eric] We could.
[Marc] Oh that's PMP to...?
Yes that should put it to AUX!
[Mike] Yeah, yeah, you can put PMP to AUX.
[Marc] Oh yeah, so you can SCE to NORMAL, OFF, AUX and PMP to NORMAL, OFF or AUX.
[Mike] Yeah.
[Marc] They both have two power supplies.
[Mike] Yeah!
[Marc] Oh, very good!
Excellent.
Now, we need to get it to the transponder, and see if we can get it onto the carriers,
and get voice from the ground, and vice versa.
[Later]
[Marc] All right.
So, Eric and Mike have been hard at getting the transponder hooked up to the PMP.
So now, we're going to try the grand transmission experiment.
Okay, why don't we turn on the spaceship transmitter?
So, make sure sure we have the PM1.
Yeah, got it!
All right, so we haven't broken things.
So, we are transmitting, and I think I'm just going to try to lock it.
This one.
And now we should have some frequency.
We do, 2.1064 GHz.
Oh yeah, so I see I'm receiving it!
So then, I need to lock it with this.
Locked!
And I go to 2.10640625 GHz.
Next step is, I lock myself on the way down.
No?
Okay.
Gain control...
I want to open the loop, maybe?
And be able to tune myself, maybe that's what I need to do.
But I get no signal...
Tada, locked!
All right.
Okay, we're double locked.
That took some effort!
Imagine they had to do that at every pass, right, figuring out what was going wrong.
So, what they did, they practiced on a test signal of a tower.
All right, so the next step, why don't we do TV?
Make sure we still can do what we did before.
So for the TV, I need the FM receiver to be on.
Mike, you need to give me FM...
[Eric] I think we might need another cable.
[Marc] ...right here.
And yeah, I got it!
It's having all kind of issues here...
It's going up, down...
Yes?
No?...
There we go.
Okay, we got we got FM.
We should be able to get some video.
And now, we're going to have the real thing.
We are going to have the TV go through the PMP.
Which we have never tested, by the way.
[Eric] Right.
All right, we're connected back there.
Oh!
[Marc] We are getting video?
[Eric] Yeah, we're getting video!
[Marc] Hey, we have video over here!
I can see Mike.
Hello!
This is the minimum we wanted.
Believe it or not, we are going to schlep that whole equipment to the DesignCon conference.
On Tuesday, in two days!
And we wanted to have at least TV working.
But now, we should be able, I think, to get voice up, sub-modulated. Power...
Well, let's simplify this, let's just do this.
Hello, hello, hello, he-llo?
Do you hear me over there?
[Mike] Yeah.
[Marc] Oh, it works?
[Eric] Yeah!
[Marc] I am transmitting voice?
Apollo 11, this is Houston.
Oh, wow, it works!
[Eric] Yeah, yeah, very clear.
[Marc] Wow, okay, that was easy!
[Eric] I was expecting some switch settings to be wrong!
[Mike] Yeah!
[Marc] Apollo 11, this is Houston.
[Mike] It works!
[Marc] So I can add the data sideband.
Data.
Okay, this is voice and data.
We don't have the data demodulation over here, we are missing the UDL box.
Well, we have it, but it's not hooked up.
Which will probably be our next thing to do.
So we're getting into bonus territory here.
I'm trying to get the CTE.
Yeah, it's counting!
So, we have the mission time over there.
Well, we will be able to get rid of all that HP, the 512 kHz source, and all the nannies.
Okay, so this is number two of the extras we wanted to do.
And number three, I'm working on it: I'm getting the Quindar tones working, I'm almost there.
Well, here, while Mike and Eric were wiring up the PMP to the control panel and the Transponder
to the control panel, I was hard artwork to shrinkify this.
This is my yet to be tested Quindar tone generator.
And the idea is to stuff it in this box.
But, let's first see if this works.
[Quindar intro beep] Hello, hello [Quindar outro beep]
[Quindar intro beep] Apollo, this is Houston [Quindar outro beep]
Okay, so that works, and that should fit in there.
And then we can try it on the big setup.
Okay, it sorta kinda works.
[Quindar intro beep] Apollo, this is Houston [Quindar outro beep]
Alright, with nary a minute to spare, we have a setup ready for demo at DesignCon.
DesignCon is a large Silicon Valley electronics conference, with a focus on high speed communications
and signal integrity.
Samtec, the company I work for, happens to sponsor the conference welcome reception,
and asked us if we’d be willing to exhibit our Apollo communications system during the
evening of the reception.
Oh, my, count us in!
So we took it all apart, 650 lbs of it, stuffed it in two vans, and set it all back up in
a hallway leading to the reception hall.
Here is a time lapse of the installation.
[Marc] We're going to power up the beast again, which is a whole adventure.
And I mess it up every time, so here we go.
It's complicated.
Yes, I have a lot more signal here.
Okay, so give me PMP.
I see it.
This one did not turn on reliably. It did turn on! 2.1064025 GHz or thereabouts.
Okay.
"Apollo, this is Houston, over".
Give me FM.
Much better!
That was it.
We received voice, we have a little glitchy video, we can't lock receive for some reason.
I had the same problem before.
Oh, we need mission time!
[Mike] Oh, yeah.
[Marc] See if we lifted it off.
We did!
Eight minutes ago.
Yep!
[Mike] Oh!
[Marc] Oh, so when you...
So, the same thing happened to me.
You barely touched the switch, and it locked.
[Mike] That's weird.
[Marc] Okay, so we have everything working at this very point.
The voice - send me some voice.
You can do the Quindar tones if you want to.
[Mike] I see.
[Quindar intro tone] [Quindar outro tone]
So the voice works.
I can hear data.
We have television.
And we have locked PM on the other side.
So everything is working!
[Janine] Yeah!
[Mores key tones]
[Quindar intro tone] Apollo 11 this is used and over [Quindar outro tone]
[Paper tape reader clicking]
Mike even brought his newly acquired CDU for everyone to admire.
It all worked great for the joy of the attending engineers.
It also became plenty obvious how difficult this system is to exhibit as a working setup.
For a permanent museum display, we’d have to simplify this by a factor of a 10.
But as long as we are around, and have enough energy, we proved to ourselves that we can
demo it as a live setup.
See you in the next episode, and maybe, at the next exhibit!