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 half, you might have followed our steady progress.
In the last episode, we showed how we finally reached the point
where we could exhibit a working setup at DesignCon. We had television, voice up,
and part of the data transmission working. You might recall that at the last minute,
I even managed to add the famous Apollo beeps, known as Quindar tones.
The real ones sounds like this: Tranquility base here. The
Eagle has landed. [beep] Roger Twank - Tranquility, we copy you on the ground,
you got a bunch of guys about to turn blue, we are breathing again. Thanks a lot [lower beep].
And my version is like this. [beep] 13 at your convenience
give a stir to your oxygen tanks [lower beep]
In this episode, I’ll explain briefly what Quindar tones are . I’ll also give some
details on how hacked a cheap commercial microphone setup to add Quindar tones.
Quindar tones were added to transmissions in the Earth to Spacecraft direction only. They were not
present in the other direction. They consisted of an intro tone, a 250 ms burst at 2,525 Hz [beep]
at the beginning of the upvoice transmission.
It was automatically triggered when the Houston CAPCOM pushed his pushed-to-talk button.
Then at the end of the transmission, as the CAPCOM released the button,
an outro tone was emitted, at a slightly lower frequency of 2,475 Hz. [lower beep]
These tones then travelled via telephone lines or other dedicated means to the actual
transmission stations, which would generally be very far from Houston.
Of the 3 major transmission deep space stations, one was at Goldstone, in California, another one
in Madrid, Spain, and a third one in Honeysuckle, Australia. They were widely and equally separated
over the globe, so that one was always in view of the spacecraft as the earth was rotating.
Once received at the ground transmit station, the Quindar tones were used to trigger the equipment.
When the intro Quindar tone was detected, it turned on part of the voice transmission chain.
The equipment was turned off after receiving the outro tone.
There was no need for that on the spaceship side,
since the transmission equipment was directly connected to the audio source.
The upshot, is that Quindar tones were originally meant to be used by machines only. However,
in practice, they proved useful to the astronauts too. The tones cued them on the beginning and the
end of the transmissions, and when it was their turn to speak. This was particularly
helpful when there was over a second delay in the transmission of voice from the earth to the moon.
The astronauts responded right away after hearing the outro beep, without waiting for the normal
blank in the conversation. It made the delay much less of a hindrance. Tones were so useful, that
they were reinstated on the Shuttle missions, even though the equipment did not need them anymore.
So, guys, this is something I wanted to do for a long time,
is the Apollo Quindar tones. And the two tones you hear, the intro [beep]
and the outro [lower beep], they were automatically generated.
So, interestingly, they are only done on the ground. These are transmission
controls. And they became so emblematic that they are just associated with space flight,
and particularly particularly the Apollo flight.
It's a convenient way to know when the senders are finished talking. [beep] Apollo 11 this
is Houston over [lower beep]. And you know it's over, it's time to respond.
So the astronauts used to key on that. They did not generate any of these tones, this is only for
Earth transmission. And I did it with a little bit of old-fashioned electronics, I'll show you how.
So my Quindar tone generator is definitely old school. You would be tempted to use only
digital electronics for it, but there is a catch:
the tones are pure sinusoids, which are not so simple to produce using digital electronics.
So, it turns out, Quindar tones are the simplest form of what's called FSK, Frequency Shift Keying,
where you use two different tones to transmit information. That's one of the
first way of encoding digital information on an analog media, as such as a modem or
a radio. And if I turn it on... And you have two tones [alternating high and low tones].
And, the reason I had one wired up, is because this is used for radio Teletype.
And I was just doing a radio Teletype transmitter. The decoder, we don't use
in this one. I'm just using this circuit and that circuit, and I'll show you what that is.
So, the bottom one is straight from the application sheet of the XR2206, which is
an FSK generator. And it's basically the HP 3300 in an IC. It uses the exact same principle. It's
a generator that you can use to do very good sine, square wave or triangles. But on top of that, they
added the possibility to choose from two different current sources. So you can switch between
two frequencies really quick, and in a phase continuous manner, which is important for FSK.
And depending on the value of the logical input you have on on this pin over here,
you get either a low tone or high tone, and it gets out. I use an oldie but goodie,
the 74123, which is a dual mono stable multivibrator.
And you can trigger them, either going down, or going up. And I have one that's
wired for going down, and one that's where for going up. And I tune them to
give me both a 250 millisecond pulse. And that's the circuit right there.
I have my little button [high beep, low beep]. You can tell, the two sides have their timing
resistor, timing capacitor, and adjusting resistor. And the two outputs come here.
And then they go into those diodes. So, you could use an OR gate,
but since I had only to use one gate, that would be wasteful.
If either of the outputs is low, it will put the output low. If they are both high,
the diodes are not conducting and the resistor will put this level high. And there's a little
capacitor and resistor to smooth the transition, so I don't get a pop. So,
the frequency comes out over here. And here, I have a little MOSFET:
on, to suppress the signal entering, off to make it go through. Circuit over there,
and that's my little gate. So if I go to the continuous signal, warning it's loud!
[loud continuous tones]
And if I get it after the gate
[individual beeps]
I then hacked a cheap intercom system from Retekess. It had a nice weighted base with a
gooseneck microphone, and a mute button that was begging to be re-used as a push-to-talk
button for Quindar tones. After a bit of reverse engineering, I was able to access a few points on
the panel daughter board, enough to steal the 12V power supply, connect the button contacts,
and find a spot to inject my tones. I’ll put a link to my lab book notes with all the gory
details, should you want to try to do the same. Now came the time to try this ungainly prototype.
[beep] Apollo 11, this is Houston, over [low beep].
OK, this seems to work convincingly. Now I just needed to shrinkify this. Note that
for the final board, I substituted a CMOS CB4096 in place of the TTL 74123 circuit,
so I could power everything from the 12V supply in the microphone base.
I did not have the time to make a nice schematic or PCB, so I just wired
everything up on a perma-proto board from Adafruit, and in the Retekess box it went.
So, okay, it doesn't quite perfectly close, but for a demo that's going to be good enough.
[beep] 13 at your convenience give a stir to your oxygen tanks [low beep].
Okay, it sorta kinda works.
[beep] Apollo this is Houston [low beep]. But this one is
such a better microphone, you can even hear it
[beep] Apollo this is Houston. It's so much gear on the better microphone [low beep]
[beep] This is the cheap microphone [low beep].
So you can hear the difference, even through the Apollo transmission system. Get good mikes!
And voila, an Apollo themed microphone you can use on any occasion, if you ever
wanted to go on the air with a flair, or find yourself having to call someone on the Moon.
See you in the next episode!