Author Topic: Digitizing my Apollo audio tapes.  (Read 1973 times)

Offline apollo16uvc

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Digitizing my Apollo audio tapes.
« on: September 17, 2017, 02:12:58 PM »
Digitization of 1/4 inch tape on 7 and 10 inch audio reel. From my personal collection, source of audio on reel unknown. I do not know what they were used for.




Original uploaded file extension: WAV

More uploads to Apollo 17 are to come, I have several tapes.

Apollo 17: https://archive.org/details/AS17R51S1V1
Apollo 11: https://archive.org/details/AS11R01S1V1

Apollo 11 has a really weird sound on the left channel, with some kind of beep every second. Right channel is voice.
If anyone could shed light on the sound on the left channel, that would be great.



Right now I am digitizing AS17-R01
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Offline ka9q

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Re: Digitizing my Apollo audio tapes.
« Reply #1 on: September 18, 2017, 05:46:22 PM »
My first thought is that the weird left-channel sound is probably a time code, probably one of the IRIG codes.

But what's really interesting is that it changes as soon as the crew turns on the TV and the ground confirms a picture.

Where did you get this??

I'm pulling down the FLAC images and will take a closer look. If it's one of the IRIG time codes I should be able to tell which one.



Offline ka9q

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Re: Digitizing my Apollo audio tapes.
« Reply #2 on: September 18, 2017, 06:06:57 PM »
The more I listen to this, the more I'm inclined to think that this is NOT a time code but rather some form of low bandwidth telemetry. Time codes are digital but this appears to be multiplexed analog frequency modulating an audio subcarrier.

The PLSSes transmitted multiplexed analog telemetry on several subcarriers above the voice. I believe medical telemetry was in there as well, probably on a separate subcarrier.

If this is what it is, this may be a find of some importance. Time to hit the references...

The FLAC files are digitized at 22050 Hz, which means they're probably filtered at 10 kHz. Can you ensure there isn't anything you might have missed higher in the spectrum? What is the tape speed?

 
« Last Edit: September 18, 2017, 06:11:52 PM by ka9q »

Offline ka9q

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Re: Digitizing my Apollo audio tapes.
« Reply #3 on: September 18, 2017, 06:32:05 PM »
This is looking more and more interesting.

The Apollo Operations Handbook for the Extravehicular Mobility Unit, Volume I (system description) for Apollo 14 (which covers the early pre-J missions) says that each PLSS generated two subcarriers, one for PLSS telemetry and the other for an electrocardiogram. EVC-1 (worn by the commander) put the EKG on a 5.4 kHz subcarrier and telemetry on 10.5 kHz. EVC-2 (worn by the LMP) put the EKG on 3.9 kHz and telemetry on 7.35 kHz.

The LMP's PLSS transmitted the two subcarriers, plus the LMP's voice, via VHF-FM to the CDR's PLSS, which mixed in the CDR's voice and his two subcarriers, transmitting the whole thing (combined voice + 4 subcarriers) to the LM by VHF-AM.

The block diagrams show the subcarrier oscillators as VCOs (Voltage Controlled Oscillators), which means the telemetry frequency modulated these subcarriers. The modulating signal commutated among 30 analog channels 1.5 times per second. 26 channels were used for actual telemetry and the rest for synchronization and calibration. Your mystery signal sounds exactly like a frequency modulated tone (though lower than any of the frequencies listed above) and repeats 1.5 times per second (rather than 1.0 times/sec as you'd expect for most time codes).

So my very VERY initial take is that you've found one of the two PLSS telemetry streams, shifted down in frequency to make it easier to record on one channel of an audio tape recorder. It's probably not one of the EKGs, which was transmitted on its own subcarrier, and in any event would not repeat at such a fixed rate given the astronauts' physical exertion (not to mention excitement).

Got any more like these?

Offline ka9q

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Re: Digitizing my Apollo audio tapes.
« Reply #4 on: September 18, 2017, 07:43:55 PM »
The more I listen to your tape and read the documentation, the more strongly I suspect that you've captured PLSS telemetry. Caveat: I haven't yet run any formal analysis on these signals other than looking at the waveforms, spectrum and autocorrelation with Audacity.

But if I understand the system correctly, I should be able to extract and plot the actual telemetry waveforms. The documentation gives the channel assignments, though without unit-specific calibration records they would be uncalibrated.

I hear occasional sudden changes in the recorded audio that make me think this was recorded from a selector switch manually set to one of the PLSS composite signals and shifted down from the actual VCO frequency to about 1600 Hz (within the audio range and easily recorded).

It is even possible that the switch settings include EKG (electrocardiogram) data, though there seems to be much less detail on that part of the subsystem than on PLSS internal telemetry (O2 pressure, water temperature, etc, etc). I don't yet hear anything that sounds like a *direct* connection between EKG electrode amplifiers and the associated voltage controlled oscillator, but it's possible that the waveform was interrupted with sync and calibration signals as were the commutated hardware analog telemetry channels.

Offline apollo16uvc

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Re: Digitizing my Apollo audio tapes.
« Reply #5 on: September 19, 2017, 10:48:06 AM »
The original uploaded file extension is WAV. 706kbs something, 16-bit. archive.org uploads the original .wav file but also converts it to mp3, flac, ogg and stuff. So the FLAC is just a converted version of the original WAV.

My USB audio card supports up to 24-bit 96Khz. Tape speed is 7 1/2 inch/s


I got one Apollo 11 tape and several Apollo 17 tapes at a thriftstore. So far none of my Apollo 17 tapes have any audio like on Apollo 11. Apollo 17 is all voice.

Have you found anything using Audacity?
« Last Edit: September 19, 2017, 12:05:14 PM by apollo16uvc »
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Offline ka9q

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Re: Digitizing my Apollo audio tapes.
« Reply #6 on: September 19, 2017, 05:14:53 PM »
I used audacity just to look at the spectrum and autocorrelation. I am also using my ears (I'm a radio ham and digital signal processing guy). I'm almost certain you've found PLSS telemetry. The occasional abrupt changes are probably a manual switch to a different channel.

There were four channels, two from each PLSS. One carried the astronaut's EKG, the other the telemetry from the suit itself.

You found these in a thrift store?!!?

Offline apollo16uvc

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Re: Digitizing my Apollo audio tapes.
« Reply #7 on: September 20, 2017, 06:42:05 AM »
Yeah I know a thriftstore that some times gets reel to reel stuff, players and tapes.
The players are usually on the cheaper side so I don't bother, but tapes are cool because it is always interesting to hear what is on them.

I have looked at the audio file spectrograms with Audacity, and the signal on the first few seconds on S1 and S2 is vastly different from the rest of the tapes. And I think somewhere on S1 or S2, later on in the tape the same signal from the beginning returns for a few seconds, maybe they lost connection for a brief period?

Maybe the signal at the beginning is some sort of calibration signal?

The tracking station at Bochum, West germany also recorded telementry and they should still have it in their tape archives. But it was most likely recorded with a modified tape recorder, so it will be difficult to play back. I am in contact with them and have emailed several audio and video museums at Germany for help.
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Offline ka9q

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Re: Digitizing my Apollo audio tapes.
« Reply #8 on: September 20, 2017, 01:12:42 PM »
I can point you to the telemetry system descriptions in the Apollo Operations Handbook, and I can explain them if you'd like. I think we have what we need to decode them, if they are in fact PLSS telemetry recordings.

I've been to Bochum and seen some of their equipment. Among other things was a standard broadcast-style videotape recorder of the era, which would have worked fine for the TV signals.

Composite and high rate telemetry would have been recorded with wideband instrumentation recorders, which were often commercial videotape recorders slightly modified for non-video waveforms.

« Last Edit: September 20, 2017, 01:14:50 PM by ka9q »

Offline dwight

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Re: Digitizing my Apollo audio tapes.
« Reply #9 on: September 20, 2017, 03:45:12 PM »
Bochum has 2" videotape recordings of Apollo 16. They have a videotape machine but it is in dire need of repair, and those tapes were never digitized.
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Offline apollo16uvc

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Re: Digitizing my Apollo audio tapes.
« Reply #10 on: September 24, 2017, 12:18:01 PM »
I can point you to the telemetry system descriptions in the Apollo Operations Handbook, and I can explain them if you'd like. I think we have what we need to decode them, if they are in fact PLSS telemetry recordings.

I've been to Bochum and seen some of their equipment. Among other things was a standard broadcast-style videotape recorder of the era, which would have worked fine for the TV signals.

Composite and high rate telemetry would have been recorded with wideband instrumentation recorders, which were often commercial videotape recorders slightly modified for non-video waveforms.

Go ahead ka9q, explain the telementry to me.

have you run the signal through a spectrum analyzer yet? I'd like photos or video of any interesting parts if you found any.

Do you have any photos of the RCA VTR and tape at Bochum?
« Last Edit: September 24, 2017, 12:20:48 PM by apollo16uvc »
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Offline apollo16uvc

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Re: Digitizing my Apollo audio tapes.
« Reply #11 on: September 24, 2017, 02:54:44 PM »
AS17-R01-S1-V1 has been uploaded to Apollo 17 audio tapes.
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Offline ka9q

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Re: Digitizing my Apollo audio tapes.
« Reply #12 on: September 25, 2017, 11:30:07 AM »
Do you have any photos of the RCA VTR and tape at Bochum?
Yes, quite a few. Not sure what you'd like to see.


Offline Obviousman

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Re: Digitizing my Apollo audio tapes.
« Reply #13 on: September 25, 2017, 05:13:07 PM »
Found them at a thrift shop? Inconceivable!

I wish I had a similar shop near me...

Offline apollo16uvc

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Re: Digitizing my Apollo audio tapes.
« Reply #14 on: September 26, 2017, 01:34:37 AM »
Do you have any photos of the RCA VTR and tape at Bochum?
Yes, quite a few. Not sure what you'd like to see.
Could you send me some of them?
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