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Unusual NBTV/SSTV format, Apollo 11

PostPosted: Tue Sep 24, 2019 6:22 pm
by ke6jjj
Hello everyone, I'm a new member to the forums. I've just joined minutes ago after coming to the NBTA website in search of something that might help me solve a very interesting puzzle.

I'm an amateur radio operator (KE6JJJ) and an audio engineer. I've recently gotten quite involved in cleaning up and restoring some of the publicly available and recently uploaded NASA audio material, including tapes that recorded the the Apollo 11 and Apollo 13 missions.

Recently I was pointed in the direction of a very curious artifact that was uploaded to the Internet archive -- a digitization of three reels of 1/4" audio tape that were found on E-bay. The uploader noted that the tapes were in stereo and that the right channel was obviously the Public Affairs and CAPCOM audio channels captured during the time of the EVA (moonwalk) of Apollo 11. But, in the uploader's words: "Left channel is a to me unknown noise with some kind of beep every second."

I investigated this recording and have almost thoroughly proven that this unknown beepy channel is in fact a kind of Slow Scan Television. But its format is very strange and is as follows:

1. The image is encoded as an FM-modulated waveform, centered roughly at 1500 hertz.
2. The waveform deviates a maximum of 300 hertz in both directions.
3. Full positive deviation (1800 hertz) indicates fully saturated white.
4. Centered deviation (1500 hertz) indicates black.
5. Full negative deviation (1200 hertz) indicates the start of horizontal sync pulse.
6. The image has 60 lines per frame, 59 of which are usable, the 60th of which remains fully negative, and is obviously the vertical sync indicator.
7. The frame is built up from the bottom scan line and progresses toward the top. (In reverse of most television signals).
8. Each scan line is 14.425 ms in duration.
9. Each frame therefore takes 865 ms to display. Or, in other words, the frame rate is 1.14 frames per second.

I've written a decoder for this format in Python, using my own personal DSP library, and have stitched it together (with the audio channel) to make a video of the result. I'll attach a single frame here just so you can get a feel for the quality. To give it an NTSC-like aspect ratio, I've stretched each horizontal scan line by a factor of 4, yielding a 320x240 image.

Can anyone here think of any video system, amateur, professional, or experimental, which would have created such a narrowband, slow TV signal like this, in 1969? Your answers might help us unravel where this tape came from, and if they point to a very professional, and perhaps, rare source, we might try to dig further into the source of these tapes. As you might know, the moon landings were captured in a very special SSTV format (10 fps, 320 lines) and stored on tapes that are now thought to have been lost or permanently erased. If this source is perhaps an unusual copy of those tapes, then it might be an incredible breakthrough, because whoever made these tapes might know where a more pristine backup might be found.

Then again, if this is just a hobbyist's run-of-the-mill collection of a very rare amateur format, then that would be helpful to know as well.

Thanks for you time, and I eagerly await your analysis.
-Jeremy Cooper

Re: Unusual NBTV/SSTV format, Apollo 11

PostPosted: Wed Sep 25, 2019 2:48 pm
by Steve Anderson
Hi Jeremy, and welcome to the forum.

I've been interested in the Apollo program (and still am) as I lived it as a teenager. More recent missions have been interesting, but to me they're no match for Apollo.

On the TV side, I have attached a pdf which doubtless you have seen, but many others here may not have seen before. Plus there's the whole 'Hoo-Haa' of what happened to the master tapes...that's a different subject. Google 'Missing Apollo tapes' if you're interested.

I've never come across this odd standard before [1], I wonder if it was someone who wanted to record the video but didn't have a VCR and converted the signal for use with a standard stereo audio recorder (not easy in the late 60s)...presumably for their use only. Somehow it found its way into the world. Or an interim and discarded experiment by NASA or a supplier?

But the picture appears to be an astronaut descending the steps on the LEM, so it must have been created after the event, or from a training/practice session?

A real puzzle!

Steve A.

[1] However, the frequencies are the same/similar to the Cop McDonald SSTV system in use at that time by radio amateurs, 1200Hz for sync-tips, 1500Hz for black and 2300Hz for peak white. As the syncs and black are the same, maybe the deviation was set somewhat low for peak white in the active video portion. If you recall (also as noted in the pdf above) the pictures were quite dark from Apollo 11 on the surface, that may explain it. If I recall it could have been a problem related to Gamma correction (or the lack of it), but I may be wrong, not unusual!

Re: Unusual NBTV/SSTV format, Apollo 11

PostPosted: Wed Sep 25, 2019 5:42 pm
by Steve Anderson
A11 TV camera Scope Of Works document...has all the signal definitions you may need...more these days just out of SSTV-like signals out of this thing...converted here on Earth by someone...

Steve A.

Re: Unusual NBTV/SSTV format, Apollo 11

PostPosted: Wed Sep 25, 2019 5:51 pm
by Steve Anderson
Prior to the Apollo series of landings there was this, interesting visual technology...very different system though...

Steve A.