Author Topic: Sound on the moon?  (Read 3573 times)

Offline BDL

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Re: Sound on the moon?
« Reply #30 on: November 01, 2018, 10:28:16 PM »
I’ve decided to watch a bunch more footage from Apollo 17 and I have indeed noticed very many of those same sounds. The audio is riddled with it.
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Offline ka9q

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Re: Sound on the moon?
« Reply #31 on: November 15, 2018, 07:39:58 AM »
These were analog radio systems, with plenty of potential noise sources of all kinds. Radio hams (like me) are very familiar with them. One possibility not yet mentioned is physical contact with or possibly even mere movement of the VHF antennas on the OPS or the LCRU (the Lunar Communications Relay Unit on the rover).

All of the Apollo radios were full duplex, so these noises could be generated even when an astronaut was not talking or his VOX was tripped.

The astronaut radios were in the PLSS but their antennas were physically mounted on the top of the OPS that sat on each PLSS; they were connected by a cable whose connectors could easily have gotten a little gritty in the lunar environment. This too could have generated noise when the cables were moved.

In the Apollo 17 video just posted I heard intriguing "chirping" sounds similar to the sound of ham slow-scan TV. From my knowledge of Apollo communications, I wonder if these could be crosstalk from the PLSS analog telemetry encoders. A commutator continuously walked through a series of analog signals, frequency-modulating the selected channel on a carrier tone above the normal voice range (but within the audible range) and added to the voice signals before transmission to the LCRU for relay to earth.

It sure would be fun to redo all this with modern digital technology...

« Last Edit: November 15, 2018, 07:42:29 AM by ka9q »

Offline bknight

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Re: Sound on the moon?
« Reply #32 on: November 15, 2018, 08:10:54 AM »
<snip>

All of the Apollo radios were full duplex, so these noises could be generated even when an astronaut was not talking or his VOX was tripped.

<snip>

Did you mean VOX was NOT tripped?
Not being a ham operator or an electronics expert, I have deferred to you for many of the electronics "anomalies" discussed in Apollo.  Do the "chirps" exist because of the internals of each components of the system, then? 
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Offline ka9q

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Re: Sound on the moon?
« Reply #33 on: November 15, 2018, 03:29:03 PM »
<snip>

All of the Apollo radios were full duplex, so these noises could be generated even when an astronaut was not talking or his VOX was tripped.

<snip>

Did you mean VOX was NOT tripped?
Yeah. Poor grammatical framing. I mean to say NOT (talking OR vox_tripped). The astronaut's transmitter stays on the air, and the ground continues to listen, even when the path between the microphone and transmitter is not active at the moment.
Quote
Not being a ham operator or an electronics expert, I have deferred to you for many of the electronics "anomalies" discussed in Apollo.  Do the "chirps" exist because of the internals of each components of the system, then?
I can't say what the exact mechanism is in this exact case, but it is common in analog radio and audio systems to have nonlinear distortion. When you sum two signals A and B, the output of the system is supposed to be simply A+B. With nonlinear distortion, the output is something else; it may be "clipped" to some limit, or it may be something else (usually less) than the actual sum. There can be any number of causes: poor design, excessive signal amplitudes, component degradation or failure, etc. Even a loose or dirty connector. This could happen anywhere along the signal chain, including in the receiver. I haven't watched a lot of the video but it did seem that it happens when the astronauts are very close to the rover camera so it could be overloading of the LCRU VHF receiver.

If you work out the math (Fourier transforms), nonlinear distortion produces frequencies not present in the original signal. If you put frequencies F1 and F2 into the system, the output may contain not only the original frequencies  F1 and F2, but also n*F1+m*F2.  If n and m are nonzero, including negative values, you get "intermodulation distortion". This is intentionally done in 'mixers', devices widely used in radio receives and transmitters to shift the frequency of a signal.

Each PLSS generates two telemetry subcarriers: the LMP at 3.9 and 7.35 kHz and the CMP at 5.4 and 10.5 kHz. Remember that the CMP receives the LMP's signal on an FM link at 279 MHz, adds his own, and transmits the sum to the LCRU (or LM) for relay to earth. Intermodulation distortion could easily produce difference frequencies between the various telemetry carriers falling into the audible range (300 to 2300 Hz). As I said before, the effect seems to happen when the astronauts are very close to the TV camera and LCRU so the commander's AM transmitter could be overloading the LCRU's receiver. You probably wouldn't get this effect on earlier (pre-J) missions using the LM for communications relay since the LM's EVA relay antenna is mounted on the top of the LM, away from the astronauts on the surface.


« Last Edit: November 15, 2018, 03:36:55 PM by ka9q »

Offline Northern Lurker

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Re: Sound on the moon?
« Reply #34 on: November 15, 2018, 03:34:55 PM »
Do the "chirps" exist because of the internals of each components of the system, then?

Chirps? Did you mean Quindar tones? https://en.wikipedia.org/wiki/Quindar_tones

Lurky

Offline bknight

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Re: Sound on the moon?
« Reply #35 on: November 15, 2018, 03:42:57 PM »
Do the "chirps" exist because of the internals of each components of the system, then?

Chirps? Did you mean Quindar tones? https://en.wikipedia.org/wiki/Quindar_tones

Lurky

My description of what all have been talking about in the video.
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Offline ka9q

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Re: Sound on the moon?
« Reply #36 on: November 15, 2018, 03:46:33 PM »
No, these are different from the Quindar tones. The Quindar tones are generated by the Capcom's console when he starts and finishes talking. I'm referring to some artifacts that are clearly on the downlink. They start around 14:25 in BDL's video and continues at varying levels for some time. It starts while somebody is cleaning the camera lens, so it's possible he bumped into a cable connector and moved it slightly. Apollo 17 was especially plagued by lunar dust getting into everything, and I wouldn't be at all surprised if it had a role here.

I might be completely wrong about all this, but I can't think of any other potential source. Maybe they added some experiment that I simply don't know about. I should probably look at the telemetry system a little more closely to see if intermodulation distortion should in fact sound like what we hear.

Offline Northern Lurker

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Re: Sound on the moon?
« Reply #37 on: November 15, 2018, 04:00:17 PM »
Oh that chirping. No idea here.

Funny how perception of a video changes depending on what you are looking or listening for. First time I watched the video, I followed the action on screen and listened to conversations and didn't notice any voice artifacts except quindar tones. On second try I ignored those and listened for thuds, I heard many of those, regardless of whether an astronaut was hammering something or not. On third try I again ignored all of those and listened to chips instead. Intresting that whining chirp that didn't distort the astronauts voice.

Lurky

Offline ka9q

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Re: Sound on the moon?
« Reply #38 on: November 15, 2018, 04:00:39 PM »
I'm looking at the PLSS telemetry system in some more detail (Apollo Operations Handbook Extravehicular Mobility Unit - Vol I System Description Apollo 15-17, section 2.5.6, Extravehicular Communication System).

There are two telemetry subcarriers from each PLSS. One appears to be dedicated to an astronaut EKG. The other carries 30 telemetry channels at a sample rate of 1.5 Hz, with 26 of those channels usable for information (the other four are for synchronization and calibration). That implies a commutation rate of 45 Hz, which to my ear is not far from the rate at which the crosstalk tone signal varies.

I'm going to search the anomaly section of the mission report to see if anything like this is mentioned. They still analyzed Apollo 17 anomalies even though they didn't fix them unless they could conceivably appear in a Skylab mission.

Offline ka9q

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Re: Sound on the moon?
« Reply #39 on: November 16, 2018, 05:10:20 AM »
I went through the mission reports for Apollos 15, 16 and 17 and I didn't see anything in the anomaly reports sections about telemetry crosstalk into the mission audio. It might have had a different source, or maybe it wasn't considered bad enough to rate a mention.

Offline BDL

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Re: Sound on the moon?
« Reply #40 on: November 27, 2018, 09:20:02 PM »
I want to actually find the clips that are in the video that this thread is based on, but I’m not sure where to find it. I’ve tried going through the Apollo Lunar Surface Journal but I’m not really sure how to use it. Can someone help?
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Offline BDL

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Re: Sound on the moon?
« Reply #41 on: November 27, 2018, 09:33:17 PM »
More specifically, I’m looking for clips of 0:28, 0:34, 1:05, 1:12, 1:40, and 1:44 in any authentic Apollo archive. These timestamps are referring to the initial video this thread was made about on page 1.

These clips are all from Apollo 16.
0:28 and 0:34 were not given by the creator(s) of the video.
1:05 - a16v.1431336
1:12 - a16v.1655407
1:40 - a16v.1244215
1:44 - a16v.1684045
« Last Edit: November 27, 2018, 09:42:46 PM by BDL »
“One small step for [a] man, one giant leap for mankind.” - Neil Armstrong, 1969

Offline ajv

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Re: Sound on the moon?
« Reply #42 on: November 27, 2018, 10:59:10 PM »
The page you want is probably the Apollo 16 Video Library page: https://www.hq.nasa.gov/alsj/a16/video16.html

The Ken Glover clips match the names you listed. There is a link to the mission transcript next to each clip.

Offline BDL

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Re: Sound on the moon?
« Reply #43 on: November 29, 2018, 11:45:28 PM »
So I went through the video archive and it turns out the noises weren’t actually in the original audio.
Any noise that can be heard can be explained by the astronaut simply breathing, stepping, or coming in contact with something - which can be proven. So, yeah. A large portion of their sounds are not actually in the original audio clips,

Conspiracy theorists are a really odd type of people, huh? But I genuinely didn’t know they’d go as far as faking their own evidence...
« Last Edit: November 30, 2018, 12:46:47 AM by BDL »
“One small step for [a] man, one giant leap for mankind.” - Neil Armstrong, 1969

Offline Allan F

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Re: Sound on the moon?
« Reply #44 on: November 30, 2018, 12:13:04 AM »
But that is the mainstay of the hoax business. Inventing and fabricating "evidence".
Well, it is like this: The truth doesn't need insults. Insults are the refuge of a darkened mind, a mind that refuses to open and see. Foul language can't outcompete knowledge. And knowledge is the result of education. Education is the result of the wish to know more, not less.