Claim: Apollo 15-17 Live TV Feed - Antenna signal would be interrupted from all the violent shaking when Astronauts touch the buggy

Rend

New Member
I came across a Moon landing hoax claim yesterday that was sent to me via video. I searched this forum and elsewhere on the internet and I did not find a place where this claim was talked about. If it has already been discussed here, I apologize and can you please point me to the location of the discussion?

Brief summary of the claim: Apollo 15-17 had a TV rover camera. This camera sent live video signal down to Earth via an umbrella shaped high gain antenna. Both the camera and the HGA are attached to the rover. The Earth subtends about 2 degrees of the sky from the moon so an optical view finder was needed to correctly point the antenna. According to NASA, it needed to be pointed pretty perfectly using the viewfinder or else there would be serious degradation of signal. Basically, Earth needs to be in the bulls-eye of the viewfinder which is a 2.5 degree circle. Earth based news crews who broadcast images from remote locations via satellite, must use stanchions to steady their broadcast trailer, because any oscillation will interrupt the signal. The crux of the argument: the astronauts shake the buggy violently any time they touch it which should interrupt or degrade the signal significantly, but the picture is fine.

Links to the video are at the bottom. They are .webm videos hosted on 4chan, so you may have to do a 4chan Captcha to see it, and possibly reload after doing the Captcha. I did download them and try to upload them here as video, but the forum doesn't accept .webm as a video format or a file format

From viewing the video, I assume this part of a much longer video with other claims in it. Unfortunately I do not know the name of the original video.

Transcription of Video Clip 1(1m44s in length):

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Transcription of Video Clip 2(1m57s in length):

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Transciption of Video Clip 3(1m39s in length):

End Trascriptions

Unfortunately, I can't provide screenshots for part 3 because it is pointless, you would need to look at the shaking yourself. I do agree with the narrator that it is a lot of shaking, but there could be several reasons why this doesn't matter.

Here are the things that Jump out at me as questionable, missing info or just plain wrong with this claim:

  1. The strength of the signal in dBs needed for a decent live video at the receiving end on Earth is not clearly shown. The antenna broadcasts with a nominal gain of 24 dB and the edge of the 10 degree cone is 20.5 dB, but it does not specify clearly that 20.5 dB is the limit for good signal.
  2. Is the footage shown actually recorded from the broadcast or are they the recorded tapes? I am fairly certain the video was also recorded locally. I wasn't alive during the actual broadcasts, but I also doubt they were perfect. Perhaps the footage shown in the video is from the recorded tapes and the broadcast tapes did have some signal degradation during shaking.
  3. The claim that news crews who send images via satellite should have an easier time because geo-stationary satellites are closer sounds totally bunk to me. Satellites are 9-12 meters. And the cone would not have time to grow as large because the distance is shorter. The 10 degree cone would be massive from the moon to earth given the distance. If I am not mistaken, given the figures by the video, the circle it would create by the time it reached Earth, would take up 10 degrees of the sky, as compared to the 2 degrees that Earth does.
  4. The sighting scope shows a little less than 18 total degrees, the bulls eye is supposedly 2.5 degrees. This means that the 2 and a half squares from the center on each side is probably 20.5 dB and the center is 24 dB. Again, I don't know how many dBs on the receiving end are required for a clear picture.
  5. The rover's camera could be controlled remotely. Perhaps the ability to pan and tilt makes it more susceptible to shocks and bouncing. It looks like the rover is shaking a lot, but perhaps small shocks just shake the camera a lot and don't affect the antenna as much. Just because the camera is shaking doesn't prove that the antenna is.
Questions I'd like help with, but am having trouble finding the answer or figuring out how to answer: How much signal strength at the receiving end was needed for a clear picture? How much movement of the scope / antenna would result in a noticeable degradation of signal? Is the footage shown in the video recorded from the live TV broadcast or from the on location recorded tapes?

Again, I could not upload these .webms on the forum so here are the links:

Original Links:
Moon Landing Hoax 1 (1m44s)
Moon Landing Hoax 2 (1m57s)
Moon Landing Hoax 3 (1m39s)
 
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Rend

New Member
How much was the rover actually shaking? Have they tried to determine that?
They are right in that it shakes pretty violently. There is no number measurement for the shake, but in the video you see the horizon bounce quite a bit. They basically just draw a line on the horizon and show how much it shakes.

Perhaps I can edit it and post an animated gif of the bounce or possibly the bounce frame by frame at the two most extreme points.

I managed to convert the last video which mostly consists of the shaking set to tuba music to animated gif. But it is 78 megs and I don’t think I can upload it on the forum. Unfortunately I am not at a computer, so I can’t chop just the gif up.

It is in source video 3 if you wanted to watch.
 
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Mendel

Senior Member.
https://en.wikipedia.org/wiki/Apoll...s_ground-commanded_television_assembly_(GCTA)

If the camera is zoomed in, the shake will look worse than it is.

https://en.m.wikipedia.org/wiki/Apollo_TV_camera
If the 43° are diagonal, then that 4:3 camera has 3/5 of that as vertical angle, so 26° vertically when zoomed out and 4.3° when zoomed in. This means the shake can be 10% of the image height in if zoomed out and over 50% of the image height if zoomed in and still not degrade the signal too much. (And it's kinda hard to see if the signal degrades with that amount of bad compression on those videos.)

Original footage, camera on rover from 40:55.
Source: https://www.youtube.com/watch?v=qhhJXrbg5lk

You can see right at the beginning what degraded footage looks like, the lines don't sync up properly because the circuitry does no longer recognize the degraded sync signal. (It could also be a video replay problem when they digitized the footage?)
image.png
 

Rend

New Member
So I watched the whole video of the Apollo 15 video you posted. It looks like the signal degrades significantly when they bump the rover. Will look at additional footage from Apollo 16-17 tomorrow.

This is probably just a case of moon landing hoax folks using recorded footage that was never transmitted live via radio from the moon to earth.

Will investigate more tomorrow. Thanks Mendel.
 

Mechanik

Active Member
It seems to me that the shaking of the rover could be well within the 10 degree signal cone that reaches Earth.

Optimal signal is within the bulls-eye, but minor shaking from touching and bumping the rover could easily move the antenna 2, or even 4 degrees off target for a moment. That's still within the 10 degree cone unless it's a very large bump. This would degrade the signal, as seen in the videos, but not necessarily cause a full loss of picture. The video stream is necessarily line-by-line transmission so a short bump would degrade a few lines, but not necessarily an entire frame/refresh cycle.

You also have to consider that the camera is mounted to the same rover frame, so bumping the frame bumps the camera and the antenna at the same time, which would either amplify or cancel out the shaking and artifacting (is that a word?) and probably did a little of both depending on the angle of the bump.
 

Rend

New Member
It seems to me that the shaking of the rover could be well within the 10 degree signal cone that reaches Earth.

Optimal signal is within the bulls-eye, but minor shaking from touching and bumping the rover could easily move the antenna 2, or even 4 degrees off target for a moment. That's still within the 10 degree cone unless it's a very large bump. This would degrade the signal, as seen in the videos, but not necessarily cause a full loss of picture. The video stream is necessarily line-by-line transmission so a short bump would degrade a few lines, but not necessarily an entire frame/refresh cycle.

You also have to consider that the camera is mounted to the same rover frame, so bumping the frame bumps the camera and the antenna at the same time, which would either amplify or cancel out the shaking and artifacting (is that a word?) and probably did a little of both depending on the angle of the bump.
That’s the thing, I would really like to know what the limits were at the receiving end (australia I believe, for at least a few missions) were. 20.5 dB at the edge of the cone could still be fine for all I know. It might have allowances down to 10 dB for all I know. Been searching for the answer but I can’t find it yet.

I am going to be really disappointed though, if this is just sneaky and the hoaxer documentary is showing recorded footage instead of transmitted stuff. I don’t want to just catch them in a dumb lie, I would rather prove fully why what they are saying is wrong.
 

Mendel

Senior Member.
You also have to consider that the camera is mounted to the same rover frame, so bumping the frame bumps the camera and the antenna at the same time, which would either amplify or cancel out the shaking and artifacting (is that a word?) and probably did a little of both depending on the angle of the bump.
How does bumping the antenna have an effect on the vertical alignment of the camera picture? I don't understand how you expect that would work.
 

Rend

New Member
How does bumping the antenna have an effect on the vertical alignment of the camera picture? I don't understand how you expect that would work.
If I had to speculate, maybe he is confused and didn’t watch the bumping and assuming the bumping is showing the antenna on footage bumping as well. Which, would be right, two things shaking could either exaggerate or soften the appearance of movement. But then again, it gets kind of muddled because he could mean several different things wrt artifacting, but I think he is just misunderstanding the claim.

Then again, I should probably just wait for Mechanik to answer.
 

Mechanik

Active Member
I'm often confused but more often just express myself poorly. In this case, it's both.

I was attempting to respond to the OP claim:
The crux of the argument: the astronauts shake the buggy violently any time they touch it which should interrupt or degrade the signal significantly, but the picture is fine
I should have stopped after my third sentence so my should have read on those sentences:
It seems to me that the shaking of the rover could be well within the 10 degree signal cone that reaches Earth.

Optimal signal is within the bulls-eye, but minor shaking from touching and bumping the rover could easily move the antenna 2, or even 4 degrees off target for a moment. That's still within the 10 degree cone unless it's a very large bump.
I should have quit then. However, I then scanned the other responses to make sure I wasn't duplicating. I also watched the first few minutes of the @Mendel video and didn't realize the rover footage was later. Your note was clear, it just didn't penetrate that I had to move the start point myself. In the footage I originally watched, the camera movement was inversely correlated with video quality.

Once I went back and watched the correct footage, it's obvious that the rover camera movement did not affect video quality, which is where the original claim started. @Rend, you accurately speculated what I was thinking, but I was commenting on the wrong video footage. Throw out everything after my first 3 sentences and we're good. For the record, the rover shaking appears minor to me and would be probably be invisible today with digital image stabilization.

Sorry for the confusion.
 

Mendel

Senior Member.
No problem, that's what clarification questions are for! B-)
In the footage I originally watched, the camera movement was inversely correlated with video quality.
I kinda wonder what transmission chain they used for that and what exactly caused that degradation, but I'm too lazy to find out right now.
 

Rend

New Member
Thanks Mechanik.

Man, I really need to get to a computer to chop up the last video to show the shaking they are talking about. So others can see.

I would like to also figure out where each of the shaky scenes are shown. Like I want to know which missions they were.

I also need to get this thread moved from the forum feedback section, because I am an idiot and posted it in the wrong place.:(
 

Mendel

Senior Member.
Man, I really need to get to a computer to chop up the last video to show the shaking they are talking about. So others can see.
The data that would be very useful is a) an estimate how much the camera is zoomed in or out, and b) a measurement how much in terms of (unedited) frame height (measured in percent or in pixels) the shake actually is. This would allow us to estimate the antenna displacement.
 

Z.W. Wolf

Senior Member.
I've considered all sorts of things including:
-the altitude of the Earth above the horizon and the antenna position in relation to the camera position
-the suspension of the Rover and various movements it could make
-the geometry of all these movements and positions
-parallax effects

But I've realized there's one factor that makes all these others irrelevant, and that is the issue of how the camera is mounted and how it moves. The assumption that the camera movement = the movement of the Rover = the movement of the antenna is false.

The camera was on a 2-axis gimbal mount, with both the azimuth axis and elevation axis driven by motors. This is not a rigid mount. There would be considerable play. The camera is heavy. Movement and inertia would cause the camera to "whiplash." Because the movement of the Rover on its suspension would mostly be up and down, the camera would "nod" on its mount more than it would "wag."

https___airandspace.si.edu_webimages_collections_full_A19760742000_03.JPG.jpg


camera 3.png



Referring to this video: Moon Landing Hoax 3 (1m39s)

Here at 0:23 the narrator talks about the horizon moving. But note that the Rover is moving up and down just as much as the horizon is in relation to that yellow arrow.

Camera.png

A relatively small motion of the Rover was causing a relatively great motion of the camera.

If the camera were rigidly mounted, the Rover would be fixed in place in the camera's field of view. But if the Rover is moving in the camera's field of view, the camera has an independent motion. In this case the camera is nodding up and down. And because the Rover is moving up and down just as much as the horizon, this proves that the wobbly camera motion is much greater than the motion of the Rover that caused the wobble.


Here again at 0:52 the body of the Rover is moving up and down just as much as the horizon. The camera is nodding in its gimbal mount.

camera 2.png


In contrast, the antenna was locked down, probably by a wing nut or the equivalent. It would be much more rigid on its mount and wouldn't whiplash. It would follow the motion of the Rover more closely. The antenna would be moving much less than the camera.

Their premise that the Rover movement = camera movement = antenna movement is false. So is the rest of their argument.
 
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Z.W. Wolf

Senior Member.
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Rend

New Member
It took me a while to visualize it, but yes this is right. I had suggested it in my OP, as number 5, but didn’t realize the evidence would be right in the video. Good stuff.

I was expecting needing to find video from Earth where they are testing the rover and recording video with another camera to show the camera wobbling. Or maybe show it being attached to the rover and showing the wobbliness at that point.
 
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Rend

New Member
Sorry to double post but I found this stabilized video of Lunar Rover from non broadcast images. I have time stamped it to 50 seconds, because it shows recording from the astronaut’s chest cam, the video has both antenna and camera in shot. It looks like the camera is indeed fairly loose on the gimbal.

Source: https://youtu.be/5cKpzp358F4&t=50s
 
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Rend

New Member
So I finally made it to a computer and chopped up the third video which shows the shaking, here they are:



























































On most of these videos, it is hard to know which clips are zoomed in, which will have a huge effect on the bounciness. On the only clip that I am fairly certain is not zoomed in, the bounce is minimal. The clip is the first one posted here (A-16 in the corner indicates it is from Apollo 16 of course). You can see a noticeable quality drop on the zoomed in images and these low quality videos are the ones with the highest amount of horizon movement.

I took screenshots of the image and I measure the horizon movement 21 pixels. This horizon movement translates to 4.38% of the screen 480 pixel resolution screen. An easy object on the rover itself to compare it to is the mast to the right of the screen. I measured where the mast goes from thick to thin. I show a jump of 38 pixels as compared to the 21 pixels the horizon moves in the same screenshots. Here are the screenshots I took below:

I got it wrong. I didn't notice that I had a black bar in the top of the second screen shot that accounts for extra pixel movement. The movement is almost exactly the same for buggy and horizon. I got 18 pixels for buggy mast movement and 21 pixels for And here I was worried about getting my cropping perfect on the bottom, when that doesn't matter, because pixels are counted from the top of course. How embarassing.

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There is another shot that might not be zoomed in which includes an astronaut actually jumping into the seat (clip 2 in this post). This probably should be the heaviest jolt of all of them and shows the least amount of movement of all of them, indicating to me that the rest are probably taken while the camera was zoomed. I don't exactly have weight information on the tools they took with the buggy, but I imagine an astronaut with his space suit is probably heavier than any of the tools and most of the science packages. Unfortunately there is nothing steady on the buggy to look at for comparison.

We can probably put this to bed on what we have now, because most of the images are probably zoomed and the movement isn't as significant in the unzoomed ones and we have videos showing the camera shaking on its pan / tilt attachment significantly more than the antenna. I wish the videos were more specific with where the locations in the video are, so I can get context for the amount of zooming. Only thing I have to go on is the mission number. Not to mention the other info that could be gathered.
 
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Apologies for the late arrival to the thread and if anything I mention below is covered more adequately above.

I think people (when discussing the broadasts from the moon, be it data, communication or TV) very much underestimate the size of the dish used to pick up the signal and the spread of the cone that the signals would have over that distance. The movement of the LRV dish would, I imagine, 'wave' the signal rather than break it so you might expect a small amount of disruption but not necessarily a complete break up. Disruption is very often evident in those broadcasts.

A quick glance at internet information for setting up a terrestrial dish for TV says that a misalignment of 0.5 degrees could lead to a 40% degradation of a signal from the satellite. Not a loss, a degradation, and this is for a very small dish, not the monsters used to receive Apollo transmissions. Have the video makers attempted to replicate the conditions tey claim would interupt the transmissions, or is it just another "gee it kinda looks funny" exercise?

There are also two elements to the signal chain here - the camera itself and the broadcast antenna, both of which are mounted separately, and the people making the claim would need to demonstrate what would happen in the circumstances they outline to prove that shaking of the rover (which mission planners will have anticipated as an issue because they were concerned about damage to the camera itself) was insurmountable. It clearly was not.

One interesting example of how the signal could break up in violent shaking is the short drive from the lunar module to the 'VIP' parking spot from which it would film the ascent to lunar orbit in Apollo 17

https://www.hq.nasa.gov/alsj/a17/a17v1695942.mpg

I'm not sure whether it was left on by accident or design. Apparently an attempt was made during Apollo 15 but with less interesting results and TV documentation at the ALSJ suggests that lower quality broadcasts (the 'FM/TV' mode) while driving was anticipated as a possiblity, and they even went to the trouble of working out how much signal loss was likely during transit to see if the relay between the LRV and LM was a good back up system should direct communication fail.

On the last point made, the location of each broadast location is known, you just need to note the station name of the broadcast and reference it with the relevant EVA map.

That brings me nicely to my final point: one thing that conspiracy theorists are never very good at it is seeing the wood for the trees. They tend to focus on in one tiny aspect of a subject in the hope that they will give it their grand "A-HA!!" moment but then fail to put that detail in its broader context, and that's where it always falls down.

The live broadasts from the moon show details that were not known about prior to the lunar missiosn but have been confirmed by probes sent subsequently. They show images of Earth entirely consistent with the known meteorological conditions of the day and that could not have been predicted beforehand. It;s also notable that the OP video attempts to poison the well with its use of jokey background music. The video's aim isn't one of genuine enquiry and clarification, it has an agenda, and I'm willing to bet it's pay per click. Weirdly, their honing in on fine details never seems to extend to reading the wealth of very detailed technical documentation available on every aspect of the missions.

Spacecraft films, erstwhile purveyors of high quality DVDs relating to the Apollo era, has made available its production 'Live from the Moon', which is available here:

Vimeo

There is also this document at the ALSJ Apollo TV.
 

Jon Adams

New Member
First, I haven't had time to see the video yet (due to awaiting an important beer shipment from Chicago via FedEx) but first thoughts:

TV transmissions in 1969-1973 in the US were NTSC analog. Requires a humongous signal to noise ratio for a super-clear broadcast quality picture, like 50 dB, but can droop to about 37 dB for a generally crappy signal. That right there is a 20 to 1 ratio, for those not dB-minded. Crappy signals lose horizontal and vertical sync (differently, as they're encoded a bit differently on the signal), so vertical roll and horizontal tearing will show up.

I will have to go back and research the radio frequency and television system used for the transmission, but it's likely to have been S band (2100 MHz). Wavelength is 14 cm for S band. Antenna size for a given gain/directionality is pretty much directly proportional to the radio frequency, so that antenna looks about a meter (?) or so across its aperture. Again, have to go do some calcs to determine gain at that aperture.

Sorry for the German, but the Wikipedia article on parabolic antenna used this plot of antenna gain vs azimuth and I didn't want to poach from something else. The Hauptkeule is the business end of the antenna, that's what you point toward the distant receiver. 10 dB is 10x, 20 dB 100x, and similarly, -10 dB is 0.1x, and -20 dB is 0.01x, etc, so one can see that the vast majority of the beam power is in a width only a small portion of the entire circle. The Nebenkeulen are sidelobes and the Ruckkeule is the back lobe, unwanted power radiation but inevitable in practical antenna patterns.
1588974688095.png
What this means is that a small wiggle in antenna point can have a quite large impact on power received at the Earth end. I'm sure they designed the link with at least 10 dB margin (I would have), so a little wiggle is ok. Again, calcs later once I know the radio frequency and estimate the antenna size better.

Cheers - Jon
 
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Jon Adams

New Member
First, I haven't had time to see the video yet (due to awaiting an important beer shipment from Chicago via FedEx) but first thoughts:

TV transmissions in 1969-1973 in the US were NTSC analog. Requires a humongous signal to noise ratio for a super-clear broadcast quality picture, like 50 dB, but can droop to about 37 dB for a generally crappy signal. That right there is a 20 to 1 ratio, for those not dB-minded. Crappy signals lose horizontal and vertical sync (differently, as they're encoded a bit differently on the signal), so vertical roll and horizontal tearing will show up.

I will have to go back and research the radio frequency and television system used for the transmission, but it's likely to have been S band (2100 MHz). Wavelength is 14 cm for S band. Antenna size for a given gain/directionality is pretty much directly proportional to the radio frequency, so that antenna looks about a meter (?) or so across its aperture. Again, have to go do some calcs to determine gain at that aperture.

Sorry for the German, but the Wikipedia article on parabolic antenna used this plot of antenna gain vs azimuth and I didn't want to poach from something else. The Hauptkeule is the business end of the antenna, that's what you point toward the distant receiver. 10 dB is 10x, 20 dB 100x, and similarly, -10 dB is 0.1x, and -20 dB is 0.01x, etc, so one can see that the vast majority of the beam power is in a width only a small portion of the entire circle. The Nebenkeulen are sidelobes and the Ruckkeule is the back lobe, unwanted power radiation but inevitable in practical antenna patterns.
1588985248499.png
What this means is that a small wiggle in antenna point can have a quite large impact on power received at the Earth end. I'm sure they designed the link with at least 10 dB margin (I would have), so a little wiggle is ok. Again, calcs later once I know the radio frequency and estimate the antenna size better.

Cheers - Jon
 
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Jon Adams

New Member
UPDATE

Well, NASA was more clever than the average cat. They used a "highly compressed" version of a standard TV signal. From Wikipedia's Apollo TV Camera":
Since digital compression video techniques weren't practical at the time (though studied by NASA as a possibility in 1965 in document NASA-CR-65508), the signal was "compressed" by simple analog means, starting by not using color, reducing the image resolution from the NTSC standard 525 lines to 320 lines, and reducing the frame rate from 30 fps to 10 fps. In this way, the Lunar TV camera was able to shrink the video signal bandwidth to 5 percent of that used by a standard NTSC signal. After Apollo 11, a larger S-band antenna was deployed by astronauts during their first EVA, eventually allowing better video from the lunar surface.[20]
B&W vs color, low frame rate, reduced resolution, they could get by with less power, less signal to noise ratio, and let's assume that they used the regular audio channel for the voice, so all they needed to do was send the video signal. Still, it was 390 thousand km away, S band, and the Earth side antennas at that time were (I think) what were called the "Apollo" antennas by the time I got to JPL 15 years later.

Apollo stations had HA-DEC 26 m (according to this link at Space.com) dishes (but I thought 34), and 26 m at 2100 MHz would have a gain of about 52-53 dB. On the lunar rover side, the gain would have been perhaps 20-25 dB for a 1 m umbrella. The link path loss between Earth and Luna is 210 dB at 2100 MHz. 210 dB is a sh*t-ton of loss, but Mars is worse... Let's assume the lander transmitter was able to dedicate on the order of 10 W to the TV transmission.

10 W transmitter: +40 dBm
Lander antenna gain: +25 dB
Path loss Luna-Earth: -210 dB (it's really not negative, since I'm calling it loss)
DSN 26 m antenna: +53 dB

+40 dBm +25 dB -210 dB +53 dB = -92 dBm received signal strength at DSN antenna on Earth.

That's a very respectable received signal. Nonetheless, the DSN receivers are world-class, and even then had ruby MASER front ends cooled with liquid helium so their noise figures (amount of self-generated noise an amplifier makes) were really good. Their noise floors with the antenna pointed into deep space (Luna would be a little noisier) would be somewhere around -190 dBm/K/Hz. The above quote states that the video bandwidth was able to be squeezed down to 5% of normal, which is about 4.5 MHz, so 225 kHz. These are all educated WAGs, so anyone else please chime in if they've got better numbers.

Boltzmann constant: -198 dBm/K/Hz
DSN receiver noise floor: 6 K = 8 dB-K
225 kHz signal bandwidth = 54 dB-Hz

-198 dBm/K/Hz +8 dB-K +54 dB-Hz = -136 dBm

Received signal at DSN is -92 dBm
Receiver noise floor is -136 dBm
Received signal to noise ratio: -92 - (-136) dBm = 44 dB.

44 dB means they had a signal to noise ratio at Earth after the receiver front end of better than 20000 x signal to noise. That's way more than what was necessary for a low-quality analog video transmission. And plenty of margin for faded synapses of time error, or some other fudge factors.

Anyway, Apollo was 15 years before I got to the Lab and started working within the DSN. Here's a picture I took of two of the biggest antennas at DSN 40 in Robledo, Spain (outside Madrid) when I was there in 1985.
DSN_Aug1985_small.jpg
The HA-DEC is the one on the left, while the 64 m dish is on the right further from the camera. Now I see why my memory was different than the article: one can see the left dish changes surface texture about 2/3 of the way out from center. That must have been the 26 m to 34 m upgrade program where they added an annulus of more reflector, so that's why I remember them as 34 m dishes, because they were by the time I came around.

Anyway, this soliloquy is really to remember how the system worked, what the basic parameters were, and how it could deliver a decent-grade analog TV signal from Luna to Earth. It still doesn't take anything away from the challenge of pointing the rover's antenna carefully and keeping it aimed at the Earth. So, back to that. From satsig.net:

1588983975318.png
The challenge, if one had 10 dB of margin, was to keep the antenna pointed within 17-20 degrees of Earth (below the bottom line). The column called "full beam width (deg" is the width of the nose of the beam pointed in the direction of the receiver. If the rover antenna was dead on point, it'd provide 24.97 dB gain for the signal. (first row). That would correspond to the 0 dB point of that relative plot in my first post. They would have been able to maintain decent video with an aim within +/- 10 deg, and maybe significantly more, depending on the amount of signal to noise margin.

Thanks for the memories - Cheers - Jon
 

Z.W. Wolf

Senior Member.
BTW, the camera used during the Apollo missions in question was not an NTSC color TV camera.
It was a field-sequential system. Mechanical TV with a rotating color filter disc.

This is why the blown off bits of insulation are multicolored in the Apollo 17 LM liftoff. The scan rate was 30 fps, but because the three different colors were scanned sequentially, the effective scan rate for each color is slow enough for us to see those fast moving bits in a sequence of the three different colors.

Source: https://youtu.be/9HQfauGJaTs
 
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Rend

New Member
@Jon Adams The 10 degrees figure definitely sounds right. The manual they quote in the video shows a cone of 10 degrees and they didn't even edit it out. But they are trying to claim 2.5 degrees is needed. I think the bullseye of the optical view finder is 2.5 degrees because the earth is 2 degrees, so it makes for easier aiming. It has nothing to do with the cone needing perfect accuracy within 2.5 degrees.

Here is the quote:

Thanks for the insight.
 

Jon Adams

New Member
Hey Rend -

You're welcome!

Thanks for reminding me of the "NASA website" quote. Mr. Burns is a fine sketch artist, but the Deep Space Network has no "85 meter dishes". In the early 70's, the largest single dish was 64 m, and there was one each at the three DSN complexes, located in the Mojave Desert 50 miles north of Barstow CA, the next in Tidbinbilla, west of Canberra ACT Australia, and the third at Robeldo, Spain, SW of Madrid.

It wasn't until the 80's that they were upgraded to 70 m dishes. This was done in preparation for the Voyager 1 and 2 flybys of Uranus and Neptune, part of the extended mission for those spacecraft. The change from 64 m to 70 m required a significant amount of engineering and construction work, all for a net increase in antenna gain of about 0.8 dB. That might not sound like much, and to most modern telecomm engineers they'd scoff at it, but that increase in gain (along with a series of other stuff, one for which I was cognizant) allowed a downlink data rate increase to something like 28 kbps at Uranus. Whoo-hoo!

Cheers - Jon
 

Z.W. Wolf

Senior Member.
Taken July 4, 1969, during a visit by Walter Cronkite and his CBS News film crew to the Goldstone Tracking Station near Barstow, CA in preparation for the Apollo 11 flight to the Moon. Walter and Tom Turnbull in front of the 85-foot diameter X-Y antenna used to communicate with the Apollo astronauts
C59-5-2l.jpg
 

Jon Adams

New Member
Ahh-Hah! The old feet vs meters problem. You solved that, @Z.W. Wolf

And that antenna is what's called the HA-DEC (Hour Angle / Declination) antenna. One axis is aligned parallel to the Earth's rotational axis like a lot of older telescopes. That way, it only requires precise movement on one axis. The original 26 m and 64/70 m dishes are AZ-EL (azimuth-elevation) and require coordinated movement on two axes to track distant spacecraft, which was a bit of a trick back in the day but is nothing nowadays - most telescopes are AZ-EL due to easier construction and lower loads on the bearings.

I suppose (but am not certain) that the term "X-Y" refers to the point that the antenna is fixed on the Z (parallel to Earth's rotational axis) direction, and so is free to move in the other two coordinates of the ECEF system. Never heard that design called that, though. Again, before my time.
 
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