If an alien civilization recieved some of our radio or TV signals (I have in mind AM, FM, VHF and UHF, though if there’s something interesting to say about newfangled digital signals and other modern abominations, I’d be interested to hear about that as well) (and assuming at least that the aliens in this civilization are familiar with visual and auditory phenomena) would it be likely to be able to interpret the signals correctly into pictures and sounds?
-FrL-
They might not be able to decode them but they should be able to tell they are artificial rather than naturally occuring in outer space.
If their sight and hearing are like ours, they’ve probably invented a device similar to a cathode ray tube TV. They’re probably able to decode analogue TV and radio signals, but probably not digital.
That’s a huge leap. We played with multiple technologies before settling on CRTs.
They’d probably be unable to decode analog video signals. Our analog standards are intimately based on everything from the precise aspect ratio of the screen to the set of colors we chose (and the fact we chose colors after we had a working black-and-white system) to the fact we settled on AC for long-range power distribution to the precise frequency used in those AC lines. Even human-made analog TVs are limited to what regions they can decode signals from.
AM and FM radio signals, on the other hand, should be trivial to decode for aliens. An analog waveform described by the varying amplitude (AM) or frequency (FM) of the carrier wave. The only catch would be if the aliens don’t have any sensory apparatus for detecting airborne compression waves. And of course there’s the whole translating Ludacris tracks into Fq’thuanese problem, but that’s a separate issue.
I disagree. To start, CRTs are just a practical device which have nothing to do with the structure of the information. An analog TV signal is highly structured both in the time and the frequency domains. Put it on a scope and you can clearly see repetitive patterns in the luminance signal. You can easily see low repetition (frames and fields) as well as higher rate repetition (lines). This would be quite trivial to decypher for any information analyst. Give it to an information analyst and it would trivial to figure out the structure of the luminance information. This is true of all analog TV systems.
Having solved that, the chroma information might be a tad more complex and this depends on the system. NTSC would probably be simpler to figure out than PAL but, having the luminance signal decoded, the chroma signals would not be too dificult even though NTSC uses a subcarrier and PAL uses a burst. of course, they may not know what colors our eyes are sensitive to so they might end up with a totally mistaken spectrum. Even the luminance signal could be interpreted negatively so that the luminance of the picture would be reversed.
Then you do not need a CRT at all, only a device that will convert the signal to a graphic. CRTs were invented first because the computers and raster devices we have today were not available but if you already have a raster display nobody would “invent” the CRT.
Something like the NSA would figure out a TV signal in no time flat.
Unless their vision was way different than ours I think this problem would be even easier to solve than the others.
If you want to “model” the color of anything, IIRC you need 3 color “channels” to do it reasonably proper. Two wont cut it, and more than 3 is overkill.
Looking at the data and knowing this themselves, as well as some other possible indicators indicators in the data, 3 color channels would probably be one their early guesses.
Now, all they need to figure out is which color is which. There arent too many combinations to have to look at.
With any luck they catch some outdoorish video.
Snow/ice is typically going to be white. Clear sky is generally blue, as well as deep water. Seems a fair chance that green is a typicall plant color. Lava reddish. And probably a bunch of other things with colors that are nearly universal, or at least fairly common. All it would take is one (or maybe a small number) of these and they could decode the color scheme to a reasonable approximation.
Also, it seems like decoding the data for the visual video (as opposed to the colors) shouldn’t be too hard either. If you don’t decode it right, its gonna look really odd. Now if you get into sophisticated digital data compression schemes, it might well turn into a needle in a haystack scenario for finding the right decoding.
But once you find the right decoding, it should be fairly obvious you’ve found it, or something reasonably close.
Of course if the alien lifestyle and lifeforms bear almost no resemblance to our own then thats probably a whole nother story.
And if they happen to get video of the Blair Witch Project or Clover Field they will just be SOL 
And if they get Tom Cruise’s infamous interview on Oprah, they will probably just nuke us from orbit to be sure.
I’m not entirely sure about this. I think that the number of primary colors is species-relative, depending on what (and how many) different kinds of receptors that species has in its eyes. And if I’m remembering that correctly, then it might not be so natural to think a visual information channel should have three color channels.
-FrL-
I’m not so sure that NTSC color information would be so easy for the aliens to decode, or even notice. The color subcarrier band is completely contained inside the band used for luminance, and the encoding is designed precisely so it will be “ignored” by a black and white receiver. A sensible color television standard — one that wasn’t burdened with backward compatibility, or constrained by a spectrum allocation that was already over and done — would have put the color information in separate bands.
Assuming the aliens noticed that odd bit of noise centered on 3.58 MHz (the modulated I and Q color signals), they might assume it’s interference from a separate transmission.
Well, yes and no IMHO.
If you wanted REALLY high def color you would have thousands of color channels or even more.
But, as a bare minimum, IIRC you NEED three. Three isnt perfect, but its good enough to get you in the right color ballpark. That isnt a biology thing, its a math and physics thing. Their scientist should be able to figure that out.
Take that bit of info along with pictures of stuff, like blue water, that both parties have in common and have some idea of what its SUPPOSED to look like to their eyes and they should be able to find the right combination.
That would be the case EVEN if their vision was fairly different from ours, because if they don’t decode it right, it won’t look remotely correct to their eyes.
Reasonable biology and physics places limits on the range of colors organisms can see.
Just my two probably not correct cents here
Color representation is a biology thing. The spectrum put out by a TV for a given image is very different from the live seen. Light in the real world is a continuous spectrum of frequencies. With a red green blue display you cannot get even close to most possible spectrums. It only looks good to us because we have only three receptors. So the two spectrums stimulate our receptors in pretty much the same way.
I’ve written software that decodes analog video signals. Just from looking at the waveforms, you can easily pick out the horizontal sync pulse, vertical sync pulse, video data and reference levels. I’ve never had to deal with color, just black and white. The hard part is dealing with noise and other impairments.
Modern digital systems are much more complex. They use complicated modulation systems, multiple layers of error correction coding and sophisticated data compression algorithms. You would need something like the alien equivalent of the NSA to reverse engineer everything.
Well, you have to define “close” and “good”
Imagine an x - y coordinate system.
You can be in positive X and positive Y, positive X and negative Y, negative X and negative Y, or negative X and positve Y.
Now imagine us humans have a rather poor sense of position.
You just get us in the right quadrant and its "good’ enough for us to tell us where we are.
Now some other species has a great sense of position in comparision to us (an analogy to them have much more than just 3 color receptors).
If they decode our stuff right, they will be in the right quadrant but with poor precision compared to what they are used to.
If they decode it wrong they won’t even be in the RIGHT quadrant.
I guess the question is…could they even tell if they are in the right quadrant (color)?
I’d still say if you had a common reference color/colors, like lava or blue water, that while they might not be particularly impressed with the color fidelity compared to their sophisticated color vision, they could likely tell the right decoding versus the wrong one.
Another way to look at this is: if they have “enough” in “common” with us sensory and environment wise, they should IMHO be able to at least be able to tell when they have the right decoding video and color wise. If they don’t they probably can’t, but in that case we probably could not relate if we were in the same room so to speak, regardless of decoding issues.
There are still locational radio beacons that broadcast continuously in Morse code. If our aliens happened to have a receiver set to, say, 110-115 Mhz, they might pick up the signal from one of those beacons. They might not be able to decode the dots and dashes, but they would quickly realize that the pattern was repeating and not naturally occuring.
How would you determine that it was not naturally occuring, especially if it was continuously repeating? Pulsars were once thought to be signals from Little Green Men because of their regularity.
A species with four different color receptors would say that you NEED four, and one with only two different color receptors would insist that two was enough. In actual practice, the more different receptors, the better, so long as you have room on the retina for all of them, and you’d really like to be able to distinguish all continuous spectral (though it’s really hard to make a sensor that can do that).
Snow is whatever color the light shining on it is-- They’d be much better served by seeing a picture of the Sun on TV (especially if they can see where the signals came from, and see our Sun’s spectrum themselves). Sky colors will vary somewhat based on local conditions, but they’re likely to be able to observe our planet, too (we’re closer technologically to being able to analyze Earth-like atmospheres than we are to picking up incidental radio transmissions from them). If they can figure out that the oozy stuff they see in some shows is lava, then they’ll know to fit a blackbody to it, but not necessarily what temperature, and green is the absolute last color I’d expect for alien plants (it’s a quirk of evolution that a green pigment happened to predominate on Earth).
Lets back this up a bit.
Could the aliens tell how many color channels there were supposed to be regardless of how many they have/use?
If they got the right number, could they make reasonable guesses as to what a/each channel represented spectrum wise?
Once they have done that, could they correctly assign the “right” color to the right channel?
My opinion is probably, probably and YES (mostly).
Let assume we send them a three channel color video with lots of video of images in nature.
They figure out that there are three channels.
They study the images and make assumptions.
They then send the video back to us and tell us the assumptions they made regarding the spectrum distribution of the channels is and what channels correspond to what colors and what those colors represent.
They rank their answers/estimates of various combinations from most likely to least likely.
My WAG is that we would tend to agree that their best guesses are what we would rank as the “most correct” video recreations of “our world” and their worst would be our worst.
Now, thats not to say they got it perfectly right, but they wouldnt be totally wrong either.
Pretty easily-- the same way stupid Earthlings figured it out, with science. 
One thing to remember in this discussion.
Simple communication requires simple decoding. Likewise, complex communication requires complex decoding.
We tend to assume that something even as simple as Morse code would be too hard for an utterly alien intelligence to decipher. But any species capable of intercepting Morse code would be capable of determining that it is a form of communication, simply by employing the pattern recognition that would be required by technology required to intercept Morse code.
We assume the worst-case scenario: these aliens all look at their world through sonar, or in the infrared spectrum. Well, guess what? So do human beings, all the time. Just not with our own biological eyes.
Communication is an information problem. Information is a math problem. Math is universal. That does not mean the aliens would understand what they’re looking at, or necessarily assemble the pattern in a way that matches what we see, or even be able to see what we see. But if they can receive the message, they will understand that it is a message.
Now, the flip side of course is that the more complex the form of communication (say, directed laser communications), the less likely that communication will be intercepted and deciphered. But most anything “simpler” would fall into the technological capacity of a species to intercept and appreciate as communication.
Of course, I’ll caveat this with the qualifier that we’re talking electronic communications here-- the mastery of advanced electronic communications will require by default the ability to appreciate simpler electronic communications. That doesn’t mean, of course, that just because humans on the radio can talk to aliens on the radio that radio-employing humans can talk to pheremone-employing bees-- the technology can not be dissimilar in nature. Electronics employs mathematical principles far less complex than biological principles.
Basically, the example is this: you might not have been able to teach the smartest Pharaoh in ancient Egyptians to understand radio, but you can teach the youngest child in kindergarten today to appreciate that heiroglyphics is a language. It’s a far cry from understanding that heiroglyphics is a language to actually understanding it, but technology has a way of becoming all-inclusive, and especially electronics technology.
I’m not as optomistic. First, this all depends on the decoder already knowing that this is a TV signal (i.e. sequence of still images which give the illusion of continous motion). For a random bug eyed monster, I’m not so sure this is a good assumption. The BEMs might think that a repeated signal broadcast across a wide area from different antennas is a readout of the Hive Queen’s pheremone levels or something.
What if the BEMs didn’t communicate by sound? There’s no reason they’d think that we’d be broadcasting a signal meant to be turned into compression waves in the atmosphere, so the chance of decoding is pretty small (not that it would mean anything much to them anyway).