TV audio is FM, actually. go to the low end of yer FM radio. around 87.7 will be the audio of channel 6 in your area. if you get to the high end, you might be able to pick up channel 8. dunno about channel 7, we only have 6 and 8 here.
Getting back to the OP, reverse engineering a TV may be further complicated if the aliens do not perceive light and sound as we do. As was said, I think the key would be that the aliens would realize that there is intelligent (ok, questionable) life in our direction (since no natural processes can create and transmit such a signal).
Certainly the strength of the signal would degrade by the inverse square law, but would the quality of the signal degrade over distance too? I assume so.
Well, yes and no, Phobos… Assuming that it’s travelling through vacuum, the quality of the signal itself would remain constant, but there would be increasing problems in trying to extract the information. There’s two effects here: First off, the signal-to-noise ratio for most detectors is about equal to the square root of the number of photons counted. This means that if they detect a hundred million photons, they’ll have 10,000 times as much signal as noise, which is easily adequate. On the other hand, if they only detect 100, the S/N ratio will be only 10, which is still acceptable, but starting to get kind of sloppy, and if they only get 4 photons, the noise will be half as loud as the signal, which really sucks.
The second problem is that the signal is trying to compete with background radiation. This is relatively uniform throughout the Universe, so ET will see the same amount of natural radiation at that frequency no matter how far away they are, but the signal is getting progressively weaker. The background adds a bunch of pure noise, without contributing any signal whatsoever, which can drive your S/N straight through the floor. This is one of the reasons that 22 cm is often chosen, because the Universe tends to be pretty quiet there, so it’s less of a problem, but there’s still some background.
derleth said:
we should broadcast loud and clear on hydrogen’s natural radiant frequency. It’s pretty quiet, and most intelligent civs would recognize hydrogen as being pretty fundamental, and its radiant frequency to be the place most others would broadcast at, simply because there is a low level of noise there.
if there’s not much noise on the signal, and most intelligent civilizations would use it, isn’t that a pretty good argument for no intelligent civs? or at least for non-communicative or isolationist civs?
i think everybody has missed an inportant point. Even if Mr. Alien had a REALLY big antenna and managed to pull the signal out of the noise (reception is generally pretty bad 50 miles out of the city, i imagine you need one hell of an antenna at 2*10^13 miles), and Mr. Alien could recognize that something intellegent created the signal, he still might have trouble. does anybody know how many channel 5’s are broadcasting in the US? i suspect it’s quite a few. it’s not a problem here since the channel 5 in your town gives a much stronger signal than the channel 5 200 miles away since it is so much closer. but to Mr. Alien, all the broadcast signals will be the same strength and will stomp all over each other. you may be tempted to ignore such concerns as Mr. Alien is clearly quite bright and can probably do a lot of neat things, but i don’t know if it would be at all possible to seperate the signals, even without the signal to noise problems he’s sure to have.
-Luckie
“A little mind is the inconsistancy of foolish hobgoblins.”
-what Emerson really meant to say
well, mr. alien will still have some time. it’ll still be awhile (iirc) before the first broadcast signals will reach anywhere. so they’ll get the i love lucys and mr. eds and what not. back in the day, there were only a few stations broadcasting. so there won’t be a glut of signals. but then again, i believe the signals were weaker. it’d probably be easier to get mexican radio back in the day, or maybe some radiation or a EMP from atomic bombs…
A couple of reasons. One, it is technically and financially feasable to detect signals over a broad range of frequencies but not to transmit them. Secondly, if we WERE transmitting like that we would not only disrupt most of the terrestrial communications, but we would NEVER hear anything over our own noise.
But suppose we were to decide to transmit only a modulated signal on the Hydrogen frequency carrier at the exclusion of all other possibilities? OK, why not? We just obtain the funding and start transmitting. The first (and terminal) problem is the funding. Then there is the power source. There are more.
No one is willing to allocate resources to something that cannot elicit a response until the signal goes outbound for X thousands of years and then takes the same amount of time
to return. Why not do it the easy way? SETI listens for something we might find tomorrow…a one-way signal.
Evolution and technology will eventually overtake our transmitted signal project. It would have to span thousands of years without interruption. But the reception process might get us some instant gratification.
If the rest of the galaxy is doing the same? Well, my expectation is that we will communicate with someone, someday. I like Arthur C. Clarke’s thought: when we develop sufficient technology to do so.
Could you clarify this for me? IIRC, this is the natural vibration frequency of hydrogen (the most abundant element in the universe). If most everything is singing at this frequency, then in what way is it quiet? 
thanks
I’m pretty sure that’s not true. I seem to recall we used the Arecibo telescope to beam a message to a globular cluster back in the 1970s. Why they picked that, I don’t know. It seemed like a bad idea to me–too far. The response time was at least 50,000 years, I think.
I’ll see if I can find the specifics of that message.
Here we go. We CAN send deliberate signals that could reach other stars. (Although I haven’t found anything to say whether or not folks in other solar systems would be able to pick up our media leakage at such a distance.)
http://www.spaceviews.com/1999/11/16b.html
"On November 16, 1974, at ceremonies to inaugurate a set of upgrades to the
Arecibo radio telescope in Puerto Rico, scientists transmitted a brief, simple
message in the direction of the cluster M13, some 25,000 light-years from the
Earth.
"The message, developed by Frank Drake, one of the pioneers in the Search
for Extraterrestrial Intelligence (SETI), and students and staff members at Cornell
University and Arecibo, was designed to be viewed as a two-dimensional image.
Encoded into that image was information about the structure and building blocks
of DNA, the location of Earth within our solar system, a stick figure representing a
human, and another figure representing the Arecibo radio telescope.
" However, the transmission was not a high-minded attempt to make contact
with extraterrestrials so much as a way of showing the power of the radio
transmitter added to the telescope during the upgrade. "It was strictly a symbolic
event, to show that we could do it," noted Donald Campbell, who was a research
associate at the observatory at the time and is now a professor of astronomy at
Cornell..."
It also mentions:
“…The Arecibo transmission had been the only deliberate attempt to send a
message beyond Earth until this past May, when a private company,
Houston-based Encounter 2001, used a radio telescope in the Ukraine to transmit
messages from members of the public who paid $14.95 each for the privilege of
sending a 30-word message to a set of several stars. The company plans similar
transmissions in 2000 and 2001.”
Also check out
http://www.setiweb.org/clinic/setimessage_.htm
for a facetious explanation of the message.
Quoth Phobos:
Yes, 22cm is one of the natural resonances of hydrogen: To be specific, it’s the hyperfine transition, for those chem or quantum types out there. This is actually the reason why it’s quiet: In addition to emitting at that frequency, hydrogen also absorbs at that frequency. As I understand it, energy is typically gained by absorbtion of the photons, and then lost by other methods, such as collisions, so less comes out than goes in. Of course, if conditions (particularly temperature and density) are right, it’s possible to have a cloud of hydrogen “singing” at this frequency, which is why it’s critically important to modulate the signal somehow to carry information.
As to why this frequency isn’t loud with alien transmissions: it’s generally considered to be the frequency of choice for first contacts, but once two civilizations know each other exist, they’d likely switch to some other frequency.
Worth reading, at least to see the cute Vic-20 like graphics. From this it looks like astronomers believe a directed narrowband 50,000 watt signal is detectable, but their aim is pretty crappy. The seti releases I was talking about in the OP had to do with broadband transmissions, not narrowband, my mistake. From the seti@home faq: