I saw something in a movie once and was wondering if it would be possible to actually use the method for SETI.

Ok, the VLA (very large array) is a bunch of (relativly) small satelight dish's acting together as one giant radio telescope.

In the movie "the arrival" a person who works for a satelight television company links several customer's dishes together to do the same thing.

My question is, if you got the right reciever and people volunteered their Direct TV or other satelight dishes when they weren't being used, would it be possible to say, make a giant radio telescope that could span whole countries.

Given it would take a lot of time to program software, build the correct motors and stuff but, I figure if you put a series computer-controlled motors on every dish and then when the person was going to bed they just start a computer program and, presto the dish tracks into the system. Then after they want to watch TV again they just exit the program and the dish goes back to the correct position to watch TV.

Once again, it would take a ton of programming and a ton of money but, I was just wondering if, in theory it could work.

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It's not a bad idea and it is technically possible, but way to complex.

The dish itself is one thing but the LNB is another. All antenna would
need the same LNB, The same receiver tuned on the same frequency and
to be precisely pointed at the right direction wich would be assigned
by a central computer. Each station would need to "know" its exact
position (DGPS) and all the datas from those different receivers
would have travel through a dedicated data line providing exact same
transfer speed. Synchronisation is essential here and a "normal" internet
connexion would not be good enough. A VLA need to be extremely well tuned
and synchronized in order to work. Creating a VLA made of home intertainment
antennas and receivers link together via Internet doesn't seem to be a good
technical solution to me. It's not impossible, but it's not worth the effort
and investment. Way to complex and unreliable.

Regars
Marc

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As I said, I just wanted to see if it could be technically possible. I fully understand that for a household antenna would be very difficult to use. I just think it would be neatm if it could happen. However, I quite agree that the delat over a standard packet-transmission connection would be impossible. I mean look at someone trying to do voice over IP with a 56k connection! Perhaps a satelight signal could coordinate everything. But yes, I fully agree that it would be one heck of an undertaking.

What if, instead, a series of radio telescopes that use the bigger dishes that you had to buy for original satelight TV were hooked up witht he same antenna, the same reciever and were all equipped with some kind of GPS. I'm not saying as many as you would get with the small dishes today. I am saying if you spread say 100 dishes that are about 15-18 ft in diameter, about 10 times larger then normal dishes today. I do know that radio signals are on a very wide wavelength so a bigger dish has a better chance of catching something. I had heard that several people have made mini radio telescopes using these older, larger dishes and rigging them up with special recievers. So it might be easier to link systems together that are like that.

Even so, there would have to be a better way to link them then through the internet. It would have to be fiber optic or something which is impractical to lay over very large distances.

Hey, it sounds like science fiction simply because it would be very complex and expensive to do. However, look at the Apollo missions, or any space exploration mission to date. What would people 50 years ago say if we asked them to fund a project to send a robot to Mars? What would people 50 years before Apollo say if we asked for money to explore the moon? So someday if someone out there did want to try this, hopefully someone will fund them.

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Your idea is interesting, but the hardware won't support it. I used to maintain DirecTV distribution systems for retail electronics showrooms. First off, the LNB (the microwave receiver at the focus of the dish) is very specific to the Ku band. This would have to be replaced. The RG-6 coaxial cable that is typically installed is very noisy and doesn't transmit microwave frequencies; the signals are downconverted to a set of intermediate frequencies (IF) from 950-1450MHz (just above UHF channel 83) and even at that the losses are large. Basically all that would be used would be the reflector dish itself, which is relatively cheap and not that precise itself.

That being said, I saw a documentary recently that talked about what looked like a mini VLA as a pet project by some millionaire. It looked like it used the same reflectors as those used on C-band satellite, and was set up in an area about the size of a large back yard. Maybe a project like this could be done by a small group like a small college or even an astronomy club. Anyone have any ideas?

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> Your idea is interesting, but the hardware won't support it. I used to
> maintain DirecTV distribution systems for retail electronics showrooms. First
> off, the LNB (the microwave receiver at the focus of the dish) is very
> specific to the Ku band. This would have to be replaced. The RG-6 coaxial
> cable that is typically installed is very noisy and doesn't transmit microwave
> frequencies; the signals are downconverted to a set of intermediate
> frequencies (IF) from 950-1450MHz (just above UHF channel 83) and even at that
> the losses are large. Basically all that would be used would be the reflector
> dish itself, which is relatively cheap and not that precise itself.
>
> That being said, I saw a documentary recently that talked about what looked
> like a mini VLA as a pet project by some millionaire. It looked like it used
> the same reflectors as those used on C-band satellite, and was set up in an
> area about the size of a large back yard. Maybe a project like this could be
> done by a small group like a small college or even an astronomy club. Anyone
> have any ideas?

Exactly. The home entertainment sat receivers are not made for searching ET.
You have LNB's for Ku or C (or both) band but the problem is the same.
Transmission lines for the micro waves. Basicaly the LNB solution is to
create a IF in order to use a coaxial transmission line (flexible and cheap)
compare to waves guide as used for radar as example. Not only the signal loss
but also the receiver's noises is a problem. The electronic noise of a home
receiver is way to high for searching ET.

From the dish being to small for wide bandwith and proper gain, the LNB
"problem", the receiver's electronic noises, etc, our home satellite
receivers system is of no use for searching ET. One would have to change
everything and invest a lot of money to make it work.

I know that some have built their own array of antenna with proper
receivers etc, but I don't know much more on the subject.



I do know enough about radio though, receivers, EMF, etc to "guess"
that building a VLA involve some high level of science that we "I"
don't have a clue about.

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The following is a repost by Misfit. Although the following article has to do with Optical SETI, amateur telescopes, etc, the premise of the article is the same as your idea, CTLW83.



by Misfit
--------------------------------------------------------------------------------
If I remember correctly there was a future project for people with remotely controlled telescopes where everyone in the project would have their 'scopes aimed at the same star, effectively increasing viewing power and clarity, and their collective CPU power would be used for occlusion analysis. However, I cannot remember the name of this project.

EDIT: Ok I cant find anything on PlanetQuest's BOINC project but I did come across the future Optical Seti project. Most likely I may be confusing the two.

The PhotonStar Project will be a distributed human project to support Optical SETI. Individuals with a PC, an Internet connection, a Global Positioning System (GPS) receiver, and a telescope will be able to attach a laser detector to their telescope and use their PC to join their telescope with thousands of others to create a giant telescope. This giant telescope will be used to detect laser pulses from a specific star system at a specific time. See a paper about the project.


EDIT: The links didn't come through on the post like I had hoped; therefore, I have pasted the links below.

http://www.photonstar.org/

http://www.coseti.org/introcoseti.htm

http://www.coseti.org/4273-08p.htm

http://setiweb.ssl.berkeley.edu/forum_thread.php?id=6872

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From the Seti League

Dear Dr. SETI:
I have a small dish, only 6 feet in diameter. It is on an ALT-Azimuth mount. Is there any SETI work I can do with such a small unit?

The Doctor Responds:
Absolutely! Although the "standard" backyard SETI dish is ten to twelve feet in diameter, nobody really knows what size is sufficient to detect an alien signal, because we've never yet found one. My calculations on the website show that a 12 foot dish will achieve a sensitivity which we assume to be sufficient to intercept the sorts of signals which advanced societies can generate -- but their capabilities are purely a matter of conjecture. If a civilization can generate four times the power we are assuming, then instead of a twelve foot dish, it will be detectable on a six footer.
Can they generate that much power? Who knows?!?

That small dish will make a nice hydrogen-line radio telescope (see the Mini-Manual on our website for an overview of what else you'll need), will easily detect the strongest half-dozen natural astrophysical sources, and who's to say it might not some day receive an artifically generated signal from Beyond?

So, good luck in building up your SETI station. I hope you'll choose to join The SETI League, and register your station as part of our Project Argus all-sky survey.

> So, good luck in building up your SETI station. I hope you'll choose to join
> The SETI League, and register your station as part of our Project Argus
> all-sky survey.

The setup above is fascinating and not that expensive (For instance, I looked up the receiver's replacement model, the Icom 8500 and found it's about $1600). I also browsed the mini manual and it all sounds straightforward enough. From the diagram above I wondered about the 44kHz sample rate of the audio card. Transmitting in the low GHz range for the carrier usually indicates the need for a high data rate in the intelligence, but then I guess the initial goal isn't to be able to actually decode the signal, just look for something that stands out from the noise (A standard US television signal operates on a horizontal frequency of 15.75kHz, so the above sample rate would get less than three samples per line, not nearly enough to tell what the signal actually contained).

The other issue in the thread, however, is how to get more than one collector on the project. Assuming you solve the coordinated aiming and tracking, which doesn't seem to be too tricky with good mechanicals and a couple known points of reference in the sky for calibration, can more than one source increase signal gathering and cancel internal noise just by algebraically adding the signals? Is it something more tricky? In other words, how do the VLAs actually combine?

Wait a minute... Isn't the concavity of the dish going to restrict the receivable bandwidth and focal point of any incoming signal? Also, wouldn't you get signal interference from the satellite system that delivers to the dish?

It's been a while since I delved in the art of reception...

> Wait a minute... Isn't the concavity of the dish going to restrict the
> receivable bandwidth and focal point of any incoming signal? Also, wouldn't
> you get signal interference from the satellite system that delivers to the
> dish?
>
> It's been a while since I delved in the art of reception...


Yes the size of the dish is directly proportional to the bandwith. Well
the bandwith itself will be determine by the receiver, but if the dish
is too small (smaller gain) for the quantity of "information" you want to
receive, it's not going to work very well. The size of the dish is directly
proportional to his gain (dB) and his bandwith.

The shape of the dish (some are ovall) is because the satellite must "see"
it like if it was round shape for a better reception (line of sight angle).

It is certain that if you search for ET by pointing your antenna right on
any broadcast satellite it would not work very well, even if your receiver
is not tuned to one of that particular satellite frequency. This satellite
will be an obstacle for any incomming ET signal, the best is to point your
antenna on a clear path. You will sometimes have interference of all kind here
and then from airplanes, satellites, storm, birds, etc.

> The setup above is fascinating and not that expensive (For instance, I looked
> up the receiver's replacement model, the Icom 8500 and found it's about
> $1600). I also browsed the mini manual and it all sounds straightforward
> enough. From the diagram above I wondered about the 44kHz sample rate of the
> audio card. Transmitting in the low GHz range for the carrier usually
> indicates the need for a high data rate in the intelligence, but then I guess
> the initial goal isn't to be able to actually decode the signal, just look for
> something that stands out from the noise (A standard US television signal
> operates on a horizontal frequency of 15.75kHz, so the above sample rate would
> get less than three samples per line, not nearly enough to tell what the
> signal actually contained).
>
> The other issue in the thread, however, is how to get more than one collector
> on the project. Assuming you solve the coordinated aiming and tracking, which
> doesn't seem to be too tricky with good mechanicals and a couple known points
> of reference in the sky for calibration, can more than one source increase
> signal gathering and cancel internal noise just by algebraically adding the
> signals? Is it something more tricky? In other words, how do the VLAs
> actually combine?


Good point. I will read and try to understand how it works. There is got
to be some interresting link about VLAs principles. As for the diagram I
am also puzzled by the use of the audio as the source for a signal search.
SETI is looking for signal's gaussian, pulses, triplets not for any particular
modulated signal...Since we don't have a clue about what ET might be sending,
on wich mode should I set my receiver ? AM, FM, CW, SSB, etc.
The diagram is surely straight forward but I am missing the basic principles
of such a system.

My first guess would be that the audio output signal is just a tone, lets
say 1 KHz, that vary in amplitude proportinally to the RF signal intensity.
Then the software could detect a signal "pattern".

> modulated signal...Since we don't have a clue about what ET might be sending,
> on wich mode should I set my receiver ? AM, FM, CW, SSB, etc.
> The diagram is surely straight forward but I am missing the basic principles
> of such a system.

If I had to throw a guess at it, I'd say set the radio to FM. I'm not that good with radio theory, but I seem to remember my old professor said no matter how fancy we get, there are three types of modulation: amplitude, frequency, and phase modulation. Then she pointed out that phase modulation is just frequency modulation with a different control. As I recall, amplitude modulation causes sidebands that are the carrier+intelligence and carrier-intelligence. Unless the intelligence signal is just a steady tone, it should appear on a spectrum analyzer as if the sidebands move.

> If I had to throw a guess at it, I'd say set the radio to FM. I'm not that
> good with radio theory, but I seem to remember my old professor said no matter
> how fancy we get, there are three types of modulation: amplitude, frequency,
> and phase modulation. Then she pointed out that phase modulation is just
> frequency modulation with a different control. As I recall, amplitude
> modulation causes sidebands that are the carrier+intelligence and
> carrier-intelligence. Unless the intelligence signal is just a steady tone,
> it should appear on a spectrum analyzer as if the sidebands move.

Yes there is three main types of modulation and phase modulation is kind
of FM. But it's not the "problem".

What I don't understand in this diagram is how to detect a pattern in
(above) the noise (searching for Gaussians, spikes and triplets)
From the audio output of a receiver ?

What comes out of the audio output is a demodulated signal, or like you
call it the intelligence in the carrier, and that is not what we are looking
for when searching for ET. What we are looking for is a "carrier". An
electromagnetic radio signal, no matter if it is modulated or not.

What the computer needs in order to detect an intelligent radio signal or a
(pattern in the EM noise) is the strength of the signal, not what it could
contain or if and how it has been modulated.

In fact, the audio input port of the computer should be somehow connected
to the RF meter of the receiver for the computer to detect a pattern in
the noise (intelligent signal)

Since it is connected to the audio output of the receiver this one is
either on AM or (and better) the result of the LNA and receiver's mode
selection produce a fixed audio frequency that will vary in amplitude
proportionally to the strength of the RF signal. The computer software
then use the amplitute variation of this audio signal to detect an
intelligent RF signal.

Now I did not study the system and found how it really works, but what
I am saying is just in accord with the basics of radio principles, added
to how SETI is working. SETI is not looking for a modulated signal and
therefore their receivers do not attempt to demodulate anything, make it
AM or FM and cetera. They are looking at the signal strength.

I hope I made it readable...I agree that one need to understand how a
receiver works in order to understand the nuances.

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