Like gathering rainwater, a collecting dish is efficient, but everything outdoors gets wet in the rain, right?

So then... what sort of math is needed to consider the shape of say, the Taj Mahal (or Yankee Stadium, or anything large and stationary) and somehow use that structure as a telescope? Is this feasible? Would distributed computing help?

Like gathering rainwater, a collecting dish is efficient, but everything outdoors gets wet in the rain, right?

So then... what sort of math is needed to consider the shape of say, the Taj Mahal (or Yankee Stadium, or anything large and stationary) and somehow use that structure as a telescope? Is this feasible? Would distributed computing help?

It must be concave, either spherical or parabolic. Then you must cover it with some reflecting material and put a receiver in its focus. Better if it is steerable, like most telescopes.No use for monuments or buildings.

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Most points won't reflect much of anything for a non-concave shape, but there will always be SOME reflection in ALL directions. If you know the vectors (by ray tracing?), then you can extract a signal. No?

The equations that define dishes are nice and simple, but we could just as well use extremely complex formulas to define other objects... maybe...

Most points won't reflect much of anything for a non-concave shape, but there will always be SOME reflection in ALL directions. If you know the vectors (by ray tracing?), then you can extract a signal. No?

The equations that define dishes are nice and simple, but we could just as well use extremely complex formulas to define other objects... maybe...

Quite a wild idea indeed...

Note that your non-concave shape will spread out the signal far and wide and very thin. The whole idea of a concave reflector is to concentrate a weak signal into a very much stronger signal at some point of focus.


Now, if you did want to get really clever, you could coat the Taj Mahal with a carefully sculpted meta-material array with the exact inverse shaped mix of negative and positive refractive index to 'shape' any apparent shape you wish. However, I would expect the unavoidable phase shifts for any incident signals to play havoc for trying to detect anything. Also, the presently known meta-materials for controlling refractive index work only over a very narrow frequency range. Arecibo is far far simpler and more effective!

There's also highly explosive political issues that would undoubtedly arise from the people that revere the Taj Mahal for aspects other than use as a radio receiver!!


For further ideas, try looking up phased arrays, the ATA, and reverse time domain sound.

Keep searchin',
Martin

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An antenna type of reasonable efficiency that does not require a spherical or parabolic surface is the corner reflector. All that is required is two flat surfaces facing in the same direction, joined together on one side and forming an angle to one another of from around 60 to 90 degrees.(think of the shape of a book open at these angles) These are normally used in arrays, but if one could find a large existing metal structure with such angles and facing upward it might conceivably be used as the reflecting portion for many dipole antenna elements stationed along the line where the reflector focuses the incoming radio waves. Such a shape might well exist in a V-shaped section of a metal roof, which I believe is called, appropriately enough, a 'valley', by the roofing industry. Michael

It is a very clever idea, i like it!

Mankind does build lots of things that could hypothetically be used for a radio dish collecting surface.

Here is a good example, the Rose Bowl Stadium, Pasadena.



Now if you could evict all the six foot six, 350 pound NFL football players, then cover the seating area and pitch with aluminium foil, and hoist a receiving antenna up high into the middle of the stadium, then you have a pretty good radio telescope....LOL

Note; I'm not volunteering to evict the NFL football players, i would hate to be the one telling them their football stadium is now being used to look for ET...LOL

John.

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The Genesis spacecraft collected samples, minute but none the less glycine a basic amino acid was found in the samples. This is the one of the basic building blocks for life. There is some dispute that the glycine levels might be due to the aluminum construction of the spacecraft collection bin. But so far the glycine levels are only consistant with the samples themselves. These samples oriniginated from Comet Temple's dust trail. This is the same spacecraft that its chute failed to deploy and it impacted the nevada desert at 120 mph. There was an internet effort to exaimine the areogel collection medium for dust tracks and you went through a short schooling of was a trail of a speck of dust or forign material. The areogel had thousands of impacting trails most at microscopic levels and some larger. This is rather a strong case for the distribution of amino acids from comets.

Any isolated conducting surface may work as a receiving antenna but we also need to know from which direction the signal is being received. Directionality is usually the key constraint required of an antenna design; unless we are studying the 3K background radiation, I suppose. Once a direction is decided, then optimizing sensitivity puts a secondary constraint to the design.

Yet the idea of functionalizing our existing structures may have merit if they could be networked into an interferometric array. Such arrays have directionality by the manner in which they are connected up. The efficiency of any one node might be meager, but by having sufficient nodes might remedy that. The rub is the cost of networking a large number of individual (poor) antennas.

Fantasizing, if we could put solar collectors on each roof of a subdivision in Az that also served as a radio antenna, the array could gather electricity during the day and gather ET signals during the night. I suppose they could also study the Sun during the day. A whole subdivision of radio-astronomers!

Well here is a mad idea that is actually possible to implement!

Something that is very cheap to buy and is very common in every country in the world is home satellite dishes for picking up TV stations. Now generally when the TV guy installs one on your house, its facing in the general direction of the nearest local TV transmission tower.

Example for a common TV satellite dish on someones house;



Here's the cool idea;

Now you could take that home satellite dish and point it vertically toward the sky. This would be bad for picking up your TV stations but it would be good for picking up radio transmissions from space!

It might look a bit like this when pointed vertically;


Now one small home satellite dish is going to be very poor for picking up radio transmissions from space. But if you had hundreds of thousands of people doing this around the world, and they were all networked together, you would have one mighty large array. The total collecting surface of hundreds of home satellite dishes would be very large and together you could use this as one large radio telescope, far more powerful than the Arecibo telescope!

The principle would be similar to the way the ATA telescope works;



In theory, this could be set up as a type of distributed computing project like SETI@home. You could do it with modified BOINC software. People would have to be willing to turn their sat dish vertical to get the best coverage. You would also have to provide some kind of "Kit" that people would buy to allow them to huck-up their sat cable to their PC. You might also have to modify the detection cone of the dish as the detector on a home sat dish would be tuned to pick up TV frequencies and not the 1.42GHz hydrogen line.

You could also hypothetically modify home cooking wok's to work as sat dishes, if you were clever;



John.

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In Italy dishes point to geosynchronous satellites which broadcast TV programs. So any ET signal would be swamped with advertisement and the usual TV stuff.
Tullio

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In Italy dishes point to geosynchronous satellites which broadcast TV programs. So any ET signal would be swamped with advertisement and the usual TV stuff.
Tullio

True, but Arecibo and the ATA has to deal with that problem also! TV transmissions are restricted to certain bandwidths. In general, nobody other than ET should be transmitting at 1.42GHz. This frequency is usually quiet! But like SETI@home, RFI would have to be removed!

John.

Any isolated conducting surface may work as a receiving antenna but we also need to know from which direction the signal is being received. Directionality is usually the key constraint required of an antenna design; unless we are studying the 3K background radiation, I suppose. Once a direction is decided, then optimizing sensitivity puts a secondary constraint to the design.

Yet the idea of functionalizing our existing structures may have merit if they could be networked into an interferometric array. Such arrays have directionality by the manner in which they are connected up. The efficiency of any one node might be meager, but by having sufficient nodes might remedy that. The rub is the cost of networking a large number of individual (poor) antennas.

Fantasizing, if we could put solar collectors on each roof of a subdivision in Az that also served as a radio antenna, the array could gather electricity during the day and gather ET signals during the night. I suppose they could also study the Sun during the day. A whole subdivision of radio-astronomers!

This seems to grasp my idea the closest, although the other comments were good too.

I was wondering whether such computations are BOINC-able, or would the math be "exponentially complex".

As a military application, imagine having no radar dish to defend because your entire base is the radar. (Not that there is time to tease out feint signals from incoming rockets... but perhaps as a spy device...)

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I think the problem with a non-parabolic reflector would be phase shift?

At the frequencies that are being analysed the signals arriving from the different areas of the reflector would be way out of phase and effectively just be 'noise'.

But I wonder how big a dish would actually be needed?

Crazy idea, but could a fixed dish be build using another natural bowl someplace? It would not even need to be steerable as the Earths rotation and seasons would bring a fair portion of the sky into view over the year. The reciever is just suspended by cables at the fixed focal point. Just record everything and start analysing, building up a complete sky map of the visible area rather than the random bits of sky from piggy backing other observations.

Surely this sort of sky survey, scanning the whole area of sky every 6 months would yeild all sorts of interesting info for astronomers, not just SETI.

I guess cost depends on how big the dish needs to be to gather a usefull signal?

Ian

Arecibo has a spherical curve, not parabolic. Does anyone know how they deal with the phase shift problem? Michael

Arecibo has a spherical curve, not parabolic. Does anyone know how they deal with the phase shift problem? Michael

From Wikipedia; Arecibo Observatory

Construction began in the summer of 1960, with the official opening on November 1, 1963.[9] As the primary dish is spherical, its focus is along a line rather than at a single point (as would be the case for a parabolic reflector), thus complicated 'line feeds' had to be used to carry out observations. Each line feed covered a narrow frequency band (2-5% of the center frequency of the band) and a limited number of line feeds could be used at any one time, limiting the flexibility of the telescope.

Also, the azimuth arm on which receiving antennas sit is moveable to allow the telescope to track objects in the sky.

John.

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Thank you, John. Michael

I always thought a golf ball would make a pretty good space-based research telescope (the dimples, being the dish, would have to be somewhat larger, lol) - be a 300 m golf ball, but it'd cover a lot of territory, constantly... could make for a good waystation too, in it's own solar orbit.

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I always thought a golf ball would make a pretty good space-based research telescope (the dimples, being the dish, would have to be somewhat larger, lol) - be a 300 m golf ball, but it'd cover a lot of territory, constantly... could make for a good waystation too, in it's own solar orbit.

That sounds like a certain space station from Star Wars...

Keep searchin',
Martin

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See new freedom: Mageia Linux
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