Detection Distance

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Profile Somebody who doesn't support SETI anymore

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Message 1743238 - Posted: 19 Nov 2015, 0:36:55 UTC

I'm sorry if this has already been asked somewhere else.

I was wondering about how far out SETI can detect an alien signal.
How far out can we detect a signal if:
-the alien race is at our current tech level?
-the alien race is 50-100 years more advanced than us?
-is very advanced and is willing to dedicate a lot of energy to transmitting a 'welcome' signal? For example, if the output of a whole dyson sphere is used to power the transmitter.
Thanks
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Message 1743242 - Posted: 19 Nov 2015, 1:24:40 UTC - in response to Message 1743238.  
Last modified: 19 Nov 2015, 1:36:24 UTC

There is no practical limit out to many many light years if an intentional, high powered focused beam of laser or microwave energy hits one of our large antennas. Beam dispersion of lasers can be quite narrow.

As for eaves dropping on a civilization with TV stations and radars perhaps up to the megawatt range; I have heard estimates of a few light years out to maybe 100. It depends on the gain of our antenna, the received power, signal to noise ratio and other factors.
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Message 1743245 - Posted: 19 Nov 2015, 1:41:42 UTC

I have read about an estimate of 1,500 light years.
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Message 1743272 - Posted: 19 Nov 2015, 4:47:20 UTC - in response to Message 1743245.  

I have read about an estimate of 1,500 light years.

That is a very liberal estimate. I have seen estimates of the range of normal radio and TV signals as low as 100 LY.

But you have to remember, a signal from 1,500 LY out has taken 1,500 years to get hear and a reply another 1,500 years.
Bob DeWoody

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Message 1743278 - Posted: 19 Nov 2015, 6:01:08 UTC

Two different answers:
First detect many of the sources that are observed are thousands of light years away, if not more;
Second decode, much shorter and will depend on the modulation techniques employed. A simple low frequency on/off pulse (similar to Morse code) the detect and decode distances are almost identical, while a complex frequency/phase modulation one is down to a few hundred light years, possibly up to a couple of thousand.

Currently SETI@Home is only working to detect not decode.
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Message 1743292 - Posted: 19 Nov 2015, 9:06:20 UTC - in response to Message 1743278.  
Last modified: 19 Nov 2015, 9:06:56 UTC

Currently SETI@Home is only working to detect not decode.

well, it's a "sad story here", that the SETi@home scientist didn't put a scientific paper about a hearing distance for:
- Arecibo
- (a new) GBT

so we can know from how far these telescopes can hear:
- normal FM/AM radio-station
- analog TV signal
- digital TV signal
- digital directed satellite TV (upload to satellite)
- DSN signal to a probe/rover
- Arecibo radar
- military radar used for NEO/NASA

maybe that's a nice thesis from someones science papers?!
(I'd be happy to make it, but...I'm not on Berkley & don't have access to all these data!)
;)

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Message 1743294 - Posted: 19 Nov 2015, 9:56:45 UTC - in response to Message 1743292.  
Last modified: 19 Nov 2015, 10:12:56 UTC

In all of these types of discussions it is vitally important to keep in mind important and distinctive situations.

1. Eaves dropping on a civilization that is similar to ours by listening to TV, Radio, Radar etc . Assuming that if there were such a civilization nearby that they would have these types of electronic emissions. This type of radiation may not be detectable very far out--perhaps as little as a very few light years--far less than 100. Since we have been listening for 50 years we may conclude that there is not a civilization that mimics our state of development that is within eaves dropping distance. This probably implies --no earth-like planet with such a civilization out to 50 light-years or so with this state of development.

2. Detecting and decoding a high-powered, focused, intentional beam that has low dispersion that happens to hit us as it is slewed around--they would not be likely to know that we are here. These distances can be much larger.

3. Possible (but not likely in my opinion) civilizations that can command enormous amounts of energy and are providing a signaling beacon such as turning on and off an entire star's worth of energy.

4. A true Earth-like planet that does not broadcast but is visible to our next generations of space or ground based telescopes. Hopefully by then we could say with certainty that they contain life of some form by analyzing their atmosphere spectrum from afar.

So I suspect that we have a very broad range of detection distances that may cover a good part of the Milky Way and possibly beyond depending on the activities of the hoped-for advanced civilization.

Who knows--maybe in Alpha Centauri a civilization may just now be putting up their first TV tower. They may be only 25 trillion miles away--maybe we could hear them ??. We must be ready to decode any and every promising reception for non-random cosmic noise and phenomena.
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Message 1743299 - Posted: 19 Nov 2015, 10:33:20 UTC

to WR

1. well, until someone does a calcs, we simply don't know! how come someone didn't already made it?! 'cause if SETi@home is good for only 30-50LY, then we just need to check those stars...there aren't so many of them within that distance... :/

2. I'm not sure if SETi@home can detect something like we use for beamed radiation (radars for NEOs, Arecibo radar or DSN transmissions)?! again, someone with access to enough data should make some calcs & put it on paper...so we can see how far do we can hear, until all disappears in common background noise...

3. are you saying something like K3 & beyond civ?! not sure if those even exist...& how would that be possible?! :/

4. those have been done up to 128LY, check article here:
http://www.livescience.com/28218-planet-exploration-studying-chemicals-light-nsf-ria.html
or even 500LY:
http://usatoday30.usatoday.com/tech/columnist/aprilholladay/2006-09-25-measuring-planets_x.htm
other examples:
http://hubblesite.org/hubble_discoveries/discovering_planets_beyond/alien-atmospheres

decode is not a problem...finding it is! ;)

still think that SETi@home should make some adjustments in way of science papers...& show how far we can detects sthg similar to us...so we can know what to expect!
all other is just "waste of time & energy"...
;)

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Message 1743311 - Posted: 19 Nov 2015, 12:36:52 UTC
Last modified: 19 Nov 2015, 13:20:24 UTC

Anyway, I may not beat Rob Smith on total credit, but in fact you are giving me a quite good hint here.

I suppose modulation principles can not be done by nature itself, by means of the random signals that constantly are being detected.

Modulation is a quite difficult subject and even a high level book about data communication in my possession only offers a couple of paragraphs to the subject.

As far as I happen to know, there are at least three different modulation techniques, or principles.

One of them is Frequency Modulation, another is Amplitude Modulation.

https://en.wikipedia.org/wiki/Modulation

https://en.wikipedia.org/wiki/Sine_wave

(by means of searching Google on the word "sinusoidal")

Those people behind the gaussian function of the Seti@home client apparently knew that a radio signal being analogly detected and therefore being a wave, most likely would not be a pure sinusoidal or sine wave, but rather a composite of several different waves, each one possibly, or theoretically translatable into a given score, possibly a gaussian score, based on the corresponding binary values such a translation would be corresponding to.

Using the Decimal or degree unit of Windows Calculator, sin(0) = 0 and sin(90) = 1

sin(45) = 1/(sqrt(2)) (or roughly 0,70710678118654752440084436210485)

sin(60) = 1/(sqrt(0,75)) (or roughly 0,86602540378443864676372317075294)

And so on.

Add this to the power as well as chi square (fit) of a given gaussian score and it becomes easy to see the complexity.

Still time to edit, we should not forget the important display in the graphics showing the sentence "Computing Fast Fourier Transform (FFT).

This computational process is happening all the time while a given task is running.

I may add some more to this a little later on.
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Message 1743351 - Posted: 19 Nov 2015, 16:26:07 UTC

A conservative estimate states that two radio telescopes like Arecibo could communicate with one another over a distance of about 10 000 light years.
Responsible scientists, including Dr. Frank Drake, have noted that even a small receiver placed at one of the gravitational focal points of the Sun, starting at about 550 astronomical units and working outward, could hear even very modest power transmitters, throughout the galaxy. I'd like to think we could manage that within 100 years from today.
The total energy of a star, converted to narrow-band radio waves could apparently be heard over wide intergalactic distances, and omnidirectionally, at least within the galaxy.
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Message 1743354 - Posted: 19 Nov 2015, 16:36:39 UTC

I remember reading that multibeam was good to about 100 light years, and astropulse was good to about 50,000 light years. I could be wrong though.

Steve
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Message 1743388 - Posted: 19 Nov 2015, 20:02:08 UTC

In my opinion if they are further away than 100LY then finding them will be a nice paragraph in the history books and interesting to know but otherwise utterly useless.
Bob DeWoody

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Message 1743548 - Posted: 20 Nov 2015, 7:13:11 UTC - in response to Message 1743351.  
Last modified: 20 Nov 2015, 7:18:43 UTC

A conservative estimate states that two radio telescopes like Arecibo could communicate with one another over a distance of about 10 000 light years.
Responsible scientists, including Dr. Frank Drake, have noted that even a small receiver placed at one of the gravitational focal points of the Sun, starting at about 550 astronomical units and working outward, could hear even very modest power transmitters, throughout the galaxy. I'd like to think we could manage that within 100 years from today.
The total energy of a star, converted to narrow-band radio waves could apparently be heard over wide intergalactic distances, and omnidirectionally, at least within the galaxy.

can you provide some links to articles, please?! ;)

I remember reading that multibeam was good to about 100 light years, and astropulse was good to about 50,000 light years. I could be wrong though.

Steve

so we can check only our small neighborhood with MultiBeam...which actually searches for SETi@home! :/

to make you a picture:

all these system already got a signal from us, almost...& there aren't many systems within a 100LY!

list:
http://www.solstation.com/stars.htm
http://www.solstation.com/stars3/100-as.htm
;)

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Message 1743644 - Posted: 20 Nov 2015, 19:01:56 UTC - in response to Message 1743548.  
Last modified: 20 Nov 2015, 19:05:20 UTC

The first link is for the distance the Arecibo facility could communicate with a similar one.
The second discusses the use of the Sun as a gravitational lens for super-magnified SETI signals.

http://www.setileague.org/articles/oseti.htm

http://www.space.com/9666-sun-gravity-tapped-call.html
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Message 1743646 - Posted: 20 Nov 2015, 19:19:19 UTC - in response to Message 1743644.  

The first link is for the distance the Arecibo facility could communicate with a similar one.
The second discusses the use of the Sun as a gravitational lens for super-magnified SETI signals.

http://www.setileague.org/articles/oseti.htm

http://www.space.com/9666-sun-gravity-tapped-call.html

The problem as I see it, is that the antenna would have to be pointing at each other for the whole period. And that is complicated by the fact that both ends probably are on spinning wobbling planets. If were to detect such a signal it could be years before the two antenna are aligned again.
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Message 1743650 - Posted: 20 Nov 2015, 19:48:50 UTC

...Not to mention the propagation time for the round trip, which would be double the number of light years away the "target" planet is, so at least 6 years, if not hundreds....
Bob Smith
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Message 1743673 - Posted: 20 Nov 2015, 22:14:42 UTC - in response to Message 1743646.  
Last modified: 20 Nov 2015, 22:15:22 UTC

The first link is for the distance the Arecibo facility could communicate with a similar one.
The second discusses the use of the Sun as a gravitational lens for super-magnified SETI signals.

http://www.setileague.org/articles/oseti.htm

http://www.space.com/9666-sun-gravity-tapped-call.html

The problem as I see it, is that the antenna would have to be pointing at each other for the whole period. And that is complicated by the fact that both ends probably are on spinning wobbling planets. If were to detect such a signal it could be years before the two antenna are aligned again.


If we detected a signal, it's reasonable to suppose that the same location in space would thereafter be monitored extensively. That would increase the chances of our hearing another signal from the same source.
Perhaps wide areas of the galaxy are swept by the signal repeatedly, at a regular rate of repetition. Alternately, if we happened to be directly between two communicating civilizations, repeated signals at any time seem a reasonable possibility.
Since we don't know the strength or beam width of the signal in advance, we can't know how 'directly' the two antennas would need to be pointed at each other to produce an intelligible signal.
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Message 1743730 - Posted: 21 Nov 2015, 1:17:33 UTC

I have participated nearly from the start but now that I am fifteen years older I have come to realise that detection of ET by us is an extreme longshot. And yet I continue to participate and will do so until I die or the project shuts down. I just think it is all worth the effort no matter how long the odds.
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Message 1743817 - Posted: 21 Nov 2015, 9:50:14 UTC - in response to Message 1743644.  
Last modified: 21 Nov 2015, 10:02:01 UTC

The first link is for the distance the Arecibo facility could communicate with a similar one.
The second discusses the use of the Sun as a gravitational lens for super-magnified SETI signals.

http://www.setileague.org/articles/oseti.htm

http://www.space.com/9666-sun-gravity-tapped-call.html

yeah, great texts...

but, we (currently in Croatia) the most powerful DBT is 5kW...that is 1/200 in less power than a 1MW in that calculation...& it's also not a Arecibo transmitter!
given that power is 1/200 less than transmitter of 1MW for a distance of 10.000ly...that gives me the distance (if I'm not mistaken) of 50ly! & antenna broadcasting a DBT signal is not as large as Arecibo, so it has a much less transmitter power broadcasting!

so given those figures, we can probably hear with SETi@home distances up to 50ly (maybe even 100ly) for a similar radio-transmissions used in DBT or DBR...
:(

please, correct me if I'm wrong...but those are SMALL figures!
maybe SETi@home should be re-written to include something like DSN signals, radar imaging of asteroids like we use Arecibo for or NORAD uses for NEO NASA project... :/

The first link is for the distance the Arecibo facility could communicate with a similar one.
The second discusses the use of the Sun as a gravitational lens for super-magnified SETI signals.

http://www.setileague.org/articles/oseti.htm

http://www.space.com/9666-sun-gravity-tapped-call.html

The problem as I see it, is that the antenna would have to be pointing at each other for the whole period. And that is complicated by the fact that both ends probably are on spinning wobbling planets. If were to detect such a signal it could be years before the two antenna are aligned again.

actually, that's not a problem...'cause Arecibo has a fixed antenna, but moveable receiver...so Arecibo can cover only part of the sky:
https://purcell.ssl.berkeley.edu/~korpela/sethi_poster/

but also soon a GBT will arrive to cover the rest of the northern sky!

unfortunately, we don't see or hear anything about under equatorial 0°... :(


edit: also, we have ATA for use with SETI organisation (which is not part of SETi@home)...but we also have a some other radio-telescopes around a World for use, like LOFAR (http://www.astronomynow.com/news/n1004/20lofar/)... ;)

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Message 1744001 - Posted: 22 Nov 2015, 8:23:07 UTC

Seti is hamstrung because it does not have it's own receiver or dish. It has to piggy back on others data. They have no control over where the dish is pointing, nor the power of the dish, or the distance that it can listen into. They simply have to make do with what they get, and they are lucky to get even that.

But there is at present an increasing world interest in the whole Seti thing which is great to see, better things may yet happen.
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