While casting around for reasons to crunch for SETI, it occured to me that the most likely type of signal that we could detect from an alien civilization is the radar that they would use to detect approaching asteroids, comets or even alien spaceships if they have hostile neighbors. That type of emission would be as high-power as the civilization could afford, to give maximum time to deflect the object, and would need to be scanned in all directions, thereby eventually being directed at earth. It would likely be a pulsed, fairly narrow beam signal on whatever frequency works best for that purpose.

A search for such signals does not require the detection of communication signals, which are not likely to be as high-powered as radar, and also not likely to be directed at us (and a non-directional signal would provide even less power to us). Furthermore, the waveform of a radar pulse would be fairly simple, and eases the task of discerning whether it represents intelligence or is merely noise. It also avoids the requirement that an alien society spend a lot of money for building a high-powered beacon to let us know that they are there, which I think is unlikely at best.

So the question is, which of the SETI approaches, MultiBeam or Astropulse, is best suited to detect a long-range radar signal? It would seem at first glance to be Astropulse, but I am not at all familiar with the details of either, so maybe someone who is could comment on that. Also a consideration of whether the present SETI receivers cover a suitable frequency range would be useful. Finally, could a better approach be developed with the foregoing in mind?

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... So the question is, which of the SETI approaches, MultiBeam or Astropulse, is best suited to detect a long-range radar signal? It would seem at first glance to be Astropulse, but I am not at all familiar with the details of either, so maybe someone who is could comment on that. Also a consideration of whether the present SETI receivers cover a suitable frequency range would be useful. Finally, could a better approach be developed with the foregoing in mind?

So far, unfortunately, none.

We are searching in what is called the "water hole" area of the spectrum. Whereas you can expect radar to utilize other parts of the spectrum and so not be seen by our present searches. The Allen Array could be funded and expanded to search more widely. The under construction SKA could also search more widely if that was funded for that task. Otherwise, s@h, The Planetary Society, and SETI Institute are all individually all at vanishingly low cost the only searches we have.


With our present resource and tech available, we have to assume that whatever ET is deliberately trying to second-guess what we can do so as to make the search easy and obvious for us. The diagram in my profile should give a few clues...

Meanwhile, there is also a lot of other science being done due to various other unexpected things to be found in the data.


As a bonus, we may determine whether or not we are alone at this time in our galaxy or even for the visible universe.

Keep searchin',
Martin

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Meanwhile, there is also a lot of other science being done due to various other unexpected things to be found in the data.

Thanks, that was all quite informative.

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They would not use radar to look for asteroids. Like us they would be using Telescopes to passively search the heavens. We could detect their airport radar at some fairly large distances --Maybe 100 light-years. These would be of the order of a few million watts in power.

So Far we have found none--or so I presume.

They would not use radar to look for asteroids. Like us they would be using Telescopes to passively search the heavens.

That is only because an asteroid has not taken out a city yet. We miss a lot with telescopes. In 100 years, it will be different.

We could detect their airport radar at some fairly large distances --Maybe 100 light-years. These would be of the order of a few million watts in power.

I doubt anywhere near that on the frequencies that SETI detects, and airport radar is directed in only one direction anyway. Perhaps most importantly, airport radar will only be around for a short time, before GPS or something else takes its place (and the place of planes for that matter). You need to find a technology that they will need for thousands, if not millions of years to have any hope of detecting them in the short distances and time spans that we cover.

I doubt anywhere near that on the frequencies that SETI detects.

Well then, we should start looking at these frequencies. This is especially true that if they are as ignorant as us to not broadcast any "We Are Here" message; this may be the only way to detect them if they do in fact exist.

Well then, we should start looking at these frequencies.

Please lobby Congress for a few million for that purpose. Lots of luck.

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Deep in the SETI@Home description

SETI@home covers a 2.5 MHz bandwidth centered at the 1420 MHz Hydrogen line from each of the 14 ALFA receivers

That was dated 2011 so not sure if it is still true.

I do remember the original purpose of SETI@Home was to look where other SETI projects were not already looking.

Also to be looking for a purposely created signal, hence the 1420Mhz hydrogen line, rather than RF signals from radar TV, etc.

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nanu

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Never engage stupid people at their level, they then have the home court advantage.....

One of my issues with all SETI searches, including this one, is the narrow band chosen to search. The thinking behind the searches is seriously flawed. We search the "water hole" because of various reasons, but the fact is here on Earth we do not transmit on these frequencies for the most part for the very reasons we search on them...all the background noise from natural emissions..

Military Radar can use up to 10GHz or beyond, civilian RADAR tends to use the 2.5GHz to around 5GHz range so there is clearly a disconnect between what we "think" an alien civilisation may do and what we do ourselves. Our communications deliberatly avoid the frequencies that S@H searches, although some are still in the "water hole" boundaries (hence satellite TV and some DTB signals breaking up in bad weather), but these arre directed signal that do not "leak out" in the conventional sense, and as our technology improves this targeted communications will become more dominant and that less detectable outside the planet.

I take part in the hope that I am thinking too much and therefore wrong, but I know in my heart I am not, thus I do not believe that S@H will be successful in the way it is currently working.

Personally, I would spend a serious amount of time doing a targeted search at all the stellar systems that have confirmed planetary systems. This is a small chance of success, but small chance is better than no chance and I would strongly suggest this search expand the frequency range to stretch from 500MHz to 10GHz.

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I do not believe that S@H will be successful in the way it is currently working.

I agree with you and hope that we are both wrong. I have ranted that we have been listening for 50 years--some efforts have spanned other frequencies. It is most likely however that there is no planet within 50-100 light years from us that has a civilization--at least one that has advanced to use broadcast TV and radar.

This suggests that we should examine every SINGLE promising signal at the Lyman line to see if contains any modulation that would indicate intelligence. Such a signal may not be repeated if it is a slewing beacon.

It is probably reasonable that an advanced civilization who wanted to broadcast a "we are here" message would use these frequencies or a multiple of them. I would try π times the Lyman b line.

Personally, I would spend a serious amount of time doing a targeted search at all the stellar systems that have confirmed planetary systems. This is a small chance of success, but small chance is better than no chance and I would strongly suggest this search expand the frequency range to stretch from 500MHz to 10GHz.

I agree, but it will take years of study before we have much idea which planets are in the habitable zone and have been around long enough to maybe have advanced life. Also, we should know something about their atmospheres and oceans or lack thereof before spending much effort. Then maybe it is worth the effort, though it will probably take at least the Square Kilometer Array that ML1 refers to above, or more likely a very large space-based radiotelescope that avoids earthly interference. It will eventually achieve results, but not to order on a given timescale.

1) Freq should lie in "transparent" area for inter-stellar matter. Or signal will extinct too fast.
2) if we bound to some random freq the number of possibilities where that random freq lies rises enormously even for our current processing power.

All these give constrains on freq we could search.