I where thinking of how SETI is searching for alien signals and couldnt stop thinking of what type of signals that could be detected.
What type of signal is expected to be detected within the SETI program?

Would a alien TV or radio broadcast 100 light years away have strong enough signal to be even detectable?
Is it an intentional attempt to contact other civilizations on other solar systems that is expected to be detected? Like sending a very strong signal far more powerfull than normal communication signal levels.

And then what type of signals are we sending out in order to establish contact with other civilizations?
Do we even send a signal on daily basis or is it just a one time shot?

Would it be possible to detect a normal radio or TV broadcast similar to earths from a planet 100 light years away with our current technology?

Would we be able to detect a signal with the power that we do have sent in order to announce for other civilizations that we do exist, this also at a distance of 100 lightyears.

Anyone who know the answer or could link to some place where this is discussed or analyzed?

You'll find similar musings over in Set@home Science board.
http://setiathome.berkeley.edu/forum_forum.php?id=9

Mod: Please be so kind as to relocate this thread : > )

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I doubt it. Radio and TV signals are omnidirectional and broadband. I have heard that these signals are difficult to detect even out at Pluto.

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I doubt it. Radio and TV signals are omnidirectional and broadband. I have heard that these signals are difficult to detect even out at Pluto.

Unless they have a telescope on Jupiter under all the gas... ;)

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I where thinking of how SETI is searching for alien signals and couldnt stop thinking of what type of signals that could be detected.
What type of signal is expected to be detected within the SETI program?

Would a alien TV or radio broadcast 100 light years away have strong enough signal to be even detectable?
Is it an intentional attempt to contact other civilizations on other solar systems that is expected to be detected? Like sending a very strong signal far more powerfull than normal communication signal levels.

And then what type of signals are we sending out in order to establish contact with other civilizations?
Do we even send a signal on daily basis or is it just a one time shot?

Would it be possible to detect a normal radio or TV broadcast similar to earths from a planet 100 light years away with our current technology?

Would we be able to detect a signal with the power that we do have sent in order to announce for other civilizations that we do exist, this also at a distance of 100 lightyears.

Anyone who know the answer or could link to some place where this is discussed or analyzed?

Dr. Frank Drake has stated that even very low power signals could be detected at stellar distances. It only requires a receiver be placed at the focal point of the sun, acting as a gravitational lens. The distance is about 51 billion miles from the Sun (550 AU) See the book 'Is Anyone Out There'? by Drake and Sobel, near the end of chapter 10 (pages 230-234 in the edition I have).

Dr. Frank Drake has stated that even very low power signals could be detected at stellar distances. It only requires a receiver be placed at the focal point of the sun, acting as a gravitational lens. The distance is about 51 billion miles from the Sun (550 AU) See the book 'Is Anyone Out There'? by Drake and Sobel, near the end of chapter 10 (pages 230-234 in the edition I have).

Drake equation

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Dimytes, you posted a similar question to this topic.

According to the FCC. Our TV broadcast has a maximum output of 1 KW.

"(4) The visual transmission amplitude characteristic shall be in
accordance with the chart designated as Figure 5 of Sec. 73.699:
Provided, however, That for stations operating on Channel 15 through 69
and employing a transmitter with maximum peak visual power output of
1 kW or less the visual transmission amplitude characteristic may be
in accordance with the chart designated as Figure 5a of Sec. 73.699."
Source: http://edocket.access.gpo.gov/cfr_2006/octqtr/47cfr73.682.htm

The question is, how far will 1,000 meezly watts go?

I know if I had a 1,000 W light bulb, I could probably see it from 5 miles
away before it dissipated into nothing. So has anyone calculated it?

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There are transmitters (or were) on Earth with powers of hundreds of kilowatts.

Radio Luxemburg used to pump out a quarter of a megawatt each evening, and this was beamed as well, not omnidirectional. OK, in this example the radiation would probably not make it through the ionosphere at any great strength.

In the UK we also have high-powered transmitters for our TV, our local one being Stockland Hill, which I understand transmits at 25Kw spead between all frequencies. These antennae (if I'm not mistaken) are colinears and tend to concentrate the radiation to a low angle, maximising signal strength where it is needed - on the horizon. Most of this energy must skip the horizon and travel off into space at a reasonable strength unhindered by the ionosphere.

I would fully expect to be able to recieve these transmissions at huge distances with appropriate equipment.

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There are emissions that are beamed on earth (Short Wave for one) that have effective radiated power in the megawatts due to beaming and antenna gain. Actual power exceeds 100,000 watts at many stations--Shortwave broadcast, TV, AM Radio outside the US.

what would the power be at the receiver at 100 light years--assume a sphere I suppose. A Space-based, narrow beam laser burst might be the way to go to try to intentionally communicate. Let's hope that someone out there is trying this or else we may be wasting our cycles.

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Let's hope that someone out there is trying this or else we may be wasting our cycles.

That's what I'm saying! Where on this huge website can I see the
sections of sky SETI@home has scanned and that we are processing?

They had better be the ones most-likely to hold life and are less
than 100 light-years away. We don't want to waist precious cycles. =)

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Let's hope that someone out there is trying this or else we may be wasting our cycles.

That's what I'm saying! Where on this huge website can I see the
sections of sky SETI@home has scanned and that we are processing?

They had better be the ones most-likely to hold life and are less
than 100 light-years away. We don't want to waist precious cycles. =)

S@H has no control over where the Arecibo telescope is pointed. The data we crunch comes from a recorder mounted on the telescope and picks up whatever the telescope happens to be pointing at. This service is provided for free (AFAIK) and the only cost to S@H is the equipment investment and disk drives.

Never the less, Arecibo is the largest radio telescope in the world...what more do you want for free???

[edit]Oh, and here's a short term mini-project Matt did for a while. The grey area is the portion of the sky visible from Arecibo.

i think you have taken a lot of these calculations on faith, we have no real idea how much of our signals leave earth orbit never mind the solar system, just because it travels inside the atmosphere at the stated frequencies and power doesn't mean it travels outside the atmosphere and through the solar system in the same way, we have never done any studies to find out, all the signals we transmit to and from crafts and satalites are directional, so we have no idea how an omni directional signals would be affected by the planets the sun and the masses of other debrie in our system, never mind what may be undetected beyond the edge of our solar system,that may affect radio and tv signals, we have no idea what may have effected any signal we detect, or if it even originated from the direction we think we are receiving it, its all just a big suck it and see, and thats part of the attraction for me, its a what if, much better than an im positive, like some believers i know, a lot of the wonder in life is not being absolutely sure, and having to trust to our feelings and sence of hope, we lose a lot in certainty and gain much from optimism.

i think you have taken a lot of these calculations on faith, we have no real idea how much of our signals leave earth orbit never mind the solar system, just because it travels inside the atmosphere at the stated frequencies and power doesn't mean it travels outside the atmosphere and through the solar system in the same way, we have never done any studies to find out, all the signals we transmit to and from crafts and satalites are directional, so we have no idea how an omni directional signals would be affected by the planets the sun and the masses of other debrie in our system, never mind what may be undetected beyond the edge of our solar system,that may affect radio and tv signals, we have no idea what may have effected any signal we detect, or if it even originated from the direction we think we are receiving it, its all just a big suck it and see, and thats part of the attraction for me, its a what if, much better than an im positive, like some believers i know, a lot of the wonder in life is not being absolutely sure, and having to trust to our feelings and sence of hope, we lose a lot in certainty and gain much from optimism.

If the Strange Signals from Space: The QE2 signal is anything to judge the weird behaviour of radio in space, then anything might be possible :D (Warning, don't take this site too seriously unless you are wearing your tin-foil hat. hehehe, that's one fun site :D)

from the given space 2001 link: (they have a few fun stories there, but this is my favourite)

The QE2 signal.
One of the best known of these time lapse signals was received by the luxury cruise ship the QE 2. Bound for America in 1978 the radio officer named Alan Holmes received a message in Morse code employing a procedure that was no longer used. To his astonishment Holmes found that when decoded the signal turned out to be a routine position check from the old liner the Queen Mary! Astonishing, because the gracious Atlantic veteran had long since ceased to rule the waves, and for 11 years had been a floating conference centre in Long Beach California!

Stunned and bewildered Holmes was at a loss to explain the incident which he described as a message "from another age"! His explanation: "This message could have bounced out into space more than ten years ago and just zipped around until it found its way back to Earth, and we picked it up"!

Strange indeed, but another curious feature of this remarkable incident was the fact the message was picked up by the one person who would have most understood its importance - almost as if beamed to him directly! Coincidence? Or was it that yet again there was an intelligence at work that was attempting to advertise its existence?

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"Living by the wisdom of computer science doesn't sound so bad after all. And unlike most advice, it's backed up by proofs." -- Algorithms to live by: The computer science of human decisions.

I've heard about these delayed signals elsewhere, and not via Von Daniken's books in case anyone's wondering.

But is it so unlikely that an alien civilisation might place a sattelite orbiting earth programmed to recieve radio signals, delay them for a predetermined period and then re-transmit them?

It is a good way of attracting the attention of a civilisation suitably evolved to notice this, and if we had the technology, quite possibly something we'd do also.

I fully believe that delayed signals have been recieved - I don't think that these stories has been fabricated, but there may be a more natural explanation such as magnetospheric ducting, which is known to create delays of a few seconds to natural VLF signals - whistlers for whant of a better name.

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Somewhere in this forum is the calculations for various transmissions and their detectable distance. Arecibo has a range of 50 light years detection at max power if being received by another Arecibo-like radio telescope at the same technological level.

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me@rescam.org

There are transmitters (or were) on Earth with powers of hundreds of kilowatts.

Radio Luxemburg used to pump out a quarter of a megawatt each evening, and this was beamed as well, not omnidirectional. OK, in this example the radiation would probably not make it through the ionosphere at any great strength.

In the UK we also have high-powered transmitters for our TV, our local one being Stockland Hill, which I understand transmits at 25Kw spead between all frequencies. These antennae (if I'm not mistaken) are colinears and tend to concentrate the radiation to a low angle, maximising signal strength where it is needed - on the horizon. Most of this energy must skip the horizon and travel off into space at a reasonable strength unhindered by the ionosphere.

I would fully expect to be able to recieve these transmissions at huge distances with appropriate equipment.

There are also some pretty powerful FM(VHF) transmitters here in the UK. Some of the BBC ones transmit 250 KW, a lot of this will disappear into space through the Ionosphere as VHF signals do 99% of the time.

I think a 250 KW VHF signal must be receivable at great distances through space? Maybe ET is listening to Radio 1 right now, the poor devils.

Fermi paradox - 'Communication is impossible due to problems of scale'


The Drake Equation: Adding a METI Factor



"I would like to notice the importance of designing and, especially, accomplishing practical projects directed to sending signals. This is the only way to understand subtle problems of contacts. Here, as it always happens, egoists end up with failure."

> Academician Andrey Sakharov, Nobel laureate. Questionnaire "CETI", 1971

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