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What source puts out the strongest power signal on earth?

  1. Jan 21, 2009 #1
    I just read that the large radio telescope in Arecibo, Puerto Rico can detect a signal that lays down only one picowatt of power over the entire earth. Out of curiosity, I imagined that there is a twin earth planet somewhere in space and wanted to calculate the maximum distance of detection based on the parameters of the telescope.

    Does anyone know what human-made source currently puts out the most powerful signal and a rough estimate of its power?

  2. jcsd
  3. Jan 21, 2009 #2


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    Fire control radars put out signals in the megawatt range, concentrated along a very narrow beam (say, a couple of degrees wide). That would be my bet.
  4. Jan 21, 2009 #3
  5. Jan 21, 2009 #4
    A typical high power Radio FM transmission would be audible weakly at 20 million km using a rooftop aerial... About one light minute.. 1/7 of the distance to the Sun.

    To reach one light year the transmitter would need to be 100 billion times more powerful.

    To reach 10 light years it would have to be 10 trillion times more powerful.

    Distances will be a lot less for TV..maybe the order of the Earth-Moon distance so around 1 - 2 light seconds.

    The numbers are enormous..mind boggling.
  6. Jan 21, 2009 #5
    Where did you read that?
  7. Jan 21, 2009 #6
    They are own calculations based on path loss, receiver sensitivity etc.

    Backed up by Seth Shostak.

    Seth Shostak (born July 20, 1943) is an American astronomer. He earned his physics degree from Princeton University and a Ph.D. in astronomy from the California Institute of Technology.

    """So here’s the bottom line: LOFAR would only be able to find TV signals comparable to ours from a distance of much less than one light-year! Turning this around, the mother of all rabbit ears couldn’t pick up the Alien Broadcasting Network at the distance of even the nearest star.

    Disappointing, but you might argue that the extraterrestrials will have much, much more powerful TV transmitters than we do. In fact, their broadcasts would have to be millions of times more powerful to even produce a blip on LOFAR, which seems a bit silly and likely to set alien roofs on fire. """

    LOFAR is a very large receiving array..

  8. Jan 21, 2009 #7


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    (link inserted by me)
    About 3.6 million watts, but it only operates at about 45% efficiency, due to its design and particular mode of operation.

    BTW; wasn't Arecibo used to transmit for SETI? If so, I wonder what kind of output power was used.

    Ah, http://www.seti.org/Page.aspx?pid=688":

    Last edited by a moderator: Apr 24, 2017
  9. Jan 21, 2009 #8
    The ERP of HAARP (effective radiated power = transmitter power x aerial gain) is of the order of 1 GigaWatt. (1000 MW)
  10. Jan 21, 2009 #9
    I think Arecibo radiated 900 kW but the aerial gain is much higher than HAARP at a much higher frequency which meant a very narrow but very powerful beam which would only hit only a very tiny area of space. A beam of a tiny fraction of degree.
  11. Jan 21, 2009 #10
    In one of my physics textbooks. According to the text, it was quoted in a statement made by Drake of SETI.
  12. Jan 21, 2009 #11
    Thanks for the great link. That's a lot of power. According to my simple calculation, it would require a source at the center of our galaxy to output a signal with a power of magnitude about 10^15 W to disperse 1 picowatt over the earth.

    EDIT: Everyone, thanks for the good info. I now have even more things to explore. =)

    EDIT2: I recall reading somewhere on wikipedia that the average total human usage power signal output is about 10^12 W (?), compared to the 20 trillion W of the SETI output signal!
    Last edited: Jan 21, 2009
  13. Jan 21, 2009 #12


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    This is all assuming the standard bandwidth of the typical FM receiver. Narrow the bandwidth up and you will dramatically increase the range. The received signal will not necessarily have the fidelity and narrow it up enough and it won't be intelligible. However, it will be detected and most likely be able to prove that it was sent by an intelligent source.
  14. Jan 22, 2009 #13
    My figures are based on standard domestic receivers and a roof top type aerials. Narrow band systems and higher gain aerials will extend the range many times but the distances are still a small fraction of a light year.
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