The AM Forum

Despite extensive scanning of the electromagnetic spectrum, why have we failed so far to find one iota of evidence of a radio signal transmitted by intelligent beings elsewhere in the universe?  Most likely,  the window of opportunity for SWL'ing a distant, inhabited planet is extremely brief.  As a civilisation advances, the possibility of intercepting its  radiocommunication in all probability, diminishes.

The SETI project is bringing its array of parallel narrow-band scanning recievers on line. We hope against hope that some not-too-circumspect intelligence is out there broadcasting narrowband signals (intentionally or not) seeking to conclusively demonstrate their presence in our universe.   While broadcasting narrowband signals,  civilizations "leak" evidence of their existence.  The narrower the frequency used to transmit data through space the higher the signal-to-noise ratio. The most efficient mode of such transmission is to digitally switch a carrier frequency "on and off". Such serial modes of transmission however, are very slow at transfering large amounts of data through space in short amounts of time. Such signals are however very useful for saying things like "look at me I am here!".

It's a solid assumption that all advancing technologies eventually pass from a narrowband to a broadband electromagnetic broadcast phase. Unfortunately, even our largest radio telescope would be hard pressed to detect broadband transmissions - such as Earth's - from as close as the Alpha Centauri system.  

Meanwhile the window on electromagnetic broadcast may even be closing here on earth. How many of us watch television programs delivered by antenna today? Less than a half-century ago every house had its own rooftop antenna, or at least a set of "rabbit ears".  One-hundred years from now the entire planet may be electromagnetically mute.


http://www.universetoday.com/am/publish/are_we_alone.html?132005

Very interesting, Don!  I'd never thought about the bandwidth issue, but makes sense.
If there are still "old buzzard" hams 100 years from now, they will keep our planet on
the non-electromagnetically mute list (especially cw ops!!).  That would be ironic, wouldn't
it, if the first contact with an extraterrestrial  civilization was via hams operating the
"antiquated" mode?  Talk about having the last laugh!!

73!

It would be interesting to see what frequencies or wavelengths actually penetrate the atomsphere and make it say, passed the moon.  We know microwave certainly can make it as JPL is constantly in communication with the Viking I and II probes to this day.  I mean since most broadcasts are pretty much aimed at listeners here on terra firma what actually is making it beyond our little orb.

Pretty much anything that isn't refracted back to earth by the ionosphere. So in general (depending on sunspots, etc) just about any RF at VHF and above. So it's not likely to  be CW ops making contact with life forms from other planets, unless they are pounding the brass on 6 or 2 meters.

You are right, Voltair.

Yesterday I fired up the 6M array and aimed it 90 degrees skyward. I suceeded in contacting extraterrestrial life. I sold the story to the Enquirer.. [not the Inquirer]   Watch for it.

The fella's name was the "Rubber Duck" from the MoonRaker Star system, caw mawn.


But, seriously... think of how much energy the sun puts out in an omnidirectional pattern.   Go out 20-30 light years and it is gone for all practical purposes.  A pulsar is a different story. But we would need a lot of BIG  mawls to be heard anywhere even with the Arecebo dish with 73.5 db gain at 1.5ghz..  Couple that with our's or other civilization's  brief RF existance envelope and the odds of being heard are about as slim as the prime minister actually going to NJ to kick Irb in the gawd damn balls..

There's a BIG difference between receiving black hole generated gamma rays or pulsar or super nova signals compared to a radio wave from some PW civilization. [unless they're using a  Moonraker, of course]

But, then again,  check out the new ETI's optical  109 db spec advantage over old microwave technology below.  Here's looking at you, kid.

T


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Some Interesting Info:

Optical SETI 101


Gain of Arecibo-type microwave dish (300 m aperture) uplink at 1.5 GHz = 73.5 dB


Gain of full Cyclops array (3 km aperture) uplink at 1.5 GHz = 93.5 dB

Project Cyclops


Gain of an infrared telescope (10 m aperture) uplink at 10,600 nm (10.6 microns) = 129.4 dB


Gain of a visible telescope (10 m aperture) uplink at 656 nm = 153.6 dB


Difference in gain between visible telescope and Arecibo dish = 80 dB (100 million)

Difference in gain between visible telescope and full Cyclops Array = 60 dB (1 million)


Arecibo dish with a 1 MW (60 dBW) continuous wave transmitter (late 20th century technology)

Effective Isotropic Radiated Power (EIRP) = 73.5 dB + 60 dB = 133.5 dBW


Equivalent of a 10 m visible telescope with 1 GW (90 dBW) continuous wave laser (ETIs' futuristic technology)

Effective Isotropic Radiated Power (EIRP) = 153.6 dB + 90 dB = 243.6 dBW


EIRP advantage of ETIs' optical uplink to that of the 20th Century terrestrial microwave uplink for continuous wave beacons = 243.6 dBW - 133.5 dBW = 109 dB (nearly 100 billion times!)

Even if we could hear something that could be considered intelligent, that doesn't mean the civilization is still around.  For example, take the Hubble Deep Space field image. In this image are hundreds of galaxies that are millions of light years away.  That alone is significant and then keep in mind the Hubble Deep Space field image is a pin prick of a point in the sky.  Then everything is moving to boot.  Then add in the light years that a signal would have to travel. Then include JJ's points. I don't think it will happen.

The Voyager I and II probes (I think in my last post I said Viking which was incorrect) are just reaching the boundary between interstellar space the heliopause.  What will be interesting to know what will happen to communications with the Voyagers once this boundary is crossed.  Maybe nothing will happen at all.  What I find interesting is these two little guys with their 15 or 20watt transmitters are still making it across the 90AU distance they have traveled.

http://voyager.jpl.nasa.gov/