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  #21  
Old 29 November 2017, 05:13 PM
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GenYus234 GenYus234 is offline
 
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Even then, the chance of picking up a usable signal is pretty minimal. This StackExchange answer says that the transmit power to Voyager is around 20 kw. This is pretty close to 1 thousand times Voyager's transmit power of 22.4 W. From the second link, the received power from Voyager is 1 x 10-19 W. Assuming similar loses, that means the signal transmitted to Voyager will be 1.0 x 10-16 W when it reaches Voyager.

Voyager 1 is about 141 AU or 0.0022 light years from Earth right now. Alpha Centauri is about 4.367 light years from our sun. Using the inverse square law of radio signals, the signal we are beaming to Voyager will be 3.9 x 106 times weaker when it reaches Alpha Centauri. That's about 2.5 x 10-23 W.

To put that in perspective, the power of a single electron flowing past a point in a second is 1.6 x 10-19 W. The power from the transmitted signal would be about one electron every 15 minutes.
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  #22  
Old 29 November 2017, 05:29 PM
jimmy101_again jimmy101_again is offline
 
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Yep, I mentioned that in my first post. The deep space communication network signal will travel the farthest. But even then, it won't make it a tiny fraction of the distance to the next nearest star before the signal power drops below background radio noise.

It would be an interesting physics problem to calculate what transmitter power level would be needed to transmit a radio signal that would reach Alpha Centaur at the cosmic radiation background power level. I would WAG it at zillions of watts.
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  #23  
Old 29 November 2017, 07:33 PM
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Even more massive than that I'd guess. The best cell phone signal (20 nW) is 500 thousand times weaker than the cosmic background radiation (10 mW).

Some rough calculations estimate that if we detonated every single nuclear weapon on the planet, the ionizing radiation would be above the cosmic background radiation as seen on Mars at Mars' closest approach.

Part of that is because ionizing radiation is only 15% or so of the energy from a nuclear blast and it would be omnidirectional. If we somehow made it so all of the energy was ionizing, it would reach Mars at about the average distance.
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  #24  
Old 29 November 2017, 07:35 PM
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I would consider the signals to Voyager extremely tiny, not high power. They're high power only in comparison to what comes back rom Voyager. The high power transmission Jimmy mentioned about Arecibo is radar for tracking things in space, not for transmission of digital signals.
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  #25  
Old 29 November 2017, 07:47 PM
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True. Still, even Arecibo was used (only once) in 1974 to transmit a deep space signal, when it sent a transmission to globular star cluster M13.

~Psihala
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  #26  
Old 29 November 2017, 07:53 PM
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Pretty sure someone actually lives in that cluster. We only have to wait another 44,000 years for their reply.
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