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Echelon Eight
Post  Post subject: SETI and the Range of Earth-based Background Signals.  |  Posted: Sat Oct 01, 2016 6:23 am

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I think I know the answer to this, but what you say is worth two cents each.

I continually hear SETI enthusiasts (of which I am one) say that, in effect, we, the people of Earth, have been transmitting our TV and radio signals into space for 50 years, and hence there is an expanding sphere of “hello”, radiating into the universe, which any listening E.T.s could “hear”.

But, I have also been told, that these weak signals are blurred into indecipherability within a light year, due to solar wind and etc. And no alien could possibly be reading anything from Earth – in the way that SETI boosters like Seth Soshtak are still saying they could.

Someone is wrong.

We're talking, as the SETI guys continually say "domestic", non-directional, background, transmissions.


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marnixR
Post  Post subject: Re: SETI and the Range of Earth-based Background Signals.  |  Posted: Sat Oct 01, 2016 1:50 pm
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not sure if I understand you correctly, but presumably the signals that get emitted from earth might be sufficient for an extraterrestrial intelligence to gather that this is not a natural signal ?

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Chrispen Evan
Post  Post subject: Re: SETI and the Range of Earth-based Background Signals.  |  Posted: Sun Oct 02, 2016 11:13 pm
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I actually think it is really hard to say what aliens can and cannot do with a radio signal. They might have a gadget similar to our visible light adaptive optics that take the background noise out of the signal.


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iNow
Post  Post subject: Re: SETI and the Range of Earth-based Background Signals.  |  Posted: Sun Oct 02, 2016 11:22 pm
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EM signals do tend to degenerate as distance increases. I think Marnix' point is the right one, though. This might be more about a binary state of detecting signals that are obviously not natural in origin (yes/no) versus having high fidelity and ability to accurately interpret those signals once received.

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Lynx_Fox
Post  Post subject: Re: SETI and the Range of Earth-based Background Signals.  |  Posted: Tue Oct 04, 2016 8:10 pm

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Also the radiated broadcast signals have been dropping dramatically as we've moved to more far more efficient transmission methods (e.g. AM carrier was mostly wasted).


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One beer
Post  Post subject: Re: SETI and the Range of Earth-based Background Signals.  |  Posted: Sun Oct 09, 2016 9:45 am
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I cannot see how there would be any signal retreivable over the distances involved - at least 4 light years to our nearest neighbour?

Our Voyager probes are the furthest signal transmitters we are in contact with, and they are just outside our own solar system at around 100 Astronomical Units.

From Wikipedia:
The Voyager Program spacecraft have the highest known path loss and lowest link budgets of any telecommunications circuit. Although the Deep Space Network has been able to maintain the necessary technological advances to maintain the link, the received field strength is still many billions of times weaker than a battery-powered wristwatch.

I used to work with terrestrial and satellite microwave transmitter links. I haven't worked out the free space path loss in space over distances of light years, but I think that unless a huge transmitter array on one planet is directed in an extremely narrow beam exactly towards a huge receiver array on another planet, nothing will be seen. Given that we don't know which planet to direct our transmissions to, the chances of us selecting a suitable planet are miniscule. Also, to see a reply, we would have to wait for at least 8 years.

I think that sadly we are simply too far away from each other to communicate - unless a civilisation works out how to modulate the output of their sun for example - and I don't understand how SETI will ever 'see' anything.

OB


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scoobydoo1
Post  Post subject: Re: SETI and the Range of Earth-based Background Signals.  |  Posted: Wed Oct 12, 2016 2:58 am
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Would interplanetary radio relay stations be feasible? Just send probes out to distance planets and "crash land" a sturdy relay transmitter. :shock:

On second thought, it may be better to simply have the relay transmitter/station thingy orbit the selected planet.


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Lynx_Fox
Post  Post subject: Re: SETI and the Range of Earth-based Background Signals.  |  Posted: Sat Oct 22, 2016 3:20 am

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One beer wrote:
From Wikipedia:
[i][b]The Voyager Program spacecraft have the highest known path loss and lowest link budgets of any telecommunications circuit.


How does this hold up after 35 years, it seems some amazing progress has been made since. In addition, Voyager only had a 25W transmitter....that's incredibly tiny (and impressive) compared to what can be put out.


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One beer
Post  Post subject: Re: SETI and the Range of Earth-based Background Signals.  |  Posted: Sun Oct 23, 2016 10:14 am
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Yes it is, and respect to the deep space network receiver engineers that they are still in contact.

But by a similar measure, there is no way that another civilisation will see anything of our radio and TV transmissions - not from at least four light years away. Such transmissions used to have powers of up to a megawatt for analogue TV but were/are radiated 360 degrees in the horizontal plane, not outwards away from the planet.

Our more recent uplink transmissions to our Communications satellites are radiated away from the Earth in narrow beams, but with lower powers, say around a kilowatt for analogue, a few hundred watts for digital, so this is not going to reach very far, and anyway, they are directed to geostationary satellites, not towards any other known planets.

As I say, I don't think the physics involved will allow us to communicate with another distant civilisation via the electromagnetic spectrum. Maybe quantum entanglement might be more fruitful?

OB


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