"However, separating any useful information from the mass of signals sharing the same radio band would pose something of a challenge."
So you seem to be talking about FOX, and all their other stations eh?
In the unlikely case that Proxima Centauri is inhabited, that its inhabitants are technologically developed ahead of Earth, and its inhabitants actually care about us, its media might is just catching up with the stories of 2008. Nearby and more contemporaneously, an ANU researcher, Ben McKinley, has run a calculation for …
I'd imagine that you'd need a rather large aerial... the neighbours would need to be exceptionally accommodating. Perhaps you could win them over by offering a feed of the German erotoscatology channels?
It might also be a bit of a challenge to filter the signal into something useful.
There were a few interesting comments about what SDR could and could not do in a recent Reg article on what might be terms a software-defined antenna. Might be worth a little archive trawl.
Short answer: SDR might do a nice job handling the signal your antenna picks up, but it still needs an appropriate antenna to provide that signal.
First: Google "EME" and "moonbounce" - there are amateur radio operators doing that all the time. It's difficult: you have to have a significant antenna system on both the transmitting and receiving end (think of the largest TV aerial you've seen, one of the 10 foot long ones, then stack 4 in an array), the transmitting end is usually running the maximum allowed power (in the US, 1000 watts), and the receiving end has a very sensitive receiver (far more so than one of those USB dongles will have). The signals sent are designed to be easy to pick up - far easier than FM broadcast, let alone TV - and even then, are often undetectable.
Even with a very large antenna, a very low noise preamp, and the best SDR, there's simply not enough information in the signals reflected off the Moon to allow you to pull out one specific broadcast station from all the others on the same frequency. *IF* you had an enormous number of antenna and receivers all over the world, and you could then use spatial diversity, you *might* be able to get enough information, based upon different paths from the stations to the Moon to all your different antenna, to pull it out - but then again, you'd likely have an antenna right next to whatever station you wanted to listen to, and could listen to it directly.
With respect to a hypothetical listener Out There, the worst thing that has happened has been the transition to digital. Analog signals have enough information in them to work out what is going on - AM is trivial (The signal "looks like" the original audio), FM almost so, and even TV could be worked out reasonably well (the color aspect would be a bit hard to work out a priori, but the horizontal scan rate and vertical scan rates are obvious in the spectrum of the signal - getting black and white would be pretty easy).
But with digital: there's not enough information in the signal to work out the theory behind MPEG. You could infer the gross framing structure, you might be able to work out the part of the signal the provides EPG data, but the audio and video streams would be a total mystery. And that assumes no encryption, and also that you can see the signal - digital signals are designed to be very much like noise, with none of the spectral redundancy that makes AM, FM, PAL and NTSC easy to work out.
Transmitters getting smaller. The trend is towards a larger number of smaller transmitters.
There are plenty of numbers for radio transmitter power all over the internet. Most do not explain if they are quoting the power output of the electronics or the power that would be required to get the same signal strength from an omnidirectional antenna as is transmitted in the preferred direction of the installed directional antenna. Digital switch over in the UK reduced the power output by a factor of about 10. There were some really big short wave transmitters intended to bounce signals off the ionosphere. The Russians found that over about 1.25MW, the signal punched a hole through the ionosphere and went on into space instead.
The largest omnidirectional transmitter I could find (probably) still operating was Vatican Radio at 500MW (I could easily be very wrong. Health issues make Vatican Radio a prominent topic on the internet). I really hope that Vatican Radio is not the clearest signal sent from Earth.
Apparently they broadcast an hourly annoncement looking for "lost orphans" that would like to become choirboys ( complete discretion required ).
There is also an annoncement for any extra stellar beings named as "Jesus" or "Mary". It is important that they contact the Vatican immediately as their presence is requested for future fund raising galas. ( The existing ones are running a little low on appeal).
Wrote : - "The largest omnidirectional transmitter I could find (probably) still operating was Vatican Radio at 500MW (I could easily be very wrong"
500MW ?! That is the output of a medium sized power station.
I thought that the signals most likely to be picked up by aliens are the focused beams of radar, which, although not carrying information, would be recognisable to aliens as being of artificial origin.
Loads of people have 1 MW AM transmitters (LW and MW, made in Europe, Russia and USA).
France has a longwave station that in it's heyday, before commercial FM got off the ground, could output up to 3 MW carrier level + 100% AM on longwave into a slightly directional antenna. Not sure how many people are still running with very high AM power levels nowadays.
I doubt there's anywhere in the universe distant enough to escape the emissions from that thing... and once the signals reach a civilisation advanced enough, it won't be long before they send someone out to shut us the fuck up.
<------------ your great grandchildren are dead
On the off-chance that you're drinking the piss not taking it...
I was referring to "Woodpecker" the Soviet ICBM detection RADAR, rather than "Woodpecker" the fermented apple abonination. I doubt the emissions arising from the latter are detected more than a few hundred metres from source - under normal conditions.
It probably won't matter to any supposed Centaurians that they can't easily disentangle the signals. The fact that there are so many, on so many different frequencies, that could not possibly have been emitted without a living intelligence, is information enough.
What will doubtless engage the Centaurians in much debate for years to come will be the question of what sort of societal structure could give rise to uber-technologists who can create the means of transmission, and some sort of degenerate subspecies that actually uses it to broadcast - not to mention what on Earth (literally) would be interested in paying attention to the results.
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Although SETI may well be a rather large waste of time and money, it would appear to be helping Dr Steven Greer to coin in the latter without too much effort.
Amongst other activities, his CSETI project has apparently taken paying trainees to a secret location where they make telepathic contact with aliens. His so-called Disclosure Project raised funds on kickstarter for a film to provide testimonial details explaining how governments are withholding information about their extra-terrestrial contacts. Coming soon to a cinema near you, presumably.
Hmm, if we can pick up stuff bounced off the moon, perhaps we can pick up stuff bounced off an object far enough away. Somewhere 25 radio (light?) years away that would just be ending the return trip so signals from 50 years ago.
Then just need those restoration boffins to extract the picture from the noise.