I would like to get to the bottom of this. Following your link, the guy says, “My calculations indicate that incidental radiation from Earth-like technology could be detected out to at least 1000 LY by our larger SETI telescopes (such as the ones used in the SETI Institute’s Project Phoenix targeted search)…”, but I do not see anything in the attached spreadsheets to justify that, unless you start making assumptions like huge power levels beamed directly towards our solar system using a high-gain antenna, with a similarly huge receiving dish pointing steadily back at it.
Think about it. The earth has only been “active” in the radio frequency ranges since around 1900. With the expansion of the internet, broadcast radio and TV signals will soon go dark, because they are just a waste of power, and take up frequencies that are better allocated for low-power communications (aircraft, self-driving cars, wifi, etc.)
So, in a few more years, perhaps only military radar will be sending out signals “loud” enough to be detected at any distance.
In order to be detected, we’ve got to have a civilization more or less at our level or above, but not too far above; within “shouting” distance; and who have been searching in the right direction during that brief tick of time.
For all we know, those ~100 years may have occurred while out ET neighbors were on their lunch break, so they never noticed us.
As for hearing their signals, we have to assume they are smart enough to send them our way, while also being dumb enough to send them in the first place. For all we know right now, sending out “Hey, look at me!” signals may be the intergalactic equivalent of hanging a “kick me” sign on our backs.
These calculations were done as part of NASA’s Project Cyclops. The entire paper is available here in PDF format: Project Cyclops: a Design Study of a System for Detecting Extraterrestrial Intelligent Life - NASA Technical Reports Server (NTRS)
A relevant part is chapter 6, starting on page 53. Summarizing the math, on page 56 it says it’s possible using then-current technology (1971) to detect non-directional extraterrestrial beacons of reasonable power out to about 1,000 light years.
In other references the cost estimate of such a system was 6-10 billion dollars.
That was 1971 dollars which would be a lot more today. OTOH that was also 1971 technology – before the Cray-1 supercomputer was invented. Today the signal processing phase of detection would be a lot cheaper, more sophisticated, or both.
Its improvements in the receiver in all sorts of ways. Is your car’s radio the same cost as a radio telescope ???
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They can use a discrimator which is very expensive and finely tuned, so as to pick up a signal of very tiny voltage
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The large antenna is an amplifier. Amplifies noise too, but it boosts the signal to the level that the discrimator can pick up. Being directional, the antenna is avoiding receiving noise from terrestial sources, so that is why it beats a simple amplifier…
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Signal processing can detect carrier inside noise. Not neccessarily recover the signal - at first they are looking for an operating transmitter, not the actual signal intended to be transmitted by the transmitter. Your radio can do that… give you a station, but you can’t work out what the words are… You know the station is there on that frequency, but you can’t work out the signal.
I disagree with this. We can’t communicate with cephalopods because they haven’t developed the kind of intelligence it requires. Alien races that have developed radio technology would presumably have developed the concept of abstract contact with other intelligent races.
Rather than humans and cephalopods Draco’s Tavern is more like the Spaniards and the Aztecs first contact.
If reasonable power means gigawatts, the beacon is a stable hydrogen maser, and your antenna array is 5 km in diameter, then, yes, they seem to be saying something like that. You had also better hope they happen to be transmitting at the moment you tune in (they estimate the probability of that could be one in a million per candidate star).
One further issue with transmissions that are not explicitly intended to be intercepted and understood by an alien culture and technology (either our communications going out, or theirs coming in) is that we have fairly quickly come to grips with how to exploit the information bandwidth to best effect - and the way you do this renders the signal indistinguishable from noise unless you know the encoding.
Consider that we already transmit almost all of our digital broadcasts with data compression. Radio, TV, all compressed. Then we we use frequency agile techniques for a whole host of reasons, but in the end the main driver is to get best use of spectrum. Spread spectrum techniques also render the signal difficult to tell from noise. (Indeed military systems aggressively make use of this.)
The end state is a radio spectrum that is basically noise. Unless you know what is in there, which will involve knowledge of the generating keys and possibly encryption keys, you will have scant chance of detecting any indication of intelligence.
It is probable that all the radio emissions from the Earth will be such within a decade.
The idea that radio transmissions will have some happy easy to decode baseband structure is hoping that the transmitting culture have no computer capacity and no knowledge of undergraduate level mathematics.
So we are left with aliens deliberately sending out simplified signals.
I guess we have done that. Ours say “Meat!! Hi there - we are made of meat!! Lovely succulent meat!!! Come and get it!!!”
It will be interesting to see what the incoming messages say. Perhaps it will be a take-away order.
The power discussed was 1 gigawatt. The original Cyclops array concept was about 10 km across, which could detect a 1GW continuous omni-directional beacon out to roughly 500-1,000 light years: http://www.nss.org/settlement/ColoniesInSpace/fig1308.jpg
That assumed a random search. If two such arrays existed on each planet and were aimed at each other, they could communicate across the entire galaxy.
Instead of arrays, a single 100-meter dish on each planet could communicate with another one 500 light years away. There is already a 100-meter fully steerable dish antenna, the Green Bank Telescope in West Virginia, USA: http://www.nrao.edu/pr/2013/GBTWVU/GBT.jpg
The proposed 10 km Cyclops array sounds big but the existing VLA can span up to 36 km diameter, albeit in a more sparse configuration: http://www.mreclipse.com/Observatory/VLA/full/VLA2001-143w.JPG
The newer ALMA in Chile is 20x more sensitive than VLA, which shows the progress in the intervening years: https://media2.s-nbcnews.com/j/newscms/2017_14/1953921/170404-atacama-telescope-mn-0825_d7660c78f3fccc16f6ae9b9b273f0c1b.nbcnews-ux-2880-1000.jpg
[Dirty Harry]
Nothin’ wrong with takeaway. As long as the right people get taken away.
[/Dirty Harry] 
Vegetarians better hope they aren’t fond of “grain fed” meat.