This is an excellent question that I wish more people would think about. Almost every RF signal generated by humans would be impossible to detect by another earth even a few light years away due to spreading loss.
Detection of a link across interstellar distances requires all of the following:
Extremely high transmit power (megawatts)
Extremely high gain, highly directional transmitter (e.g Arecibo type dish)
Extremely high gain, highly directional receiver (another Arecibo)
Both antennas pointing exactly at each other at the correct time (the beamwidth of Arecibo was just a few arcmin, covering about 5e-8 of the sky)
Extremely narrow bandwidth and/or completely deterministic signal (very little information)
Our terrestrial RF emissions do not meet these criteria and could not be observable by another earth. Certainly not broadcast signals like radio/tv. The only signals that possibly could be detected are the few times we have intentionally transmitted a beacon from Arecibo, but given the infrequency of these, the likelihood anyone was listing in our direction is very low.
Edit: I just ran the numbers: an Arecibo-like dish (300m, 20K noise temp) could detect a typical TV broadcast (1MW, 6MHz, 0dBi antenna) to a distance of 5.3AU, about the distance to Jupiter.
jpdoane t1_j9tqg86 wrote
Reply to Would an Earth-like planet with identical technology be able to detect signals from us? by lukinhasb
RF engineer here.
This is an excellent question that I wish more people would think about. Almost every RF signal generated by humans would be impossible to detect by another earth even a few light years away due to spreading loss.
Detection of a link across interstellar distances requires all of the following:
Our terrestrial RF emissions do not meet these criteria and could not be observable by another earth. Certainly not broadcast signals like radio/tv. The only signals that possibly could be detected are the few times we have intentionally transmitted a beacon from Arecibo, but given the infrequency of these, the likelihood anyone was listing in our direction is very low.
Feel free to play with this tool yourself: https://www.satsig.net/seticalc.htm
Edit: I just ran the numbers: an Arecibo-like dish (300m, 20K noise temp) could detect a typical TV broadcast (1MW, 6MHz, 0dBi antenna) to a distance of 5.3AU, about the distance to Jupiter.