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>> Extrapolating from the Voyager power levels and distance, I make it that
>> we need a 350 GW signal to be transmitted from 200 ly away.
>
> The SETI equipment might even be somewhat more sensitive because they are
> using larger disks. Then again they don't know what exact frequency to
> tune into.
>
> BTW I arrive at something more like 47 MW if the voyager is transmitting
> all its power, which is unlikely, so the number could even be much lower.
I assumed that the power needed goes up with the square of distance, so used
Google to calculate:
"(200 light years / 16.8e9 km)^2 * 23 W"
which actually gives 300 GW, but I think that's a big underestimate, as
presumably Voyager is directing its 23 W directly at Earth, and not
radiating out in a sphere. If an alien world 200 ly away is radiating in
all directions equally, it would need to be outputting much more than 300 GW
in total.
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