>> 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.

Post a reply to this message