And more info:

Eric Korpela wrote:
> Nicolas Alvarez wrote:
>> Eric Korpela wrote:
>>> SETI@home has a sensitivity of about 1e-25 W/m^2, so if I'm doing my
>>> math right, a transmitter at 200 ly would need to be about 7e+12 W EIRP
>>> (effective isotropic radiated power). If the transmitter was attached to
>>> a telescope the size of AO, it would have a gain of about 2 million, so
>>> the actual transmitter would need to be about 3.5 MW total power.
>>>
>>> Of course for a directional transmitter ET would need to suspect we are
>>> here.
>>
>> What if it's not directional but broadcast? How much power do the
>> 200ly-far aliens need to send a radio signal covering an entire
>> hemisphere*, so that a reasonable amount still reaches us (or rather
>> SETI's antenna)?
>
> That would be 7 TW. Which is the amount of power you can generate with a
> solar array 150 km x 150 km* in size (assuming 24% efficiency). That would
> be a bit more than our society could afford to spend on trying to
> broadcast our position.

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