http://www.faqs.org/faqs/astronomy/faq/part6/section-12.html http://www.faqs.org/faqs/astronomy/faq/part6/section-12.html In the middle of the table is an inter

http://www.faqs.org/faqs/astronomy/faq/part6/section-12.html http://www.faqs.org/faqs/astronomy/faq/part6/section-12.html In the middle of the table is an interesting chart that shows the distance that radio can be detected. You will notice that for large distance you need terawats of power and a very low band widths, fractions of a Hz. A big TV station doesnt make it out of the Solar System, while a very powerful, low bandwidth, focused source can be detected for hundreds of light years. Unless someone is pointing at us at the same time we are pointing at them, we will probably miss them. We can detect quasars billions of light years away because they are big mothers, but really hard to modulate, and turned off by now.