Question About SETI & Time Chauvinism

[sophiecentaur]

For long distances everything is a point source, and even with non-isotropic emission the intensity drops with the inverse distance squared. You can't focus signals over a distance of more than (emitter diameter)²/wavelength (order of magnitude estimate).

You can regard what happens as the directive antenna (or light projector) illuminating a portion of a sphere. This would be the equivalent (as far as an on-beam receiver as what you would get from an isotropic radiator with a power of 1/(illuminated area). In antenna spec they use a term Max EIRP or Maximum Effective Isotropic Radiated Power. A receiver wouldn't know the difference between a 1kW isotropic source and a 1W source with a directive antenna with Gain of 30dB.

 

[Kevin the Crackpot]

Thank you.