Suppose they succeed in sending a micro craft to Alpha Centauri, how would it communicate with us? Micro craft implies micro transmitter. How big a dish do you need to detect a light bulb at a distance of 4 light years?
Earth-bound radio amateurs bounce 100 watt signals off the Moon and receive with a TV-style Yagi antenna: "Recent advances in digital signal processing have allowed EME contacts, admittedly with low data rate, to take place with powers in the order of 100 Watts and a single Yagi antenna." https://en.wikipedia.org/wiki/EarthÂMoonÂEarth_communication Today's ability to do low-power *spread spectrum* communications is amazing. Back in the 1990's, I visited a company that did low-power spread spectrum communications for electric/gas/water meters. * total cost O($100) at *that* time * battery life ~10 years * data rate O(1 bit/sec) * distance O(5-10 miles) * No(!) antenna; transmitter buried in the ground I would imagine that things are only better/faster/cheaper today. The basic fact you need to know is the ratio E_b/N_0, which is "the energy per bit to noise power spectral density ratio". E_b/N_0 > ln(2) = -1.59 dB (Shannon) https://en.wikipedia.org/wiki/Eb/N0 http://www.sss-mag.com/ebn0.html At 11:15 AM 4/16/2016, Dave Dyer wrote:
How big a dish do you need to detect a light bulb at a distance of 4 light years?
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Dave Dyer -
Henry Baker