I haven't seen the Hohlraum article before - interesting stuff. And for the earth-side receiver, I was generally assuming hugely-sensitive equipment. But I may be underestimating the sensitivity of what we can build - clearly we can detect individual photons, so the probe emitter would just need to ensure it sends enough that the receiver can capture enough to reconstruct the message...
In any case, interesting stuff :) I'm sure there's a calculation that we could do to figure out the actual power requirements given background radiation and receiver sizes, but I don't know the associated math.
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A thought just occurred to me - given a big reflector, you could emulate a transmitter by varying its reflectiveness / target, beaming a massively-powerful, regular pulse from Earth, and watching what comes back. That could eliminate transmitters (and their power requirements) entirely from the probe, though you still have the solar wind problem if it's really big.
Your second idea has already been done, to a certain degree.
http://www.hindawi.com/journals/wcn/2005/930810/abs/ is one example of a (highly miniaturised) sensor network that communicates with a corner-cube retroreflector returning modulated laser light back to the base-station. It has no active comms emission.
In any case, interesting stuff :) I'm sure there's a calculation that we could do to figure out the actual power requirements given background radiation and receiver sizes, but I don't know the associated math.
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A thought just occurred to me - given a big reflector, you could emulate a transmitter by varying its reflectiveness / target, beaming a massively-powerful, regular pulse from Earth, and watching what comes back. That could eliminate transmitters (and their power requirements) entirely from the probe, though you still have the solar wind problem if it's really big.