Ok, so following on from several responses in the "What happens if we discover Alpha Centaury simply does *not* have planets?" thread, I'd like to pose a question:
"What size receiver antenna would need to be used to receive an intelligible message from a probe, say, one light year distant? (For modelling purposes, I'd define 'intelligible' as being similar to say, the quality of messages Voyager 1 sent Earth, when it was ~120 AUs distant).
The purpose of this being, to quantify just how far away in technology development terms we really are, when it comes to attempting meaningful interstellar communications using RF technology. (Even though one light year is not really an interstellar distance for us ...).
So, to simplify the calculations, (and the model), say our probe has:
- the same transmitter power as Voyager 1, which was ~22 Watts (might increase this later on);
- X-band communications to be used (8.4 GHz);
- the same maximum downlink bit rate as Voyager (160/1400 bps);
- the same EIRP (Equivalent Isotropically Radiated Power) as Voyager 1 is capable of (~84.7 dBm). Interestingly, the Mars Reconnaisance Orbiter ends up being only about 0.8 dB different from this, even though it has 100 Watt transmit power! Mind you also, MRO's bitrate ends up being ~6Mbps ... but I think that's another story;
- the same receive signal-to-noise ratio as for the Voyager signal, when it was at 120 AUs from Earth;
- seeing as the Deep Space Network radio telescopes were used for Voyager, let's assume their general specs as well (with the exception of the required antenna aperture size);
- the best noise floor approximation I can come up with is ~ -175.8 dBm.
So, in other words, Voyager 1 is the probe, and it has made it to one light year distant, its power supply is still producing the same power as when it was commissioned, and we're trying to receive its signal. What size receiver antenna, (parabolic reflector), is needed?
Any takers ?