That's a pretty good rule of thumb until you get into some really weird stuff. The link budget for bouncing radio signals off the moon (EME) is something like

That's a pretty good rule of thumb until you get into some really weird stuff. The link budget for bouncing radio signals off the moon (EME) is something like 260 dB. A while ago I had a chance to see the ground station at NASA Goldstone where they manage the radio links to Mars and the outer planets. There was a terminal open with ~single digit bits / second coming in from one of the Voyager probes. Having a 70 meter dish and a cryogenic receiver helps, but the link budget there has got to be truly staggering...