The "path loss equation" goes something like: At the receiver, you have "minimum detectable signal", MDS, measured in dBm. At the transmitter, you have power

The "path loss equation" goes something like: At the receiver, you have "minimum detectable signal", MDS, measured in dBm. At the transmitter, you have power out, measured in dBm. Add transmitting antenna gain, in dB, subtract propagation loss through medium(s), add receiving antenna gain, and if that number is greater than MDS, you win! The Really Great Science in Voyager is the added factor of "coding gain" -- sophisticated error correction codes can give you a many dB adder, at the expense of data rate (nobody cheats Claude Shannon).