Internet says approximately -160.48 dBm, which is one thousandth of the minimum strength that the most sensitive commercial FM radio receivers can discriminate.
Hence the huge receiving dishes, and apparently one 100 foot dish alone does not collect enough energy to reconstruct the signal, so multiple are required at each Deep Space Network receiving station.
And due to the rotation of the Earth, we need three DSN stations to maintain constant communication with Voyager.
