In comp.dsp John Larkin wrote: < Femtovolts, with an FM receiver? Good ones need microvolt or so. A 3 < dB noise figure, optimistic for a radio, is ballpark 1 nV RMS noise < per root Hz, and an FM radio has a couple of hundred KHz bandwidth.
How about traditional satellite TV? As I remember, it is about six watts per channel. If the signal covers most of the continental US, a 10m dish has about 1/(500000)**2 the area of the US, so about
6W/2.5e11 or about 2.4e-11W At 75 ohms that is about 40uV. I would expect that to be a lot less than FM radio with 100kW transmitters.
On the other hand, my cable modem has about +16dBm input at 75 ohms. About 1.7V, maybe enough for a small light bulb. (I believe that is only for the specific signal it is receiving, not counting the hundreds of other cable channels.)
-- glen