Comment by pgorczak

I found [1] which reports noise temperatures around 20–30 K for the 34 m antenna that receives Voyager data [2].

The equivalent noise spectral density is around -215 dB/Hz!

[1] https://descanso.jpl.nasa.gov/monograph/series13/DeepCommo_C...

[2] https://voyager.jpl.nasa.gov/mission/science/