Gerald Youngblood (K5SDR) of FlexRadio wrote of optimal receiver noise figure relationship to antenna noise
in a blog posting about SDR receivers.
This article discusses that posting in the context of linear receivers, ie effects of intermodulation distortion are not included.
His gives the following advice:
For optimal weak signal performance near the atmospheric (antenna) noise floor you want your receiver noise floor (sensitivity/MDS) to be 8 to 10 dB below the noise coming from the antenna. For strong signal reception, less sensitivity is almost always better.
The terminology is not industry standard, but that is quite usual for hams who have a need to redefine well known terms, and this is really loose with implied equivalence (eg sensitivity/MDS).
ITU-R P.372-14 speaks of natural noise as including atmospheric noise due to lightning
, and also speaks of man made noise.
It is likely Youngblood is actually talking about man made noise since he uses man made noise figures from an earlier revision of P.372.
Optimal
is a compromise between weak signal performance (ie S/N degradation due to internal receiver noise) and handling of strong signals that might clip in the ADC of an SDR receiver.
He gives a table of measured MDS (minimum discernable signal, which actually is synonymous with Noisefloor) for recommended configurations of a Flex 6600 radio on several bands.

Above is Youngblood’s data with my calculated values in yellow and orange for: Continue reading Optimum receive system noise figure for given ambient noise – Flex 6600
Last update: 22nd September, 2019, 8:13 AM