19 in video systems a 50 db signal to noise ratio is a generally.
Current noise floor.
In signal theory the noise floor is the measure of the signal created from the sum of all the noise sources and unwanted signals within a measurement system where noise is defined as any signal other than the one being monitored.
Mean noise pow er would be 174 dbm 10 log 4x10 9 174 dbm 96 db 78 dbm.
The noise floor will naturally go up as the band opens at night as you are able to hear more distant natural and man made noise sources.
Noise is naturally stronger with decreasing frequency and s meters are rarely calibrated to any standard so a s7 noise floor on 40 meters may just be ordinary.
Generally measured in db of its maximum undistorted output signal to its residual output noise or noise floor up to 120 db of dynamic range may be required in high performance sound systems in typical homes.
A skilled operator might only be able to distinguish a signal 3 db above the noise floor s n 3 db or 75 dbm.
Analyzing noise in general can be difficult as there are a variety of intrinsic noise sources and these intrinsic noise sources are unique to different systems.
A typical radar receiver would require a s n of 3 to 10 d b to distinguish the signal from noise and would require 10 to 20 db to track.