Ans) By locating the receivers at far waway places.
Now what is external noise?
- it is the Atmospheric Noise < 30 MHz ( it is very little in VHF and above.)
- it is Extra terrestrial noise 8 MHz to 1.49 Mhz ( e. g. solar noise, not much of it penetrates below 20 Mhz, penetrates down ionosphere )
- it is Industrail Noise 1 to 600 MHz
Receieved Noise increases as the receiver BW increases.