N。=,N=2.5W P(0)=~=025×0W=1P()1f≤5K1 P(f) 0.25×10-3W/Hz f(KHz)9 4. N Ni 2.5W 4 1 0 = = ( ) 2 1 0.25 10 / 2 ( ) 0 3 0 W Hz P f f N P f n m n = =  = − f  5KHz 0.25 10 W / Hz −3  -5 5 f(KHz) ( ) 0 P f n