Why the spectrum I get from 'Visualiza​tion'-'Fre​quency response' in 'comm.RayleighChannel' is sometimes different from the spectrum I culculate from 'PathGainsOutputPort'?

Here is my codes, if I change 'Seed' number from '1' to '73', the spectrums will be different, why this happens？Thanks for help.

clear; clc; close all; 
rchan = comm.RayleighChannel('SampleRate',1000, ... 
    'PathDelays',[0 1e-3 2e-3],...
    'AveragePathGains',[0 -3 -6], ...
    'MaximumDopplerShift',0, ...
    'PathGainsOutputPort',true,...  
    'RandomStream','mt19937ar with seed','Seed',1,... 
    'Visualization','Frequency response');
[chanOut,pathGain] = rchan(1);
h = pathGain(1,:);
Nfft = 1000;
H = fft(h,Nfft); 
H_power_dB = 10*log10(abs(H.*conj(H)));
figure;
plot((-Nfft/2+1:Nfft/2),H_power_dB,'k-');
hold on; xlabel('Frequency[Hz]'), ylabel('Channel power[dBw]');

Answer 1

[Chaitanya Mallela]

Seed property corresponds to the generation of random stream.Seed serves as a unique identifier of a pseudo-random sequence i.e., for each particular seed there is a unique pseudo-random sequence.Once the seed is specified the same random stream is generated for each time when simulated.