How to limit the frequency range while plotting frequency response of Z transfer function using FREQZ command?

Question

Samir Gautam 2019-3-29

0
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https://ww2.mathworks.cn/matlabcentral/answers/453189-how-to-limit-the-frequency-range-while-plotting-frequency-response-of-z-transfer-function-using-freq

Hi all,

I want to plot the frequency response of a comb filter which has notches at the frquencies multiple of 50Hz. I want to plot it within a range of 1Hz to 1 KHz.. The transfer function is as below:

I am using the following command to plot the frequency response,

fs=10000;
n=5000;
N=202;
for i=1:N   
        numc(i)=0;   
end
for k=1:N  
        denc(k)=0;   
end
numc(1)=150.6;
numc(2)=-150.1;
numc(201)=-150.6;
numc(202)=150.1;
denc(1)=200;
denc(2)=-200;
denc(201)=-109.7;
denc(202)=109.7;
%sys=filt(numc,denc,Tsam)
freqz(numc,denc,n,fs);

I have two questions:

(1) How can i limit the range of the frequency range such that the n evaluation points are within that range.

(2) Best value of n : If n is integer multiple of 512, the plots are smooth, however if not, it looks as if some evaluation points are missing. Some figures attached below:

So how can i plot the frequency response which is smooth over the selected range of frequency. And how do i find the optimum value of n. I appreciate your suggestions in this regard.

Thank you!

Best Regards