Try this:
Fs = 500; % Sampling Frequency
fcomb = [19 19.5 20.5 21 177 177.5 182.5 183]; % Frequency Vector
mags = [0 1 0 1 0]; % Magnitude Vector
dev = [0.5 0.1 0.5 0.1 0.5]; % Deviations
[n,Wn,beta,ftype] = kaiserord(fcomb,mags,dev,Fs);
hh = fir1(n,Wn,ftype,kaiser(n+1,beta),'noscale');
figure
freqz(hh, 1, 2^20, Fs)
FrqLim = [0 250]; % Frequency Limits (Optional)
set(subplot(2,1,1), 'XLim',FrqLim) % Optional
set(subplot(2,1,2), 'XLim',FrqLim) % Optional
It should do what you want.
The ‘Optional’ set calls after freqz allow you to ‘zoom in’ on various parts of the spectrum if you want to, in order to see it more clearly and adjust the passbands to your requirements. Here, they are set to present the entire filter spectrum.
