Spectrogram function with respect to doppler signals

Hi, I have a radar signal which I have acquired using the data acquisition toolbox of MATLAB and have plotted a freq v/s time waveform of the signal (of 2000 data samples) using the spectrogram function. The problem is, the duration of the doppler signal is around 20ms and from the spectrogram plot, I am getting the duration of the doppler signal to be around 300ms. If I try limiting the data samples (to say around 400) and then using spectrogram function to plot the data, I am able to get a time duration of 20ms but I am unable to see any frequency content for that 20ms duration. i.e as the time resolution increases the frequency resolution decreases and i am not able to see any frequency content for that small duration. I have heard that its possible to get a clear spectrogram plot with frequencies even in 20ms duration interval. So can someone pl. help me out with this problem? I am attaching the code and the spectrogram plot for your reference %code

fs=8000; y=dop(8000:10000);

figure; windowsize = 128; window = kaiser(windowsize,5); nfft = windowsize; noverlap = windowsize-1; [S,F,T] = spectrogram(y,window,noverlap,nfft,fs); imagesc(T,F,log10(abs(S))) set(gca,'YDir','Normal') xlabel('Time (secs)') ylabel('Freq (Hz)') title('Short-time Fourier Transform spectrum')

Please observe the point 1 to 1.2 on the time axis. That is the duration of my actual doppler and it is for a period of 200ms. The question is to obtain the same plot for a duration of 20ms.