How to sample a very small duration signal

I have a signal with time duration T= 20 micro seconds and have to sample it at 100 MHz.Then I need only 50 samples from the sampled signal. Which is the correct way to do it? 1. t = 0:1/fs: T-(1/fs) and select the first 50 samples OR 2. t = 0:1/fs: 1-(1/fs) and select the first 50 samples ?

Answer 1

[Star Strider]

When in doubt, experiment!

For example:

T= 2E-5;                            % Signal Duration (seconds)
fs = 1E+8;                          % Sampling Frequency (Hz)
t = 0:1/fs: T-(1/fs);               % Time Vector
Tlims = [t(1)  t(end)]              % Time Vector: Beginning & End (seconds)
Tlimus = Tlims * 1E+6               % Time Vector: Beginning & End (microseconds)

Tlims =
            0    1.999e-05

Tlimus =
            0        19.99

So the first time vector assignment will give you the correct times, and a (1x2000) length vector. (The 1E+6 conversion factor is in units of microseconds/second, to confirm that the vector is correct for what you want to do.)