How to integrate LFM signal into pulse

I am trying to generate a Linear Frequency Modulated (LFM) Pulse waveform like below.

I generated periodic chirp signals but the problem is i can not put inside these chirps into pulse boundaries. I mean outside of the duty cycle is not zero. How can I solve this problem? By the way, I am not using a toolbox. Thank you for your help.

Answer 1

[Chunru]

fl = 100;   % Hz
fu = 200;
fs = 1000;
pw = 0.1;   % sec
pri = 1;    % sec

% LFM
t = (0:1/fs:pw)';
x = cos(2*pi*(fl*t + .5*(fu-fl)/pw*t.^2));
% One pulse
x(end+1:round(pri*fs)) = 0;

% Npulses
Npulses = 3;
y = repmat(x, [3 1]);
t = (0:length(y)-1)'/fs;

plot(t, y)

[tinkyminky93]

Error in line

x(end:round(pri*fs)) = 0

Array indices must be positive integers or logical values.

It gives error, can you help?

[Chunru]

What is your pri and fs?

[tinkyminky93]

I copied and pasted your values, its the same

[Chunru]

The code above runs on-line. What is your version of matlab?

[tinkyminky93]

R2021b, I found my fault. So how can i make the amplitude 1 which starts from 0 and goes to 1? Seems like it is oscillating at -1,1

And when I change the frequencies as F1=3e3 and F2=1e9, the Signal chirps up and down. I need just upchirp how can I solve it?

[Chunru]

So how can i make the amplitude 1 which starts from 0 and goes to 1? Seems like it is oscillating at -1,1

==> I don't understand your question.

And when I change the frequencies as F1=3e3 and F2=1e9, the Signal chirps up and down. I need just upchirp how can I solve it?

==> What is fs you used in this case?

[tinkyminky93]

I mean the Signals positive peak is 1 and the negative peak is -1. I want the signal to oscillate between 0 and 1.

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My fs is 1000 for this situation, what should I use for only just upchirp?

[Chunru]

You can try the following (but you need to know why your need to have that kind of amplitude):

fl = 100;   % Hz
fu = 200;
fs = 1000;
pw = 0.1;   % sec
pri = 1;    % sec
% LFM
t = (0:1/fs:pw)';
x = 0.5*(1+cos(2*pi*(fl*t + .5*(fu-fl)/pw*t.^2)));
plot(t, x)