Chirp (Swept-frequency cosine) Signal Generation

Hello everyone,

I am trying to generate the chirp signal which can be also named as Swept-frequency cosine. My signal's frequency should increase with respect to triangular signal as you can see. The problem is that, I did the increasing part but I could not integrate the decreasing part to the increasing part. It should be continuous, vary with the triangular signal and this signal must be one piece. My code is written below. Thanks for your helps...

t = 0:1/10000:2;

y = chirp(t,0,1,25);

plot (t,y);

hold on

T = 10*(1/50);

fs = 10000;

t = 0:1/fs:4;

x = sawtooth(2*pi*0.25*t,1/2);

plot(t,x, 'green', 'linewidth', 3);

grid on

Expected Signal Waveform:

My signal:

Answer 1

[Star Strider]

Change the first plot call to:

plot (t,y, t(end)+t,fliplr(y));

If I understand correctly, that should do what you want.

[enrique128]

can we define it as a signal sir? I will use it in while loop so, only changing the plot call will not solve my problem :(

[Star Strider]

I am not certain what result you want.

It is straightforward to create a single time vector and a single signal vector:

tv = t;
yv = [y fliplr(y(1:end-1))];

Then to plot them:

figure
plot(tv, yv)

Using ‘y(1:end-1)’ in the flipped version prevents duplication of the centre element. It also makes the two vectors equal length.

[enrique128]

You understand it correctly sir, it works for me so much thanks! The result I want is, increasing frequency until the sharp point of triangular wave, then decreasing frequency until the end of the triangular wave. To get this result, I need to define this waves in a single signal. For example lets say increasing signal A and decreasing signal B, then my all signal is sig= A+B so that it it the summation of two signals and increases&decreases until the values that I want. Hope it is clear for you sir.

[Star Strider]

As always, my pleasure!

I do not entirely understand the addition operation, however. My code concatenates the vectors instead: [A B].

[enrique128]

Sir now I want to define this signal in while loop and I want signal to continue until the point that I want. When I write your code it finishes at 4. What should I do to make this signal infinite length? Thanks :)

[Star Strider]

I am not certain what you want to do. One option is simply to repeat it, another option is to use the repmat function for ‘y’ and create ‘t’ using the linspace function, so it matches the length of the extended ‘y’ vector.

[enrique128]

How can I simply repeat it by linspace? Thanks in advance.

[Star Strider]

I would do something like this:

t = linspace(0, numel(y), numel(y)/fs;

Experiment with tha, since I am not certain what you want. (The linspace function is easier to use in this instance than the colon operator.)

[enrique128]

Sir all I want to do is make this signal periodic. It says

Error using plot

Vectors must be the same length.

Error in Untitled2 (line 9)

plot (tv,y, t(end)+t,fliplr(y));

[Star Strider]

I was thinking of something like this:

tv = t;
yv = [y fliplr(y(1:end-1))];
figure
plot(tv, yv)

yve = repmat(yv, 1, 3);
tve = linspace(0, numel(yve), numel(yve))/fs;

figure
plot(tve, yve)
grid
xlim([min(tve) max(tve)])

I only extended it to 3 times its original length here.

Experiment with it to get the result you want.