how can i plot a sine wave which is 5*sin(2*pi*50*t) for 20 seconds and 5*sin(2*pi*55*t) for next 30 seconds and again repeating 5*sin (2*pi*50*t)

 i need to plot a sine wave of 5*sin(2*pi*50*t) for 20 seconds and 5*sin(2*pi*55*t) for 21 to 50 seconds..how can i plot a above mentioned  signal using matlab programme?

Answer 1

[Wayne King]

Your title has something very different from your actual post, so I'm not sure what you actually want. And following your post, did you really want a 1 second gap with no sine wave? This does want you state in the actual body of your post.

 t = 0:1/200:50;
 x = zeros(size(t));
 x = 5*sin(2*pi*50*t).*(t<=20)+5*sin(2*pi*55*t).*(t>20);
 plot(t,x)

[mskumarsajeesh mskumar]

hi thanks for reply... i need to plot a sine wave .... the specifications are....magnitude is 5 and frequency is 50 hz[5*sin(2*pi*50*t)],the wave should follow the frequency of 50 hz for first 20 seconds.then it is changing frequency to 55 Hz and magnitude is still 5 for next 30 seconds.[5*sin(2*pi*55*t)].how can i plot this signal?

[Wayne King]

Basically, that is exactly the answer I gave you initially. I have removed the 1 second pause now. See the above example.

[mskumarsajeesh mskumar]

Its worked correctely thanks for your help...