plot a inear sweep & stepped sweep

Hello,

I am try to plot a linear sweep & stepped sweep. (The attached picture)

condition:

Freauency range from 20Hz-20kHz

Time from 0-100ms

How the code can do it ? Tnanks!

[Rik]

What have you tried so far? And do you only want to have the plot, or do you need the time,frequency pairs at some resolution?

[ting po chun]

Hi,

This my code so far.

fc1=20;   %start frequency (Hz)
fc2=20e3;  %end frequency (Hz)
dt=25e-6;    %time step (s)
A0=0;       %mean value of signal
A1=1;       %amplitude of oscillation
Tend=1;     %chirp duration (s)
t=0:dt:Tend;                                %time vector
theta=2*pi*(fc1*t+(fc2-fc1)*t.^2/(2*Tend)); %theta vector
plot(t, theta)

and I want use the linear function is f(t)=fc1+(fc2-fc1)/t

and i want use the stepped function is f(t)=fc1+(fc2-fc1)n/N-1

N is the stepped and n is the frequency index from 0~N-1

[Image Analyst]

Would the built-in chirp function help you?

help chirp

 CHIRP Swept-frequency cosine generator.
    Y = CHIRP(T) generates samples of a swept-frequency signal at the time 
    instances defined in array T. By default, the instantaneous frequency
    at time 0 is 0, and the instantaneous frequency one second later is 100
    Hz.    
 
    Y = CHIRP(T,F0,T1,F1) generates samples of a linear swept-frequency
    signal at the time instances defined in array T. The instantaneous 
    frequency at time 0 is F0 Hz. The instantaneous frequency F1 is 
    achieved at time T1.
 
    Y = CHIRP(T,F0,T1,F1,method) specifies alternate sweep methods.
    Available methods are 'linear', 'quadratic', and 'logarithmic'; the
    default is 'linear'. For a logarithmic-sweep, F0 must be greater than 
    or equal to 1e-6 Hz, which is also the default value.
 
    Y = CHIRP(T,F0,T1,F1,method,PHI) specifies an initial phase PHI in 
    degrees. By default, PHI = 0.
 
    Y = CHIRP(T,FO,T1,F1,'quadratic',PHI,'concave') generates samples of a
    quadratic swept-frequency chirp signal whose spectrogram is a parabola 
    with its concavity in the positive frequency axis.
 
    Y = CHIRP(T,FO,T1,F1,'quadratic',PHI,'convex') generates samples of a
    quadratic swept-frequency signal whose spectrogram is a parabola with
    its convexity in the positive frequency axis.
    
    Y = CHIRP(...,sigtype) specifies sigtype as 'real' or 'complex'; the 
    default is 'real'. When sigtype is set to 'real', CHIRP generates real  
    chirp signals. When set to 'complex', CHIRP generates complex chirp 
    signals. 
 
    EXAMPLE 1: Compute the spectrogram of a linear chirp.
      t = 0:0.001:2;                    % 2 s at 1 kHz sample rate
      y = chirp(t,0,1,150);             % Start at DC, cross 150 Hz at 
                                        % t = 1 s
      spectrogram(y,256,250,256,1E3);   % Display the spectrogram
 
    EXAMPLE 2: Compute the spectrogram of a quadratic chirp.
      t = -2:0.001:2;                   % +/-2 s at 1 kHz sample rate
      y = chirp(t,100,1,200,'q');       % Start at 100 Hz, cross 200 Hz at
                                        % t = 1 s
      spectrogram(y,128,120,128,1E3);   % Display the spectrogram
 
    EXAMPLE 3: Compute the spectrogram of a convex quadratic chirp
      t = 0:0.001:1;                    % 1 s at 1 kHz sample rate
      fo = 25;                          % Start at 25 Hz,
      f1 = 100;                         % go up to 100 Hz
      y = chirp(t,fo,1,f1,'q',[],'convex');
      spectrogram(y,256,200,256,1000);  % Display the spectrogram.
 
    EXAMPLE 4: Compute the spectrogram of a concave quadratic chirp
      t = 0:0.001:1;                    % 1 s at 1 kHz sample rate
      fo = 100;                         % Start at 100 Hz,
      f1 = 25;                          % go down to 25 Hz
      y = chirp(t,fo,1,f1,'q',[],'concave');
      spectrogram(y,256,200,256,1000);  % Display the spectrogram.
 
    EXAMPLE 5: Compute the spectrogram of a logarithmic chirp
      t = 0:0.001:10;                   % 10 s at 1 kHz sample rate
      fo = 10;                          % Start at 10 Hz,
      f1 = 400;                         % go up to 400 Hz
      y = chirp(t,fo,10,f1,'logarithmic');
      spectrogram(y,256,200,256,1000);  % Display the spectrogram
 
    EXAMPLE 6: Compute a complex-valued linear chirp
      t = 0:0.001:2;                    % 2 s at 1 kHz sample rate
      fo = -50;                         % Start at -50 Hz,
      t1 = 1;
      f1 = 200;                         % cross 200 Hz at t = 1 s
      y = chirp(t,fo,t1,f1,'complex'); 
      spectrogram(y,256,200,256,1000,'centered'); % Display the spectrogram
 
    See also GAUSPULS, SAWTOOTH, SINC, SQUARE.

    Documentation for chirp
       doc chirp

[ting po chun]

Thanks for your help. But i want to plot like the picture. one line is linear other one is stepped.

Answer 1

[KALYAN ACHARJYA]

t=0:8:100;
f=linspace(20,2000,length(t));
stairs(t,f);
xlabel('Time');
ylabel('Frequency');
hold on
plot(0:100,linspace(20,2000,101))
hold off    

If the use of the inbuilt stair function is not allowed, modify the code according to the requirements, finding alternative methods such as the step function or other approaches can be done.

[ting po chun]

Thank so much & thank all of your help

[ting po chun]

Now i have the other queston.

I want to plot a stepped frequency singal (like the picture)

(Time during 0 to 1 sec)