MATLAB >> chirp function

by Tim Teatro » Mon, 26 Apr 2004 18:07:38 GMT

Hi. I'm realy sorry to ask this, but do I have to load something before I
can use the chirp function? I can't seem to find an m-file for it in the
matlab directory.

thanks

MATLAB >> chirp function

by loren.shure » Mon, 26 Apr 2004 19:45:08 GMT


In article < XXXX@XXXXX.COM >, XXXX@XXXXX.COM
says...

chirp.m is a function in the Signal Processing Toolbox. Perhaps you don't have
that on your path.

--Loren

MATLAB >> Chirp Function

by Dali » Tue, 27 Sep 2005 18:04:33 GMT

Hi everybody.

Currently, I'm writing a program using the built-in chirp function.
The duration of my chirp is very short: between 0.4 to 1 microsecond.

When the frequency range of my chirp is between 0 and 10 MHz, my
Chirp is okay and its autocorrelation function gives a sinc function
as the theory says.
But when I change the frequency range between 10 to 20 MHz, then the
sinc is completely degraded. In fact, the amplitude of its side lobes
increase a lot.
I don't think it's a problem of aliasing because my sampling
frequency is very high.
So I don't understand this problem because according to the theory,
the shape of the sinc depends of the bandwidth and not the starting
frequency.
Is there anyone who knows the answer to my problem?

Thanks a lot

MATLAB >> Chirp Function

by Jordan Smith » Thu, 01 Jun 2006 12:00:41 GMT

I want to make a chirp function that varies the frequency on time. I
have tried to use the chirp function but I want to make the chirp
function to do the following:

Have slight noise / begining of the function... increase the
amplitude continue to vary the frequency based on the time. Finally
decrease the amp. at the end of the time desired. I have something
like this; however, it just makes a single jump.

I am not sure what else to do... Sort of new at this whole MATLAB
thing.
See below two methods:

Here is one method I've tried:
% inputs--
% TW: Time bandwidth product
% p: oversampling factor
% sampfreq: sampling frequency to be used

%s: Single LFM chirp created per input specs
%h: The match filter impulse response (i.e. h(t))
%y: (TESTING PURPOSES ONLY)
% The result of passing created chirp through
% match filter
%T: Time duration of LFM chirp (units: sec)
%W: Swept Bandwidth of LFM chirp (units: Hz)
%Ts: Sampling period (1/fs)

sig2=100;
sampfreq=1;
TW=30000;
p=1;
Ts=.0001;
Ts = 1/ (sampfreq) %1/(20*(10 ^6)) % 1 / (p*W)

T = TW * p *Ts

W = TW / T

N = round( T/Ts); % round(T*W*p)
n = [0:N-1]';

s = exp(j*pi* (W/T) *(n*Ts - T/2).^2 );
h = exp(-j*pi* (W/T) *(n*Ts - T/2).^2 );

y = conv(s,h);

for n = 1:length(sig2) %create 700 point signal with chirp
column = 253+n; % chirp in the middle
blank2(1,column)=sig2(1,n);
end
blank2(1,446:700) = 0;

h=h';
for n = 1:length(h)
column = 253+n;
h2(1,column)=h(1,n);
end
h2(1,446:700) = 0;
n = (.2) .* crandn(1,700) ;
q=std(n);
q/(sqrt(10))
mean(real(sig2))
clear blank2noise
blank2noise=blank2+n;
y = conv(blank2noise,h);
figure, plot(real(y));

Method 2:
just trying to use the chirp and trying to sum two different chirps
one from going dc to say 100hz and then from 100hz to 0 again.

MATLAB >> Chirp Function

by Jordan Smith » Fri, 02 Jun 2006 00:56:54 GMT

I want to create a chirp function that looks like the following
description:

time varying harmonic /w amplitude at near zero going to X amount and
then decreasing back to 0.

Any suggestions?

MATLAB >> Chirp Function

by Jordan » Fri, 02 Jun 2006 01:32:30 GMT

Actually sorry about this.

What I ment to really ask was this:

I am trying to make an LFM chirp however everytime i make one I get a
weird fourier transform. I am trying to get it so that it looks like
this:
< http://cnx.org/content/m11718/latest/> ;

I am using the following code. Anyone suggestions?

sig2=100;
sampfreq=50;
TW=50;
p=10;
Ts=.001;

Ts = 1/ (sampfreq) %1/(20*(10 ^6)) % 1 / (p*W)

T = TW * p *Ts

W = TW / T

N = round( T/Ts); % round(T*W*p)
n = [0:N-1]';

s = exp(j*pi* (W/T) *(n*Ts - T/2).^2 );
h = exp(-j*pi* (W/T) *(n*Ts - T/2).^2 );

y = conv(s,h);

for n = 1:length(sig2) %create 700 point signal with chirp
column = 253+n; % chirp in the middle
blank2(1,column)=sig2(1,n);
end
blank2(1,446:700) = 0;

clear blank2noise
blank2noise=blank2+n;
% figure, plot(real(blank2noise))
y = conv(blank2noise,h);
figure, plot(real(y))
z=abs(fft(y));
figure,plot(z);

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fs = 500;                           % Sample frequency
N = 512;                            % Signal length
f1 = 20;                            % Starting frequency in Hz
f2 = 200;                           % Frequency after 1
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T=(1/fs);                           % Sample Period
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% Converts input signal
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