问题
I am trying to Frequency modulate a sine signal using Matlab. I have written the following code for the same:
fc = 5000; %Carrier Frequency
fs = 1000; %Signal Frequency
t = 0:0.00001:0.002;
x = sin(2*pi*fs*t);
dev = 50;
subplot(2,1,1);
plot(t,x);
y = fmmod(x,fc,fs,dev);
subplot(2,1,2);
plot(t,y);
It is able to display the first plot command but not the second one. It throws an error: `fmmod' undefined near line 10 column 5. What is wrong in the above code?
回答1:
The following function will generate a FM modulated signal - it's not as good (flexible, etc) as fmmod but if you don't have the Comm System Toolbox this may be a good alternative.
function [s t] = makeFM( x, Fc, Fs, strength )
% for a signal x that modulates a carrier at frequency Fc
% produce the FM modulated signal
% works for 1 D input only
% no error checking
x = x(:);
% sampling points in time:
t = ( 0 : numel( x ) - 1 )' / Fs;
% integrate input signal
integratedX = cumsum( x ) / Fs;
s = cos( 2 * pi * ( Fc * t + strength * integratedX ));
Put this in your path and call it with similar arguments to the fmmod function (but without optional parameters):
fc = 5000; %Carrier Frequency
fs = 1000; %Signal Frequency
t = 0:0.00001:0.002;
x = sin( 2*pi*fs*t );
dev = 50;
subplot(2,1,1);
plot(t,x);
y = makeFM(x, fc, 2.5*fc, dev); % note sampling frequency must be > carrier frequency!
subplot(2,1,2);
plot(t,y);
Let me know how that works for you.
回答2:
I guess this is more simple approach
clc;
clear all;
close all;
fm=input('Message Frequency=');
fc=input('Carrier Frequency=');
mi=input('Modulation Index=');
t=0:0.0001:0.1;
m=sin(2*pi*fm*t);
subplot(3,1,1);
plot(t,m);
xlabel('Time');
ylabel('Amplitude');
title('Message Signal');
grid on;
c=sin(2*pi*fc*t);
subplot(3,1,2);
plot(t,c);
xlabel('Time');
ylabel('Amplitude');
title('Carrier Signal');
grid on;
y=sin(2*pi*fc*t+(mi.*sin(2*pi*fm*t)));%Frequency changing w.r.t Message
subplot(3,1,3);
plot(t,y);
xlabel('Time');
ylabel('Amplitude');
title('FM Signal');
grid on;
来源：https://stackoverflow.com/questions/19097771/matlab-fm-modulation