Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

how to calculate the frequency of a signal ...

Status
Not open for further replies.
S

savage67

Member level 1
Joined
Sep 25, 2006
Messages
40
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,286
Activity points
1,587
pxx = x.*conj(x)/512;

i m writing a program in matlab to make the fft analysis of the signal which the user determine
but i dont know how to measure the period of tha signal..

how to calculate the frequency or period of a signal which has two component with different frequencies
like A.sin(w1.t)+B.cos(w2.t)
plz help meee
 

It strongly depends upon coeficients A,B,w1, w2.
But in most cases signal would not be periodical but pseudoperiodical if not even nonperidical.
f(t)=A.sin(w1.t)+B.cos(w2.t)

The definition for peridical signals says:
f(t)=f(t+T), where t is time and T period.
so you should solve the equation:
A.sin(w1.t)+B.cos(w2.t) =A.sin(w1(t+T))+B.cos(w2(t+T))
and get T if f(t) would be periodical but I don't thik it is since it has boath frequencies w1 and w2
 

as long as w1 and w2 are far enough, you should see 2 peaks after fft analysis.
 

In help of Matlab you can find an example:

t = 0:0.001:0.6;
x = sin(2*pi*50*t)+sin(2*pi*120*t);
y = x + 2*randn(size(t));
plot(1000*t(1:50),y(1:50))
title('Signal Corrupted with Zero-Mean Random Noise')
xlabel('time (milliseconds)')

X = fft(x,512);
Y = fft(y,512);
Pxx = X.* conj(X) / 512;
Pyy = Y.* conj(Y) / 512;

f = 1000*(0:256)/512;
plot(f,Pyy(1:257))
title('Frequency content of y')
xlabel('frequency (Hz)')

x : periodical signal
y ; with additional noise

Visualisation of Pyy or Pxx reveals the frequency content of the signals y and x
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top