![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/173911/image.jpeg)
FM modulation - all negative values somehow become positive
2 visualizzazioni (ultimi 30 giorni)
Mostra commenti meno recenti
xiaofan yang
il 23 Mar 2016
Risposto: Vidya Viswanathan
il 31 Mar 2016
I'm having a weird issue. I'm testing a simple FM modulator - demodulator. I run the code below and this is the graph I get
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/158588/image.png)
As you can see all the negative values magically become positive. But I'm really just doing a simple modulation and demodulation. What is the issue here?
Fs = 20e6;
fc=200;(Hz)
fDev = 150000;
t = (0:1/Fs:0.2)';
x = sin(2*pi*30*t)+2*sin(2*pi*60*t);
txsig = fmmod(x,fc,Fs,fDev);
dataOut = fmdemod(txsig,fc,Fs,fDev);
plot(t,x,'c',t,dataOut,'b--');
xlabel('Time (s)')
ylabel('Amplitude')
legend('Original Signal','Demodulated Signal')
0 Commenti
Risposta accettata
Vidya Viswanathan
il 31 Mar 2016
Hi,
I notice that the value of frequency deviation that you have specified is very high. This could result in over modulation which is probably why you are not getting the original signal back. If you specify the value of frequency deviation to a lower value, say 50, you would be able to restore the original signal. For example,
Fs = 20e6;
fc=200;(Hz)
fDev = 50;
t = (0:1/Fs:0.2)';
x = sin(2*pi*30*t)+2*sin(2*pi*60*t);
txsig = fmmod(x,fc,Fs,fDev);
dataOut = fmdemod(txsig,fc,Fs,fDev);
plot(t,x,'c',t,dataOut,'b--');
xlabel('Time (s)')
ylabel('Amplitude')
legend('Original Signal','Demodulated Signal')
The plot obtained for the above code is shown below.
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/173911/image.jpeg)
I hope this answers your query.
Regards,
Vidya
0 Commenti
Più risposte (0)
Vedere anche
Prodotti
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!