MATLAB: FSK using baseband modulation

Question

Hello,

I want to create a FSK modulator using the "*M-FSK Modulator Baseband*" block, the input is Bernoulli Binary Generator (0, 1) , but i cant get the good output ( 2 different frequencies ) on the scope in real time !!??

Block diagram : http://imageshack.us/photo/my-images/854/blocks.jpg/

Good Output signal : http://imageshack.us/photo/my-images/820/outputu.jpg/

Bad Output signal : http://imageshack.us/photo/my-images/825/signalsk.jpg/

P.S : the output shown is bad because the frequency is the same whatever the input is 0 or 1. !!!

Thanks a lot,

Bye

Answer 1

The output of the Simulink model is correct. The reason that it is not the same as the "Good Output signal" is that the Simulink signal is the complex baseband equivalent of the desired FSK signal, whereas the "Good Output signal" is the real-valued passband signal. Although these two signals are not the same, they are related.

In fact, you can generate the real-valued passband signal in the Simulink model by adding a handful of blocks that represent the passband modulation. To do so, multiply the output of the baseband modulator by a complex exponential at the desired passband frequency, and then view the real- and imaginary- parts on the scope.

HTH.