Forums

AM modulation

Started by louis July 30, 2005
Hi there, i was just playing around with the modulation function on
Matlab

here are the simple commmands I run:

� t = 5;
� t=0:0.01:10;
� y=power(sin(pi*t/(2*T)), 0.5);
� mod = modulate(y, 250, 44100, 'am');
� plot(t, mod)

so I wanted to know what I should choose my sampling frequency to be -
right now it is set to 44100, but how do I know this is appropriate? When
I plot (t,mod), it seems that it is very dependent on the sampling
frequency. Try my commands out yourself and you will see what I mean,
but can someone explain to me why this is such an issue? I woudl have
thought that as long as my sampling frequency was greater than 2*fc (where
fc in this example is set to be 250) then it wouldnt matter if I set my
sampling frequency to be at something much greater than the nyquist rate
like 44100 or 88200 for example; but plotting:

� mod = modulate(y, 250, 44100, 'am');

gives me a much different graph than plotting:

� mod = modulate(y, 250, 88200, 'am');

I just dont understand theoretically, if someone could explain it owuld be
great!
thank you!!!
-LD
		
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oops sorry I did a typo, it should actually be:

� T = 5;
� t=0:0.01:10;
� y=power(sin(pi*t/(2*T)), 0.5);
� mod = modulate(y, 250, 44100, 'am');
� plot(t, mod)

		
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