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Hi! can you guide me to plot power spectra of ASK signal?

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Ny Sokunthea
Ny Sokunthea 2014-9-28
编辑： Rick Rosson 2014-9-30
I have:
- Number of data bits (1s and 0s) = 100
- Sampling frequency, fs = 100Hz
- Number of data points (samples) = 100 X fs = 10000 data points
- Block size of the FFT, N = 4096
I solve it many days, but still I can't solve it. Could you help me as fast as possible? I really need it now ! Thanks !!!
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Rick Rosson
Rick Rosson 2014-9-28
编辑：Rick Rosson 2014-9-28
I don't think that is correct. You mentioned in the comments below that the bit time Tb is 1 second per bit. So that implies that the data rate R = 1/Tb is 1 bit per second.

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回答（1 个）

Rick Rosson
Rick Rosson 2014-9-28
编辑：Rick Rosson 2014-9-28
Here's a start:
Tb = 1; % seconds per bit
R = 1/Tb; % bits per second
M = 100; % bits
b = ( rand(M,1) > 0.5 );
figure;
stem(0:M-1,b);
d = 1 - 2*b;
x = repmat(d,100,1);
x = x(:);
Fs = 100; % samples per second
N = Fs*M/R; % samples
dt = 1/Fs;
t = dt*(0:N-1)';
figure;
plot(t,x);
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Ny Sokunthea
Ny Sokunthea 2014-9-29
Yes, I tried your code last night. I understand yours. But I don't know how to use fft function to plot power. Please guide me with this function.
Rick Rosson
Rick Rosson 2014-9-30
编辑：Rick Rosson 2014-9-30
Based on your comment above, and according to the plot that you attached, it appears that you need to move the signal from the baseband to the passband at a center frequency of Fc = 4 Hertz. If you start with the code that I posted, you should be able to up convert the baseband signal x to the passband using a pure tone cosine wave to modulate the signal.
Once you have done that, you can then transform your passband signal from the time domain to the frequency domain using either fft or pwelch.
Good luck!

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