0 个投票

in butter(1,wn) i know wn is normal frequency =(cut off/nyq.freq) in amplitude modulation what will be wn=? if carrier freq=fc and i calulat 0:.001:1 sample and message freq fm

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Rick Rosson
Rick Rosson 2012-1-6

0 个投票

Code:
dt = 0.001; % sampling time (seconds per sample)
Fs = 1/dt; % sampling rate (samples per second)
Fnyq = Fs/2; % Nyquist frequency (hertz)
Fco = fm + bw; % Cut-off frequency (hertz)
wn = Fco/Fnyq; % Normalized cut-off (dimensionless)
Explanation:
  • dt is the sampling time (in seconds per sample)
  • Fs is the sampling rate (in samples per second)
  • Fnyq is the Nyquist frequency (in hertz)
  • Fco is the cutoff frequency (in hertz)
  • bw = bandwidth (in hertz)
  • Fc is not needed to compute wn
You should make sure that the following conditions are true:
bw << fm << fc
and
bw << fm << Fs
HTH.
Rick

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excellent ,now if i have a message like cos(2*pi*fm*t), and i want to build function which make frequency modulation
for this message it does not work and if it work(some times) the receiver can not be bone my problem is to how to make discriminator and how to put the message in frequency and how to see spectrum of signal and somthing else i add to am signal a noise (awgn) is this code correct
snr=10^(snr/10);
vn=var(tx)/snr; %AWGN channl
n=sqrt(vn)*randn(1,1001);
tx=tx+n;
assuming t=0:.001:1
and tx is the transmitted signal

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Rick Rosson
Rick Rosson 2012-1-5

0 个投票

Please try:
dt = 0.001;
Fs = 1/dt;
Fnyq = Fs/2;
Fco = fm + bw;
wn = Fco/Fnyq;
HTH.

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i can not understand what you write please, more details.
thanks
Rick Rosson
Rick Rosson 2012-1-6
Try it.
Walter Roberson
Walter Roberson 2012-1-6
Fs - sampling frequency
Fnyq - nyquist frequency
fm - message frequency
Fco - cutoff frequency
wn - wn to use for butter()
I have not figured out what bw is, or where fc fits in.
Rick Rosson
Rick Rosson 2012-1-6
bw = bandwidth (in hertz)
Fc is not needed to compute wn
Rick Rosson
Rick Rosson 2012-1-6
The idea of bandwidth is that the message has a spectrum that extends across a range of frequencies centered at f = fm. You can assume that the range is [ fm-bw ... fm+bw ].
Rick Rosson
Rick Rosson 2012-1-6
You should also make sure that the following conditions are true:
bw << fm
and
fm << fc

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