numpy - Something wrong with my fft() in python -

i have function supposed plot amplitude spectrum of between 10mhz , 11.4mhz. function: cos(6.72*(10**7*t) + 3.2*sin(5*(10**5*t))) know plot supposed like, mine wrong. i'm pretty sure it's programming error, not math/theory error because i'm doing matlab example showing, feel python doing i'm not understanding. i'm supposed sample function 8192 times @ 10ns apart, multiply hamming window, , plot amplitude spectrum in db between 10mhz , 11.4mhz. carrier (10.7mhz) should around 55 db. second pair of sidebands greatest amplitude @ 60 db. then, fifth pair of sidebands 20 db point, around 40 db. can spot wrong code explains why mine doesn't show this?

import numpy import scipy import scipy.fftpack import matplotlib import matplotlib.pyplot plt scipy import pi import pylab pylab import * import cmath import sys sys.setrecursionlimit(10000)  samples = 8192  #defining test function t = scipy.linspace(0.01, 32/390625, samples, false)   #sample samples times @ 10ns apart #the samples non-inclusive, goes 0 samples-1. x_t = cos(6.72*(10**7*t) + 3.2*sin(5*(10**5*t)))  #define x(t) acc = lambda t: (x_t)                             #define x[t] in terms of t variable in python's eyes   signal = acc(t)                 #make signal function of t plt.subplot(211)                #set plot plt.xlabel('ohmega (hz)')       #label x axis plt.ylabel('amplitude of sampled x(t) (db)')  #label y axis  window = numpy.hamming(samples)    #make hamming window    w = scipy.linspace(0, 100*10**6, samples, false)   #create ohmega between 1/(10ns) signal = signal * window        #multiply hamming window signal = scipy.fft(signal)      #take fft signal = abs(20*log10(signal))  #get magnitude in db scale  plt.xlabel('ohmega')            #label x axis plt.ylabel('|f[w]|')            #label y axis #marker, stemlines, baseline = stem(w,signal, 'b-..')    #plot stemlines plot(w,signal, 'b-') plt.xlim(10*10**6, 11.4*10**6)  #set x-limits  plt.show()                      #show plot 

thanks help!

edit:

my code now:

import numpy import scipy import scipy.fftpack import matplotlib import matplotlib.pyplot plt scipy import pi import pylab pylab import * import cmath import sys sys.setrecursionlimit(10000)  samples = 8192  #defining test function t = scipy.linspace(0.01, 32/390625, samples, false)         #sample samples times @ 10ns apart #the samples non-inclusive, goes 0 samples-1. x_t = cos(6.72*(10**7*t) + 3.2*sin(5*(10**5*t)))            #define x(t) acc = lambda t: cos(6.72*(10**7*t) + 3.2*sin(5*(10**5*t)))  #define x[t] in terms of t variable in python's eyes   #signal = acc(t)                 #make signal function of t plt.subplot(211)                #set plot plt.xlabel('ohmega (hz)')       #label x axis plt.ylabel('amplitude of sampled x(t) (db)')  #label y axis  window = numpy.hamming(samples)    #make hamming window    w = scipy.linspace(0.01, 100*10**6, samples, false)   #create ohmega between 1/(10ns) signal = lambda t: abs(20*log10(scipy.fft(acc*window))) #acc = acc * window        #multiply hamming window #acc = scipy.fft(acc)      #take fft #acc = abs(20*log10(acc))  #get magnitude in db scale  plt.xlabel('ohmega')            #label x axis plt.ylabel('|f[w]|')            #label y axis #marker, stemlines, baseline = stem(w,signal, 'b-..')    #plot stemlines  plot(w,signal, 'b-') plt.xlim(10*10**6, 11.4*10**6)  #set x-limits  plt.show()                      #show plot 

and error...:

    traceback (most recent call last):   file "/home/hollis/documents/elen 322/elen_322_#2.py", line 39, in <module>     plot(w,signal, 'b-')   file "/usr/lib/pymodules/python2.7/matplotlib/pyplot.py", line 2467, in plot     ret = ax.plot(*args, **kwargs)   file "/usr/lib/pymodules/python2.7/matplotlib/axes.py", line 3893, in plot     line in self._get_lines(*args, **kwargs):   file "/usr/lib/pymodules/python2.7/matplotlib/axes.py", line 322, in _grab_next_args     seg in self._plot_args(remaining, kwargs):   file "/usr/lib/pymodules/python2.7/matplotlib/axes.py", line 300, in _plot_args     x, y = self._xy_from_xy(x, y)   file "/usr/lib/pymodules/python2.7/matplotlib/axes.py", line 240, in _xy_from_xy     raise valueerror("x , y must have same first dimension") valueerror: x , y must have same first dimension 

while i've seen , fixed error before, have no idea how fix now. apparently signal sampled 8192 times , variable determining sampled different dimensions. i'm lost on one...

your error might come way define x(t) :

x_t = cos(6.72*(10**7*t) + 3.2*sin(5*(10**5*t)))  #define x(t) acc = lambda t: (x_t)  #define x[t] in terms of t variable in python's eyes 

when python executes first line, assigns variable x_t value of formula you're given using current value of t ( scipy.linspace(0.01, 32/390625, samples, false) ). doesn't interpret t variable.

to fix change second line :

acc = lambda t: cos(6.72*(10**7*t) + 3.2*sin(5*(10**5*t))) 

edit : noticed did same signal. writing : signal = acc(t) (even if fixed acc) assign result of function acc(t) (with current value of t) variable signal. won't function. (why don't use acc instead of signal acc function of t anyway ?)