def am_rx_BPF(N_order = <NUM_LIT:7>, ripple_dB = <NUM_LIT:1>, B = <NUM_LIT>, fs = <NUM_LIT>):
b_bpf,a_bpf = signal.cheby1(N_order,ripple_dB,<NUM_LIT:2>*np.array([<NUM_LIT>-B/<NUM_LIT>,<NUM_LIT>+B/<NUM_LIT>])/fs,'<STR_LIT>')<EOL>return b_bpf,a_bpf<EOL>
Bandpass filter design for the AM receiver Case Study of Chapter 17.

Design a 7th-order Chebyshev type 1 bandpass filter to remove/reduce
adjacent channel intereference at the envelope detector input.

Parameters
----------
N_order : the filter order (default = 7)
ripple_dB : the passband ripple in dB (default = 1)
B : the RF bandwidth (default = 10e3)
fs : the sampling frequency 

Returns
-------
b_bpf : ndarray of the numerator filter coefficients
a_bpf : ndarray of the denominator filter coefficients

Examples
--------
>>> from scipy import signal
>>> import numpy as np
>>> import matplotlib.pyplot as plt
>>> import sk_dsp_comm.sigsys as ss
>>> # Use the default values
>>> b_bpf,a_bpf = ss.am_rx_BPF()

Pole-zero plot of the filter.

>>> ss.zplane(b_bpf,a_bpf)
>>> plt.show()

Plot of the frequency response.

>>> f = np.arange(0,192/2.,.1)
>>> w, Hbpf = signal.freqz(b_bpf,a_bpf,2*np.pi*f/192)
>>> plt.plot(f*10,20*np.log10(abs(Hbpf)))
>>> plt.axis([0,1920/2.,-80,10])
>>> plt.ylabel("Power Spectral Density (dB)")
>>> plt.xlabel("Frequency (kHz)")
>>> plt.show()