Am receiver

Hello friends,

I(shijesh) made debute to USRP & GNUradio a few days back.
I have a querry as mentioned after the environment observations given
below

My environment is :
O.S :: Ubuntu 7.04 Feisty fawn
CPU :: Core2 DUO Intel
gcc :: 4.2.0
SWIG :: 1.3.31
GNU CODE VERSION :: 3.0.4

when i tried to receive AM with the program “am_rcv.py” , it didn’t
work. Later on when i went through the code i realised that, it did not
feature the option for changing the SOUND CARD RATE , so i modified
the program as shown below, but even then it was all in vain

###### program for receiving AM ########***
#!/usr/bin/env python
from gnuradio import gr, eng_notation
from gnuradio import audio
from gnuradio import usrp
from gnuradio.eng_option import eng_option
from optparse import OptionParser
import sys
import math
from gnuradio.wxgui import stdgui, fftsink
import wx
class am_rx_graph (stdgui.gui_flow_graph):
def init(self,frame,panel,vbox,argv):
stdgui.gui_flow_graph.init (self,frame,panel,vbox,argv)

######modified for including option for changing the sound card rate
#######

    parser=OptionParser(option_class=eng_option)
    parser.add_option("-O", "--audio-output", type="string", 

default="",
help=“pcm device name. E.g., hw:0,0 or
surround51 or /dev/dsp”)

    (options, args) = parser.parse_args()
    if len(args) != 0:
        parser.print_help()
        sys.exit(1)

    self.frame = frame
    self.panel = panel

    self.vol = 0
    self.state = "FREQ"
    self.freq = 0

###################### modification ends ######################
station = parseargs(argv[1:])
offset_freq = 30e3
IF_freq = offset_freq - station
adc_rate = 64e6
usrp_decim = 250
if_rate = adc_rate / usrp_decim # 256 kHz
if_decim = 4
demod_rate = if_rate / if_decim # 64 kHz
audio_decimation = 2
audio_rate = demod_rate / audio_decimation # 16 kHz

    # usrp is data source
    src = usrp.source_c (0, usrp_decim)
    src.set_rx_freq (0, IF_freq)
    actual_IF_freq =src.rx_freq(0)
    actual_offset = actual_IF_freq + station

    #print actual_IF_freq
    #print actual_offset

    src.set_pga(0,20)
    # sound card as final sink
    audio_sink = audio.sink (int (audio_rate), options.audio_output, 

False)

    channel_coeffs = \
                   gr.firdes.low_pass (1.0,           # gain
                                       if_rate,   # sampling rate
                                       9e3,         # low pass 

cutoff freq
10e3, # width of
trans. band
gr.firdes.WIN_HANN)
ddc = gr.freq_xlating_fir_filter_ccf
(if_decim,channel_coeffs,-actual_offset,if_rate)
magblock = gr.complex_to_mag()
volumecontrol = gr.multiply_const_ff(.003)
# Deemphasis. Is this necessary on AM?
TAU = 75e-6 # 75us in US, 50us in EUR
fftaps = [ 1 - math.exp(-1/TAU/if_rate), 0]
fbtaps= [ 0 , math.exp(-1/TAU/if_rate) ]

    deemph = gr.iir_filter_ffd(fftaps,fbtaps)
      # compute FIR filter taps for audio filter
    width_of_transition_band = audio_rate / 8
    audio_coeffs = gr.firdes.low_pass (1.0,            # gain
                                       if_rate,      # sampling rate
                                       9e3,         #audio_rate/2 - 

width_of_transition_band,
4e3, #
width_of_transition_band,
gr.firdes.WIN_HANN)

    # input: float; output: float
    audio_filter = gr.fir_filter_fff (audio_decimation, 

audio_coeffs)

    print len(channel_coeffs)
    print len(audio_coeffs)

    # now wire it all together
    self.connect (src, ddc)
    self.connect (ddc, magblock)
    self.connect (magblock, volumecontrol)
    self.connect (volumecontrol,deemph)
    self.connect (deemph,audio_filter)
    self.connect (audio_filter, (audio_sink, 0))
      if 1:
        pre_demod = fftsink.fft_sink_c (self, panel, 

title=“Pre-Demodulation”, fft_size=128, sample_rate=if_rate)
self.connect (src, pre_demod)
vbox.Add (pre_demod.win, 1, wx.EXPAND)
if 0:
post_demod = fftsink.fft_sink_c (self, panel, title=“Post
Demodulation”, fft_size=256, sample_rate=demod_rate)
self.connect (ddc, post_demod)
vbox.Add (post_demod.win, 1, wx.EXPAND)
if 0:
post_filt = fftsink.fft_sink_f (self, panel, title=“Post
Filter”, fft_size=512, sample_rate=audio_rate)
self.connect (magblock,post_filt)
vbox.Add (post_filt.win, 1, wx.EXPAND)

def parseargs (args):
nargs = len (args)
if nargs == 1:
freq1 = float (args[0]) * 1e3
else:
sys.stderr.write (‘usage: am_rcv freq1\n’)
sys.exit (1)
return freq1
if name == ‘main’:
app = stdgui.stdapp (am_rx_graph, “AM RX”)
app.MainLoop ()
############################program endss########################

I have used the following command for the execution
###############################################################
[email protected]:/home/sabu#
GNUradio/gnuradio-3.0.4/gnuradio-examples/python/usrp/am_rcv.py 1164000
-o plughw:0,0
#############################################################
I know that it is a silly question for all of u friends, but for me it
really will be worth, Please extend your helping hand.

SHIJESH AK
INDIA