#!/usr/bin/env python
#
#                    Weaver SSB demodulation
#
#
#                                          af_loi
#                                            |
#                               --[lpf2i]---(X)---|
#                               |         af_mixi |
#                               |                 |
# signal --[freq xlating]--[split]               (+)----- ssb_demod
#          [fir filter  ]       |                 |  + USB
#                               |         af_mixq |  - LSB
#                               --[lpf2q]---(X)---|
#                                            |
#                                          af_loq
#
#
# Based on code from:
#
#  http://webpages.charter.net/cswiger/weaver.html
#
from gnuradio import gr
from gnuradio import audio
import sys

def build_graph (input_filename, tune_freq, bfo_freq, side_band):

    rf_LO = tune_freq + bfo_freq
    af_LO = bfo_freq

    if side_band == 'L' or side_band == 'l':
        rf_LO = tune_freq - bfo_freq
    else:
        rf_LO = tune_freq + bfo_freq

    af_LO = bfo_freq


    rf_sample_rate = 256e3
    af_sample_rate = 32e3

    fir_decimation = (long)( rf_sample_rate / af_sample_rate ) 

    fg = gr.flow_graph ()

    src = gr.file_source (gr.sizeof_gr_complex, input_filename)

    xlate_taps = gr.firdes.low_pass ( 1.0, rf_sample_rate, 20e3, 10e3, gr.firdes.WIN_HAMMING )

    xlate = gr.freq_xlating_fir_filter_ccf ( fir_decimation, xlate_taps, rf_LO, rf_sample_rate )

    split = gr.complex_to_float ()

    af_loi = gr.sig_source_f (af_sample_rate,gr.GR_COS_WAVE,af_LO,1,0)
    af_loq = gr.sig_source_f (af_sample_rate,gr.GR_SIN_WAVE,af_LO,1,0)

    lpf2_taps = gr.firdes.low_pass ( 1.0, af_sample_rate, 1.8e3, 600, gr.firdes.WIN_HAMMING)
    lpf2i = gr.fir_filter_fff (1, lpf2_taps)
    lpf2q = gr.fir_filter_fff (1, lpf2_taps)

    af_mixi = gr.multiply_ff ()
    af_mixq = gr.multiply_ff ()

    if side_band == 'L' or side_band == 'l':
        sum = gr.sub_ff ()
    else:
        sum = gr.add_ff ()

    scale = gr.multiply_const_ff(.02)

    out = audio.sink (long(af_sample_rate))

    fg.connect (src, xlate)
    fg.connect (xlate, split)

    fg.connect ((split, 0), lpf2i)
    fg.connect (lpf2i, (af_mixi, 0))
    fg.connect (af_loi, (af_mixi, 1))
    fg.connect (af_mixi, (sum, 0))

    fg.connect ((split, 1), lpf2q)
    fg.connect (lpf2q, (af_mixq, 0))
    fg.connect (af_loq, (af_mixq, 1))
    fg.connect (af_mixq, (sum, 1))

    fg.connect (sum, scale)
    fg.connect (scale, out)

    return fg

def main (args):
    if len(args) != 4:
        sys.stderr.write ('usage: ssb_rcv_file filename freq(Hz) bfo(Hz) sideband{U,L}\n')
        sys.exit (-1)

    fg = build_graph (args[0], float(args[1]), float(args[2]), args[3][0])

    fg.start ()       
    raw_input ('Press Enter to quit: ')
    fg.stop ()

if __name__ == '__main__':
    main (sys.argv[1:])