#

# Copyright 2005,2007 Free Software Foundation, Inc.

# 

# This file is part of GNU Radio

# 

# GNU Radio is free software; you can redistribute it and/or modify

# it under the terms of the GNU General Public License as published by

# the Free Software Foundation; either version 3, or (at your option)

# any later version.

# 

# GNU Radio is distributed in the hope that it will be useful,

# but WITHOUT ANY WARRANTY; without even the implied warranty of

# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

# GNU General Public License for more details.

# 

# You should have received a copy of the GNU General Public License

# along with GNU Radio; see the file COPYING.  If not, write to

# the Free Software Foundation, Inc., 51 Franklin Street,

# Boston, MA 02110-1301, USA.

# 

import math

from gnuradio import gr, optfir

from gnuradio.blks2impl.fm_emph import fm_preemph

class wfm_tx(gr.hier_block2):

    def __init__(self, audio_rate, quad_rate, tau=75e-6, max_dev=75e3):

        """

        Wide Band FM Transmitter.

        Takes a single float input stream of audio samples in the range [-1,+1]

        and produces a single FM modulated complex baseband output.

        @param audio_rate: sample rate of audio stream, >= 16k

        @type audio_rate: integer

        @param quad_rate: sample rate of output stream

        @type quad_rate: integer

        @param tau: preemphasis time constant (default 75e-6)

        @type tau: float

        @param max_dev: maximum deviation in Hz (default 75e3)

        @type max_dev: float

        quad_rate must be an integer multiple of audio_rate.

        """

        gr.hier_block2.__init__(self, "wfm_tx",

                                gr.io_signature(1, 1, gr.sizeof_float),      # Input signature

                                gr.io_signature(1, 1, gr.sizeof_gr_complex)) # Output signature

        # FIXME audio_rate and quad_rate ought to be exact rationals

        audio_rate = int(audio_rate)

        quad_rate = int(quad_rate)

        if quad_rate % audio_rate != 0:

            raise ValueError, "quad_rate is not an integer multiple of audio_rate"

        do_interp = audio_rate != quad_rate

        if do_interp:

            interp_factor = quad_rate / audio_rate

            interp_taps = optfir.low_pass (interp_factor,   # gain

                                           quad_rate,       # Fs

                                           16000,           # passband cutoff

                                           18000,           # stopband cutoff

                                           0.1,              # passband ripple dB

                                           40)              # stopband atten dB

            print "len(interp_taps) =", len(interp_taps)

            self.interpolator = gr.interp_fir_filter_fff (interp_factor, interp_taps)

        self.preemph = fm_preemph (quad_rate, tau=tau)

        k = 2 * math.pi * max_dev / quad_rate

        self.modulator = gr.frequency_modulator_fc (k)

        if do_interp:

            self.connect (self, self.interpolator, self.preemph, self.modulator, self)

        else:

            self.connect(self, self.preemph, self.modulator, self)