Imported Upstream version 3.2.2

[debian/gnuradio] / gnuradio-core / src / python / gnuradio / blks2impl / fm_emph.py

diff --git a/gnuradio-core/src/python/gnuradio/blks2impl/fm_emph.py b/gnuradio-core/src/python/gnuradio/blks2impl/fm_emph.py
new file mode 100644 (file)
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+++ b/gnuradio-core/src/python/gnuradio/blks2impl/fm_emph.py
@@ -0,0 +1,151 @@
+#
+# 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.
+# 
+
+from gnuradio import gr
+import math
+
+
+#
+#           1
+# H(s) = -------
+#         1 + s
+#
+# tau is the RC time constant.
+# critical frequency: w_p = 1/tau
+#
+# We prewarp and use the bilinear z-transform to get our IIR coefficients.
+# See "Digital Signal Processing: A Practical Approach" by Ifeachor and Jervis
+#
+
+class fm_deemph(gr.hier_block2):
+    """
+    FM Deemphasis IIR filter.
+    """
+    
+                           
+    def __init__(self, fs, tau=75e-6):
+        """
+        @param fs: sampling frequency in Hz
+        @type fs: float
+        @param tau: Time constant in seconds (75us in US, 50us in EUR)
+        @type tau: float
+        """
+        gr.hier_block2.__init__(self, "fm_deemph",
+                               gr.io_signature(1, 1, gr.sizeof_float), # Input signature
+                               gr.io_signature(1, 1, gr.sizeof_float)) # Output signature
+                               
+        w_p = 1/tau
+        w_pp = math.tan (w_p / (fs * 2)) # prewarped analog freq
+
+        a1 = (w_pp - 1)/(w_pp + 1)
+        b0 = w_pp/(1 + w_pp)
+        b1 = b0
+
+        btaps = [b0, b1]
+        ataps = [1, a1]
+
+        if 0:
+            print "btaps =", btaps
+            print "ataps =", ataps
+            global plot1
+            plot1 = gru.gnuplot_freqz (gru.freqz (btaps, ataps), fs, True)
+
+        deemph = gr.iir_filter_ffd(btaps, ataps)
+       self.connect(self, deemph, self)
+
+#
+#         1 + s*t1
+# H(s) = ----------
+#         1 + s*t2
+#
+# I think this is the right transfer function.
+#
+#
+# This fine ASCII rendition is based on Figure 5-15
+# in "Digital and Analog Communication Systems", Leon W. Couch II
+#
+#
+#               R1
+#         +-----||------+
+#         |             |
+#  o------+             +-----+--------o
+#         |      C1     |     |
+#         +----/\/\/\/--+     \
+#                             /
+#                             \ R2
+#                             /
+#                             \
+#                             |
+#  o--------------------------+--------o
+#
+# f1 = 1/(2*pi*t1) = 1/(2*pi*R1*C)
+#
+#         1          R1 + R2
+# f2 = ------- = ------------
+#      2*pi*t2    2*pi*R1*R2*C
+#
+# t1 is 75us in US, 50us in EUR
+# f2 should be higher than our audio bandwidth.
+#
+#
+# The Bode plot looks like this:
+#
+#
+#                    /----------------
+#                   /
+#                  /  <-- slope = 20dB/decade
+#                 /
+#   -------------/
+#               f1    f2
+#
+# We prewarp and use the bilinear z-transform to get our IIR coefficients.
+# See "Digital Signal Processing: A Practical Approach" by Ifeachor and Jervis
+#
+
+class fm_preemph(gr.hier_block2):
+    """
+    FM Preemphasis IIR filter.
+    """
+    def __init__(self, fs, tau=75e-6):
+        """
+        @param fs: sampling frequency in Hz
+        @type fs: float
+        @param tau: Time constant in seconds (75us in US, 50us in EUR)
+        @type tau: float
+        """
+
+       gr.hier_block2.__init__(self, "fm_deemph",
+                               gr.io_signature(1, 1, gr.sizeof_float), # Input signature
+                               gr.io_signature(1, 1, gr.sizeof_float)) # Output signature
+                               
+        # FIXME make this compute the right answer
+        
+        btaps = [1]
+        ataps = [1]
+
+        if 0:
+            print "btaps =", btaps
+            print "ataps =", ataps
+            global plot2
+            plot2 = gru.gnuplot_freqz (gru.freqz (btaps, ataps), fs, True)
+
+        preemph = gr.iir_filter_ffd(btaps, ataps)
+       self.connect(self, preemph, self)