From 5d69a524f81f234b3fbc41d49ba18d6f6886baba Mon Sep 17 00:00:00 2001
From: jcorgan
Date: Thu, 3 Aug 2006 04:51:51 +0000
Subject: Houston, we have a trunk.

git-svn-id: http://gnuradio.org/svn/gnuradio/trunk@3122 221aa14e-8319-0410-a670-987f0aec2ac5
---
 gnuradio-examples/python/apps/hf_radio/hfir.sci | 59 +++++++++++++++++++++++++
 1 file changed, 59 insertions(+)
 create mode 100644 gnuradio-examples/python/apps/hf_radio/hfir.sci

(limited to 'gnuradio-examples/python/apps/hf_radio/hfir.sci')

diff --git a/gnuradio-examples/python/apps/hf_radio/hfir.sci b/gnuradio-examples/python/apps/hf_radio/hfir.sci
new file mode 100644
index 000000000..a2d5e2a62
--- /dev/null
+++ b/gnuradio-examples/python/apps/hf_radio/hfir.sci
@@ -0,0 +1,59 @@
+// designs a complex tap fir filter akin to the hilbert transformer.
+//
+// The hilbert transformer is classified as a linear phase fir
+// with allpass magnitude response and 90 degree phase response for
+// positive frequencies and -90 degrees phase for negative frequencies.
+// Or, if you prefer, normalized frequencies between .5 and 1 since
+// negative frequencies don't really have much meaning outside the complex
+// domain.
+//
+// Normally one would use the hilbert transformer in one leg of a complex
+// processing block and a compensating delay in the other.
+//
+// This one differs in the following respects:
+//  It is low pass with a cutoff of .078125
+//  The filter is a lowpass kaiser windowed filter with parameter 3
+//  The phase response is 45 degrees for positive frequencies and -45
+//   for negative frequencies.
+//  The coefficent set is used in one path and the same coefficients
+//   are used time reversed in the other. This results in the net effect
+//   of +/- 90 degrees as in the usual hilbert application.
+//
+// The coefficient set can be used in the gnuradio frequency translating
+// fir filter for ssb demodulation.
+//
+// This isn't as computationally efficient as using the hilbert transformer
+// and compensating delay but fascinating none the less.
+//
+// This program is for the scilab language a very powerful free math 
+// package similar to Matlab with infinitely better price/performace.
+//
+// compute the prototype lowpass fir
+// length is 255 (odd) for the same symmetry reasons as the hilbert transformer
+
+len = 1023;
+l2 = floor(len/2);
+md = l2 + 1;
+l3 = md + 1;
+
+h = wfir( 'lp', len, [10.0/256 0], 'kr', [3 0] );
+
+H = fft(h);
+
+H(1:l2)=H(1:l2)*exp(%i*%pi/4);
+H(md)=0+%i*0;
+H(l3:len)=H(l3:len)*exp(-%i*%pi/4);
+
+j=real(ifft(H));
+k(1:len)=j(len:-1:1);
+x=j+%i.*k;
+X=fft(x);
+plot(abs(X))
+
+f = file('open','taps')
+for i=(1:len)
+  fprintf( f, '%f%+fj', j(i), k(i) )
+end
+
+file('close',f)
+
-- 
cgit