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Re: [Discuss-gnuradio] FIR filters and set_history()

From: George Nychis
Subject: Re: [Discuss-gnuradio] FIR filters and set_history()
Date: Wed, 06 Feb 2008 12:40:08 -0500
User-agent: Thunderbird (X11/20071022)

Dan Halperin wrote:

In the normal code in the trunk, this works just as expected. But when
you make your custom vectors, you only pull noutput_items out of the
input buffer, not noutput_items+history.

You're exactly right with this, I'm forgetting that I'm creating new input buffers but only extracting noutput_items from the original input buffer. I tested this and get the exact output I'm looking for now.

One line diff:
-  split_complex(in, noutput_items, in_real, in_imag);
+  split_complex(in, noutput_items+history(), in_real, in_imag);

I needed to pull history() additional items from the input queue, which makes sense.

Also, my understanding of a normal matched filter is that it does the
normal complex multiplication (by the conjugate, but I'm assuming you've
done that already before building the taps), not the real-wise and
complex-wise ... inner product, I guess? ... as you've defined it.

I had thought I could use gr_fir_filter_ccc, setting my taps to be the time reversed version of the input signal, but found that it wasn't correlating. I think what I was missing is the fact you are suggesting that the taps be the complex conjugate of the input signal?

- George

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