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Re: [Discuss-gnuradio] Correlation Estimation Block Oddity

From: Andy Walls
Subject: Re: [Discuss-gnuradio] Correlation Estimation Block Oddity
Date: Wed, 29 Apr 2015 13:08:50 -0400

On Wed, 2015-04-29 at 09:09 -0700, Johnathan Corgan wrote:
> On Wed, Apr 29, 2015 at 8:50 AM, Richard Bell
> <address@hidden> wrote:
>         Thanks for replying. The question is, how do I do this? We
>         both agree the zeros need to go. What I'm not sure on is how
>         to do that. I'd rather keep this contained to GRC, because I
>         don't like maintaining python files not connected to grc. Can
>         you explain how you do this or provide an example?
> Since GRC parameters can be Python expressions, you can use formulas
> to do this.
> If 'seq' is the original sequence to be modulated, use 'seq+seq' in
> the parameter to the modulate_vector variable block.
> If the variable is named 'mod_vec', use:
> mod_vec[len(mod_vec)/2:]
> ...as the taps for the correlation estimator.



On a related note, I just tested the PSK modulator and it does generate
a long lead-in of zeros.  :/

The GMSK modulator "digital.gmskmod_bc(sps, pulse_duration, bt)", which
I usually use, doesn't do this.  I can see some lead-in due to the BT
and pulse duration, but I expect that.

Scanning the python code under gr-digital, it looks something in the
generic_mod might account for those leading zeros.  The GMSK modulator
doesn't use the generic_mod class.


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