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Re: [Discuss-gnuradio] USRP Tx Rate Conversion

From: Wireless Monster
Subject: Re: [Discuss-gnuradio] USRP Tx Rate Conversion
Date: Thu, 17 Apr 2008 11:35:34 -0400

The spectrum looks clean so probably the LPF is not requirered.

I just got my hands on a USRP board and started playing with it for fun. If I came to something interesting (i.e. complete GSM modulator) I will contribute it to the project.

Thks again and Rgds,

On Thu, Apr 17, 2008 at 11:26 AM, Brian Padalino <address@hidden> wrote:
On Thu, Apr 17, 2008 at 11:11 AM, Wireless Monster
<address@hidden> wrote:
> Brian, Dan,
> It is working now. Thanks again for your help.
> One more basic "signal processing question" ... knowing that the input and
> output are complex (GMSK modulated signal), should I use complex or real
> coefficients for the resampler filter  (rational_resampler_ccc, vs.
> rational_resampler_ccf) ?

I wouldn't use a ccf.  I'd either use an fff on each the real and
imaginary portions of the signal, or I'd use a ccc on the combined
signal, but that's just my own personal opinion.

> Regarding Ed, question on the LPF after the resampler, I am not sure... it
> does not seems to be needed... any clue?

Look at the spectrum coming out of your rational resampling filter and
make sure there are no spurs or images outside the intended band.
That's probably the easiest thing to do, though I don't think there is
a need.  The source for the filter is located here:


There is a little bit of python taking place to actually generate the
code for all the filter types, but you can get the general idea of how
it works.

On a side note, do you have a GSM modulator that you are thinking of
contributing to the project?  Or is this strictly for personal


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