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Re: [Discuss-gnuradio] Definition of "radians per sample"

From: Daniele Nicolodi
Subject: Re: [Discuss-gnuradio] Definition of "radians per sample"
Date: Thu, 26 Mar 2015 09:52:51 +0100
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:31.0) Gecko/20100101 Thunderbird/31.5.0

Hello Mohamed,

I didn't consider the difference between baseband and passband bw, but
isn't the difference by a factor two going in the wrong direction here?

If I assume that the PLL blocks want the bw defined as passband, when I
get the signal out of the PLL blocks at baseband, I should see a bw that
is half of the one I specified at passband, not twice it.

If I assume that the PLL blocks want the bw defined as baseband, I
should see no difference in bw.

I'm still puzzled.


On 25/03/15 15:25, Mohamed ABOUZRAR wrote:
> Hi Daniele,
> I'm quite sure that there is a miss understanding of  the bandwidth
> notion here,
> Your first formula is certainly the right known one, so make sure you
> use the baseband bandwidth, which is equal to half passband bw.
> hope that helps.
> Regards,
> Mohamed
> On Wed, Mar 25, 2015 at 2:09 PM, Daniele Nicolodi <address@hidden
> <mailto:address@hidden>> wrote:
>     Hello,
>     the documentation for the PLL blocks in GNURadio says: "All settings
>     max_freq and min_freq are in terms of radians per sample, NOT HERTZ."
>     Therefore I thought that to specify a bandwidth `bw` it would have to
>     converted from natural frequency units (Hz) into radians per sample with
>     something like:
>     bw_rad_per_sample = bw * 2*pi / sampl_rate
>     where `sampl_rate` is of course the sampling rate in Hz.
>     However, looking at the PSD of the input and outputs to the PLL blocks,
>     it looks like my understanding is wrong and that the bandwidth should be
>     computed as
>     bw_rad_per_sample = bw * pi / sampl_rate
>     which differs from the former by a factor of 2.
>     Is the documentation right, and my understanding of it wrong, or the
>     documentation is wrong?  In the former case, I think it would be better
>     to clarify it a bit.
>     Thanks! Cheers,
>     Daniele
>     _______________________________________________
>     Discuss-gnuradio mailing list
>     address@hidden <mailto:address@hidden>
>     https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
> -- 
> /*MSc, Supélec,*/
> /*Ingénieur d'Etat, INPT.*/

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