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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.
Cheers,
Daniele
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
>
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>
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> /*MSc, Supélec,*/
> /*Ingénieur d'Etat, INPT.*/