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Re: [Discuss-gnuradio] A question on wfm_rcv_gui.py
From: |
Sachi |
Subject: |
Re: [Discuss-gnuradio] A question on wfm_rcv_gui.py |
Date: |
Sun, 20 Mar 2005 21:50:52 -0800 (PST) |
Thanks Eric, so the usrp accepts negative
IF¡¡frequency?
Sachi
--- Eric Blossom <address@hidden> wrote:
> On Sun, Mar 20, 2005 at 04:47:11PM -0800, Sachi
> wrote:
> > I still can't figure it out. Can anyone of you
> guys
> > help me with it?
> >
> > > Hi guys
> > >
> > > I got a bit confused by the code for FM
> demodulator.
> > > In function parseargs(), why we return freq1 -
> 128e6
> > > instead of freq1 itself? What does 128M stand
> for?
> > >
> > > Thanks
> > >
> > > Sachi
>
> Let me take a shot at it. Matt wrote it, but I
> think he's off-line
> for the weekend.
>
> wfm_rcv_gui was written assuming that there was no
> RF front end doing
> any downconversion.
>
> The A/D sample rate is 64M.
>
> The Nyquist zones are therefore:
>
> [0, 32M] normal
> [32M, 64M] inverted
> [64M, 96M] normal
> [96M, 128M] inverted
>
> etc.
>
> The problem is that 96M, one of the folding points,
> occurs right in
> the middle of the broadcast band.
>
> This means that 95.0 and 97.0 both alias down to the
> same frequency
> and can't be distinguished from each other.
>
> freq1 - 128M will give a valid frequency if freq1 is
> >= 96M.
>
> Bottom line: it's a kludge that sort of works.
>
> Eric
>
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