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Re: [Discuss-gnuradio] Question on IF filter design for FM demodulation
From: |
Matt Ettus |
Subject: |
Re: [Discuss-gnuradio] Question on IF filter design for FM demodulation |
Date: |
Fri, 7 Jan 2005 16:30:29 -0800 |
User-agent: |
Internet Messaging Program (IMP) 4.0-cvs |
> I am amazed that even this design (wfm_rcv.py) works:
It does, quite well.
> Before the downconversion at the FPGA the entire FM band (88-108 MHz) is
> present inside the useful spectrum (with the desired station centered at
> 5.75 MHz).
Only 6MHz of it is presemt, but that doesn't matter
> However, decimating at the FPGA by a factor of 250 will essentially
> spread the entire spectrum of the desired station (not a problem),
> but also all other (neighboring) stations will be aliased on top of the
> desired one. These stations will appear in the desired band completely
> unattenuated.
> It seems to me that before decimation at the FPGA, a LPF is required
> (probably in two stages as Matt suggested).
> Can this be done in the FPGA of the USRP?
When we say "decimation" we mean "decimation with proper filtering first".
There are 8
CIC decimators and 8 CIC interpolators in the FPGA.
Matt
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