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[Discuss-gnuradio] Re: Distorted Spectrum after applying gr.freq_xlating
From: |
Bruhtesfa Ebrahim |
Subject: |
[Discuss-gnuradio] Re: Distorted Spectrum after applying gr.freq_xlating_fir_filter_ccc |
Date: |
Wed, 21 Jan 2009 11:24:15 +0100 |
Michael Dickens wrote:
> On Jan 19, 2009, at 5:46 AM, Bruhtesfa Ebrahim wrote:
>> Details:
>> - The sampling rate of the original recieved signal from USRP was
>> 64MHz/128=500KHz, so I used decimation factor of 500 in the xlating
>> filter such that the output baseband signal will have a sampling
>> rate of 500KHz/500=1KHz.
>> - since the frequency offset of the signal in 1st figure is
>> -7.68KHz, i used the opposite freq_offset=7680 in the xlating filter.
>> - i used cut off frequency =500Hz and width of transition band=200Hz.
>
> Everything looks OK "on paper", but I think your filtering will be
> tight given the sample rate of the output of the xlating filter. It
> very well might be that the offset needs to be the actual value (not
> the negative of it) ... I really don't remember any longer.
>
> My advice is to play with the xlating filter using more bandwidth:
> reduce the decimation to, say, 50 (BW = 100k), and change the filter
> to be wider and more relaxed (say, BW=25k, transition=15k, in order to
> encompass both the original signal as well as the shifted copy of it
> if the offset is not exactly correct). I think if you play with the
> variables a bit using more bandwidth, you'll figure out what's going on.
>
> Good luck! - MLD
Thank you so much for all your help Michael!!!
I will try it out.
Bruhtesfa
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