[Discuss-gnuradio] Re: Distorted Spectrum after applying gr.freq_xlating_fir_filter_ccc

[Bruhtesfa Ebrahim]

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

-- 
Posted via http://www.ruby-forum.com/.