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[Discuss-gnuradio] USRP Custom Filter Taps

From: Daniel Garcia
Subject: [Discuss-gnuradio] USRP Custom Filter Taps
Date: Wed, 27 Sep 2006 21:50:26 -0700 (PDT)

I am working on an NTSC receiver using the USRP/TVRX board. I am tunning the 
board to 63.25 MHz with decimation set to 10; this gives me 6.4 MHz of 
bandwidth. The NTSC channel is 6 MHz wide so with these settings I get some 
interference from the adjacent channels. 

Is there a way to set the filter taps used by the USRP so that I could make a 
filter to remove the frequency infomation at the extreme right and left of the 
sampled data? I can use an FIR filter in the PYTHON runtime but it uses lots of 
CPU power.

I read on a previous thread that it is possible to invert the spectrum of the 
sampled signal so that the tuned frequency would be the FM carrier. The end 
result being a stream from the USRP where 0 Hz is the center frequency of the 
audio carrier the the video carrier is at 4.5 MHz. Is this possible? The 
advantage here is that the baseband audio does not need to be shifted before fm 
demodulation; also the video carrier does not need to be shifted before 
demodulation (AM). 


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