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Re: [Discuss-gnuradio] TV_RX anti-aliasing filter


From: Matt Ettus
Subject: Re: [Discuss-gnuradio] TV_RX anti-aliasing filter
Date: Wed, 26 Sep 2007 14:04:09 -0700
User-agent: Thunderbird 2.0.0.0 (X11/20070326)

Nirali Patel wrote:
> Hello everyone,
>
> I am a new user and recently set up the USRP and TV_RX boards to receive FM 
> radio and now trying to take the dive into capturing HDTV. I had a basic, 
> maybe dumb question on the presence of a low pass filter before the A/D 
> converter. Does anyone know if the TV_RX board has an anti-aliasing low pass 
> filter on it? Or within the Microtune 4937 tuner module? I looked at the 
> schematic for the daughter board and the data sheet for 4937 but I am not 
> sure if there is one. The TV_RX I got has an IF frequency of 44MHz and I 
> understand that undersampling it at 64 Msps with the A/D converter causes it 
> to fold to 20 MHz. I wanted to know whether there is or there needs to be a 
> low pass filter before the A/D converter to suppress any energy in the lower 
> frequencies before sampling.
>   

The output from the tuner module has already been filtered by a SAW
filter, so there is no need for any further filtering.  There is only
significant energy in the desired band.

Matt





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