"Hernán Sánchez" wrote in message
oups.com...
"The signal (at IF) is at 44MHz and the bandwidth is 1MHz. How can I
design the antialiasing filter for undersampling with that information?"

Slap a bandpass filter that's 1MHz wide at 44MHz around the signal input path.
Sample at something better than 2MHz (depending on how ideal your bandpass
filter is -- realistically you'll probably need to sample at 2.5MHz or
better... and things are simpler if you could manage to sample at 4MHz so that
44MHz ends up translated directly to DC rather than some offset).