windowing DFT vs FFT (newbie)

Hello,

I wrote a program in Java that does a DFT on raw 8bit samples stored in
memory from a RF ADC (Post processing). This allows me to easily adjust the
span (zoom) when I'm viewing the spectrum. Works great, but slow as hell. So
I'm now trying an FFT with a Chirp Z-Transform so I can zoom in on the
desired frequency and look for subtle modulation characteristics. I borrowed
this code from the net (see below) and seems to work as expected. The
spectrum looks like my DFT spectrum without any windowing applied. So I then
tried to window (Hamming) my data before applying the CZT to reduce the
tails on my recovered carrier, however this only smoothes the tails out and
does not reduce there apparent power like my DFT Hamming window does. Am I
doing something fundamentally wrong? How do I reduce/remove the tails from
my spectrum when I do the CZT? Here is the site where I borrowed the code:
http://www.nauticom.net/www/jdtaft/JavaCZT.htm


0
kholmes (2)
8/28/2003 8:44:43 PM
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