> I then saw the post on the USRP filter response by Firas [1] where he > showed that for an overall decimation rate of 64 the CIC filter response > had better than a 55 dB anti-alias rejection. [2] But I'm seeing only 42 > dB (overall response). > > Does anyone have any ideas that explain this 13 dB discrepancy in the > filter response? Or am I missing something obvious... > > [1] http://lists.gnu.org/archive/html/discuss-gnuradio/2007- > 05/msg00191.html > [2] http://www.nabble.com/file/8500/%280%20- > %2032%29MHz%29%20CIC%20Frequency%20Response%20%28CIC%20decimation%20%3D3 2% > 29.JPG
[Kell, Scott] To illustrate what I'm talking about, I set the USRP as follows: Data rate: 500 kSamples/sec, Center frequency: 1250 kHz I put a 9dBm tone in at 50 kHz and measured the largest alias in my "passband". I then did the same at 100 kHz, 150 kHz, 200 kHz, ... 32 MHz. I then plotted this "response". [3] It just doesn't seem to be as good as what I thought it would be. [4] Any ideas? Thanks! [3] http://picasaweb.google.com/sctkell/USRPResponse?authkey=Z3gyRLgXOZc#524 9597153645337122 [4] http://www.nabble.com/file/8500/%280%20-%2032%29MHz%29%20CIC%20Frequency %20Response%20%28CIC%20decimation%20%3D32%29.JPG _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio