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RE: [Discuss-gnuradio] USRP receiver filter response
From: |
Kell, Scott |
Subject: |
RE: [Discuss-gnuradio] USRP receiver filter response |
Date: |
Wed, 24 Sep 2008 10:53:36 -0400 |
> 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