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From: | Richard Jaeger |
Subject: | [Discuss-gnuradio] USRP Gain |
Date: | Mon, 1 Sep 2008 15:26:12 -0500 |
For decimations below 96, the gain is fairly constant, changing +/- a couple of dB. However, for decimations above about 96, the voltage gain in dB is growing approximately linearly with D: (for example, when I change D from 100 to 160 the overall gain increases by about 5.5 dB. When I change D from 160 to 222, the voltage gain increases by another 5.5 dB). So the gain itself is growing exponentially with decimation rate.
I believe that the gain of a basic CIC filter is proportional to D (but not exponentially). Is this the source of the gain variation that I am seeing, or is some scaling or normalization going on elsewhere that I am overlooking?
The documentation indicates that 4-stage CIC filters are used, and the 4-channel configuration eliminates the half-band filters. Is there any information on how the decimation is distributed across the 4 stages as a function of overall decimation?
Thanks for the help. Dick...
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